Note: Descriptions are shown in the official language in which they were submitted.
11~)77S2
The present invention relates to a process for
continuous, stable production of methyl methacrylate syrups
of high polymer content, and particularly to a process for
continuous, stable production of the syrups of high polymer
content which have a proper viscosity suitable for operation
and enable shortening of casting time with no lowering of
the quality of methyl methacrylate cast sheet.
More particularly, the present invention relates
to a process for continuous, stable production of prepolymer
syrups of high polymer content by successively passing a
methyl methacrylate monomer and a radical-polymerization
initiator through reaction zones of specified reaction
conditions, and particularly to a process for continuous,
stable production of the syrups having a narrow distribution
of polymerization degree, a low concentration of remaining
initiator and a high polymer content.
The prepolymer syrups are suitable for various
us0s such as casting liquids for preparation of cast sheets
and glass fiber reinforced cast sheets, intermediate materials
for preparation of molding materials after removing a vola-
tile component in the prepolymer syrups, main components of
polymerizable adhesives or paints, raw materials of resin
concrete compositions and the like. Among these, the pre-
polymer syrups are particularly suitable for use as the
casting liquid for preparation of cast sheets and glass
fiber reinforced cast sheets.
Generally, methyl methacrylate cast sheets are
batchwise produced by injecting a polymerizable liquid
composition comprising an initiator and a methyl meth-
acrylate syrup into a mold having a space enclosed with
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two pieces of glass plate and a gasket therebetween,
followed by polymerization by heating (hereinafter referred
to as simply "cell casting process").
In this method, the syrup containing a suitable
amount of polymer is used, in order to elevate the operation
efficiency of injection, to elevate the quality of the
resulting cast sheet and to shorten the casting time. Prior
to injection, the syrup is mixed with an initiator and other
necessary additives, and deaerated under reduced pressure in
order to remove dissolved air from it. The syrup is then
injected into a space enclosed with two pieces of glass
plate and gasket between the plates. In injection of the
syrup, a too low viscosity of the syrup causes liquor leak,
while a too high viscosity prolongs the injecting time. In
either case, the operation efficiency of injection is
lowered so that the syrup viscosity needs to be within a
proper range~ As is well known, further, the use of syrup
decreases the quantity of heat generated on polymerization
and shrinkage of polymer on polymerization, so that the
surface state of resulting cast sheet is improved and
control of sheet thickness becomes easy. Consequently, a
high polymer content of syrup is desirable. Also, the
casting time is much shortened as an increase in the polymer
content of syrup. The highest possible polymer content is
thus desirable from this point of view. It is also necessary
for the syrup used for this purpose to have a high storage
stability, not to hinder polymerization on casting and not
to lower the quality of cast sheet.
Methacryl cast sheets have 50 far been produced by
the cell casting process in which polymerization is carried
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77~2
out between two pieces of glass plate. Recently, however,
this process is being replaced by the casting process of
continuous form in which polymerization is continuously
carried out between two pieces of moving endless belts. For
example, Japanese Patent Publication No. 2991~/1976 discloses
a process for continuously producing a resin plate, using a
pair of endless belts arranged and constructed so that the
lower run of the upper belt is positioned above the upper
run of the lower belt, which comprises feeding a polymeri-
zable liquid composition, together with a pair of continuous
gaskets, into a spacing defined between the lower run of
upper belt and the upper run of the lower belt both of which
are arranged such that the pair of the endless belts are
driven concurrently in the same direction at substantially
the same speed, said gaskets being arranged so as to circum-
scribe the spacing serving as a pair of seals to confine a
cavity whilst moving concurrently with the belts in contact
with the opposing surfaces of the belts, passing the composi-
tion through a portion of the path of the belts where said
composition is completely polymerized, and removing the
polymerized plate from the end portion of the belts at the
discharge side thereof.
In this process, however, an equipment cost
occupies a large portion of manufacturing cost so that
shortening of casting time is required more severely than in
the cell casting process. The shortening of casting time
can be achieved by increasing the polymer content of syrup
as much as possible with the viscosity of the syrup main-
tained within the range not lowering the operation effic~ency
of injection. In this case, the syrup should be such that
~1~77S2
it prevents the quality of the resulting cast sheet from
lowering as much as possible and more preferably it elevates
the quality. Because, a lowering in the quality of the
resulting cast sheet decreases the commercial value of the
cast sheet and thus cancels out an effect of decreasing the
manufacturing cost by shortening of casting time. When the
cast polymerization is carried out using a syrup containing
polymer having lower weight average polymerization degree
due to an increase of the polymer content of syrup for
shortening of casting time, the following defects easily
appear in the resulting cast sheet in general: the mechanical
strength of the sheet lowers owing to a decrease in the
average polymerization degree of the sheet; and owing to
polymer of low polymerization degree in the syrup, the
foaming of the sheet easily occurs on heat-molding; the
molding temperature range of the sheet becomes narrow; and
the solvent resistance of the resulting sheet becomes bad.
The viscosity of syrup at constant temperature is
determined by a polymer content and a weight average poly-
merization degree of polymer, and it increases with the
increase of each factor. ~ccordingly, a lower weight
average polymerization degree is desirable in order to
increase the polymer content of syrup as much as possible
with the viscosity of the syrup maintained withln the range
not to lower the operation efficiency of injection. On the
other hand, however, polymers of low polymerization degree
in the syrup are one of the factors by which said decrease
in the average polymerization degree of sheet and said
foaming of the sheet on heat-molding are caused. The amount
of such polymers is almost determined by a num~er average
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polymerization degree. It may therefore be said that a
higher number average polymerization degree is desirable.
In polymers having a distribution of polymerization degree,
a weight average polymerization degree is generally larger
than a number average polymerization degree. Breadth of a
distribution of polymerization degree is generally expressed
in a polydispersity which is a ratio of the two polymeri-
zation degrees. In this expression, generally the syrups
having a lower polydispersity are desirable.
When the concentration of remaining initiator in
syrup is high, polymerization further proceeds during
cooling on syrup production or storage, which results in a
rise in the polymer content and viscosity of the syrup.
Thus, syrups of constant quality can hardly be obtained.
Even though the concentration is so small that such progress
of polymerization is not substantially observed, it causes a
change in the quality of syrup in storage, and a lowering in
the quality of cast sheet obtained from such syrup, for
example, an increase in the remaining monomer content of the
cast sheet and a trend to cause foaming of the sheet on heat
molding. Accordingly, it is necessary to decrease the
concentration of the remaining initiator as much as
possible. The shortening of casting time may also be
achieved by increasing the concentration of the initiator
used on casting in place of an increase in the polymer
content of syrup. In this case, however, the average
polymerization degree of cast sheet necessarily decreases,
causing a great reduction in quality. Therefore, this
method may not be said to be a favorable one.
Hitherto, there are proposed various processes for
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production of the syrup. Any of these processes satisfies a
part of the conditions described above, but none of them
satisfies all the conditions. For example, shortening of
casting time causes a lowering in the mechanical strength of
the cast sheet, an easy foaming of the sheet on heat mold-
ing, a narrowing in the molding temperature range of the
sheet and a decrease in the solvent resistance of the sheet.
As described above, the shortening of casting time does not
always ralse economy.
Production of the syrup by a batchwise process is
generally carried out using a vessel-type reactor with a
stirrer. In this process, the monomer is heated to high
temperature and then a required amount of initiator is added
thereto, or a mixture of the monomer and the initiator is
heated to high temperature; polymerization is carried out
sufficiently until the concentration of the remaining
initiator is reduced to substantially a negligible one; and
then the reaction mixture is cooled and withdrawn as a
syrup. In this process, the initiator concentration is high
at the initial stage of reaction, but it decreases rela-
tively rapidly with the progress of the reaction. The
polymerization degree of polymers thus obtained varies over
a wide range between considerably low polymerization degree
at the initial stage and extremely high polymerization
degree at the final stage. Thus, the polymers in the syrup
have an extremely broad distribution o~ polymerization
degree, and their weight average polymerization degree is
high while their number average polymerization degree is
low. A weight average polymerization degree is directly
related to the viscosity of a syrup, and its large value
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means a high viscosity when syrups of the same polymer
content are compared with one another. As a result,
injection of the syrup into a glass cell or a space between
endless belts becomes difficult. In order to facilitate the
injection, the polymer content of syrup needs to be limited
to a low level, by which shortening of casting time can not
be much expected. Low values of the number average poly-
merization degree mean that polymers of low polymerization
degree causing quality reduction are contained in the syrup
in relatively large amounts. And, syrups containing such
polymers cause a decrease in the average polymerization
degree of cast sheet produced therefrom and foaming of the
sheet on heat molding.
In this process, however, when the initial concen-
tration of initiator is increased, the weight average
polymerization degree of polymers in the resulting syrup
decreases, and the upper limit of the polymer content of the
syrup rises with the syrup viscosity maintained within the
range wherein injection of syrup is easy. ~ecause of these,
the casting time is shortened to a large extent. On the
other hand, the number average polymerization degree also
decreases proportionally, accelerating the quality reduction
of cast sheet. The concentration of remaining initiator of
syrups obtained by this method îs generally sufficiently
low, so that the syrups have a relatively good storage
stability. In this batchwise process, when a sufficiently
long time is not spent for polymerization, syrups having a
relatively narrow distribution of polymerization degree are
produced. Since, however, the initiator remains in a high
concentration, polymerization further proceeds during cool-
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ing and storage, thus increasing the viscosity. An in-
hibitor is sometimes added to elevate the storage stability
of syrup, but this method disadvantageously prolongs poly-
merization time on casting and causes coloration. In the
batchwise produc~ion of syrup, it is not desirable to
control the formation of polymers of high polymerization
degree by addition of a chain transfer agent, because, when
the agent remains in the syrup, it adversely affects cast-
ing, thus resulting in prolongation of polymerization time,
lowering in the average polymerization degree of the cast
sheet or coloring of the cast sheet.
On the other hand, there are proposed various
processes for continuous production of the syrup. Of
these, a method with a tubular reactor comprising continu-
ously supplying the monomer and an initiator to the reactor
at one end and continuously withdrawing the resulting syrup
at the opposite end, can not substantially overcome the
drawbacks of the foregoing batchwise processes. That is,
judging the phenomena which occur when a reaction solution
flows through a long and narrow tubular reactor in the
lengthwise direction from the standpoint of the progress of
polymerization, this method shows the same progress of
polymerization as in the batchwise processes with a vessel-
type reactor except an influence by back mixing. The
polymerization proceeds in such a manner that the initiator
concentration is high in the vicini~y of a feed inlet,
decreases relatively rapidly as the reaction sol~tion flows
forward, up to a substantially negligible amount in the
vicinity of the outlet. The polymerization degree of the
resulting polymers varies over a very wide range between a
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~1~7752
considerably low polymerization degree in the vicinity of
feed inlet and an extremely high one in the vicinity of
outlet. Thus, the polymers in the syrup have an extremely
broad distribution of polymerization degree.
In this process, when sufficient reaction temper-
ature and residence time are not used for polymerization,
syrups having a relatively narrow distribution of poly-
merization de~ree are produced. The syrups thus obtained
are poor in storage stability like the case wherein a
sufficiently long time is not spent for polymerization in
the batchwise process with a vessel-type reactor. In other
words, with a continuous tubular reactor, shortening the
casting time without lowering the quality of the cast sheet
can not be much expected.
There is also proposed a process wherein the
monomer and an initiator are continuously supplied to a
vessel-type reactor with a stirrer at the inlet and the
resulting syrup is continuously withdrawn at the outlet. In
the process disclosed in British patent 937,215, polymeri-
zation is carried out at such temperature and conditions
that decomposition of initiator is just completed at the
time when a required conversion is reached. The principle
of this process is based on the following features of the
batchwise polymerization process: when the reaction temper-
ature is sufficiently high as compared with the decomposi-
tion temperature of initiator, the initiator rapidly de-
composes, and during that period polymerization proceeds to
a certain conversion. But, after lapse of the time required
for complete decomposition of initiator, the rate of reac-
tion becomes very slcw since the reaction proceeds by the
11077~;2
mere action of heat. Further, when the polymerization is
carried out at temperatures and conditions at which the
initiator has just been decomposed, it becomes easy to
control the reaction and to limit the conversion to a
required range. In other words, at high temperatures, the
Trommsdorff effect is apparently reduced to a large extent,
and the state of reaction approaches a dead-end type poly-
merization. Said patent says that carrying out polymeri-
zation at such temperature and condition is very suitable
for control of partial polymerization of methacrylate in any
of the batchwise and continu01ls processes.
In the batchwise processes and continuous ones
with a tubular reactor, however, syrups obtained at such
temperature and condition contain polymers having an ex-
tremely broad distribution of polymerization degree as
described hereinbefore in detail. Consequently, shortening
of casting time does not always raise economy.
On the other hand, when the polymerization is
carried out at such temperature and condition in the process
with a continuous stirred tank reactor, it is difficult to
produce syrups having a high polymer content by a stable and
stationary operation since the rate of polymerization is
accelerated by the Trommsdorff effect, and besides the
syrups obtained have the following defects: in this method,
since an initiator is always supplied to the reactor even at
a temperature causing rapid decomposition o~ the initiator,
a rapid decrease in initiator concentration by prolongation
of reaction time does not occur. An initiator concentration
at a stationary state in the continuous stirred tank reactor
wherein complete mixing is achieved, is equal to the concen-
1~3i77~2
tration of remaining initiator at the outlet of the reactorand is expressed in an equation; I = I /(1 + K~), wherein I
is a concentration of remaining initiator (weight %), Io is
a concentration of supplied initiator (weight %), K is a
decomposition rate constant of the initiator (sec 1) and
3 is an average residence time (sec). At temperatures at
which rapid decomposition of initiator takes place, K is
large enough to meet Ka ~ 1 so that an equation; I = Io/Ke,
applies approximately. That is, a decrease in the concen-
tration of remaining initiator is only for such a degree
that the concentration decreases in inverse proportion to a
reaction time even though the reaction time is prolonged.
During the period of the reaction, there is no time at
which the initiator has just been decomposed, and there is
no reaction time after which the rate of reaction becomes
very slow. It may not always be easy to stop the poly-
merization at a required stage, unlike the batchwise process
and the continuous process with a tubular reactor. Further,
in bulk polymerization of methyl methacrylate monomers,
acceleration of the rate of polymerization, which is called
the Trommsdorff effect, is known. This effect refers to the
phenomenon of increase in polymerization rate constant as
an increase in polymer content. Considering the case of
extending a reaction time in the process with a continuous
stirred tank reactor, the polymer content increases even
though said acceleration is not observed, and therefore it
is necessary, as described above, to control the reaction
tlme strictly in order to stop the polymerization at a
re~uired stage. Vnder conditions wherein production of
syrups of high polymer content is intended, however, the
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polymer content increases rapidly by prolongation of reac-
tion time on account of the aforesaid acceleration phenomenon;
and when the content exceeds a certain limit, a stable and
stationary operation becomes no longer possible even under
an isothermal condition, whereby the reaction system becomes
unstable in concentration. Thus, this process has the
defect that production of syrups of high polymer content is
difficult or impossible. Furthermore, in the process with a
continuous stirred tank reactor, the concentration of the
remaining initiator only decreases slowly with a lapse of
reaction time even at temperatures at which rapid decomposi-
tion of initiator takes place in the batchwise process as
above. Consequently, the syrups obtained have a higher
concentration of the remaining initiator than in the batch-
wise process, so that the viscosity of the syrup unavoidably
increases by progress of polymerization during cooling or
storage.
In order to obtain a syrup of high heat stability
which does not cause such polymerization, it is necessary to
decrease the concentration of remaining initiator in the
syrup to as low a level as possible. For this purpose, the
reaction needs to be carried out at a temperature much
higher than that at which rapid decomposition takes place in
the batchwise process. ~owever, in the reaction under such
condition, the following defect appears: a certain period
of time is required for a monomer and an initiator freshly
supplied to the reaction mixture in the reactor to be
uniformly mixed. Under such condition, however, decomposi-
tion of initiator proceeds before sufficient mixing is
achieved, and as a result, syrups produced have a very broad
7752
distribution ranging from a very low polymerization degree
to a very high polymerization degree. Cast sheets resulting
from such syrups are poor in quality since they contain
polymers of low polymerization degree. Furthermore, the
viscosity of the syrups is high for the polymer content on
account of the broad distribution of polymerization degree,
which makes it difficult to increase the polymer content and
to shorten the casting time.
In order to overcome the defect of the aforesaid
process, U.S. patent 3,474,081 discloses a process wherein
polymerization is carried out using at least two continuous
stirred tank reactors connected in series. This patent
says: In this process, 40 to 95 % by weight of polymers in
the syrup is produced in the first reactor and the rest is
produced in the second reactor and thereafter. Since the
polymers in the syrup are separately produced in at least
two concentrations of initiator, the polymers comprise at
least two parts, a part of high molecular weight and a part
of low molecular weight. The weight average molecular
weight of the former part is at least two times as large as
that of the latter part, and the latter part occupies 40 to
95 % by weight of polymers in the syrup. When the content
of the low molecular weight part is high within the above
range, the resulting syn~p has a relatively low useful
viscosity and a high solid content. It may be considered
that this method was developed with the intention of in-
creasing the content of low molecular weight part in the
polymer to limit the weight averzge polymerization degree
which directly affects the syrup viscosity to a low level,
thereby obtaining a syrup having a relatively low viscosity
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1~7752
and a high polymer content.
But, polymers of low polymerization degree cause a
reduction in the average polymerization degree of cast sheet
and an easy foaming of the sheet on heat molding. Syrups
of which the polymer content is increased by increasing the
content of the part of low polymerization degree make it
possible to shorten the casting time, but they lower the
quality of cast sheet Further, the followings are known
from the relationship between the distribution of poly-
merization degree of polymers in a syrup obtained by this
method and the concentration of the remaining initiator: in
the first reactor, polymers of low polymerization degree are
produced in a relatively low proportion within the above
range when an average residence time in the reactor is
relatively short as compared with the half-life period of
the initiator. In order to sufficiently decrease the
concentration of the remaining initiator in the final syrup,
an increase in the number of reactors is necessary. In this
case, the average polymerization degree of polymers produced
in ea~h reactor rapidly increases as the polymers move
forward the final reactor in the same manner as in the
continuous tubular reactor. As a result, the polymer in the
final syrup contains the part of high polymerization degree
in large amounts and has a broad distribution of polymeri-
zation degree, and the viscosity of the syrup becomes high
for the polymer content.
In the first reactor, on the other hand, polymers
of low polymerization degree are produced in a high propor-
tion within the above range when a reacticn time in the
reaction is sufficiently long as compared with the half-life
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1~77S2
period of the initiator. In this case, the concentration of
the remaining initiator can be decreased relatively easily
with two xeactors or more. Since, however, the concen-
tration of remaining initiator in the first reactor is very
much different from that in the second reactor, the weight
average polymerization degree of the part of high polymeri-
zation degree is so large as more than 2 times that of the
part of low polymerization degree. For this reason, although
the content of the part of high polymerization degree is
low, the polymer in the syrup has a relatively broad distri-
bution of polymerization degree. That is, a large decrease
in the concentration of remaining initiator results in broad
distribution of polymerization degree. It may therefore be
the case that still this process does not satisfy the purpose
of shortening the casting time without lowering the quality
of the cast sheet.
Japanese Patent Publication No. 35357/1973 discloses
a process for con~inuous production of a prepolymer of
methacrylic esters characterized by using a reactor compris-
ing a former part and a latter part, the former one having
at least one continuous stirred tank reactor connected in
series and the latter one having at least one tubular reactor
connected in series, and fixing the conversion of reaction
mixture at the outlet of the former part to 9 to 12 %. This
process relates to the removal of heat generated which
becomes a problem in the continuous process with a stirred
tank reactor. In this process, a plural number of stirred
tank reactors connected in series is used for production of
prepolymers with high conversion, on the basis of the
finding that a maximum conversion in one vessel is only 2.5
37752
~ in order to control te exothermic reaction stably.
Furthermore, said reactor is connected to a tubular reactor
in order to facilitate the control of production quantity
with no change ln quality and to prevent blockage of tubular
reactor which is a weak point of the reactor.
In this process, the conversion in the former part
is restricted to 9 to 12 ~ in order to control the reaction
stably. Consequently, this process does not satisfy the
object of producing syrups of high polymer content which are
suitable for shortening of casting time. Further, the
concentration of remaining initiator in the syrup is kept
relatively large since the polymerization is carried out at
50 to 100C. This process is not also satisfactory in this
respect.
An object of the present invention is to provide a
process for continuous production of a prepolymer syrup
having a high polymer content and containing a polymer
which has a very narrow distribution of polymerization degree.
Another object of the present invention is to provide a
process for the continuous production of a prepolymer syrup
having an extremely low concentration of initiator remaining
in the syrup. Further, another object of the present inven-
tion is to provide a process for the continuous production of
a prepolymer syrup which is capable of stable and steady oper-
ation. Other objects and advantages of the present invention
will become apparent from the explanation described below.
The inventors extensively studied to overcome
these drawbacks, and as a result, in the process for
continuous production of methyl methacrylate syrups which
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~7752
comprises continuously supplying a methyl methacrylate
monomer and a radical-polymerization initiator to a reaction
zone thereby polymerizing the monomer partially and then
continuously withdrawiny the resulting syrup, the inventors
found a process for continuous, stable production of methyl
methacrylate syrups of high polymer content by using a
reaction zone comprising one or at least two series connected
stirred tank reactors, continuously supplying the monomer to
the reactor or the first reactor, continuously supplying the
intiator at the same time to the reactor or at least two
reactors including the first one, and sp~cifying the reac-
tion temperature and average residence time in each reactor.
Particularly, the inventors found that, when the number of
reactor is at least two, a higher polymer content syrup can
be obtained very effectively, with a narrow distribution of
polymerization degree maintained, by balancing the amounts
of the initiators added to the stirred tank reactors one
another thereby controlling the overall distribution of
polymerization degree of polymers produced in said reaction
zone to a narrow range. Further, when the number of the
stirred tank reactor in the reaction zone is one, but
optionally, when at least two stirred tank reactors in the
reaction zone are used, the resulting syrups are introduced
into a reaction zone composed of one or at least two, pre-
ferably 1 to 5, tubular reactors which are connected in
series, and passed thrvugh said succeeding reaction zone
under conditions of specified reaction temperature and
average residence time in each tubular reactor. By this
process, the concentration of the remaining initiator in the
resulting syrup can be reduced very effectively, with a
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~1~37752
narrow distribution of polymerization degree maintained.
According to the present invention, there is
provided a process for the continuous production of a
prepolymer syrup comprising (A) continuously supplying a
monomer comprising methyl mathacrylate as a main component
and a radical-polymerization initiator to a reaction zone
wherein substantially a complete mixing is achieved, during
which the reaction zone is kept under such a condition that
the concentration of the remaining initiator is 1/2 to 1/1,000
times that of the initiator supplied, or (A') continuously
supplying said monomer to a first reaction area in a reaction
zone (hereinafter referred to as "first reaction zone")
wherein at least two reaction areas, in which substantially
a complete mixing is achieved, are arranged in series,
continuously supplying a radical-polymerization initiator
simultaneously to at least two reaction areas including the
first one, and passing the monomer through the reacti.on
areas successively thereby polymerizing the monomer into
syrup, during which the reaction areas are kept under such
a condition that the concentration of the remaining initiator
in at least the reaction areas to which the initiator is
supplied is 1/2 to 1/1,000 times that of the initiator supplied,
and then, optionally, in the case of ~A'), (B) introducing
the resulting reaction mixture into a reaction zone (herein-
after referred to as "second reaction zone'l) wherein a
piston flow is substantially achieved, and passing it
through the zone, dur~ng which the temperature of the zone
and the average residence time of the mixture are maintained
so that the rest of the polymer in the final syrup is
produced in the zone and the concentration of remaining
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initiator is reduced to substantially a negligible amount,
thereby obtaining the final syrup, the distribution of
polymerization degree of the polymer in the syrup being 3.0
or less as expressed in a polydispersity which is a ratio of
weight average polymerization degree to number average
polymerization degree.
As the methyl methacrylate monomers used in the
present invention, monomers or monomer mixtures commonly
used for the production of this kind of syrup are used as
they are. Of these, a monomer containing methyl meth-
acrylate as a main component, is particularly preferred.
Methyl methacrylate may be used alone or in mixture with at
least one ethylenically unsaturated monomer copolymerizable
therewith such as alkyl acrylates (e.g. methyl acrylate,
ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-
hydroxyethyl acrylate, ethyleneglycol diacrylate), alkyl
methacrylates (e.g. ethyl acrylate, lauryl methacrylate,
2-hydroxyethyl methacrylate, ethyleneglycol dimethacrylate),
unsaturated nitriles (e.g. acrylonitrile, methacrylonitrile),
unsaturated amines (e.g. acrylamide), unsaturated carboxylic
acids (e.g. acrylic acid, methacrylic acid), vinyl compounds
le.g. vinyl chloride, styren~, ~-methylstyrene) and the
like. In this case, the amount of said monomer copolymeri-
zable with methy~ methacrylate is less than ~0 ~ by weight,
preferably up to 20 ~ by weight, based on the mixture. It
is necessary, in general, to limit the amount of these
ethylenically unsaturated compound to the above ran~e in
order that the resulting cast sheet is improved in quality
without losing characteristics as a methyl methacrylate cast
sheet,
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775Z
As the radical-polymerization initiator used in
the present invention, those which generate a radical
relatively rapidly at 90 to 200C, preferably 110 to 180C,
are used. of these, those having a half-life period of less
than 5 seconds at less than 180C, preferably less than
140C, are preferred, For example, there may be given a~o
compounds such as azobisisobutyronitrile, azobisdimethyl-
valeronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile)
and azobiscyclohexanenitrile, and peroxides such as benzoyl
peroxide, lauroyl peroxide, acetyl peroxide, capryl per-
oxide, 2,4-dichlorobenzoyl peroxide, isobutyl peroxide,
acetylcyclohexyl sulfonyl peroxide, tert-butyl peroxy-
pivalate, tert-butyl peroxy-2-ethylhexanoate, isopropyl
peroxydicarbonate, isobutyl peroxydicarbonate, sec-butyl
peroxydicarbonate, n-butyl peroxydicarbonate, 2-ethylhexyl
peroxydicarbonate and bis(4-tert-butylcyclohexyl) peroxy-
dicarbonate. These initiators may be used alone or in
combination. Particularly, when initiators having a half-
life period of less than 5 seconds at less than 140C are
used, the reaction is favorably carried out at the lower
side of the reaction temperature range of 90 to 1~0~. In
this case, a load of pre-heating of monomer and that of
cooling of syrup can be diminished, and besides pressure
conditions can also be relieved.
~ he amount of the initiator is generally 0.001 to
1 ~ by weight, preferably 0.01 to 0.5 ~ by weight, based on
the methyl methacrylate monomers. ~hen high polymer contents
are required, the concentration of the supplied initiator is
adjusted to a high level, while when high number average
polymerization degrees are required, said concentration is
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adjusted to a low level.
In the production of syrups according to the
present invention, the number average polymerization degree
and weight average polymerization degree of polymers in the
syrup, and the viscosity of the syrup can easily be adjusted
to a required level without a chain transfer agent, by
mutual regulation of reaction temperature, concentration of
the supplied initiator and average residence time of the
reaction mixture. But, chain transfer agents may be used so
far as they do not lower the quality of syrups or cast
sheets.
A methyl methacrylate monomer and a radical-
polymerization initiator are continuously supplied to the
first reaction area in the first reaction zone wherein
reaction areas, in which substantially a complete mixing is
achieved, are arranged in series. Under conditions wherein
substantially a complete mixing is achieved, the distri-
bution of polymerization degree of resulting polymers is
very narrow, and its value expressed in a polydispersity,
of the most probable distribution based on the assumption
that polymerization is all terminated by disproportionation.
Mext, when the number of the reaction area in the
first reaction zone is at least two, an additional initiator
is supplied to at least one of the reaction areas in the
first reaction zone which follows the first one. In the
reaction areas to which an additional initiator is supplied,
the additional initiator and the reaction mixture coming
from the pre~eding area are mixed su~stantially completely,
and therefore the distribution of polymerization degee of
pol~mers newly produced in said reaction areas is very
- 23 -
11~7752
narrow, and its polydispersity is substantially less than
2,2. Said reaction zone may contain reaction areas to which
an additional initiator is not supplied. The number average
polymerization deqree of polymers newly produced in said
reaction areas is generally larger than in the other ones,
but its polydispersity is substantially less than 2.2. Par-
ticularly, when the reaction mixture from the preceding
areas has a relatively high concentration of remaining
initiator, the polymer content of the syrup produced in said
whole reaction zone can be increased with little or no
broadening of the distribution of polymerization degree of
polymers in the syrup. Generally, however, it is desirable
to supply the initiator to every reaction area in order that
the distribution of polymerization degree of polymers in the
final syrup is kept narrow.
In the first reaction area and other areas to
which an additional initiator is supplied, the reaction
temperature and the average residence time of the reaction
mixture in each area should be kept so that the concen-
tration of the remaining initiator is 1/2 to 1/1,000 time,
preferably 1/5 to 1/1,000 time, particularly preferably
1/10 to 1/500 time, that of supplied initiator. When the
concentration of the remaining initiator is low ~lithin this
range, particularly a stable, steady operation can be
carried out. When the concentration exceeds this range, the
operation easily becomes thermally unstable, and in order to
carry out a stable, steady stationary operation, it i5
necessary to limit the amount of polymer produced in the
area to an extremely low ievel. Consequently, the number of
reaction areas should be much increased to obtain final
- 24 -
~)77SZ
syrups having a h-gh polymer content. While when said
concentration is below this range, the supplied initiator is
decomposed before complete mixing of the initiator and the
reaction mixture is achieved. As a result, polymers them-
selves newly produced in the area have a broad distribution
of polymerization degree.
In the reaction axeas to which an additional
initiator is not supplied, the absolute value of the concen-
tration of the supplied initiator is small and the amount of
polymers newly produced is also small, so that a stable,
steady operation can be carried out relatively easily.
Consequently, a concentration ratio of the remaining ini-
tiator to the supplied initiator in said reaction areas is
not particularly limited, ~ut it is preferably within the
above range.
In the present invention, the reaction temperature
of the first reaction zone is not particularly limited, but
it is generally 90 to 200C, preferably 110 to 180C.
Particularly, when at least two reactors are used in the
zone, the reaction temperature of each reaction area in the
zone is regulated, depending upon the decomposition temper-
ature of the initiator, so that a concentration ratio of the
remaining initiator to the supplied initiator may be within
the above range, The average residence time of the reaction
mixture in the first reaction zone is regulated, like the
concentration of the supplied initiator, according to the
polymer content and the number average polymerization degree
o~ the required final syrups, and it is generally 1 to 30
minutes, preferably 2 to 15 minutes. In the case of using
at least two reaction areas in the first reaction zone, the
- 25 -
il~775Z
average residence time in each reaction area is generally
0.1 to 20 minutes, preferably 0.2 to 5 minutes.
Maintenance of reaction temperature in the stirred
tank reactor is generally achieved by furnishing the reactor
with a ~acket at the outside, and circulating a heat medium
of controlled temperature through the jacket. In the
present invention, however, it is difficult to maintain a
required temperature by this method since the rate of
reaction is very high. Particularly in the case of commercial
scale production, the reaction system becomes thermally
unstable so that stable, steady operation is impossible. In
the present invention, the quantity of heat generated by
polymerization is almost equal to that of sensible heat
required for raising the temperature of the reaction mixture
to a required one, and the temperature of the reaction
mixture is kept by heating or cooling according to a required
polymer content and reaction temperature. The temperature
of the first reaction zone is preferably controlled hy
changing a temperature to which the monomer is pre-heated
prior to supply to the first reaction area. It is more
effective to furnish each reaction area in the zone with a
jacket at the outside, and to circulate a heat medium.
Pre-heating of monomer may be carried out by any method, if
non-flowing portion of the monomer is not present and
temperature control is possible. Preferably, however, the
pre-heating is carried out, for example, ~y passing the
monomer through a single tube e~uipped with a ~acket at a
Reynolds' number of more than 5,000, preerably more than
20,000, and circulating a heat medium of controlled temper-
ature through the jacket,
- 26 -
1~7752
The monomer and the initiator may be supplied as a
pre-heated mixture of both, but it is preferred to supply a
pre-heated monomer and a cooled initiator-containing solu-
tions may be previously mixed with at least one of the
additives commonly used for production of cast sheet and the
like, for example, ultraviolet absorbers, antioxidants,
pigments, dyes and the like.
The reaction areas in the first reaction zone need
to have functions to rapidly mix the monomer or initiator
with the reaction mixture constant. For this purpose, any
reaction equipment and stirring means may be used if sub-
stantially a complete mixing is achieved. Preferably, how-
ever, a means by which stirring is carried out at a Reynolds'
number of more than 2,000, preferably more than 5,000, is
used. For example, a continuous vessel-~ype reactor equipped
with a ribbon stirrer is used for this purpose.
A larger number of the reaction areas, in which
substantially a complete mixing is achieved, is desirable
for the purpose of elevating the safety of operation. But,
an extremely large number makes the operation troublesome
and increases the cost of products. Usually, the number is
1 to 1~, preferably 2 to 5.
In the case of using at least two reaction areas,
the amount of polymer produced in each reaction area is
controlled according to the polymer content of the final
syrup and the number of the reaction areas. But, an extreme
difference in the amount among the reaction areas is not
desirable since it makes the stability of operation poor or
makes the installment of reaction areas meaningless.
~enerally, the amount is almost same in every reaction area,
775Z
or it is made smaller gradually towards the final reaction
area. The latter is preferred. In the former and latter
cases respectively, the average residence time in every
reaction area is also kept almost same in general, and it is
made shorter gradually towards the final reaction area.
In the reaction areas to which an additional initiator is
not supplied, a shorter residence time of the reaction
mixture is generally selected than in the areas to which the
additional initiator is supplied. Consequently, the amount
of polymer produced is relatively small.
The amount of initiator supplied to reaction area
depends upon the amount and the number average polymeri-
zation degree of polymers produced in the area, the reaction
temperature of the area and the concentration of the remain-
ing initiator in the preceding area. When said concen-
tration is made small by raising the reaction temperature,
the amount of initiator is regulated depending upon the
amount of the polymers produced or the average residence
time in said area. Generally, the amount is almost same,
and preferably it is made smaller gradually towards the
final reaction area. In the present invention, when the
number of reaction area is one, the use of second reaction
~one is necessary. However, when the number of reaction
areas in that is at least two, the use of second reaction
zone is optional but preferable.
The amount and the num~er average polymerization
degree of polymers produced in the first reaction zone
depend upon the kind and the concentration of the initiator
supplied to each reaction area, and the reaction temperature
and the average residence time of reaction mixture in each
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~7752
reaction area. And, preferred concentration of the supplied
initiator, reaction temperature and average residence time
of the reaction mixture are selected depending upon the
polymer content and the number a~erage polymerization degree
of the required final syrup and the number of reaction
areas. The number average polymerization degrees of poly-
mers newly produced in the reaction areas are different one
another. In order to narrow the distribution of polymeri-
zation degree of polymers produced in the whole first reaction
zone, however, it is desirable to permit these number average
polymerization degrees to agree with one another as much as
possible. For this purpose, the amounts of initiator supplied
to the reaction areas are regulated mutually. When a maximum
to minimum ratio of number average polymerization degree of
polymers produced in each reaction area is maintained
generally at less than 3, preferably less than 2, the distri-
bution of polymerization degree of polymers coming out of
the first reaction zone is generally less than 2.5, pre-
ferably less than 2.2, as expressed in a polydispersity.
In the present invention, the amount of polymer
produced in each reaction area in the first reaction zone
depends upon the number of reaction area, but it is
generally xelatively low levels such as 3 to 35 ~ by weight,
preferably 5 to 25 ~ by weight, particularly. Accordingly,
in the case of using at least two reaction areas, the
quantity of heat generated in each area is also relatively
small. The temperature in the first zone is generally 90 to
200C, preferably llO to 180C so as to allow the initiator
to be decomposed rapidly. The temperature of the whole
first reaction zone can effectively be controlled beyond
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1~7752
expectation by changing the temperature of the monomer
supplied to the first reaction area. Particularly, when the
amount of polymer produced in the first reaction area is
large within the above range and the amounts of polymer
produced in the subsequent areas are small within said
range, steady operations in the subsequent areas can be
carried out thermally stably by controlling the reaction
temperature in the first reaction area, even though the
subsequent areas are under substantially an adiabatic
condition. Further, since the amount of polymer produced in
each area can be selected within relatively low levels, a
difference in polymerization rate constant between the
reaction mixtures entering the reaction area and leaving the
same area, can be made small. As a result, acceleration of
the rate of polymerization owing to the Trommsdorff effect
is apparently extremely diminished and syrups of extremely
high polymer content can favora~ly be obtained by a stable
steady operation.
When the number of reaction area in the first
reaction zone is one or, if desired, at least two, the
reaction mixture from the first reaction zone is then
introduced into the second one wherein a piston flow is sub-
stantially achieved, and, while being passed through the
zone, the rest of the polymer is produced and the concen-
tration of the remaining initiator is decreased. Since an
initiator is no longer supplied to the reactlon mixture
passing through the zone, the concentration of the remaining
initiator can be reduced very easily unlike the case of the
first reaction zone wherein an initiator is constantly
supplied and substantially a compiete mixing is achieved.
- 30 -
~1~7~SZ
Furthermore, since the amount of polymer produced is small,
the distribution of polymerization degree of polymers in the
final syrup i~ unexpectedly maintained narrow, although
polymers of relatively large polymerization degree are
produced. It is sufficient that the temperature of the
second reaction zone is one at which the remaining initiator
is rapidly decomposed. Generally, the temperature is one at
which the half-life period of initiator is less than 20
seconds, preferably less than 5 seconds. Preferably, the
temperature is not less than the one of the first reaction
zone. Particularly, it is desirable to maintain the reac-
tion conditions so as to raise the temperature of the reac-
tion mixture substantially adiabatically by polymerization
heat while the mixture passes through the zone.
In the second reaction zone, since nothing is
supplied to the reaction mixture, mixing is not essentially
necessary. Besides, since the amount of polymer produced is
small, reaction control is very easy even under adiabatic
conditions. Consequently, any of reaction equipments and
stirring means may be used if a substantial piston flow is
achieved. When stirring is not carried out at all, however,
attachment of polymers to the wall of reactor occurs, which
makes the piston flow substantially difficult and causes
blockage of reactor tube if the attachment further proceeds.
Stirring is therefore desirable. As the stirring means, the
following ones are employed: stirrers having a back mixing
coefficient of less than 20 %, preferably less than 10 ~ are
used, and stirring is carried out at a Reynolds' number of
more than 2,0Q0, preferably more than 5,000; and self-wiping
type stirrers having a back mixing coefficient of less than
- 31 -
775Z
20 %, preferably less than 10 ~ are used. For example,
tubular reactors having a similar structure to a twin-screw
extruder are used for this purpose. The second reaction
zone may be equipped with a jacket at the outside to control
the temperature by a heat medium. But, to keep the zone
under substantially an adiabatic condition is more desira~le
since the remaining initiator i5 decreased more rapidly.
The vapor pressure of reaction mixture in both
reaction zones is generally higher than atmospheric pressure.
For facilitating the control of residence time and temper-
ature in both reaction zones thereby maintaining the qualities
of final syrups, for example, polymer content, viscosity and
concentration of remaining initiator, substantially constant,
it is desirable to apply a pressure higher than the vapor
pressure, generally 1 to 20 atmospheres, preferably 2 to 10
atmospheres, to the reaction mixture so as to allow the
mixture to keep s-ibstantially a liquid phase.
The average residence time of reaction mixture in
the second reaction zone is 0.05 to 5 times, preferably 0.1
to 2 times as long as that of the first reacton zone.
It is preferred that the average residence time is long
enough to decrease the concentration of the remaining ini-
tiator to substantially a negligible amount. Long average
residence time does not affect polymerization, because the
concentration of the reamining initiator is so substantially
negligible that the polymerization proceeds thermally very
slowly. Consequently, an increase in polymer content and
viscosity is negligibly small. But, a longer average
residence time than necessary is useless since a larger
reaction zone i9 re~uired. Also, a~erage residence time of
- 32 -
1~77SZ
less than 0.05 time as long is not desirable since the
concentration of the remaining initiator is not so much
reduced.
The concentration of the remaining initiator in
the reaction mixture coming out of the second zone is
negligibly small and the concentration decreases rapidly as
the mixture proceeds towards the outlet of the zone. In
correspondence to this, the number average polymerization
degree of polymers newly produced in the zone rapidly
increases, while the amount of the polymer rapidly decreases
as the mixture proceeds towards the outlet of the zone. As
a result, the number average polymerization degree of polymers
produced in the zone is unexpectedly not so large as
compared with that of the first zone, and further it becomes
possible to decrease the concentration of the remaining
initiator in the final syrup to substantially a negligible
amount and to mairltain the distribution of polymerization
degree of polymers in the syrup very narrow. Thus, the
distribution of polymerization degree of polymer is less
than 3, preferably less than 2.5, particularly preferably
less than 2.2, as expressed in a polydispersity which is a
ratio of weight average polymerization degree to number
average polymerization degree.
The polymer in the resulting final syrup contains
generally 60 to 99.5 ~ by weight, preferably 90 to gg.5 % by
weight, particularly preferably 95 to 99.5 ~ by weight, of
the syrup produced in the first reaction zone.
The concentration of the remaining initiator in
the reacticn mixture coming out of the second reaction zone
is negligibly small, i.e. less than 1 ppm, preferably less
- 33 -
~7752
than 0.1 ppm, particularly preferably less than 0.01 ppm.
The final syrup obtained by the above method shows little or
no increase in polymer content and viscosity even though it
is left at the temperature at which it is produced. It is
however general to store the syrup until production of a
cast sheet. And, for the purpose of avoiding an increase in
polymer content and viscosity during storage of syrup and
supply of initiator, other additives and syrup and prevent-
ing a lowering in processability of syrup and quality of
cast sheet, the syrup is generally cooled to less than
100C, preferably 80C.
The syrups obtained in the present invention have
a concentration of the remaining initiator negligibly
smaller than 1 ppm, for example, 0.01 ppm. Therefore, the
increase of polymer content and viscosity is negligible even
though the syrup is not cooled rapidly after it comes out of
the second reaction zone, so that syrups of constant quality
are easily obtained and said increase is not also observed
during storage. Further, the syrups of the present inven-
tion have a good storage stability. For example, there is
no increase in the content of the remaining monomer in cast
sheet owing to the quality change of syrup during storage,
or no lowering in the quality of the cast sheet such as
foaming on heat molding. As described abo~e, the syrup of
the present invention has a superior storage stability.
Polymers in the syrups of the present invention
have an extremely narrow distribution of polymerization
degree, and the distribution is less than 3, preferably less
than 2.5, particularly preferably less than 2.2, as expressed
in said polydispersity. Accordingly, the number average
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7752
polymerization degree, which affects the average polymeri-
zation degree of cast sheet, can be made relatively high,
and the weight average polymerization degree, which affects
the viscosity of syrup, can be made relatively low. Conse-
quently, syrups having a relatively low viscosity and a high
polymer content can be obtained, and besides cast sheets
can be produced in a shortened casting time without lowering
of quality. When the syrups of the present invention are
polymerized without shortening the casting time, the average
polymerization degree of cast sheet can be increased, so
that cast sheets having a particularly superior quality can
be obtained. Furthermore, when the syrups of the present
invention having a relatively low polymer content are used
for casting, casting time can be shortened by increasing the
concentration of initiator, and in this case, a lowering in
the ~uality of cast sheet is relatively small.
The polymer content of the syrup of the present
invention is 15 to 80 ~ by weight. When the content is
below this range, an effect to shorten the casting time is
relatively small, while when the content exceeds this range,
the viscosity of the syrup becomes high even at extremely
high temperatures, and thus substantially a complete mixing
can not be achieved. The viscosity of the syrup obtained in
the present invention is O.S to 10,000 poises at 25C. When
the viscosity is below this range, the syrup leaks when
injected on ~asting. However, when the viscosity is higher
than 1,000 poises (which is a high level within the above
range), injection becomes difficult. Therefore, syrups
having a viscosity of 0.5 to 1,000 poises are used as they
are. Of the syrups of the present invention, those having a
- 35 -
i~77SZ
polymer content of 20 to 40 % by weight and a viscosity of 5
to S00 poises are particularly suitable for continuous
casting such as the process described hereinbefore, since
they have a good processability on injection and are usable
in drastically shortened casting time without lowering the
quality of the cast sheet. As the number average poly-
merization degree of polymers in the final syrup, a range of
300 to 6,000 is selected. Particularly, a range of 300 to
2,000 is selected for the syrups of high polymer content
suitable for continuous casting. In order to elevate the
quality of cast sheet, however, it is preferred to select as
high a number average polymerization degree as possible so
far as the viscosity does not become excessively higher than
the required polymer content.
In producing cast sheets, the syrups of the
present invention may be used as they are, or they may be
concentrated or diluted with a monomer or the same kind of
syrup so as to have a polymer content of 15 to 50 % by
weight, preferably 20 to 40 % by weight and a viscosity
(25C) of 0.5 to 1,000 poises, preferably 5 to 500 poises.
In some cases, the homogeneity and productivity of syrup
used for casting can be elevated advantageously by these
treatments. The syrups of the present invention have a low
viscosity fox their high polymer content, and have a good
storage stability. The syrups are therefore preferably used
not only for cast sheet and glass fiber reinforced cast
sheet but also for molding materials, adhesives, paints,
resin concrete compositions and the like.
The present invention will be illustrated specifically
with reference to the following examples, hut the present
- 36 -
~1~77S2
invention is not limited to these examples. In the
examples, percentages are by weight.
In the examples, the viscosity of syrup was
measured at 25C by means of a B-type viscometer. The
number average polymerization degree and the distribution of
polymerization degree of polymers in the syrup were measured
by gel-permeation chromatography using polystyrene gel as a
packing and tetrahydrofuran as an eluting agent, provided
that the distribution of polymerization degree was expressed
in a polydispersity.
Foaming of cast sheet on casting was evaluated by
the visual examination of foams in the cast sheet. Foaming
of cast sheet on heating was evaluated by heating the cast
sheet in a circulating hot-air oven at 180~C for 30 minutes
and examining foams in the cast sheet visually.
Reduced viscosity was measured at 25C using a Q.l
~ chloroform solut.ion of the cast sheet. Concentration of
remaining monomer was measured by gas-chromatography using
methylene chloride solution of the cast sheet.
Example 1
A 2-stage continuous reaction equipment havin~ the
following structure was used: the equipment consisted of a
former part and a latter part; in the former part was set up
a vessel-type reactor with a ri~bon-like propeller; in the
latter part was set up a tu~ular reactor having a mixing
shaft to which pins were fixed at a right angle to the
shaft, and to the inside wall of the reactor were fixed pins
at a right angle to the wall and towards the mixing shaft,
and both pins were aranged so that they could wipe off
matters attached to the opposite pins. A volume ratio of
11~775z
vessel-type reactor to tubular was 1 : 0.25. Methyl
methacrylate containing 0.047 % of azobisisobutyronitrile,
an initiator, was continuously supplied to the vessel-type
reactor so that an average residence time in the reactor was
147 seconds. The temperature and pressure in each reactor
were maintained at 160C and 6.0 atmospheres, respectively.
The feed liquor was pre-heated to akout 80~C by means of a
single tube equipped with a jacket.
The syrup from the tubular reactor had a polymer
content of 26.6 % and a viscosity of 21.0 poises at 25C.
Ninety-five percent of the total polymer was produced in the
vessel-type reactor. The concentration ratio of the remain-
ing initiator to the supplied initiator in the vessel-type
reactor was 1/32. The concentration of the remaining ini-
tiator in the final syrup was less than 0.01 ppm, and the
syrup did not show a change in both polymer content and
viscosity at all even though kept still at 60C for 5 hours.
The polymer in the syrup had a number average polymerization
degree of 745, and its distribution of polymerization degree
was 2.17, as expressed in a polydispersity which is a ratio
of weight a~erage polymerization degree to number average
polymerization degree. The viscosity of the syrup was low
for the high number average polymerization degree of the
polymer and the high polymer content of the syrup.
A polymerizable ~iquid composition was prepared by
dissolving 0.05 % of azobis(dimethylveleronitrile) in this
syrup. After deaeration under reduced pressure, the com-
position was polymerized in~o cast sheet using the well
known continuous polymerization equipment. The equipment
was constructed as follows: two pieces of mirror-polished
- 38 -
11~7752
stainless steel band (width, 500 mm; thickness, 0.6 mm) were
set up horizontally with one upon the other; the length of
polymerization zone was lO,000 mm in horizontal distance, of
which the first 6,740 mm corresponded to a heat-polymeri-
zation area heated with 85C water, the second 2,170 mm
corresponded to a heat-treatment area heated with 120C hot
air and the last l,090 mm corresponded to a cooling area
cooled with cold air. The distance between the upper and
lower bands was adjusted to make the thickness of cast sheet
3 ~m. The above polymerizable composition was continuously
supplied to a space between the bands, and the bands were
run at a rate of 374 mm~min so that said composition passed
through the heat-polymerization area during 18 minutes. The
product had a reduced viscosity o~ 2.37 dl/g and a remaining
monomer content of 0.8 %. ~he product had a good appearance
without foaming by polymerization or heating.
Comparative ExamPle l
Syrup was produced using the vessel-type reactor
alone in the former part of the continuous equipment in
Example 1. The ~ind and the concentration of the initiator,
and the a~erage residence time, temperature and pressure in
the reactor were completely the same as in Example l.
The resulting syrup had a polymer content of 25.0
% and a viscosity of 10.3 poises. The polymer in the syrup
had a numher average polymerlzation degree of 725 and its
distribution of polymerization degree was 2.02, as expressed
in a polydispersity. But, the concen~ration cf the remaining
initiator in the syrup was as large as 15.2 ppm. When the
syrup was kept still at 60C, it lost fluidity completely in
1 ho~r ~y rapid progress of polymerization, and thus the
- 39 -
7752
syrup could not withstand long-term storage.
The resulting syrup was mixed with 0.04 % of
azobis(dimethylvaleronitrile) and polymerized using the same
continuous polymerization equipment as in Example 1.
Polymerization was carried out under the same conditions as
in Example 1 except that the syrup was passed through the
heat-polymerization area during 24 minutes. The resulting
cast sheet had a reduced viscosity of 2.69 dl/g and included
no foam by polymerization. But it had a remaining monomer
content as high as 4.2 %, and it showed foaming by heating.
When the syrup was passed through the heat-polymerization
area during 21 minutes without changing other conditions, a
striking foaming by polymerization occurred and the cast
sheet obtained had no commercial value. When a mixture of
this syrup and 0.05 % of azobis(dimethylvaleronitrile) was
passed through the heat-polymerization area during 21
minutes, the resulting syrup included no foam by polymeri-
zation but showed a striking foaming by heating.
Comparative Example 2
A 2-stage continuous reaction equipment having the
following structure was used: the equipment consisted of
the ~irst and theisecond vessel-type reactors with a ribbon-
like propeller; and both reactors were connected in series
and a volume ratio of the first to the second was 1 : 2.
Methyl methacrylate containing 0.047 % of azobis-
isobutyronitrile was continuously supplied to the first
reactor so that an average residence time in the reactor was
147 seconds. The temperature and pressure of each reactor
were kept at 160C and 6.0 atmospheres, respectively.
The syrup thus obtained had a polymer content of
- 40 -
1~775Z
31.4 ~ and a viscosity of 1,100 poises. The proportion of
polymer produced in the first reactor was 80 % of the total
polyme~. The concentration of the remaining initiator in
the syrup was 0.23 ppm. When the syrup was kept still at
60C for 3 hours, the polymer content and the viscosity of
the syrup increased to 31.6 % and 2,500 poises, respec-
tively. The polymer in the syrup had a number average
polymerization degree of 870, and its distribution of
polymerization degree was 3.32, as expressed in poly- -
dispersity.
This syrup was mixed with 0.04 ~ of azobis-l
(dimethylvaleronitrile) and polymerized using the same
equipment as in Example 1. Polymerization was carried out
unde~ the same conditions as in Example 1 except that the
syrup was passed through the heat-polymerization area
during 17 minutes. Thus, a cast sheet was o~tained. This
syrup was so highly viscous that it was hardly injected
into a space between the belts. The cast sheet included
foams by polymerization.
This syrup was diluted with the monomer to the
same viscosity, 21.0 poises, as in Example 1. The polymer
content of the diluted syrup was 21.5 %. The diluted syrup
was mixed with 0.05 % of azobis(dimethylvaleronitrile) and
polymerized in the same manner as above except that the
syrup was passed through the heat-polymerization area during
25 minutes. The resulting product had a reduced viscosity
of 2.74 dl/g and a remaining monomer content of 1.9 %. The
product included no foam ~y polymerization but showed
foaming by heating. The same diluted syrup was mixed with
0.08 ~ of azobis(dimethylvaleronitrile) and polymerized in
- 41 -
11~`775Z
the same manner as above except that the syrup was passed
through the heat-polymerization area during 21 minutes. The
product had a reduced viscosity of 2.17 dl/g and a remaining
monomer content of 1.7 ~. The product included no foam by
polymerization but showed a striking foaming by heating.
The syrup was diluted with the monomer to the same polymer
content, 26.6 %, as in Example l. The viscosity of the
diluted syrup was 170 poises.
Comparative Example 3
Syrup was produced by using the same reactor as in
Comparative Example 1. Methyl methacrylate containing 0.45
~ of azobisisobutyronitrile was continuously supplied to the
reactor so that an average residence time in the reactor was
14.6 minutes. The pressure and the temperature in the
reactor were kept at atmospheric pressure and 85C, respec-
tively. The concentration ratio of the remaining initiator
to the supplied initiator at the outlet of the reactor was
about 90/100. At the initial stage of polymerization, a
syrup having a polymer content of about 25 ~ and a viscosity
of about 12 poises was obtained. But, as the polymerization
proceeded, maintenance of the reaction temperature became
difficult, and after about l hour, the reaction temperature
rapidly increased and the polymerizatiGn became violent. As
a result, the contents in the reactor solidified and continu-
ation of reaction was impossible.
~xample 2
Syrup was produced using the same equipment as in
Example l except that the volume of each reactor was 5
liters. An ethyl acrylate solution (2~GC) containing ~.7 %
of azobisisobutyronitrile was continuously supplied to the
- 42 -
1~7752
vessel-type reactor at a rate of 0.21 liter/min. And,
methyl methacrylate pre-heated to 120C was continuously
supplied to the same reactor at a rate of 1.9 liter/min.
The temperature and the pressure in each reactor were main-
tained at 160C and 6.0 atmospheres, respectively. A
concentration ratio of the remaining initiator to the
supplied one in the vessel-type reactor was 1/32.
The syrup coming out of the tubular reactor had a
polymer content of 31.9 ~ and a viscosity of 45.g poises at
25C. The concentration of the remaining initiator in the
syrup was less than 0.01 ppm. The polymer in the syrup had
a number average polymerization degree of 615 and its
distribution of polymerization degree was 2.18, as expressed
in polydispersity.
Example 3
Syrup was produced using a 2-stage continuous
reaction equipment having the following structure: two
vessel-type reactors with a ribbon-like propeller were
connected in series; and a volume ratio of first reactor to
second one was 3 : 1. Methyl methacrylate containing 0.047
% of azobisisobutyronitrile was continuously supplied to the
first reactor to make an average residence time in the
reactor 147 seconds. A methyl methacrylate solution
containing 2 % of azobisisobutyronitrile was continuously
supplied to the second reactor so that the amount of azo-
bisisobutyronitrile added was 0.017 ~ of the reaction
mixture. The temperature and pressure in each reactor were
kept at 160C and 6.0 atmospheres, respectively. The feed
liquor to the first reactor was pre-heated to 80C using a
single tube equipped with a jacket. The temperature of the
- 43 -
~3775Z
initiator containing solution supplied to the second reactor
was 25C.
The syrup from the second reactor had a polymer
content of 31.8 % and a viscosity of 90.8 poises at 25C.
The weight ratio of polymer~ produced in the reactors was 73
: 27. The polymer in the syrup had a number average i
polymerization degree of 750 and its distribution of poly-
merization degree was 2.05, as expressed in polydispersity.
Continuous operation was carried out under the conditions
described above for 700 hours. During that time, the
reaction temperature was substantially constant, and the
polymer content and the viscosity of the syrup obtained did
not show a substantial variation. Consequently, the
progress of reaction was extremely stable operationally.
Example 4
Syrup was produced using a 3-stage continuous
reaction equipment having the following structure: the
equipment consisted of a former part and a latter part; two
vessel-type reactors with a rib~on-like propeller were set
up in the former part and both reactors were connected in
series; in the latter part was set up a tubular reactor
having a m xing shaft to which pins were fixed at a right
angle to the shaft, and to the inside wall of the reactor
were fixed pins at a right an~le to the wall and towards the
mixing shaft; and both pins were arranged so that they could
wipe off mattexs attached to the opposite pins. A v~lume
ratio of first vessel-type reactor to second one to tu~ular
reactor was 1 : 0.33 : 0.25.
Methyl methacrylate containing 0.047 ~ of azobis-
isobutyronitrile, an initiator, was continuously supplied to
- 44 -
~)7752
the first vessel-type reactor to make an average residence
time in the reactor 147 seconds. A methyl methacrylate
solution containing 2 % of azobisisobutyronitrile was
continuously supplied to the second reactor so that the
amount of azobisisobutyronitrile added was 0.017 % of the
reaction mixture. The reaction mixture from the second
reactor was passed through the tubular reactor to finish
polymerization. The temperature and pressure of each
reactor were kept at 16~C and 6.0 atmospheres, respec-
tively. The feed liquor to the first reactor was pre-heated
to 80C by means of a single tube equipped with a jacket.
The temperature of the initiator solution supplied to the
second reactor was 25C.
The syrup from the tubular reactor had a polymer
content of 33.5 % and a viscosity of 176 poises at 25C.
The weight ratio of polymers produced in the reactors was 70
: 25 : 5, The concentration ratios of the remaining ini-
tiator to the supplied initiator in the first and the second
reactors were 1/32 and 1/11, respectively. The concen-
tration of the remaining initiator in the final syrup was
less than 0.01 ppm. The syrup did not show a change in both
polymer content and viscosity even though kept still at 60C
for 5 hours. The polymer in the syrup had a number average
polymerization degree of 755 and its distribution of poly-
merization degree was 2.13, as expressed in polydispersity
which is a ratio of weight average polymerizat~on degree to
number a~erage polymerization degree. The viscosity of the
syrup was low for the high number average polymerization
degree of the polymer and the high polymer content of the
syrup.
- 45 -
1~7752
A cast sheet was produced, using the continuous
polymerization apparatus as in Example 1, in the same manner
as in Example 1 except that a polymerizable liquid composi-
tion was prepared by dissolving 0.04 ~ of azobisdimethyl-
valeronitrile as polymerization initiator in the syrup and
the polymerizable liquid composition was passed through the
heat-polymerization area during 15 minutes. The product had
a reduced viscosity of 2.37 dl/g and a remaining monomer
content of 0.9 ~. The prod~ct had a good appearance without
foaming by polymerization or heating.
Example 5
Syrup was produced using the same equipment as in
Example 1 except that the volume of each reactor was 5
liters. Methyl methacrylate pre-heated to 130C was
continuously supplied to the first vessel-type reactor at a
rate of 3.27 liter/min, and at the same time an ethyl
acrylate solution (25C) containing 0.29 % of azobisiso-
butyronitrile (an initiator) was continuously supplied to
the same reactor at a rate of 0.36 liter/min. Further, a
methyl methacrylate solution (20C) containing 3 % of
additional azobisisobutyronitrile was continuously supplied
to the second vessel-type reactor at a rate of 0.035
liter/min. The temperature of each vessel-type reactor was
kept at 160C~ The temperature of the tubular reactor
increased to 162C as a result of adiabatic temperature-
increase. The pressure of each reactor was ~ept at 6.0
atmospheres. The concentration ratio of remaining initiator
to supplied initiator in the vessel-type reactor was 1/32.
The syrup from the tubular reactor had a polymer
content of 32.0 %, a viscosity of 159 poises at 25C and a
- 45 -
~7752
remaining initiator concentration of less than 0.01 ppm.
The polymer in the syrup had a number average polymerization
degree of 790 and its distribution of polymerization degree
was 2.18, as expressed in polydispersity.
A cast plate was produced, using the continuous
polymerization apparatus in Example 1, in the same manner as
in Example 1 except that a polymerizable liquid composition
was prepared by dissolving 0.04 ~ of azobisdimethylvalero-
nitrile in the syrup and polymerizable liquid composition
was passed through the heat-polymerization area during 16
minutes. The product had a reduced viscosity of 2.49 dl/g
and a remaining monomer content of 0.5 %. The product
included no foam therein and caused no foaming by heating.
Examples 6 to 14
The same equipment as in Example 4 was used except
that the volume ratio of first vessel-type reactor to second
one was changed as shown in Table 1 and that the volume of
the tubular reactor was 0.5 time that of the first vessel-
type reactor. Various radical-polymerization initiators as
shown in Table 1 were used, and each initiator was contin-
uously supplied to the first and the second reactors so that
the weight ratio of initiator to reaction mixture had a value
shown in Table 1. Methyl methacrylate was used as a monomer
and it was polymerized at varied average residence time and
reaction temperatures shown in Table 1. As a result, syrups
of such polymer content, viscosity and number average
polymerization degree as shown in Table 2 were obtained.
The concentration ratios of remaining initiator to supplied
one in the first and the second reactors were as shown in
~able 1. ~ny one of the syrups had a concentration of
- 47 -
i~L377SZ
remaining initiator of less than 0.01 ppm, and did not show
a change in either polymer content or viscosity even though
it was kept still at 60C for 3 hours. Further, the distri-
bution of polymerization degree of the polymer in each syrup
was less than 2.2, as expressed in polydispersity.
Cast plates were produced, using the continuous
polymerization apparatus in Example 1, in the same manner as
in Example 1 except that azobisdimethylvaleronîtrile in
amount as shown in Table 3 was added to the syrups and the
resulting polymerizable liquid compositions were passed
through the heat-polymerization zone during time as shown in
Table 3, respectively. Intrinsic vicsosities and remaining
monomer contents of the products thus obtained ~cast sheets)
had values as shown in Table 3. All of them included no
foam and caused no foaming by heating.
A half to 1 cc of dichloromethane was dropped on
each ~f test pieces of the cast sheets described above and
after 10 seconds, was wiped off using a guaze. Then, it was
observed whether or not there was a solvent blot on each
test piece. The test pieces had no blot except that the
test piece of Example 7 had a slight blot. Further, test
pieces were subjected to the accelerated weathering test
during 500 hours according to ASTM D-1499. However, the
test pieces showed no change in the external appearance.
- 4~ -
11~77sz
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- 49 -
1~775Z
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11~77sz
Example lS
The same equipment as in Example 1 was used except
that the volume ratio of first vessel-type reactor to
second vessel-typ~ reactor to tubular reactor was 1 : 0.5 :
0.5. Methyl methacrylate containing 0.046 % of azobis-
isobutyronitrile was continuously supplied to the first
vessel-type reactor so that an average residence time in the
reactor was 97.8 seconds. A methyl methacrylate solution
containing 2 % of azobisisobutyronitrile was continuously
supplied to the second reactor so that the amount of azobis-
isobutyronitrile added was 0.024 % of the reaction mixture.
Polymerization was carried out while maintaining the temper-
ature and pressure in each reactor at 160C and 6.0 atmo-
spheres, respectively.
The syrup from the tubular reactor had a polymer
content of 2~.8 % and a viscosity of 23.0 poises at 25C.
The weight ratio of polymers produced in the reactors was 62
: 32 : 6. The concentration ratios of the remaining ini-
tiator to supplied initiator in the first and the second
reactors were 1/21 and l/ll, respectively. The concen-
tration of the remaining i~itiator in the final syrup was
less than 0.01 ppm, The polymer in the syrup had a number
average polymerization degree of 605, and its distribution
of polymerization degree was 2.15, as expressed in poly-
dispersity.
A cast plate was produced using the continuous
polymerizatio~ apparatus in Example 1 in the same manner as
in Example l except that 0.04 ~ of azobisdimethylvalero-
nitrile was added to this syrup and the resulting poly-
merizable liquid composition was passed through the heat-
- 52 -
)7752
polymerization area during 18 minutes. The obtained product
had a reduced viscosity of 2.26 dl/g and residual monomer
content of 1.2 %, and included no foam and caused no foaming
by heating.
Example 16
A 4-stage continuous reaction equipment having the
following structure was used: the equipment consisted of a
former part and a latter part; three vessel-type reactors
with a ribbon-Like propeller were set up in the former part
and the three reactors were connected in series; in the
latter part was set up a tubular reactor having a mixing
shaft to which pins were fixed at a right angle to the
shaft, and to the inside wall of the reactor were fixed pins
at a right angle to the wall and towards the mixing shaft;
and both pins were arranged so that they could wipe off
matters attached to the opposite pins. A volume ratio of
first reactor to second one to third one to tubular reactor
was 1 : 0.5 : 0.5 : 0.1.
Polymeri7ation was carried out as follows:
methyl methacrylate containing 0.046 ~ of azobisisobutyro-
nitrile was continuously supplied to the first vessel-type
reactor to make an average residence time in the reactor
97.8 seconds. A methyl methacrylate solution containing 2
of additional azobisisobutyronitrile was continuously
supplied to the second and third reactors so that the
amounts of azobisisobutyronitrile added were 0.024 % and
0.032 %, respectively, of the reaction mixtures. Temper-
atures in the reactors were 160, 162, 164 and 165C, re-
spectively, and pressure in each reactor was 6.3 atmospheres.
The syrup from the tubular reactor had a polymer
- 53 -
11q~77~2
content of 45.3 % and a viscosity of 1,680 poises at 25C.
The weight ratio of polymers produced in the reactors was 43
: 22 : 32 : 3. ~he concentration ratios of remaining ini-
tiator to supplied initiator in the first, second and third
reactors were 1/21, 1~13 and 1/15, respectively. The concen-
tration of the remaining initiator in the final syrup was
less than 0.01 ppm. The polymer in the syrup had a number
average polymerization degree of 615 and its distribution of
polymerization degree was 2.12, as expressed in polydis-
persity. When the syrup was diluted with the monomer to a
polymer content of 35.0 %, the diluted syrup had a viscosity
of 95.5 poises at 25C.
A cast plate was produced in the same manner as in
Example 1 except that a polymerizable liquid composition
having a polymer content of 35 ~ and a viscosity of 95.5
poises, prepared by diluting this syrup with methyl meth-
acrylate and adding 0.04 ~ of azobisdimethylvaleronitrile to
the diluted syrup, was used and said composition was passed
through the heat-polymerization area during 14 minutes. The
product had a reduced viscosity of 2.02 dl/g and included no
foam and caused no foaming by heating.
Example 17
The same equipment as in Example 16 was used
except that the volume ratio of the reactors was 1 : 0.5 :
0.33 : 0.2. Polymerization was carried out as follows:
methyl methacrylate was continuously supplied to the first
reactor to make an average residence time in the reactor 106
seconds. Azobisisobutyronitrile was continuously supplied
to the vessel-type reactors so that the amounts of azobis-
isobutyronitrile added were 0.104 %, 0.054 % and 0.054 %~
11~77S2
respectively, of the reaction mixture. Temperatures in t~e
reactors were 160, 163, 165 and 166C, respectively, and
pressure in each reactor waæ 6.3 atmospheres.
The syrup from the tubular reactor had a polymer
content of 62.5 % and a viscosity of 8,700 poises at 25C.
The concentration ratios of the remaining initiator to the
supplied one in the first, second and third reactors were
1/24, 1/15 and 1/12, respectively. The concentration of the
remaining initiator in the final syrup was less than 0.01
ppm. The polymer in the syrup had a num~er average poly-
merization degree of 415 and its distribution of polymeri-
zation degree was 2.lQ, as expressed in polydispersity.
When the syrup was diluted with the monomer to a polymer
content of 40.3 %, the diluted syrup had a viscosity of 55.0
poises at 25C.
A cast plate was produced in the same manner as in
Example 1 except that a polymerizable liquid composition
having a polymer content of 40.3 % and a viscosity of 550
poises, prepared by diluting this syrup with methyl meth-
acrylate and adding 0.05 ~ of bis(4-tert-butylcyclohexyl)-
peroxydicarbonate to the resulting syrup, was used and the
polymerizable liquid composition was passed through the
heat-polymerization area during 13 minutes. The product had
a reduced viscosity of 1.82 dl/g and a residual monomer
content of 1.3 % and included no foam and caused no foaming
by heating.
Example 18
The same e~uipment as in Example 1 was used
except that the volume ratio of vessel-type reactor to
tubular reactor was 1 : 0.2. A methyl methacrylate monomer
- 55 -
775~
containing 0.007 % of azobisdimethylvaleronitrile as a
polymerization initiator was continuously supplied to the
vessel-type reactor to make an average residence time in the
reactor 225 seconds. The temperature and the pressure in
each reactor were maintained at 130C and 5.0 atmospheres,
respectively. A concentration ratio of residual initiator
to supplied one was 1/40. The syrup coming out of the
tubular reactor had a polymer content of 10.5 %, a viscosity
of 2.8 poises at 25C, and a residual initiator concen-
tration of less than 0.01 ppm. The polymer in the syrup had
a number average polymerization degree of 2,810 and its
distribution of polymerization degree was 2.02, as expressed
in polydispersity.
The syrup was introduced into an evaporator and
the monomer in the syrup was evaporated under reduced
pressure to obtain a syrup having a polymer content of 18.1
~ and a viscosity of 243 poises and then 0.07 % of azobis-
dimethylvaleronitrile was added to the resulting syrup to a
polymerizable liquid composition.
A cast plate was produced using the continuous
polymerization apparatus in Example 1 in the same manner as
in Example 1 except that said compositiGn was passed through
the heat-polymerization area during 19 minu~es. The product
had a reduced viscosity of 3.90 dl/g and a residual monomer
content of 0.9 ~ and included no foam and caused no foaming
by heating,
Example_l9
A syrup having a polymer content of 25.5 % and
a viscosity of 70.0 poises was prepared using the equipment
of Example 1 and methyl methacrylat~ monomer containing
- 56 -
11~77SZ
0.045 % of azoblsdimethylvaleronitrile in the same manner as
in Example 1 except that the temperature was 145C and said
monomer was passed through the vessel-type reactor so that
the average residence time in the vessel-type reactor was
304 seconds. The residual monomer concentration of the
syrup obtained was less than 0.01 ppm and the polymer in the
syrup had a number average polymerization degree of 1,080
and its distribution of polymerization degree was 2.06, as
expressed in polydispersity. The syrup was diluted with
methyl methacrylate to obtain a diluted syrup having a
polymer content of 14.3 ~ and a viscosity of 1.1 poises. A
polymerizable liquid composition was prepared by dissolving
0.1 % of azobisisobutyronitrile in the diluted syrup and
deaerated under reduced pressure. The composition was
injected into a glass cell. The cell was assembled with two
pieces of glass plate and gasket, the glass plates being
properly apart from each other so as to produce a cast sheet
of 3 mm in thickness, and the gasket being placed between
the plates so as to form an enclosed space. The composition
was polymerized at 65C for 4 hours and then at 120C for 2
hours to complete the polymerization. Cast sheet was thus
obtained. This product had a reduced viscosity of 6.5 dl/g
and a remaining monomer concentration of 0.4 %. Neither
foaming during polymerization nor foaming by heating was
observed, and the product had a beautiful appearance.
Example 20
A syrup, having a polymer content of 32.5 ~ and a
viscosity of 5.2 poises at 25C, was prepared using the
equipment of Example 1 by adding 0.15 % of azobisisobutyro-
nitrile as a polymerization initiator to a monomer mixture
11~775Z
of styrene (30 %) and methyl methacrylate (70 ~) and
polymerizing said monomer mixture under conditions at which
a temperature was 150C and an average residence time in the
vessel-type reactor was 180 seconds. The residual initiator
concentration of obtained syrup was less than 0.01 ppm. The
polymer in the syrup had a number average polymerization
degree of 340, and its distribution of polymerization degree
was 1.95, as expressed in polydispersity.
A polymerizable liquid composition was prepared by
dissolving 2 parts by weight of ethyleneglycol dimeth-
acrylate as a crosslinking agent and 1.5 parts by weight of
benzoylperoxide as a polymerization initiator in 100 parts
by weight of the syrup.
After deaeration under reduced pressure, the
composition was injected into a polymerization mold for
preparing a flat resin plate uniformly filled with 25 parts
by weight of chopped strand of glass fiber (refractive
index, 1.52) and immersed in the chopped strand. Then, the
polymerization mold was dipped in a heating bath at a
temperature of 85C during 1 hour to cure the composition by
polymerization, No foam produced during the polymerization
was observed in the obtained fiber reinforced resin plate
having a thickness of about 1 mm and the resin plate had
excellent transparency, a good appearance and a high bending
strength of 1.620 kg/cm2 measured according to ASTM D-790.
- 58 -
