CA1182249A - Method for the suspension polymerization of styrenic monomers - Google Patents
Method for the suspension polymerization of styrenic monomersInfo
- Publication number
- CA1182249A CA1182249A CA000398258A CA398258A CA1182249A CA 1182249 A CA1182249 A CA 1182249A CA 000398258 A CA000398258 A CA 000398258A CA 398258 A CA398258 A CA 398258A CA 1182249 A CA1182249 A CA 1182249A
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- Prior art keywords
- suspension
- polymerization
- initiator
- free radical
- monomer
- Prior art date
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Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F12/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F12/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring
- C08F12/02—Monomers containing only one unsaturated aliphatic radical
- C08F12/04—Monomers containing only one unsaturated aliphatic radical containing one ring
- C08F12/06—Hydrocarbons
Abstract
A METHOD FOR THE SUSPENSION POLYMERIZATION
OF STYRENIC MONOMERS
ABSTRACT OF THE DISCLOSURE
In a method for the suspension polymerization of one or more styrenic monomers, optionally with up to 35% by weight, based on the total monomers, of one or more non-styrenic vinyl monomers, a suspension of the monomer(s) is produced as droplets dispersed in a continuous water phase. The monomer(s) in the suspension is then partially polymerized by free radical initiation in the presence of at least one substantially water insoluble free radical initiator until 50% to 90% conversion is achieved. Thereafter the amount of substantially water insoluble free radical initiator(s) in the suspension is increased and the suspension polymerization is completed, again by free radical initiation. The temperature of the suspension is maintained at at least 110°C during the entire polymerization.
OF STYRENIC MONOMERS
ABSTRACT OF THE DISCLOSURE
In a method for the suspension polymerization of one or more styrenic monomers, optionally with up to 35% by weight, based on the total monomers, of one or more non-styrenic vinyl monomers, a suspension of the monomer(s) is produced as droplets dispersed in a continuous water phase. The monomer(s) in the suspension is then partially polymerized by free radical initiation in the presence of at least one substantially water insoluble free radical initiator until 50% to 90% conversion is achieved. Thereafter the amount of substantially water insoluble free radical initiator(s) in the suspension is increased and the suspension polymerization is completed, again by free radical initiation. The temperature of the suspension is maintained at at least 110°C during the entire polymerization.
Description
A METHOD FOR THE SUSPENSION POLYMERIZATION
OF ST~RENIC MONOMERS
This invention relates to a method for the suspension polymerization of styrenic monomers.
Pblymerization of styrene and other styrenic monomers may take place by a variety D~ techniques such as bulk or solvent polymerization, emulsion polymeri~ation or suspension polymerization. In each of th~se techniques9 polymerization results from a free radical induced, chain-propagation mechanism. Stated in simple terms, styrenic monomers form polymers whPn contacted with free radicals. Accordingly) in order to cause styrenic monomers to polymerize, it is necessary to combins these monomers with free radicals.
~There are two known techniques ~or providing free radicals ;for the polymerization of styrenic monomers. One such technique is simply to heat the styrenic monomers to a temperature, e.g., above 120C, which causes the generation of free radicals by thermally induced interactions among these styrenic monomers. This technique is often re~erred to as thermal initiation. Another technique is distinguished from thermal initiatlon in that it involves combining catalytic quantities of free radical initiators with the styrenic monomers. These free radical initiators generate free radicals by thermally induced decomposition. Accordin~ly, both the "thermally induced" technique and the initiator induced technique are therm~l in the sense that they both involve heating of the polymerization system. However, the initiator induced technique generally takes place at a lower temperature than the thermally initiated technique, the temperature of the initiator induced technique being such that ~ree radicals are generated substantially ~rom initiator decomposition as opposed to the interaction of styrenic monomPrs, particularly in the initial stages of the polymerization.
Free radicals not only initiate poly~erization, kut also ~he rate at whlch polymerization proceeds lncreases as the concentration of free ,~
radicals in the styrenic monomers increases. Also, the concentration of free radicals generated by a siven quantity of styrenic monomers or free radical initiators increases as temperature increases. Accordingly, increasing temperature generally tends to increase rates of reaction at least immediately after the temperature is increased. However, if the temperature is held constant the polymerization rate will tend to decrease over time, because as the polymerization proceeds less and less styrenic monomer and/or free radical initiator are left to generate more free radicals. Accordingly, in order to drive the polymerization to completion, it is known to increase the temperature as the reaction proceeds. It is also known to use a plurality of free radical initiators which decompose at different temperatures. When such a plurality of free radical initiators is used, the temperature may be maintained at one temperature until one free radical initiator is substantially decomposed, and then the temperature may be increased to decompose the remaining initiators.
Free radicals can also be generated by incrementally incorporating free radical initiators with the styrenic monomers as the polymerization progresses. Such an incremental incorporation is known in the case of bulk or emulsion polymerizations. However, in the case of suspension polymerizations, special problems are presented with incremental additions of free radical initiators, due to the manner in which styrenic monomers are polymerized in such suspension polymerizations.
In suspension polymerizations, styrenic monomers are present in a suspension of droplets dispersed throughout a continuous water medium. Although the free radical initiators used in such suspension polymerizations are soluble in styrenic monomers, these initiators are substantially insoluble in water. Accordingly, it is most customary to incorporate all of the initiator or initiators with the styrenic monomers before the suspension polymerization is started.
U.S. Patent No. 2,907 9 756 suggests that an incremental addition of initiators may be made in the suspension polymerization of styrene but only during the initial sta~es of the polymerization. More particularly, it is stated that it is necessary to add all of the initiator before polymerization has progressed to such an extent that intimate mixing of catalyst and styrene monomer is precluded. Specifically, addition of initiator is terminated when the suspension reaches a temperature of about 115C (See Column 6, lines 8-14 of U.S. Patent No. 2,907,756).
Referring to Table II of Doak U.S. Patent 2,907,756 (See Column 7, lines 7-22), the percent c~nversion of the polymerization reaches about 4g% at the time the suspension reaches a temperature oF about 115UC .
It is understandable why U.S. Patent No. 2,907~756 discourages the addition of initiator to the suspension during the later stages of polymerization. At these stages, two barriers to prevent mixing of initiators and monomers are present, namely, (1) the continuous water phase, in which the initiator is insoluble, and
OF ST~RENIC MONOMERS
This invention relates to a method for the suspension polymerization of styrenic monomers.
Pblymerization of styrene and other styrenic monomers may take place by a variety D~ techniques such as bulk or solvent polymerization, emulsion polymeri~ation or suspension polymerization. In each of th~se techniques9 polymerization results from a free radical induced, chain-propagation mechanism. Stated in simple terms, styrenic monomers form polymers whPn contacted with free radicals. Accordingly) in order to cause styrenic monomers to polymerize, it is necessary to combins these monomers with free radicals.
~There are two known techniques ~or providing free radicals ;for the polymerization of styrenic monomers. One such technique is simply to heat the styrenic monomers to a temperature, e.g., above 120C, which causes the generation of free radicals by thermally induced interactions among these styrenic monomers. This technique is often re~erred to as thermal initiation. Another technique is distinguished from thermal initiatlon in that it involves combining catalytic quantities of free radical initiators with the styrenic monomers. These free radical initiators generate free radicals by thermally induced decomposition. Accordin~ly, both the "thermally induced" technique and the initiator induced technique are therm~l in the sense that they both involve heating of the polymerization system. However, the initiator induced technique generally takes place at a lower temperature than the thermally initiated technique, the temperature of the initiator induced technique being such that ~ree radicals are generated substantially ~rom initiator decomposition as opposed to the interaction of styrenic monomPrs, particularly in the initial stages of the polymerization.
Free radicals not only initiate poly~erization, kut also ~he rate at whlch polymerization proceeds lncreases as the concentration of free ,~
radicals in the styrenic monomers increases. Also, the concentration of free radicals generated by a siven quantity of styrenic monomers or free radical initiators increases as temperature increases. Accordingly, increasing temperature generally tends to increase rates of reaction at least immediately after the temperature is increased. However, if the temperature is held constant the polymerization rate will tend to decrease over time, because as the polymerization proceeds less and less styrenic monomer and/or free radical initiator are left to generate more free radicals. Accordingly, in order to drive the polymerization to completion, it is known to increase the temperature as the reaction proceeds. It is also known to use a plurality of free radical initiators which decompose at different temperatures. When such a plurality of free radical initiators is used, the temperature may be maintained at one temperature until one free radical initiator is substantially decomposed, and then the temperature may be increased to decompose the remaining initiators.
Free radicals can also be generated by incrementally incorporating free radical initiators with the styrenic monomers as the polymerization progresses. Such an incremental incorporation is known in the case of bulk or emulsion polymerizations. However, in the case of suspension polymerizations, special problems are presented with incremental additions of free radical initiators, due to the manner in which styrenic monomers are polymerized in such suspension polymerizations.
In suspension polymerizations, styrenic monomers are present in a suspension of droplets dispersed throughout a continuous water medium. Although the free radical initiators used in such suspension polymerizations are soluble in styrenic monomers, these initiators are substantially insoluble in water. Accordingly, it is most customary to incorporate all of the initiator or initiators with the styrenic monomers before the suspension polymerization is started.
U.S. Patent No. 2,907 9 756 suggests that an incremental addition of initiators may be made in the suspension polymerization of styrene but only during the initial sta~es of the polymerization. More particularly, it is stated that it is necessary to add all of the initiator before polymerization has progressed to such an extent that intimate mixing of catalyst and styrene monomer is precluded. Specifically, addition of initiator is terminated when the suspension reaches a temperature of about 115C (See Column 6, lines 8-14 of U.S. Patent No. 2,907,756).
Referring to Table II of Doak U.S. Patent 2,907,756 (See Column 7, lines 7-22), the percent c~nversion of the polymerization reaches about 4g% at the time the suspension reaches a temperature oF about 115UC .
It is understandable why U.S. Patent No. 2,907~756 discourages the addition of initiator to the suspension during the later stages of polymerization. At these stages, two barriers to prevent mixing of initiators and monomers are present, namely, (1) the continuous water phase, in which the initiator is insoluble, and
(2) the substantial amount of polymer which has formed. However, in spite of these barriers it has unexpectedly been found that initiator can indeed be effectually added to the later stages of a suspension polymerization, when such addition is made in accordance with the present invention.
Accordingly, the invention resides in a method for the suspension polymerization of one or more styrenic monomers, optionally with up to 35% by weight, based on the total monomers, of one or more non-styrenic, vinyl monomers, comprising the steps of:
(a) producing a suspension of the monomer(s) as droplets dispersed in a continuous water phase;
(b) partially polymerizing the monomer(s) in said suspension by free radical initiation in the presence of at least on~ substantially water insoluble free radical initiator until 50% to 90% conversion is achieved; and then F-0883 ~4~
~c) increasing the amount of substantially water insoluble free radical initiator(s) in said suspension and substantially completing the suspension polymerization by free radical initiation, wherein the temperature of the suspension is at least 110C during the entire polymerization.
rhe method of the present invention concerns the suspension polymerization of styrenic monomers. The term "styrenic monomers"
as used herein is intended to mean aryl vinyl monomers such as styrene, ring-substituted alkyl styrenes and ring-halo-substituted styrenes. Particular styrenic monomers include styrene, paramethylstyrene, metamethylstyrene, vinyl toluenes (i.e., a mixture of paramethylstyrene and metamethylstyrene), para-t-butylstyrene and parachlorostyrene, a preferred styrenic monomer being paramethylstyrene. In addition to styrenic monomers, the polymerization system may contain up to about 35% by weight of one or more copolymerizable non-styrenic, vinyl monomers, based upon the entire weight of monomers present in the system. Such non-styrenic vinyl monomers include acrylic monomers such as acrylonitrileO Accordingly, the method of the present invention may be used to produce polymers which are copolymers as well as polymers which are homopolymers.
The suspension in which polymerization occurs is preferably stabilized throughout the entire polymerization by means of one or more stabilizers or suspending agents. For example, monomer may be mixed with water and a minor amount of a stabilizer or suspending agent such as tricalcium phosphate. Additionally, a small quantity (e.g., û.Oûl to û.05~ by weight of the total charge) of a surface-active agent is preferably used to reduce surface tension.
Surface active agents include nonionic, anionic or cationic materials including alkyl aryl sulfonates and octylphenoxy polyether alcohols. A preferred surface active agent is partially sulfonated polyparamethylstyrene extender which contains about 10 mole percent a F-0883 ~5 sulfonic acid groups. Such sulfonated polyparamethylstyrene extenders are described in U.S. Patent No. 4,237,255.
The ~ater to monomer plus polymer ratio of the suspension may be9 for example, f~om about 1.1.2 to about 3:1, preferably, the ratio of water to monmer plus polymer should be as small as possible tn make efficient use of available reactor volume. More particularly9 the water to monomer plus polymer ratio should preferably not exceed 1.2:1 during the entire polymerization.
Although water may be added during the polymerization to compensate for minor volumetric shrinkage of the liquid phase as the polymerization proceeds, ~t is preferred to maintain a constant water to mnnomer plus polymer ratio throughout the entire polymerization.
The desired droplet size of the monomer may be achieved by an appropriate rate of stirring of the suspension. Generally9 the droplets may range from about 50CO Angstroms to about 0.5 cm in diameterO Preferably, the droplets may be at least 0.15 cm in diameter or, in other terms, may be of sufficient size to obtain polymer particles o~ which better than 9U% are retained on a 100 mesh screen.
The suspension may also contaln other additives. For example, a ~oloring agent or dye may also be included in the suspension. More particularly, in the case of paramethylstyrene, a blueing agent may be used. It is further possible to include additives which stabilize the polymers which are produced from the suspension. One such stabilizer is a phenolic antioxidant, e.g.9 IRGANOX 10767 a trademark of Ciba-Geigy. Extrusion aids such as mineral oil may be included to aid in extrusion of the resulting polymer.
In the two-stage suspension polymerization of the invention9 the first partial polymerization stage is achieved by an initiator initiated technique by incorporation of at least one substantially water insoluble free radical initiator into the suspension. Examples of such free radical initiators include ~, F-0883 -6~
organic peroxy compounds such as lauroyl peroxide, benzoyl peroxide, t-~utylperben20ate, and t-butylperoxyacetate. It will be understood that the above-mentioned organic peroxy compounds are not neoessarily absolutely water insoluble, particularly when used at temperatures in accordance with the present invention. Nonetheless, these compounds are substantially water insoluble and are quite distinguishable from the water soluble initiators used in emulsion polymerizations, such as potassium persulfate.
The substantially water insoluble initiators are preferably added to the polymeri~ation suspenslon as suspensions themselves or as solutions in water miscible solvents. An example of such a suspension of an initiator is a suspension of benzoyl peroxide in methylene chloride containing a suspending agent such as "~elvatol", a trademark of Monsanto9 which is a polyvinyl alcohol. An example of a solution of an initiator which may be added to the polymerization suspension is a solution of t-butylperoxyacetate dissolved in methanol.
The initiator should preferably have a half life of from about 20 to about 30 minutes, most especially about 25 minutes, at `the temperature of the suspension during the polymerization.
Preferably, a conversion of at least 40~, most especially 55% or more, is attained in the first hour of the polymeri~ation.
The end of the first stage of the polymerization may be expressed in terms of the percent conversion achieved. More particularly, the first stage ends after the conversion is at least about 50% but before the conversion reaches about 90%. Preferably, 'the first stage ends after 60-80% oonversion of the monomer.
The second stage (effecting at least 10% conversion) also takes place in the presence of at least one substantially water insoluble free radical initiator, which again is preferably chosen from said organic peroxy compounds listed above. More particularly, after about 5C%, but before about 9W0, conversion is achieved the initiator content of the suspension is increased, e.g., by adding initiator to the suspensionO It will be understood that the amount .
~ ~, .. . . . ... . . . ... . . . . .. . .. . . . . . . .
F~0883 ~7~
of initiator in the suspension may be increased before the conversion reaches 50~ and/or after the conversion reaches 90%, as long as the amount of initiator in the suspension is increased when the conversion is between 50% and about 90%.
During the entire polymerization process the temperature of the suspension should be maintained at at least 110C, preferably 120C or more. The temperature should not, however, be allowed to rise so high as to generate excessive free radicals since the resulting polymer may have an undesirably low molecular weight, characterized by, eg, a high melt index. Suspension instability problems may also be encountered if the temperature of the suspension becomes excessively high. ~herever styrene or paramethylstyrene is polymerized by the method of the invention9 the temperature of the suspension should be at least 120C, most especially approximately 130C.
Preferably, the temperature of the suspension is substantially constant throughout the entire polymerization.
According to such a preferred substantially isothermal technique, the temperature preferably does not vary by more than about 5C
during the entire polymerization.
It is to be appreciated that, at the high temperatures used in the method of the invention, polymerization may proceed not only by free radical initiation but also by thermally induced interactions of the styrenic monomers, particularly at the latter stages of the polymerization.
It will be understood that one or more initiators may be used during the polymerization. These initiators may be added all at once at the beginning of each of the first and second stages of the polymerization but are preferably added in a continuous or an incremental fashion.
A preferred manner of performing an incremental addition of initiator to the suspension may be expressed in terms of the amount of initiator which is initially added to the reactor and the rate of decomposition of the initiator determined on the basis of F-088~ -8-the decomposition of the initiator in an inert solvent at the temperature corresponding to that of the suspension. More particularly, an increment of time sufficient to achieve about a 50%
decomposition of trhe initial charge of initiator may be permitted to pass before a second charge of initiator is added to the suspension. The amount of initiator added in the second charge is preferably su~ficient to replenish the amount of initiator such that the amount of non-decomposed initiator in the suspension after the second charge of the initiator is approximately equal to the amount of initiator present in the suspension immediately after the initial charge of initiator. Subsequent additions of initiator may be made in a manner analogous to the second addition of initiator.
Preferably at least 3 additions of initiatorJ each addition taking place at different conversions of the monomer, may take place in an incremental addition of initiator. Thus7 for example, t-butylperoxyacetate may be added at brief intervals ~e.g., at about 25 minute intervals) while the suspension is maintained at a temperature of about 130~.
It will be understood that the above-mentioned manner of conducting an incremental addit.ion is but one example of such an incremental addition technique. This and other techniques are demonstrated in the Examples given hereinafter. Preferably, initiator is added to the suspension as continuously as possible to compensate for initiator which has decomposed. Also, the rate at which initiator is added to the suspension is preferably constant after initiator is initially added to the suspension.
Polymerization of the styrenic monomer or monomers is substantially complete when at least about 99%, and preferably at least about 99.9~, of the monomer or monomers have polymerized.
This may be achieved in 8 hours or less, preferably 5 hours or less.
The polymer may be isolated from the suspension by any convenient means known by those skilled in the art, such as washing.
In accordance with the present invention, it is possible to obtain polymers having desirable properties. For instance, polymers F-08~3 9 produced in accordance with the present invention may have a rela-tively narrow range of malecular weights. This range may be expressed quantitatively in terms of the molecular weight distribution (MWD) of the polymer, ~hich is the ratio of the weight average molecular weight (MW) to the weight number molecular weight (MN). More particularly, the M~D for paramethylstyrene homopolymers, produced according to the present invention, may be about 3-5.
It is also possible to achieve a desirably extrudable polymer in accordance with the present invention, even in the absence of an extrusion aid incorporated into the polymer, as evidenced by a relatively low die swell index. It is noted that die swell index is a measure of extrudate diameter to die diameter.
Thus, the die swell index for a paramethylstyrene homopolymer produced according to the present invention may be from about 1.6 to about 1.8. By way of contrast, when a paramethylstyrene polymer is produced according to a conventional suspension process (e.g., where both benzoyl peroxide and t-butylperbenzoate are added to the suspension at the start of the polymerization), the resulting polymer may typically have a MWD of from 5 to 10 and a die swell index of from 1.8 to 2Ø
In accordance with the two-stage polymerization technique of the present invention, initiator levels can be reduced 50-9~%
over conventional polymerizations in which all the initiator is added to the suspension at the beginning of the polymerization.
Furthermore, cycle times can be reduced up to 25% for batch preparations of comparable styrenic polyrners. Moreover, molecular weights and distributions may be easily controlled to narrow limits.
The method of the present invention is particularly useful for the preparation of low melt index extrusion grade polymers and the preparation of fractional melt index polymers which can be useful for oriented films, blow molding resins, etc. This method is also particularly appropriate for continuous suspension polymerizations.
The invention will now be more particularly described with reference to Examples 1 and 2 and to the accompanying Figures 1 and 2 which plot and tabulate for the respective Examples the %
conversion of paramethylstyrene monomer to polymer and amount of lnltiator added against time.
A 2 liter autoclave was charged with 6309 of p-methylstyrene (containing 31 mg of IRGANOX 1076, 1.2 mg of"Perox"
blue dye and 80 mg of sul~onated poly-p~methylstyrene~ together with 0.159 of'`Lupersol 7a'~a 7a% solution of t-butylperoxyacetate) and 660 ml of water containing 12.49 of tricalcium phosphate. This mixture was purged with nitrogen and heated to 130 with stirring.
After 25 minutes at 130C~Lupersol 70~(75 mg) was injected into the autoclave (as a 10% solution in methanol). A total of 5 injections of'`Lupersol 70~were added at 25 minute intervals. Heating was maintained at 130 ~or a total of 5 hours, when the conversion had reached 99.98%. The product isolated from this reaction had a melt index (Cond G) o~ 1.8 and had a GPC molecular weight (based on polystyrene calibration standards) of: MW=304,000; MN=94,000; and MWD=3.2. A total of 0.084 parts of~Lupersol 70"per hundred parts of monomer were used in the polymerization. The catalyst additions and polymerlzation rate data are summari~ed in Figure 1.
A 2 liter autoclave was charged with 6309 of p-methylstyrene (containing 32 mg of IRGANOX 1076, 1.2 mg. of"Perox"
blue dye and 80 mg of sulfonated poly p-methylstyrene) together with 0.309 of"Lupersol 70"(a 70~ solution of t-butylperoxyacetate) and 660 ml of water containing 12.49 of tricalcium phosphate. This mixture was purged with nitrogen and heated to 130~C with s~irring.
After 25 minutes at 130C, 1.8 ml of a 10% solution o~'Lupersol 70"
*Trademark **Trademark .~"..,~
.. . ...
in methanol was in~ected into the autoclave. Subsequently9 and at 25 minute intervals, two additional injections of"Lupersol 7~'were made, each injection being 2.7 ml of a 10% solution o~'Lupersol 7G "
in methan~. Hbating was maintained at 130C for a total of 5 hours, when the conversion had reached 99.86%. The product isolat2d ~rom this reaction had a melt index (Cond G) of 2.6, a die swell index o~ 1.63 and a GPC molecular weight (based on polystyrene calibration standards) o~: MW=310,000; MN=89,860; and MWD=3.45.
The catalyst additions and the polymerization rate data are summar~zed in Figure 2.
The values for percent conversion cited herein are based upon the total amount o~ monomer present in the suspension before any polymer thereof is ~ormed.
... ... .. . , . .. ,,, . , .,, . ~ ,, ~
Accordingly, the invention resides in a method for the suspension polymerization of one or more styrenic monomers, optionally with up to 35% by weight, based on the total monomers, of one or more non-styrenic, vinyl monomers, comprising the steps of:
(a) producing a suspension of the monomer(s) as droplets dispersed in a continuous water phase;
(b) partially polymerizing the monomer(s) in said suspension by free radical initiation in the presence of at least on~ substantially water insoluble free radical initiator until 50% to 90% conversion is achieved; and then F-0883 ~4~
~c) increasing the amount of substantially water insoluble free radical initiator(s) in said suspension and substantially completing the suspension polymerization by free radical initiation, wherein the temperature of the suspension is at least 110C during the entire polymerization.
rhe method of the present invention concerns the suspension polymerization of styrenic monomers. The term "styrenic monomers"
as used herein is intended to mean aryl vinyl monomers such as styrene, ring-substituted alkyl styrenes and ring-halo-substituted styrenes. Particular styrenic monomers include styrene, paramethylstyrene, metamethylstyrene, vinyl toluenes (i.e., a mixture of paramethylstyrene and metamethylstyrene), para-t-butylstyrene and parachlorostyrene, a preferred styrenic monomer being paramethylstyrene. In addition to styrenic monomers, the polymerization system may contain up to about 35% by weight of one or more copolymerizable non-styrenic, vinyl monomers, based upon the entire weight of monomers present in the system. Such non-styrenic vinyl monomers include acrylic monomers such as acrylonitrileO Accordingly, the method of the present invention may be used to produce polymers which are copolymers as well as polymers which are homopolymers.
The suspension in which polymerization occurs is preferably stabilized throughout the entire polymerization by means of one or more stabilizers or suspending agents. For example, monomer may be mixed with water and a minor amount of a stabilizer or suspending agent such as tricalcium phosphate. Additionally, a small quantity (e.g., û.Oûl to û.05~ by weight of the total charge) of a surface-active agent is preferably used to reduce surface tension.
Surface active agents include nonionic, anionic or cationic materials including alkyl aryl sulfonates and octylphenoxy polyether alcohols. A preferred surface active agent is partially sulfonated polyparamethylstyrene extender which contains about 10 mole percent a F-0883 ~5 sulfonic acid groups. Such sulfonated polyparamethylstyrene extenders are described in U.S. Patent No. 4,237,255.
The ~ater to monomer plus polymer ratio of the suspension may be9 for example, f~om about 1.1.2 to about 3:1, preferably, the ratio of water to monmer plus polymer should be as small as possible tn make efficient use of available reactor volume. More particularly9 the water to monomer plus polymer ratio should preferably not exceed 1.2:1 during the entire polymerization.
Although water may be added during the polymerization to compensate for minor volumetric shrinkage of the liquid phase as the polymerization proceeds, ~t is preferred to maintain a constant water to mnnomer plus polymer ratio throughout the entire polymerization.
The desired droplet size of the monomer may be achieved by an appropriate rate of stirring of the suspension. Generally9 the droplets may range from about 50CO Angstroms to about 0.5 cm in diameterO Preferably, the droplets may be at least 0.15 cm in diameter or, in other terms, may be of sufficient size to obtain polymer particles o~ which better than 9U% are retained on a 100 mesh screen.
The suspension may also contaln other additives. For example, a ~oloring agent or dye may also be included in the suspension. More particularly, in the case of paramethylstyrene, a blueing agent may be used. It is further possible to include additives which stabilize the polymers which are produced from the suspension. One such stabilizer is a phenolic antioxidant, e.g.9 IRGANOX 10767 a trademark of Ciba-Geigy. Extrusion aids such as mineral oil may be included to aid in extrusion of the resulting polymer.
In the two-stage suspension polymerization of the invention9 the first partial polymerization stage is achieved by an initiator initiated technique by incorporation of at least one substantially water insoluble free radical initiator into the suspension. Examples of such free radical initiators include ~, F-0883 -6~
organic peroxy compounds such as lauroyl peroxide, benzoyl peroxide, t-~utylperben20ate, and t-butylperoxyacetate. It will be understood that the above-mentioned organic peroxy compounds are not neoessarily absolutely water insoluble, particularly when used at temperatures in accordance with the present invention. Nonetheless, these compounds are substantially water insoluble and are quite distinguishable from the water soluble initiators used in emulsion polymerizations, such as potassium persulfate.
The substantially water insoluble initiators are preferably added to the polymeri~ation suspenslon as suspensions themselves or as solutions in water miscible solvents. An example of such a suspension of an initiator is a suspension of benzoyl peroxide in methylene chloride containing a suspending agent such as "~elvatol", a trademark of Monsanto9 which is a polyvinyl alcohol. An example of a solution of an initiator which may be added to the polymerization suspension is a solution of t-butylperoxyacetate dissolved in methanol.
The initiator should preferably have a half life of from about 20 to about 30 minutes, most especially about 25 minutes, at `the temperature of the suspension during the polymerization.
Preferably, a conversion of at least 40~, most especially 55% or more, is attained in the first hour of the polymeri~ation.
The end of the first stage of the polymerization may be expressed in terms of the percent conversion achieved. More particularly, the first stage ends after the conversion is at least about 50% but before the conversion reaches about 90%. Preferably, 'the first stage ends after 60-80% oonversion of the monomer.
The second stage (effecting at least 10% conversion) also takes place in the presence of at least one substantially water insoluble free radical initiator, which again is preferably chosen from said organic peroxy compounds listed above. More particularly, after about 5C%, but before about 9W0, conversion is achieved the initiator content of the suspension is increased, e.g., by adding initiator to the suspensionO It will be understood that the amount .
~ ~, .. . . . ... . . . ... . . . . .. . .. . . . . . . .
F~0883 ~7~
of initiator in the suspension may be increased before the conversion reaches 50~ and/or after the conversion reaches 90%, as long as the amount of initiator in the suspension is increased when the conversion is between 50% and about 90%.
During the entire polymerization process the temperature of the suspension should be maintained at at least 110C, preferably 120C or more. The temperature should not, however, be allowed to rise so high as to generate excessive free radicals since the resulting polymer may have an undesirably low molecular weight, characterized by, eg, a high melt index. Suspension instability problems may also be encountered if the temperature of the suspension becomes excessively high. ~herever styrene or paramethylstyrene is polymerized by the method of the invention9 the temperature of the suspension should be at least 120C, most especially approximately 130C.
Preferably, the temperature of the suspension is substantially constant throughout the entire polymerization.
According to such a preferred substantially isothermal technique, the temperature preferably does not vary by more than about 5C
during the entire polymerization.
It is to be appreciated that, at the high temperatures used in the method of the invention, polymerization may proceed not only by free radical initiation but also by thermally induced interactions of the styrenic monomers, particularly at the latter stages of the polymerization.
It will be understood that one or more initiators may be used during the polymerization. These initiators may be added all at once at the beginning of each of the first and second stages of the polymerization but are preferably added in a continuous or an incremental fashion.
A preferred manner of performing an incremental addition of initiator to the suspension may be expressed in terms of the amount of initiator which is initially added to the reactor and the rate of decomposition of the initiator determined on the basis of F-088~ -8-the decomposition of the initiator in an inert solvent at the temperature corresponding to that of the suspension. More particularly, an increment of time sufficient to achieve about a 50%
decomposition of trhe initial charge of initiator may be permitted to pass before a second charge of initiator is added to the suspension. The amount of initiator added in the second charge is preferably su~ficient to replenish the amount of initiator such that the amount of non-decomposed initiator in the suspension after the second charge of the initiator is approximately equal to the amount of initiator present in the suspension immediately after the initial charge of initiator. Subsequent additions of initiator may be made in a manner analogous to the second addition of initiator.
Preferably at least 3 additions of initiatorJ each addition taking place at different conversions of the monomer, may take place in an incremental addition of initiator. Thus7 for example, t-butylperoxyacetate may be added at brief intervals ~e.g., at about 25 minute intervals) while the suspension is maintained at a temperature of about 130~.
It will be understood that the above-mentioned manner of conducting an incremental addit.ion is but one example of such an incremental addition technique. This and other techniques are demonstrated in the Examples given hereinafter. Preferably, initiator is added to the suspension as continuously as possible to compensate for initiator which has decomposed. Also, the rate at which initiator is added to the suspension is preferably constant after initiator is initially added to the suspension.
Polymerization of the styrenic monomer or monomers is substantially complete when at least about 99%, and preferably at least about 99.9~, of the monomer or monomers have polymerized.
This may be achieved in 8 hours or less, preferably 5 hours or less.
The polymer may be isolated from the suspension by any convenient means known by those skilled in the art, such as washing.
In accordance with the present invention, it is possible to obtain polymers having desirable properties. For instance, polymers F-08~3 9 produced in accordance with the present invention may have a rela-tively narrow range of malecular weights. This range may be expressed quantitatively in terms of the molecular weight distribution (MWD) of the polymer, ~hich is the ratio of the weight average molecular weight (MW) to the weight number molecular weight (MN). More particularly, the M~D for paramethylstyrene homopolymers, produced according to the present invention, may be about 3-5.
It is also possible to achieve a desirably extrudable polymer in accordance with the present invention, even in the absence of an extrusion aid incorporated into the polymer, as evidenced by a relatively low die swell index. It is noted that die swell index is a measure of extrudate diameter to die diameter.
Thus, the die swell index for a paramethylstyrene homopolymer produced according to the present invention may be from about 1.6 to about 1.8. By way of contrast, when a paramethylstyrene polymer is produced according to a conventional suspension process (e.g., where both benzoyl peroxide and t-butylperbenzoate are added to the suspension at the start of the polymerization), the resulting polymer may typically have a MWD of from 5 to 10 and a die swell index of from 1.8 to 2Ø
In accordance with the two-stage polymerization technique of the present invention, initiator levels can be reduced 50-9~%
over conventional polymerizations in which all the initiator is added to the suspension at the beginning of the polymerization.
Furthermore, cycle times can be reduced up to 25% for batch preparations of comparable styrenic polyrners. Moreover, molecular weights and distributions may be easily controlled to narrow limits.
The method of the present invention is particularly useful for the preparation of low melt index extrusion grade polymers and the preparation of fractional melt index polymers which can be useful for oriented films, blow molding resins, etc. This method is also particularly appropriate for continuous suspension polymerizations.
The invention will now be more particularly described with reference to Examples 1 and 2 and to the accompanying Figures 1 and 2 which plot and tabulate for the respective Examples the %
conversion of paramethylstyrene monomer to polymer and amount of lnltiator added against time.
A 2 liter autoclave was charged with 6309 of p-methylstyrene (containing 31 mg of IRGANOX 1076, 1.2 mg of"Perox"
blue dye and 80 mg of sul~onated poly-p~methylstyrene~ together with 0.159 of'`Lupersol 7a'~a 7a% solution of t-butylperoxyacetate) and 660 ml of water containing 12.49 of tricalcium phosphate. This mixture was purged with nitrogen and heated to 130 with stirring.
After 25 minutes at 130C~Lupersol 70~(75 mg) was injected into the autoclave (as a 10% solution in methanol). A total of 5 injections of'`Lupersol 70~were added at 25 minute intervals. Heating was maintained at 130 ~or a total of 5 hours, when the conversion had reached 99.98%. The product isolated from this reaction had a melt index (Cond G) o~ 1.8 and had a GPC molecular weight (based on polystyrene calibration standards) of: MW=304,000; MN=94,000; and MWD=3.2. A total of 0.084 parts of~Lupersol 70"per hundred parts of monomer were used in the polymerization. The catalyst additions and polymerlzation rate data are summari~ed in Figure 1.
A 2 liter autoclave was charged with 6309 of p-methylstyrene (containing 32 mg of IRGANOX 1076, 1.2 mg. of"Perox"
blue dye and 80 mg of sulfonated poly p-methylstyrene) together with 0.309 of"Lupersol 70"(a 70~ solution of t-butylperoxyacetate) and 660 ml of water containing 12.49 of tricalcium phosphate. This mixture was purged with nitrogen and heated to 130~C with s~irring.
After 25 minutes at 130C, 1.8 ml of a 10% solution o~'Lupersol 70"
*Trademark **Trademark .~"..,~
.. . ...
in methanol was in~ected into the autoclave. Subsequently9 and at 25 minute intervals, two additional injections of"Lupersol 7~'were made, each injection being 2.7 ml of a 10% solution o~'Lupersol 7G "
in methan~. Hbating was maintained at 130C for a total of 5 hours, when the conversion had reached 99.86%. The product isolat2d ~rom this reaction had a melt index (Cond G) of 2.6, a die swell index o~ 1.63 and a GPC molecular weight (based on polystyrene calibration standards) o~: MW=310,000; MN=89,860; and MWD=3.45.
The catalyst additions and the polymerization rate data are summar~zed in Figure 2.
The values for percent conversion cited herein are based upon the total amount o~ monomer present in the suspension before any polymer thereof is ~ormed.
... ... .. . , . .. ,,, . , .,, . ~ ,, ~
Claims (13)
1. A method for the suspension polymerization of one or more styrenic monomers, optionally with up to 35% by weight, based on the total monomers, of one or more non-styrenic,vinyl monomers, comprising the steps of:
(a) producing a suspension of the monomer(s) as droplets dispersed in a continuous water phase;
(b) partially polymerizing the monomer(s) in said suspension by free radical initiation in the presence of at least one substantially water insoluble free radical initiator until 50% to 90% conversion is achieved; and then (c) increasing the amount of substantially water insoluble free radical initiator(s) in said suspension and substantially completing the suspension polymerization by free radical initiation, wherein the temperature of the suspension is at least 100°C during the entire polymerization.
(a) producing a suspension of the monomer(s) as droplets dispersed in a continuous water phase;
(b) partially polymerizing the monomer(s) in said suspension by free radical initiation in the presence of at least one substantially water insoluble free radical initiator until 50% to 90% conversion is achieved; and then (c) increasing the amount of substantially water insoluble free radical initiator(s) in said suspension and substantially completing the suspension polymerization by free radical initiation, wherein the temperature of the suspension is at least 100°C during the entire polymerization.
2. A method as claimed in Claim 1, wherein said one or more styrenic monomers are selected from the group consisting of styrene, paramethylstyrene, metamethylstyrene, vinyl toluene, para-t-butylstyrene and parachlorostyrene.
3. A method as claimed in Claim 1 or Claim 2, wherein a paramethylstyrene homopolymer is formed which has a molecular weight distribution (MWD) of about 3-5 and a die swell index of from about 1.6 to 1.8.
4. A method as claimed in Claim 1, wherein said substantially water insoluble free radical initiator is selected from the group consisting of lauroyl peroxide, benzoyl peroxide, t-butylperbenzoate and t-butylperoxyacetate.
5. A method as claimed in Claim 1, wherein a 60-80% conversion of the monomer is achieved in said step (a).
6. A method as claimed in Claim 1, wherein said droplets are 0.15-0.5 cm in diameter.
7. A method as claimed in Claim 1, wherein the temperature of the suspension is at least 120°C during the entire polymerization.
8. A method as claimed in Claim 1, wherein said polymerization is substantially isothermal.
9. A method as claimed in Claim 1, wherein initiator is added to the suspension incrementally or continuously.
10, A method as claimed in Claim 9, wherein initiator is added to the suspension at a constant rate after said initiator is initially added to the suspension.
11. A method as claimed in Claim 1, wherein the conversion of monomer is at least 40% in the first hour of the polymerization and the polymerization is substantially complete in 8 hours or less.
12. A method as claimed in Claim 1, wherein the conversion of monomer is at least 55% in the first hour of the polymerization and the polymerization is substantially complete in 5 hours or less.
13. A method as claimed in Claim 1, wherein the water to monomer plus polymer ratio of the suspension is substantially constant throughout the entire polymerization and is no greater than 1.2:1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/248,660 US4367320A (en) | 1980-12-31 | 1981-03-27 | Process for suspension polymerization of styrenic monomers |
| US248,660 | 1981-03-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1182249A true CA1182249A (en) | 1985-02-05 |
Family
ID=22940104
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000398258A Expired CA1182249A (en) | 1981-03-27 | 1982-03-12 | Method for the suspension polymerization of styrenic monomers |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4367320A (en) |
| EP (1) | EP0061890A1 (en) |
| JP (1) | JPS5829805A (en) |
| AU (1) | AU548169B2 (en) |
| CA (1) | CA1182249A (en) |
| ES (1) | ES8303454A1 (en) |
| ZA (1) | ZA822047B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4730027A (en) * | 1982-06-28 | 1988-03-08 | Huntsman Chemical Corporation | Method of making styrene-type polymer comprising suspension polymerization conducted in aqueous medium containing combination of polyvinyl alcohol and sulfonated polystyrene or sulfonated styrene-maleic anhydride copolymer |
| JPS62276049A (en) * | 1986-05-20 | 1987-11-30 | 株式会社 荏原総合研究所 | Dustless antiseptic cloth |
| JPH02255708A (en) * | 1989-03-30 | 1990-10-16 | Idemitsu Petrochem Co Ltd | Production of styrene-based polymer |
| US5444141A (en) * | 1994-07-06 | 1995-08-22 | Arco Chemical Technology, L.P. | Process for making vinyl aromatic/allylic alcohol copolymers |
| DE69506280T2 (en) * | 1994-12-14 | 1999-08-12 | Dow Chemical Co | PRODUCTION OF HIGH MOLECULAR WEIGHT POLYSTYRENE BY FREE-RADICAL POLYMERIZATION CATALYZED BY VINYLIC ACID |
| US6084044A (en) * | 1994-12-14 | 2000-07-04 | The Dow Chemical Company | Catalyzed process for producing high molecular weight monovinylidene aromatic polymers |
| DE69600907D1 (en) * | 1995-07-18 | 1998-12-10 | Sumitomo Chemical Co | Process for controlling the rate of polymerization of a styrene resin |
| DE102004037929A1 (en) * | 2004-08-04 | 2006-03-16 | Rohmax Additives Gmbh | Process for the radical polymerization of ethylenically unsaturated compounds |
Family Cites Families (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE530706A (en) * | ||||
| BE488445A (en) * | 1948-04-29 | |||
| NL235733A (en) * | 1958-02-03 | |||
| US3328374A (en) * | 1965-03-01 | 1967-06-27 | Dow Chemical Co | Process for the suspension polymerization of styrene |
| ES353646A1 (en) * | 1967-07-31 | 1969-10-16 | Koppers Co Inc | Expandable Polymers |
| DE1902646A1 (en) * | 1968-01-22 | 1969-09-04 | Fuji Photo Film Co Ltd | Method of suspension polymerization |
| US3647723A (en) * | 1968-09-20 | 1972-03-07 | Kaucuk Narodni Podnik | Process for preparing expandable vinyl aromatic polymers |
| BE728872A (en) * | 1969-03-20 | 1969-08-01 | ||
| US3652526A (en) * | 1969-12-24 | 1972-03-28 | Monsanto Co | Polymerization process for vinylidene monomers |
| GB1346299A (en) * | 1970-12-03 | 1974-02-06 | Bp Chem Int Ltd | Production of vinyl aromatic polymer beads |
| US3786115A (en) * | 1970-12-23 | 1974-01-15 | Nihon Polystyrene Kogyo K K | Suspension polymerization process |
| US3931133A (en) * | 1970-12-31 | 1976-01-06 | Aquitaine Total Organico | Suspension polymerization process for ethylenic monomers |
| JPS5033917B2 (en) * | 1972-10-31 | 1975-11-04 | ||
| US4091054A (en) * | 1973-07-23 | 1978-05-23 | Sekisui Kagaku Kogyo Kabushiki Kaisha | Process of preparing styrenic polymer particles |
| DE2361743C2 (en) * | 1973-12-12 | 1982-07-01 | Bayer Ag, 5090 Leverkusen | Styrene-acrylonitrile copolymers with high heat resistance |
| DE2609104A1 (en) * | 1976-03-05 | 1977-09-15 | Basf Ag | PROCESS FOR THE PRODUCTION OF STYRENE SUSPENSION POLYMERISATES |
| US4271281A (en) * | 1980-05-29 | 1981-06-02 | American Hoechst Corporation | Process for preparing styrenic polymer particles |
-
1981
- 1981-03-27 US US06/248,660 patent/US4367320A/en not_active Expired - Fee Related
-
1982
- 1982-03-12 CA CA000398258A patent/CA1182249A/en not_active Expired
- 1982-03-16 AU AU81555/82A patent/AU548169B2/en not_active Ceased
- 1982-03-24 EP EP82301523A patent/EP0061890A1/en not_active Withdrawn
- 1982-03-25 ZA ZA822047A patent/ZA822047B/en unknown
- 1982-03-26 JP JP57048791A patent/JPS5829805A/en active Pending
- 1982-03-26 ES ES510835A patent/ES8303454A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5829805A (en) | 1983-02-22 |
| AU8155582A (en) | 1982-09-30 |
| US4367320A (en) | 1983-01-04 |
| ES510835A0 (en) | 1983-02-01 |
| ZA822047B (en) | 1983-11-30 |
| AU548169B2 (en) | 1985-11-28 |
| ES8303454A1 (en) | 1983-02-01 |
| EP0061890A1 (en) | 1982-10-06 |
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