Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
Process for Preparin~
Imidized Acrylic Polymers
FIELD OF THE INVENTION
This invention relates to a proce~s for
imidizing acrylic polymers; and more particularly to
a continuous process carried out in an in~ernally
baffled tube.
BACR~ROUND OF TB~ INVENTION
Methyl methacrylate ~MA~ homopolymer and
copolymers with, e.g., acrylates, styrene or
butadiene, can be imidized by reacting the polymer
with ammonia or alkyl- or aryl- amines to form imide~
as shown in th~ e~uation following:
C~3 CH3 CH3 D ~H~ ~CH3
~--CH2~ 2~C ~ H~--C C--
C-O ~=C R~
The cyclic imide polymers can also be
obtained by heating selected amides or nitriles.
Most such processes are batch operations. Recently a
continuous imidization procedure was described in
U.S. Patent 4,246,374 in which a methacrylate or
acrylate polymPr is placed in a vented screw extruder
with an amine and the imide is formed as the
materials are moved through the extruder at elevated
temperatures under essentially anhydrous conditions.
SUMMARY OF THE INVENTION
A novel continuous process for imidizing
methacrylic and acrylic resins has now been found
which does not need to employ a screw extruder and in
which temperature and pressure can be more carefully
controlled than in a screw extruder.
~D~5085 35
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0~
The novel process is a process for imidizin~
a methacrylate or acrylate polymer which comprises in
~equence
a) mixing a molten methacrylate or acrylate
5 polymer with ammonia or an alkyl- or aryl- primary
amine 9
b~ introducing the molten mixture into a
baffled tubular reactor which provides dispersed
plug-~low,
c) raising the temperature of the mixture
inside ~he tubular reactor to between 200C and
300C, and
d) conducting ~he molten mixture through
the tubular reactor in a ~ime adequate to accomplish
imidization but less than necessary for ~ubstantial
degradation of polymer.
DESCRIPTION OF T~E INVENTIO~
The polymer to be imidized is an acrylic
andjor methacrylic polymer. It conta~ns adjacent
units of
R
C~2 C~
C=O
R'
wherein R is -CH3 or -~, and R' is alkyl of 1-10
carbon atoms. These polymers may also contain units
derived from up to 40% by weight me~hacrylic or
acrylic acid, styrene, butadiene, ethylene or
acrylonitrile and the like. Polymers containing at
least 75~ methyl ~ethacrylate are preferred. The
molecular weight of the polymers may vary over a wide
range. Those having an inherent viscosity of at
least 0.3 measured in a .5% solution of mixture of
methanol and methylene chloride (20~80) at 25C are
preferred. The polymer to be imidized may be
employed in any form, but generally the pol.ymer is in
~he form of powder or granules prior to melting.
The ammonia or alkyl- or aryl- primary amine
employed generally will have the formula R"NH2
wherein R" is H, alkyl of 1-12 carbon atoms,
cycloalkyl of 7 to 11 carbon atoms or aryl of 6-10
carbon atoms, preferably phenyl. Examples of amines
10 useful herein include methyl, ethyl, n-propyl,
n-butyl, heptyl, hexyl, octyl, nonyl, decyl, dodecyl,
hexadecyl, octadecyl, isobutyl, sec-butyl, t-butyl,
isopropyl, 2-ethylhexyl, phenethyl, allyl, benzyl,
para-chlorobenzyl and dimethoxyphenethyl amines;
1~ besides, alanine, glycine, 3'-aminoacetophenone,
2-aminoanthraquinone and p-aminobenzoic acid. Other
suitable amine~ are cyclohexylamine,
2-amino ~,6-dime~hylpyridine, ~-aminophthalimide,
2-aminopyrimidine, 2-aminothiazole, S-aminothiazole,
2~ 5-amino-1-H-tetrazole, aniline, bromoaniline,
dibromoaniline, tribromoaniline, chloroaniline,
dichloroaniline~ trichloroaniline, p-phenetidine and
p-toluidine.
In ~he process of this invention the polymer
in molten form and ammonia or amine are mixed just
prior to or just after entry înto the tubular
reactorO One method of mixing i5 to feed the polymer
into an extruder to melt the polymer and to propel
the molten polymer into the tubular reactor. Once
the polymer is melted, the ammonia or amine can be
added. Care is taken to add the ammonia or amine
just prior to or just after entry into the tubular
reactor. Addition earlier than that may lead to some
premature reaction, thus rendering useless the
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careful temperature and pressure control obtained by
carrying out the reaction in the tubular reactor.
~ emperatures of reaction are as l~w as can
be used to maintain ~ short reac~ion time and as high
5 as can be tolerated to avoid excessive degradation of
the polymer. Use of an internally baffled tubular
r~actor with high efficiency of mixing and the
attendant uniformity of temperatures across contained
materials permit the use of ~hort reac~ion times a~
relatively high temperatures withou~ a fear of hot
spots in ~he reaction medium. Such hot spo~s and
uneven radial temperature distribution result in
degradation of the polymer and otherwise unacceptable
or undesirable polymeric material. Wher~ residence
time of cont3ined materials can be maintained
practically constant and where temperature gradients
perpendicular to the axis of flow can be maintained
very low, it has been found advantageous ~o conduct
the reaction at high temperatures with short time
rather than at low temperatures with longer time.
Important factors for successfully
accomplishing the reaction include close overall
con~rol of the temperature of reactant materials and
maintenance of a short and uniform residence time of
materials in the reactor. If there are large
temperature differences within the reactant melt,
there will be inconsistent degrees of reaction, i.e.,
incomplete reaction in low temperature zones and
polymer degradation in high temperature zones. In a
tubular reactor, the temperature differences
perpendicular to gross material flow ~radially) must
be minimized. To minimize such temperature
differences, there must be efficient radial
dispersion of materials in order that heat transfer
will occur from one location in ~he reactor,
radially, to another. Axial temperature control is
also important to prevent inconsistent degrees of
reaction which might arise from varying exposure to
proper temperatures of reaction~ A steady state
5 operation is necessary for conducting acceptable
continuous reaction processes, A reactor which
exhibits the required ~emperature control, ~ffi~iency
in heat transfer, and uniformity of residence time,
is a tubular reactor internally fitted with a series
10 of helix baffles of alternating opposite pitch. Such
a reactor is disclosed in U.S. Patent No. 3,286,992.
To achieve a polymer of uniform guality, it
is important that all of the reactant material be
exposed to substantizlly the æame reaction
15 temperatures for ~ubstantially ~he same time. This
is def ined as "dispersed plug flow". 5uch dispersed
plug flow provide that each element of molten
polymer is in the reactor for substantially the same
time and that there is considerable movement of
20 domains of the molten polymer with respe~t ~o other
domains of the molten polymer in a radial direction,
rather than in an axial or longitudinal d;rection.
In the present process, the polymer is
heated to the reaction temperature prior to entry
into the reactor, and the ammonia or amine is added
just prior to or just after entry. In the reactor,
the temperature is maintained at ~00C to 300C,
preferably 240 to 280~C. In the reactor the
reactants are intimately mixed and each element of
material experiences practically the same reaetion
temperature for practically the same duration. The
duration of reaction is generally less than about ten
minutes and more than about one-quarter minute. The
most preferred duration is fr~m about five minutes to
about one-half minute - the shorter maximum time
being important to prevent excessive degradation,
crosslinking, and other undesirable side reactions.
It has been found that close temperature
control, small radial temper~ture gradients, and
5 uniform, short residence time permit good reaction
without excessive degradation which would be expected
at the high temperature. On completion of the
reaction, the resulting imide is removed and
vola~iles vented. The resulting imide is then cooled
10 and cut into pellets.
The degree of imidization of the acryli~
polymer can easily be controlled in the process
a~cording to the invention and various degrees of
imidlzation can be reachcd as a function of the
desired properties. The desired degree of
imidization can be adjusted easily through adjustment
o the reaction parameters, ~uch as the dwell time
and the temperature. Although imidizatson of the
polymer as low as only 1% is possible, as a rule, an
imidization of at least 10% is effected, to reach a
noteworthy improvement in properties of the acrylic
polymer.
No catalyst is required in the process
according to the invention. This has the great
advantage that removal of the catalys~ is dispensed
with. ~owever, small quantities of a catalyst can
increase the reaction velocity if desired.
A solvent is not necesjary in the process of
this invention and it is preferred to operate in the
absence of a solvent. ~owever, if desired, a solvent
may be used to decrease the viscosity of the molten
mass or to carry a catalyst.
The imides made by the process of this
invention are useful as thermoplastic moldin~ resins,
and can be extruded in the form of fibers, tubes or
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film and the like. The molding resins can be used to
prepare molded articles such as toys, pens, housings,
etc.
The process of this invention is
5 particularly useful in preparing imides which contain
1-40 weight percent cyclic anhydride units. These
imides thus contain recurring units of
a) R
. 'CH2-C - _
C=~
0~'
~ CH2 c ~ ~ C ~
Lo~c~o c~o~
2d c ~ ~ CH2`~ R
_ - C~2-C ~--
_ 0 ~7 0
R"
wherein R is -C~3 or -H: R' is alkyl of 1-10 carbon
atoms; and R" is H, alkyl of 1-10 carb~ns, cycloalkyl
of 7-11 carbons, cyclophenyl, or phenylalkyl of 7-9
carbon atoms wherein the phenyl groups can contain
lower alkyl, lower alkoxy or halo su~stituents; and
wherein units of a) con~titute 20 to 94 weight
percent of the recurring units, units of b)
constitute 1-40 weight percent of the recurring
units, and units of c) constitute 5-8G weight percent
of the recurring units, said percents totaling 100%.
DESCRIPTION OF PREFERRED EMBODIMENTS
In the following examples, polymer is hea-ted
and fed to and through a baffled tubular reactor by
means of force provided by a screw extruder. The
internally-baffled tubular reactor exhibiting
dispersed plug flow used in the examples was supplied
by the Kenics Corporation, Danvers, Mass., U.S.A.
A one-inch Killian~ extruder with a vacuum
port and two-stage screw was fitted at its die exit
with an adaptor plate, three one-inch diameter Kenics
Thermogenizer~ sections in succession Eollowed by a
valve die. The Killian extruder was used to melt and
move the polymer into the Kenics sections. A
diffusion plate 1/8" thick with 64 holes was placed
in the leading Kenics edge. This plate, used to aid
mixing, was about 1" downstream of an injection probe
exiting 1/4" into the melt stream (fitted into an
adaptor plate) and about 1 1/2" upstream of the first
element of the first Kenics section. Ammonia or
amine was entered through the injec-tion probe or
through the vent port of the Killian extruder. A
screen pack was placed after the last Kenics section
and before the valve die to aid in pressure control.
A heated transfer pipe was used to convey the melt
from the valve die to the rear vacuum part of a
Werner and Pfliederer* 28-mm twin screw extruder
which was used to remove volatiles. The feed throat
of the 28-mm extuder was used as a vacuum to vent
volatiles and the front vacuum port was used to
devolatilize the imide product as well. The emerging
imide strand was then quenched and cut.
Unless otherwise indicated~ percentages are
by weight.
* denotes trade mark
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EXAMPLE 1
Thi~ example demonstrates that the
imidization reaction occurs in the baffled ~ubular
reactor and no~ in either of ~he ex~ruders. Two fine
(DY) and two coarse (CY) Koch~ baffled plug-flow
mixers replaced the leading Kenics elements in the
first of the three Kenics secticns and two coarse
(CY) Koch~ elements replaced he leading Kenics
elements in the second Renics section. The 1"
Killian extruder was run at 144 rpm wi~h temperature
settings of 250~C rear zone, 225C center 20ne, and
225C ~ront zone. The Kenics sections were all set
~o provide a t~mperature of 280C; ~he die Yalve and
the ~ransfer pipe were set at 225C. The 28-mm twin
~crew extruder had a straight through screw design
with ~he exception of one set of reverse elements
between the two regular vac~um ports to provide a
melt ~eal. I~ was run between 108 and 135 rpm with
the following temperature settings: rear ~1) a 50C~
~2) z 200DC, (3), (4), (5), and die - 250C.
Four batches were run using cyclohexyl amine
and polyme~hyl me~hacryla~e of IV of between .47 and
. 53 . Dur ing ba~ches 1 and 2 the ~mine was pumped
into the vacuum port of the 1'l Rillian extruder
25 during ba~ches 3 and 4, i~ was pumped in~o the
injection probe set into the adaptor plate. In
ba~ches 1 and 3 the final product was isolated as cut
pellets after it was devolatilized in the 28-mm
extruder, ~or batches 2 and 4 samples were removed
30 from a melt thermocouple hole at the downstream end
of the transfer pipe just prior to where the melt
would come in contact with the screw of the twin
screw e~truder. Table 1 shows that 63% of the amine
reacted with polymer when mixed solely in the tubular
35 reactor ~batches 3 and 4) and that only 57% of ~he
~L2~L9~
amine reacted with polymer when amine was entered
into the Rillian extruder and product was passed
through the twin screw extruder (batch 1~. Since
higher conversion was obtained in batches 3 and 4
than in batch 1, one can conclude ~hat the reaction
occurs in the tubular reactor.
TABLE 1
Finished ~ N
Amine Polymer in Amine
Pump Pumped Product~ Final Con~
Pressure In At: ion Rate Pro- % ver-
Batch (Psi) (ml/min) ~/minl du~t Imide sion
. .
1 900 12.5 38.6 2.~4 37.5 57%
2 ~00 12.5 ~* 2.35 39.3 Not
~easured
3 900 12.0 41.4 2.22 37.3 63%
1~ ~ goo 12.0 "* 2.~2 37~3 63%
*Could not be actually measured but no con~rols were
~hanged during short term of ~hese s~ates; ~herefore,
rates probably unchan~ed.
EXAMPLE 2
The sarne apparatus was used as in Example 1
except only two DY ~och~ mixers in the leading
portion of the ir t Kenics section replaced any
~enics elements. The one-i~ch ~illian extruder was
run at 145 rpm with temperature settings of 175~C
~rear), 225C (center), and 2S0C (front). The
temperature of the three Xenics ~ections was set at
280C. The 28-mm twin screw extruder was run at
130 rpm with the ~ollowing temperatures being
recorded: 1 - 140C (rear), 2 - 245C, 3 - 245C,
4 ~ 250C, 5 - 242C, and die - 215C. Cyclohexyl
amine was pumped into the vacuum port of the Killian
extruder at a rate of 16.1 ml/min at a pressure of
800 psi. A po~ymer composed of units of methyl
methacrylate/styrene/butadiene (70/25/5) was fed to
3~
-
the one-inch extruder and a devolatilized final
product prod~ced at a rate of 41.9 ~Jmin which
contained 2.58% N nitrogen corresponding to 43.2%
N-cyclohexyl imide structure having a Tg of 144C as
5 determined by DSC.
EXAMPLE 3
The same apparatus was used as in Example 1
except ~or the presence of 2DY and 4CY Koch elements
in the ~irst Kenics section, 8CY elements in the
10 second, and 2CY elements in the thirdO ~he one inch
Rillian extruder was run a~ 144 rpm with temperatures
of 250C (rear), 234C (center), and 227C ~fron~).
The three Kenics sec~ions were each set at 280C~
The 28-mm twin screw e~truder was run at 104 rpm wi~h
temperatures of 1 - 153C (rear), 2 - 247C,
3 - 275C, 4 - 277Cf 5 - 273C, and die - 284C-
Aniline was pumped into the va~uum port o~ the
Killian extruder at 9.5 ml/minq The poly~er employed
was a copolymer of methyl methacrylate/methacrylic
acid (87/13, I.V. in CH2Cl2 - 0.53). Imide
product was produced at 35 g/min which contained
1.50% ni~rogen correspondiny to 24.6~ N-cyclohexyl
imide of methacrylic acid.
EXAMPLE 4
The same apparatus and temperatures were
used as in Example 3~ Ammonia was pumped in at the
adaptor pla~e at a rate of 5 g/min. ~he pressure was
controlled by the die valve to a level of 2000 psi.
Polymer was introduced at a rate of 40 g/min. The
polymer employed was a terpolymer having the
components methyl methacrylate/styrene/butadiene in a
weight ratio of approximately 75/20/5, with an I.~.
in CH2C12 of 0.51. The imidized resin produced
contained 4.65% N and had a ~9 of 159C.
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EXAMPLE 5
This example demonstrates reaction of
cyclohexylamine and methacrylate polymer to ~orm both
cyclic imide ~nd anhydride units.
The one-inch Killian ex~ruder was run at 144
rpm with temperature settings of 250C rear, 2~5C
center and front zone. The baffled tubular rea~tor
employed comprised the three Renics sections. In
section 1, the Kenics baffles were replaced wi~h Koch
10 DY and GY baffles. ~n ~ection 2~ the first Kenics
baffle was replaced with a Koch CY baf~le. The
sections were ~et at 280C. The valve die and
transfer pipe were set at 225C. The 28 mm W-P
extruder had a ~traight through ~rew design with the
lS excep~ion of one set of reverse e~ements between ~he
regular vacuum ports ~o provide a melt seal and was
run at lOB-135 rpm with te~perature settings of 50C
(rear), 200~C (center) and 250C ~die).
A copolymer of methyl methacrylate and ethyl
20 acrylate (95.5~4~5~) with an inherent viscosity oE
0.575 was fed to the 1" extruder at about 37 g/min
and cyclohexyl amine pumped in at point A (the vacuum
port of the Xillian extruder) or point B (the
injection probe), at 900 psi and at abou~ 1~.4 g/min
25 (22 wt %). Imidized polymer was removed for sampling
as it existed the baffled tubular reactor (Point I)
or after devolatilization in ~he twin screw extruder
~Point II). Resulks were as follows:
12
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13
Amine Polymer
Addition Sample Imide Anhydride**
Point Point Units* Units
1 A II 37.5 wt ~ 7.5 wt %
2 A I 39.3 5.2
3 B II 37.3 5.6
4 B I 37.3 5.~
*Imide content from nitrogen analysis and infrared
spectra
**Anhydride content ~rom ~itration and infrared
spectra
