Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE PREPARATION OF
BROMINATED POLYSTYRENE HAVING IMPROVED
COLOR CHARACTERISTICS
TECHNICAL FIELD
This invention generally relates to a brominated polystyrene having
improved color characteristics. More particularly, the invention relates to a
process for the bromination of polystyrene with a unique combination of
brominating agent, catalyst, reaction time, isolation procedure and
temperature
controls, such that the resulting brominated polystyrene has improved color
characteristics.
BACKGROUND OF THE INVENTION
It is known in the art that brominated polystyrene imparts flame
retardant. properties to polymers. For example, the use of polybrominated
polystyrenes as flame retardant additives for polyolefin-based molding
materials
is described in U.S. Pat. No. 3,474,067. That patent describes combinations of
molding materials based on polyethylene and polypropylene with several
different
nuclear-brominated polystyrenes together with synergists such as antimony
trioxide. The use of poly-(tribromostyrene) was particularly emphasized, as in
Table I of the patent. However, the patent does not disclose the molecular
weight of the brominated polystyrene, nor how it was produced.
U.S. Pat. No. 3,975,354 describes a flame-resistant thermoplastic glass-
fiber reinforced polyester molding composition, containing a saturated
polyester,
a synergist and from 3 percent to 30 percent by weight of the composition of
poly(2,4,6-tribromostyrene). The patent reported that the poly(2,4,6-tribromo-
styrene) was a commercially available product with a density of 2.3 grams/cm3
and a bromine content of 69 percent. The process for making the product is not
described in this patent.
The direct nuclear halogenation of polystyrene in solution, in the
presence of iron chloride or aluminum chloride, with elemental chlorine, is
described in British Pat. No. 364,873.
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The direct bromination of polystyrene is described in U.S. Pat. No.
3,050,476. A suspension of polystyrene particles is heated in the presence of
bromine, to cause bromine to combine chemically with the polymer particles.
Bromine is added to a very low level of bromination.
U.S. Pat. No. 3,845,146 describes the bromination of aromatic
compounds such as lower alkyl benzenes, utilizing bromine chloride as the
brominating agent, with a catalyst such as aluminum chloride. The reaction is
conducted in a closed reaction vessel under autogenous pressure, often in the
range from about 50 psig to 100 psig.
Cubbon and Smith describe the synthesis and polymerization of
tribromostyrene in an article in Polymer, 10, 479-487 (1969). Tribromostyrene
is prepared in a multiple step reaction, by first effecting the addition of
hydrogen
bromide to the double bond of styrene to produce 2-bromoethylbenzene, then
reacting that material with elemental bromine in the presence of iron
chloride,
to introduce bromine into the nucleus. Hydrogen bromide is then removed, to
re-introduce the double bond, by reaction with potassium ethoxide, at about
30 C. The product was identified through its nuclear magnetic resonance
spectrum as 2,4,5-tribromostyrene. The rate of polymerization of this
tribrominated styrene was observed in benzene solution at 30 C. Upon
comparing its rate of polymerization with that of dibromostyrene, the
conclusion
was reached that the introduction of bromine atoms activates the vinyl group
toward polymerization, with the tribromostyrene polymerizing at a more rapid
rate than the dibromostyrene, which in turn polymerizes at a more rapid rate
than styrene.
In German Pat. No. 1,570,395, Example 2 purports to describe the
production of poly-(2,4,6-tribromostyrene), and Example 4 purports to describe
the production of, simply, poly-(tribromostyrene).
Several other patents have issued that describe the production and
flame retardant use of brominated polystyrene oligomers. These oligomers may
be prepared by the action of elemental bromine on the hydrogenated polystyrene
oligomer, as in the Naarmann et al. U.S. Pat. Nos. 4,074,033 and 4,143,221,
where the catalyst used was aluminum chloride (a Lewis acid catalyst), or
alternatively, by the polymerization of brominated styrene.
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ln U.S. Pat. No. 4,107,231, such brominated oligomers are described
as useful in imparting flame retardant properties to linear polyesters. The
degree
of polymerization of the oligomer may be in the range from 3 to 20. The use of
a tribrominated oligomer is mentioned.
In U.S. Pat. No. 4,137,212, similar brominated polystyrene oligomers,
with a degree of polymerization of from 3 to 90, are disclosed as useful for
flameproofing molded nylon compositions. The tribrominated oligomer is
mentioned.
In U.S. Pat. No. 4,151,223, the brominated oligomer may have a
degree of polymerization in the range from 3 to about 100, and is described as
useful for imparting flame-retardant properties to fibers and filaments of
linear
thermoplastic polyesters. This patent points out that the halogenated
oligomeric
styrene may be either chlorinated or brominated, and the degree of
halogenation
may run the complete spectrum.
U.S. Pat. No. 4,352,909 describes the preparation of tribrominated
polystyrene polymers. Said process employs bromine chloride as the brominating
agent and thus, typically from 1 to 2 weight percent of the product is
chlorine.
U.S. Pat. No. 4,200,703 discloses a process for the manufacture of
heat-stable, nuclear brominated polystyrene. The process involves brominating
in bromine chloride or bromine, at a temperature of from -20 C to 40 C, a
polystyrene dissolved in a chlorinated hydrocarbon in the presence of a Lewis
acid catalyst and from 0.02 to 2 moles, per mole of Lewis acid catalyst, of a
nucleophilic substance which acts as a Lewis base, such as water, for the
Lewis
acid. The process is capable of making high molecular weight products without
subjecting the polystyrene starting material to hydrogenation. The products
are
generally free of cross-linking. However, the color of the solid products
ranges
from ochre-colored to pale beige to "white" to pale yellow.
European Pat. App. No. 0 201 411 discloses a brominated polystyrene
similar to that of U.S. Pat. No. 4,200,703 wherein the polystyrene is
anionically
polymerized and has a degree of polymerization greater than 400.
When brominated polystyrene is employed as a flame retardant
additive in thermoplastics, its color is a property of primary importance to
the
manufacturer of the thermoplastic materials. The thermoplastic manufacturer
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desires to produce the thermoplastic articles in a wide range of colors. The
more
highly colored an additive, the more difficult it becomes to match (produce) a
broad range of colors. The more fightly colored the additive, the easier it
becomes to produce a wide range of colors. Therefore, in view of the needs of
the manufacturer of thermoplastic parts, and in view of the inadequacy of
prior
art processes to produce a brominated polystyrene having the desired light
color
characteristics, a need exists for a brominated polystyrene with an improved
light
appearance as manufactured so that the end user can formulate a wide range of
colors and thereby better meet the needs and demands of the marketplace.
SUMMARY OF INVENTION
It is therefore, an object of the present invention to provide a
brominated polystyrene having improved color characteristics.
It is another object of the present invention to provide a process which
allows the operator to select various reaction components and reaction
parameters to obtain brominated polystyrenes having the best color
characteristics for the choices made among the variables.
It is another object of the present invention to identify the various
reactants and reaction parameters that influence the color characteristics
obtainable in the bromination of polystyrenes.
At least one or more of the foregoing objectives, together with the
advantages thereof over existing prior art forms, which shall become apparent
from the specification which follows, are accomplished by the invention as
hereinafter described and claimed.
In general, a process for the preparation of brominated polystyrene, as
an additive for polymer matrices to impart flame retardancy, includes
preparing
a solution of a polystyrene reactant comprising from about five to about 20
percent by weight of a polystyrene reactant, in a halogenated hydrocarbon
solvent; gradually adding a Lewis acid bromination catalyst to form a
solution;
adding to the solution from about 1 to about 3.3 moles of a brominating agent,
per mole of polystyrene reactant repeating units, and reacting the polystyrene
reactant with the brominating agent at a reaction temperature of from about
-20 C to about 50 C; wherein the improvement comprises controlling the color
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characteristics of the resultant brominated polystyrene reactant by selecting
a
polystyrene reactant having a weight average molecular weight of from about
500 to about 1,500,000; selecting a catalytically effective amount of the
catalyst
on the basis of having a strength sufficient to effect bromination of the
polystyrene reactant without inducing alkylation of the polystyrene reactant
by
the halogenated hydrocarbon solvent; selecting a brominating agent from the
group consisting of bromine chloride and bromine; operating at the lowest
possible temperature within the range, consistent with the brominating agent
and
the catalyst selected; and isolating the brominated polystyrene reactant,
wherein
the color properties of the resultant brominated product are improved by
selection and consideration of reaction time and temperature, catalyst,
brominating agent and method of product isolation.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
One preferred embodiment of the process of the present invention may
be represented by the following equation:
_~-CH-CHZ_~- ~-CH-CH2-n
3BrC1 SbC13
C
1 1 6 H2-CH2 Br3 + 3HCI
C1 C1
(Equation I)
As Equation I indicates, the reaction in this embodiment of the
invention is generally conducted in a solvent, preferably a chlorinated hydro-
carbon solvent. Preferred solvents include halogenated hydrocarbons such as
carbon tetrachloride, chloroform, methylene chloride, 1,2-dichloroethane, 1,2-
dibromoethane,1,1,2-trichioroethane,1,1,2,2-tetrachloroethaneandthelike. The
preferred solvent is EDC (1,2-dichloroethane). Mixtures of solvents can also
be
employed.
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The polystyrene reactant is first dissolved in a solvent to form a
solution having a concentration of about five to about 20 percent by weight.
The
catalyst is then added followed by the gradual addition of the brominating
agent
and the resulting mixture is allowed to react with effective temperature
control.
The brominating agent is selected from the group consisting of bromine
chloride, elemental bromine or a mixture of both. Pure bromine chloride is
about 70 percent by weight bromine. For practical reasons bromine chloride
having a total bromine content of from about 65 to about 75 percent by weight
is employed. While the brominating agent is preferably added neat, the process
can be employed utilizing a solution of the brominating agent in a halogenated
hydrocarbon solvent, the same as the solvent for polystyrene or a different
solvent, compatible therewith. From about 2.8 moles to about 3.3 moles of the
brominating agent are added per mole of polystyrene in order to obtain up to
three bromines per polystyrene repeating unit. More generally, the amount of
brominating agent is determined by the amount of bromination that is desired
in
the polystyrene product and thus, to achieve between one and three bromines
per repeating polystyrene unit, from one to about 3.3 moles of brominating
agent
are employed, the latter amount being slightly in excess of 3 moles in order
to
ensure complete bromination. Relative amounts of bromine chloride and
bromine in a mixture are not a limitation of the present invention and are
determined somewhat with respect to the bromination catalyst, as will be
explained hereinbelow.
The catalyst is a weak Lewis acid halogenation catalyst, preferably
antimony trichloride or antimony tribromide. By "weak" it is understood to
mean that the catalyst is incapable of catalyzing a Friedel-Crafts alkylation
reaction or, in this specific system, the reaction of a halogenated
hydrocarbon
with an aromatic substrate such as polystyrene. In the case of a
polyhalogenated
solvent such a reaction would result in an undesirable crosslinking reaction.
A catalytically effective amount of the weak Lewis acid catalyst must
be employed. Catalyst levels in the range of from about 0.2 percent to about
10
percent by weight are desired. The exact amount of catalyst will depend on its
activity. For antimony trichloride, and using bromine chloride as the
brominating
agent, catalyst levels lower than about 5 percent by weight in laboratory
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experiments may result in slower reaction rates and the production of an
underbrominated product, unless a larger excess of bromine cliloride is
employed. While the reaction is technically feasible with very small amounts
of
catalyst and very large amounts of brominating agent over that theoretically
required, or at the other end of the scale, with large amounts of catalyst and
very
little excess of brominating agent over that theoretically required, the
overriding
factor in determining amount of catalyst is the strength of the Lewis acid. In
other words, for stronger Lewis acid catalysts, lower amounts are employed
while
for weaker Lewis acids greater amounts are employed.
Catalyst mixtures are also possible which further allows control over
the strength of the Lewis acid catalyst employed in the process. Such mixtures
include not only two or more Lewis acids but also mixtures with one of more
Lewis bases, such as but not limited to water, alcohols, ethers, esters,
carboxylic
acids, acid chlorides, ketones, aldehydes, amines, nitriles and the like. For
a
more complete discussion of various Lewis bases and acids, see U.S. Pat. No.
4,200,703.
Selection of the brominating catalyst or catalyst mixture is also a function
of the
particular brominating agent empioyed. As will be appreciated by those skilled
in the art, bromine chloride, for instance, is a more reactive brominating
agent
and it is therefore possible to achieve higher levels of bromination with
weaker
catalysts. Where bromine is employed, it is necessary to employ more active
catalysts in order to achieve the higher levels of aromatic bromination. Where
the brominating agent is a mixture of bromine chloride and bromine, any
relative
ambunts of the two can be balanced against the catalyst selected and vice-
versa,
as will be appreciated by those skilled in the art.
The reaction between the brominating agent and the polystyrene
reactant can be carried at any temperature within the range of from about -20
C
to about 50 C. Generalfy, the lower end of the temperature range is preferred
in order to obtain the best color. However, at lower temperatures, the rate of
reaction is slowed and in fact, may not be a rate that is commercially
acceptable.
Consequently, it may be necessary to compromise with regard to temperature in
order to achieve a reaction rate that is commercially acceptable. In the
laboratory work reported hereinbelow, a five hour reaction rate was deemed to
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be satisfactory. We have also observed that the reaction rate is influenced by
the
brominating agent selected and by the catalyst selected.
The polystyrene reactant that is employed may be either an oligomer
or a polymer. Accordingly, the initial molecular weight of the polystyrene is
from about 500 Mw to about 1,500,000 Mw and preferably from about 500 Mw
to about 500,000 Mw. The process is also effective for the bromination of
substituted polystyrene, the substitution being nuclear. Obviously, nuclear
substituents will affect the position(s) at which the bromination occurs and
the
amount of additional bromination that takes place. Examples of the substituted
polystyrenes that may be brominated in accordance with the process of the
invention include halogenated and alkylated polymers such as poly-(bromo-
styrene), poly-(chlorostyrene), poly-(dichlorostyrene), poly-(dibromostyrene),
poly-
(chloro-bromo-styrene), poly-(4-methyl styrene) and poly-(mono-lower alkyl
styrene). Halogen substituents include chlorine and bromine and alkyl
substituents include lower alkyl group having from one to about four carbon
atoms. Accordingly, the term polystyrene reactant, or just polystyrene, as
used
throughout the specification and claims, shall refer to the foregoing
homopolystyrene and oligomers as well as substituted polystyrenes within the
scope of this invention.
The reaction is carried out to introduce up to three bromine atoms on
each aromatic nucleus. Hydrogen chloride or hydrogen bromide is produced as
a byproduct of the reaction, depending upon whether bromine chloride or
bromine is used.
While the invention can be employed, as indicated in Equation I above,
for the production of what is essentially tribrominated polystyrene, the
process
of the invention is of general utility for the production of brominated
polystyrene
products having any desired degree of bromination up to three.
Prior art bromination techniques, applied to styrene polymers or
oligomers, are currently less effective than the present process in producing
a
suitably light colored material. Products can be produced by the preferred
process of the invention at any desired level of bromination with very good
color
characteristics, i.e., very light in color, so that the highly brominated
products are
desirable flame retardant additives for the plastics industry. Products having
a
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lower degree of bromination than essentially tribromination are also useful as
flame retardant additives.
In order to carry out the reaction of the invention in accordance with
the more preferred embodiments thereof, the polystyrene reactant should be
selected to have a weight average molecular weight of about 500 or more, and
preferably, 150,000 or higher, up to about 1,500,000. The polystyrene reactant
is dissolved in ethylene dichloride, or other suitable solvent as discussed
above,
in a reaction vessel that is equipped with mechanical agitation. The catalyst
is
added to the polystyrene solution. The brominating agent is then added to the
reactor gradually, over a period of time that generally amounts to several
hours,
in order to react within a reasonable time as discussed hereinabove.
During this addition, the temperature of the solution in the reactor is
maintained within a controlled range, generally from about -20 C to about 50
C.
The reaction goes forward at lower temperatures but at a slower rate. It also
goes forward at higher temperatures, but as the temperature increases, the
color
of the product will deteriorate. The reaction is exothermic, so that cooling
is
employed. Where color of the product is an important consideration, as it
often
is, particularly with respect to a tribrominated polystyrene product, it is
considered essential to maintain effective control of the temperature of the
reaction mixture. When the brominating agent addition is complete, the
reaction
mixture is stirred for another period of time, sufficient to permit the
reaction to
go to completion.
While reaction times are based in part upon the reaction temperature,
such times can vary greatly between about one and 20 hours. Where the catalyst
of preference is relatively strong or reactive, reaction temperatures or times
or
both can be decreased. In an instance where the reaction cannot be
sufficiently
cooled to lower ranges, control over the color characteristics of the
polystyrene
additive can be accomplished by decreasing the reaction time. It is to be
appreciated that the objective is providing the best color possible and
accordingly, within the spirit of the invention, reaction time and temperature
will
be determined and selected with consideration of the brominating catalyst, the
brominating agent and, the method of precipitation. It will be also
appreciated
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that greater or lesser periods of time are not necessarily precluded, the
range
being expressed primarily satisfies most commercially acceptable periods.
After the reaction is considered to be complete, any excess brominating
agent is destroyed, as by the addition of a reducing agent such as an aqueous
solution of an alkali metal bisulfite. Agitation of the reaction mixture is
then
stopped, and phase separation occurs.
Product recovery can be accomplished by any recognized and
acceptable method, such as for instance, by water flashing or non-solvent
precipitation. In the latter method, the non-solvent that is miscible with the
organic liquid in which the reaction product is dissolved, is maintained in a
separate vessel at ambient temperature. Suitable non-solvent liquids include
alka-
nols and preferably methanol or a ketone, such as acetone, to precipitate the
product. The contents of the reaction vessel are slowly added to the non-
solvent
as it is agitated. Under the proper conditions, the brominated polymer
precipitates in the form of fine particles, which can be recovered by
filtration
and dried. In the water flashing method, the solution of product is gradually
added to boiling water, causing the solvent to flash off, and leaving the
product
as a slurry in water. The product is then conventionally recovered.
Nevertheless, the method of product isolation is also a factor in
controlling the color properties of the brominated product. Investigations
reported herein support non-solvent precipitation over water flashing as
another
means of obtaining better color.
An essentially tribrominated product is one where the bromine content
is at least 66 percent. The process of the invention is such, however, that
when
the brominating agent is bromine chloride, some nuclear chlorination always
takes place in addition to nuclear bromination. Accordingly, generally, in
such
cases the bromine content of the product is in the range of from about 66
percent by weight to about 69 percent by weight of the product, and the
chlorine
content is typically about 0.5 to 1 percent by weight of the product, but may
go
as high as up to about 2 percent by weight of the product.
A typical tribrominated polystyrene product produced by the practice
of the preferred process may be found, upon analysis, to contain about 66
percent to about 69 percent by weight of bromine, about 0.5 percent to 2
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percent by weight of chlorine, and generally, from about 0.2 percent to 0.5
percent by weight of volatiles. If the yield of the reaction is calculated,
based
upon three bromine atoms being substituted on each aromatic ring nucleus, the
process of the invention typically produces a yield of about at least 90
percent
or higher.
In practicing the preferred process, particularly on an industrial scale,
many departures from the foregoing general process description can be made,
within the scope of the invention. For example, commercially available bromine
chloride can be added directly to the reactor, or a bromine chloride solution
can
be employed. Usually some excess of bromine chloride must be used, but the
amount in excess depends upon the reaction conditions, such as, for example,
moisture content in the solvent, selection of catalyst, the reaction
temperature,
and the like.
The organic solvent that is selected as the reaction medium should
dissolve the reactants and be inert or of very low reactivity toward them.
Especially suitable are those halogenated, particularly chlorinated, aliphatic
hydrocarbons that are saturated. Carbon saturation in the solvent is needed
primarily to avoid halogen addition. Suitable solvents, as noted above,
include
carbon tetrachloride, chloroform, 1,1,2,2-tetrachloroethane, methylene
chloride,
1,2-dichloroethane, 1,1,2-trichloroethane, 1,2-dibromoethane, and the like
with
EDC (1,2-dichloroethane) being preferred. If methylene chloride is employed,
the
proper equipment should be employed to contain it because it tends to escape
due to its low boiling point and high volatility.
When using a weak Lewis acid catalyst, which is a single entity, the
solvent should be substantially anhydrous, since water may destroy or
deactivate
the catalyst. Ordinarily, commercial grades of solvent are used. Generally,
the
manufacturer specifies a maximum moisture level and for present purposes, the
use of commercial solvents has been found to be satisfactory. However, it is a
wise precaution to ascertain the moisture level and if possible azeotrope the
solvent to dry it. The small amount of moisture normally present in
commercially
available halogenated hydrocarbon solvents does moderate the activity of the
catalyst, however, so that in some cases, more or less catalyst may be
required
for a given result, depending upon the total amount of moisture present.
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Any brominated polystyrene product has inherent flame retardant
properties. For use as a flame retardant additive to a host polymer, it is
usually
desirable to use the smallest feasible amount of the additive. For this
reason,
generally, it is preferred to produce and use as a flame retardant additive
polystyrene with higher bromine content. In the industry, it is common to
adjust
the amount of brominated additive employed in the plastic composition to
attain
a particular degree of resistance to ignition. In general, the higher the
bromine
content of a particular additive, the more efficient it is and the less of
that
additive is required. The smaller the amount of additive employed, generally
speaking, the better the economics. While in some cases the use of a flame
retardant may enhance certain physical properties of the overall composition,
more generally, the use of an additive tends to degrade desirable physical
characteristics and for this reason also, lesser amounts of additives are
preferred
when equivalent results can be attained.
While these considerations should seem to indicate that complete
bromination would be desirable, it is not practical in this particular case.
As
repeated demonstrations of the invention have indicated, when the point of
trihalogenation is reached in ethylene dichloride used as a solvent, the
halogenated polystyrene starts to form a separate phase. This change does not
relate to cross-linking but rather to a change in solubility in the particular
solvent
that is being used. This phase separation makes it difficult to process the
product
and recover it. For this reason, the preferred process of the invention is
ordinarily practiced to produce a trihalogenated polystyrene product, that is,
an
essentially tribrominated polystyrene product.
GENERAL EXPERIMENTAL
The invention will now be further described in detail by descriptions
of specific demonstrations thereof. In the following examples and throughout
this application, all parts and percentages are by weight and all temperatures
are
expressed in degrees Celsius, unless expressly stated to be otherwise. The EDC
solvent employed was dried to less than 100 ppm moisture by azeotropic
distillation or dried over molecular sieves.
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EXPERIMENTAL PROCEDURE
Into a 1 L resin flask equipped with a mechanical stirrer, thermometer,
spiral condenser, and a 500mL jacketed pressure equalized addition funnel was
placed 50.1g (0.481 mole based upon styrene repeating units) of polystyrene
and
350mL of 1,2-dichloroethane (EDC). To the stirred solution was added 2.5g
(0.01096 mole) antimony trichloride (added as a solution in EDC - 0.2g/mL) and
the solution was cooled to 20 C. A bromine chloride solution composed of
187.5g (1.625 mole) bromine chloride, 2.7g (0.0169 mole) bromine and 187.5g
EDC was added continuously to the polystyrene solution over 3 hours while
maintaining the bromination temperature at 20 C 2 C. The system was
typically stirred for approximately two more hours in order to achieve a
bromine
content in the final product of 66 percent minimum (total bromination time was
5 hours).
Aqueous sodium bisulfite 180g (20 percent by weight) was added at
such a rate as to not exceed 35 C. A weight of deionized water equal to the
weight of the aqueous sodium bisulfite used was added to the mixture. The
mixture was stirred for an additional 10-15 minutes and then transferred to a
2L
separator funnel.
The organic layer was removed and washed three times with 1 L fresh
deionized water. During the third wash, the pH of the aqueous layer was
adjusted to approximately seven by the incremental addition of approximately
60g of saturated aqueous sodium bicarbonate solution. After the third wash,
the
organic phase was placed in an appropriately sized additional funnel. This was
added to a 3L Morton- resin flask equipped with a mechanical stirrer,
distillation
head, condenser, receiver, and heating mantle. The flask also contained 2L
boiling deionized water which was being vigorously agitated. During the
addition of the solution to the boiling water, the EDC flashed off as a
EDC/water
azeotrope.
The temperature during this operation was maintained between 91 C
and 100 C. When the addition of the solution was completed, the resulting
slurry was held at approximately 100 C for an additional hour.
The product was collected by filtration, washed on the filter with 4L
hot deionized water and then 4L cold deionized water. The product was vacuum
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dried at 100 C at 5-10 torr for 48 hours. The yield of product was around
138-148g.
A number of polystyrene brominations similar to the general procedure
were conducted at 40 C, 20 C and 0 C in order to demonstrate the color
properties thereof versus reaction temperature. Color was determined using two
different methods. The first, was ASTM D1544-68 Method, also referred to as
the Gardner Color Scale Method. The second was Total Color Difference (AE),
using the Hunter L, a, b scales, for product solutions in chlorobenzene, 10
percent by weight concentration versus chlorobenzene, according to the
formula:
DE _ (0L) 2 + (AaL ) 2 + (ObL ) 2
Results are reported in TABLE I.
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TABLE I
COLOR VERSUS REACr1ON TEMPERATURE
Ex. No. Reaction Gardner AE
Temp. C Color
1 Series ta 40 3 28.6
2 20 1 16.9
3 0 < 1 6.9
4 Series f1b 40 3 30.0
5 20 1 17.1
6 0 < 1 8.9
7 Series Ilta 40 3 30.6
8 20 1 14.9
9 0 < 1 8.2
a) Using Chevron EA3000 polystyrene, 300,000 Mw_
b) Using Polysar HH101-300 polystyrene, 270,000 Mw
As shown in TABLE I, the more desirable lower tiE numbers and the
better Gardner colors were obtained at lower temperatures.
Another color versus reaction temperatttre series of experiments was
conducted using a lower molecular weight polystyrene than those employed for
*
the data reported in Table 1. The polystyrene was Hercules Res M1187, known
to have a weight average molecular weight of about 900. The results are
reported in TABLE II.-
TABLE 11
COLOR VERSUS REACTION TEMPERATURE
Ex. No. Bromination Temperature AE
uC
1 20 50.2 to 51.0
2 0 30.2
3 -10 25.5 to 27.4
*Trade-mark
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In order to demonstrate the relationship between bromination time and
final product color, in a bromination that is otherwise similar to the general
procedure, but conducted at 35 C, three experiments were conducted at varying
times. The polystyrene utilized was Chevron EA 3000, 300,000 Mw, dissolved
in EDC to form approximately a 9.1 percent by weight solution and utilizing
antimony trichloride as the catalyst. Total Color Difference (AE) for product
solutions in chlorobenzene, 10 percent by weight concentration was measured.
Results are reported in Table Ill.
TABLE Ill
COLOR OF BROMINATED POLYSTYRENE VERSUS BROMINATION TIME
Ex. No. Total Bromination DE
Bromination Temp C
Time (hrs)
1 4 35 20.75
2 7 35 25.15
3 10 35 30.36
The data in Table Ill establishes the relationship between bromination
time and final product color at 35 C. In general, the better colors, lower
QE, are
a result of the shorter bromination times.
In the next series of work, comparisons were made among three
different catalysts, the two brominating agents and three different
temperatures
for the bromination of polystyrene, utilizing Chevron AE 3000, 300,000 Mw,
dissolved in EDC to form approximately a 10.25 percent by weight solution. The
amount of the respective catalysts in polystyrene (weight percent) was 5% for
Examples No. 1-6; 3.88% for Examples No. 7-12; and, 4.68% for Examples No.
13-18. Color properties were measured and have been reported, with the
components reacted and reaction data, in Table IV hereinbelow.
TABLE IV
~
~
COLOR PROPERTIES AS A RESULT OF PROCESS VARIABLES
Ex. No. CATALYST BR AGENT BR TEMP C REACTION % BR SOLID AE SOLUTION AE
TIME HR
1 SbC13 BrC) 0 5.03 64.51 7.66
2 SbCl3 BrC1 20 5.25 66.59 14.45
3 SbCl3 BrCi 40 4.18 68.74 24.15
4 SbCI3 Br2 0 5.00 42.36 11.16
5 SbCi3 Br2 20 5.00 42.81 18.02
6 SbC13 Brz 40 5.00 42.39 32.41
7 AIC13 BrCI 0 3.18 66.99 10.69
8 AIC13 BrCI 20 3.17 66.62 13.38
9 AIC13 BrCI 40 3.00 68.56 29.69
10 AICI3 Br2 0 3.48 67.34 22.45
11 AICI3 Br2 20 3.82 67.38 49.29
12 A1CI3 Br2 40 3.95 68.03 82.50
13 FeCI3 BrCI 0 3.20 65.46 10.38
14 FeCI3 BrCI 20 3.10 67.09 15.07
15 FeCI3 BrCI 40 3.48 68.40 15.41 a
TABLE IV (CONTINUED)
EXP. No. CATALYST BR AGENT BR TEMP C REACTION % BR SOLID AE $OLUTION AE
TIME HR
16 FeCl3 Br2 0 5.55 66.90 37.14
17 FeCl3 Br2 20 4.07 67.81 52.79
18 FeCl3 Br2 40 3.67 67.91 70.47
a) Color difference noted visually, but instrumentation could not
differentiate
~r
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As can be seen from the foregoing data in Table IV, the best color was
produced, in an overall sense, at the lower range of reaction temperature;
using
bromine chloride as the brominating agent and with antimony trichloride as the
catalyst. Nevertheless, the benefits of the process of the invention are
equally
demonstrated by the data. Considering, for instance, if the brominating agent
available or desired in a given situation is bromine, by lowering the reaction
temperature to 0 C, (Ex. No. 4) a better color resulted than where bromine
chloride was reacted at 20 C (Ex. No. 2), in both instances, using antimony
trichloride as the catalyst. As another instance, where the reaction
temperature
cannot be lowered as readily, employing bromine chloride as the brominating
agent produces a better color than using bromine (Ex. No. 6 vs. Ex. No. 3). As
another instance, while ferric chloride may not provide the best results as a
catalyst, by lowering the reaction temperature and selecting bromine chloride
as
the brominating agent, the better color values can be obtained (Ex. Nos. 13-
15).
In fact, comparing the solution AE values, one can see that selection of
ferric
chloride, bromine and 0 C could provide color comparable to the use of
antimony trichloride and bromine at 40 C and thus, it should be apparent that
one or more process parameters can be varied to accommodate a specific process
parameter.
In the final series of work, comparisons were made to demonstrate the
combined effects of reaction temperature and isolation procedure on color. The
brominations and two methods of product isolation were conducted as follows.
The polystyrene selected was DOW XP 6065, 200,000 Mw. All color deter-
minations were run as a 4% solution in chlorobenzene on a Gardner XL-20
*
Tristimulus Colorimeter from Pacific Scientific using Illuminant "C".
Into a 1 L resin flask equipped with a heating mantle with a controller,
mechanical stirrer, thermometer, distillation head with a vertical sidearm
take-off
tube (Lab Glass LG-1 781 T), spiral condenser, and a 500 mL jacketed pressure
equalized addition funnel was placed 50. 1 g (0.481 mole based upon styrene
repeating units) of polystyrene and 600 mL of 1,2 dichloroethane (EDC). With
stirring the solution was heated to reflux and 60 mL of EDC/H20 was removed
in order to remove water from the system as an azeotrope. The solution was
cooled to 20 C and 12.5mL of a solution of antimony trichloride in EDC
*Trade-mark
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(0.2g1mL) was added. A bromine chloride solution composed of 187.5g (1.625
mole) bromine chloride, 2.7g (0.0169 mole) bromine and 187.5g EDC was added
continuously to the polystyrene solution over 3 hours while maintaining the
bromination temperature at 20 C 2 C. The system was typically stirred for
approximately two more hours in order to achieve a bromine content in the
final
product of 66 percent minimum (total bromination time was 5.0 hours).
Aqueous sodium hydroxide 100mL (25 percent by weight) was added
at such a rate as not to exceed 35 C. The mixture was stirred for an
additional
10-15 minutes and then transferred to a 2L separatory funnel.
The organic layer was removed and washed two times with 700mL
fresh deionized water. After the second wash, the 700mL of organic phase was
split in half.
PRODUCT ISOLATION BY FLASHING THE SOLVENT OFF IN BOILING WATER
One half of the organic phase was diluted with 200 mL of EDC and
was placed in an appropriately sized addition funnel. This was added to 1.21,
of
vigorously agitated boiling deionized water contained in a 2L Morton resin
flask
equipped with a mechanical stirrer, distillation head, condenser, receiver,
and
heating mantle. During the addition of the organic solution to the boiling
water,
the EDC flashed off as a mixture of EDC and water and a slurry resulted in the
flask.
The temperature during this operation was maintained between 91 C
and 100 C. When the addition of the solution was completed, the resulting
slurry was held at approximately 100 C for an additional hour.
The product was collected by filtration, washed on the filter with 2L
hot deionized water and then 2L ambient temperature deionized water. The
product was vacuum dried (water aspirator) at 60 C for 12 hours and then to a
constant weight at 120 C under vacuum (5 - 10 torr). The yield of product was
around 65-75 grams.
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PRODUCT ISOLATION BY PRECIPITATING THE POLYMER SOLUTION IN A NON-SOLVENT
The other half of the organic phase was diluted with 200mL of EDC
and was placed in an appropriately sized addition funnel. This was added to
1.21.
methanol contained in a 4L Morton resin flask equipped with a mechanical
stirrer. The precipitation was conducted at room temperature with a two and
one half hour addition followed by an additional 15 minutes of stirring.
The product was collected by filtration, reslurried in methanol for 30
minutes and collected again by filtration. The product was vacuum dried (water
aspirator) at 60 C to a constant weight in 12 hours. The yield of product was
around 65-75 grams. Whiteness index (WI) and yellowness index (YI) were
determined according to ASTM E1313-73. Results are reported in TABLE V
hereinbelow. The formulae for WI and YI are as follows:
WI = 0.1 L(L - 5.7b) - The higher the Whiteness Index (WI), the whiter
the color of the sample.
Yf = 100 (0.72a + 1.79b) - The lower the Yellowness Index (YI), the
L
more the sample approaches being white.
TABLE V
COLOR VERSUS REACTION TEMP AND ISOLATION PROCEDURE
Ex. No. BrT C WI YI
1 MPa 20 42.3 15.4
2 Wb 20 37.4 17.2
3 MP 35 12.3 25.6
4 W 35 3.3 28.2
a) MP means the sample was precipitated in methanol.
b) W means the sample was isolated from boiling water.
The data in Table V clearly shows two trends. First, the color of the
brominated polystyrene was better when the bromination was conducted at lower
temperatures holding all other variables constant. Second, the color was
better
(whiter) when the brominated polystyrene was isolated by a non-solvent
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precipitation (methanol) rather than flashing off the solvent in boiling
water.
Similar conclusions can be drawn by extrapolation from the data in the
foregoing
Tables.
Thus it should be evident that the process of the present invention is
highly effective in preparing a brominated polystyrene having improved color
characteristics.
Based upon the foregoing disclosure, it should now be apparent that
the use of the process described herein will carry out the objects set forth
hereinabove. It is, therefore, to be understood that any variations evident
fall
within the scope of the claimed invention and thus, the selection of specific
component elements can be determined without departing from the spirit of the
invention herein disciosed and described. In particular, the brominating
agent,
catalysts and reaction temperatures and times and other reaction conditions
according to the present invention are not necessarily limited to those
discussed
herein. Thus, the scope of the invention shall include all modifications and
variations that may fall within the scope of the attached claims.
