Classifications

• • 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
  • C08F279/00—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00
• • 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
  • C08F279/00—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00
  • C08F279/02—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00 on to polymers of conjugated dienes

Definitions

• the present invention is related to methods and compositions useful to improve the manufacture of copolymers of vinyl aromatic monomers such as styrene. It relates more particularly to methods of copolymerizing vinyl aromatic monomers with multifunctional initiators in the presence of diene polymers.
• the polymerization of styrene is a very important industrial process that supplies materials used to create a wide variety of polystyrene-containing articles. This expansive use of polystyrene results from the ability to control the polymerization process. Thus, variations in the polymerization process conditions are of utmost importance since they in turn allow control over the physical properties of the resulting polymer. The resulting physical properties determine the suitability of polystyrene for a particular use. For a given product, several physical characteristics must be balanced to achieve a suitable polystyrene material.
• Mw average molecular weight
• MFD molecular weight distribution
• MFI melt flow index
• G' storage modulus
• Rubber toughened materials such as high impact polystyrene, which is composed of rubber particles in a polystyrene matrix
• factors that influence rubber morphology such as rubber particle size, rubber particle size distribution, swell index, grafting, and the rubber phase volume, as measured by the ratio of the % gel to % rubber (G/R) are also critical to balance physical and mechanical properties.
• Mono- and bifunctional peroxide initiators are commonly used in the manufacture of rubber-modified polystyrene (PS), and peroxides have been used to increase the rate of polymerization and to modify the degree of chemical grafting between polystyrene and the elastomer (typically polybutadiene rubber) used to modify PS.
• elastomer typically polybutadiene rubber
• Increasing the rate of polymerization by using initiators causes the molecular weight of the PS matrix to decrease; chemical grafting may or may not increase depending on the levels and the temperature at which the initiator is used.
• HIPS high impact polystyrene
• HIPS high impact polystyrene
• a method for producing an improved copolymerized product that involves copolymerizing at least one vinylaromatic monomer with at least one diene polymer in the presence of at least one multifunctional initiator.
• the multifunctional initiator may be a trifunctional or tetrafunctional peroxide.
• a copolymerized product is recovered that has a ratio of % gel to % rubber (G/R or rubber phase volume) that increases as swell index increases.
• G/R or rubber phase volume % gel to % rubber
• an improved copolymerized product made by copolymerizing at least one vinylaromatic monomer with at least one diene polymer in the presence of at least one multifunctional initiator.
• the multifunctional initiator may be a trifunctional or tetrafunctional peroxide.
• a copolymerized product is recovered that has a G/R that increases as swell index increases.
• the multifunctional initiator is either a trifunctional or tetra ⁇ functional peroxide, and the amount of multifunctional initiator is sufficient to produce a copolymerized product that has a G/R that increases as swell index increases.
• articles made from the resins and copolymerized products of this invention are provided.
• FIG. 1 is a graph of % polystyrene v. time in hours for equivalent peroxide functionalities, where the feed is styrene;
• FIG. 2 is a graph of % polystyrene v. time in hours for equivalent peroxide functionalities, where the feed is styrene but contains 7% Diene 55;
• FIG. 3 is a graph of Mw in thousands as a function of % conversions for isothermal polymerization at 11O 0 C for equivalent peroxide functionalities;
• FIG. 4 is a plot of % solids as a function of time for various levels of JWEB 50 tetrafunctional initiator for a feed of styrene including 4% Bayer 380;
• FIG. 5 is a plot of G/R ratio v. swell index for commercial FINA HIPS materials; and [0018]
• FIG. 6 is a plot of gel/rubber ratio vs. swell index for experiments with tetrafunctional initiator (JWEB50) and various commercial grades.
• the inventors have explored the potential for providing branched polystyrene having at least some increased branching by using tetrafunctional initiators or trifunctional initiators.
• the invention concerns initiating polymerization of a vinyl aromatic monomer such as styrene in various solvents and in the optional presence of a polydiene, such as polybutadiene, with a multifunctional initiator (e.g. tri- or tetrafunctional) and to use the multifunctional initiator to obtain branched structures.
• a multifunctional initiator e.g. tri- or tetrafunctional
• the rubber phase volume is a key parameter that can be estimated from solution properties.
• the rubber phase volume refers to the rubber particles or discontinuous phase, which consists of rubber, trapped polystyrene (occlusions) and grafted polymer.
• a convenient way to classify HIPS materials is by calculating the dry gel obtained for a given rubber level.
• the gel/rubber ratio can vary from 1 to 4 for swell indices of 10 -12, and as the swell index increases the G/R ratio decreases.
• the G/R ratio is the ratio of the % gel to % rubber, and is also termed the rubber phase volume (RPV).
• This ratio is important in the manufacture of HIPS materials because it represents the "rubber efficiency" of the process, i.e., how much rubber must be used to obtain similar product quality.
• I-CI Iodine Monochloride
• the G/R increases from about 1 to about 4 as the swell index increases from about 8 to about 20.
• the G/R ranges from about 1 to about 3 while the swell index ranges from about 12 to about 20.
• the G/R ranges from about 1.5 to about 3.0 while the swell index ranges from about 10 to about 14. This unexpected phenomenon is discussed further with respect to the data below.
• the melt flow index (MFI) for the resins of this invention range from about 2 to about 7. In another non-limiting embodiment of the invention, the MFI range from about 3 to about 5.
• tetrafunctional materials can be schematically represented by the shape of a cross. If at the end of each arm of the cross, the potential for initiation or chain transfer exists, it is possible to envision polystyrene molecules that will have higher molecular weight than by using bifunctional initiators only. Similarly to tetrafunctional initiators, trifunctional initiators simply have three "arms" or starting points instead of the four found in tetrafunctional initiators.
• tetrafunctional initiators are used to optimize the melt properties resulting from the formation of branched structures.
• the tetrafunctional initiator With the tetrafunctional initiator, four linear chains for one branched molecules are formed.
• the amount of linear chains, initiated by the alkyl radi ⁇ cals will lower the effect brought by the branched chains, initiated by the tetrafunctional radicals.
• multifunctional peroxides can be used to increase polymerization rates and chemical grafting, while maintaining or increasing PS matrix molecular weight. The potential use of these multifunctional initiators in the production of HIPS allows higher production rates while maintaining molecular weights and improving rubber phase volume.
• the composition of the invention can include a polydiene-modified monovinyl aromatic polymer, and can include a rubber (polybutadiene)-modified polystyrene.
• Styrene monomer can be polymerized in the presence of from about 2 to about 15 weight percent rubber to produce a copolymer having impact resistance superior to that of polystyrene homopolymer.
• a rubber that can be used in making the subject compositions is polybutadiene.
• the resultant thermoplastic composition, which can be made with these materials, is high impact polystyrene, or HIPS.
• the predominant morphology of the polymer made from embodiments of the invention is cell or "salami" with some core-shell structure, meaning that the continuous phase of polystyrene comprises a plurality of dispersed structures in which polystyrene is trapped within rubber particles having a distinct membrane and small quantities of polystyrene are occluded inside single cell polybutadiene shells grafted to the aromatic polymer.
• Styrene polymerization processes are well known.
• the compositions of the invention can be made by batch polymerization in the presence of from about 2 to 15, and in some embodiments can be from about 4 to about 12, weight percent polybutadiene using multifunctional initiators at concentrations of from about 50 to about 1200 ppm and using a solvent. In another non-limiting embodiment of the invention the concentration of multifunctional initiator may range from about 100 to about 600 ppm.
• the multifunctional initiator is a trifunctional or tetrafunctional peroxide and is selected from the group 1 consisting of tri- or tetrakis t-alkylperoxycarbonates, tri- or tetrakis-(t-butylperoxycarbonyloxy) methane, tri- or tetrakis-(t-butylperoxycarbonyloxy) butane, tri- or tetrakis (t- amylperoxycarbonyloxy) butane, tri- or tetrakis (t-C 4-6 alkyl monoperoxycarbonates) and tri- or tetrakis (polyether peroxycarbonate), and mixtures thereof.
• group 1 consisting of tri- or tetrakis t-alkylperoxycarbonates, tri- or tetrakis-(t-butylperoxycarbonyloxy) methane, tri- or tetrakis-(t-butylperoxycarbonyloxy)
• the tetrafunctional initiator has four t-alkyl terminal groups, where the t-alkyl groups are t-butyl and the initiator has a poly(methyl ethoxy) ether central moiety with 1 to 4 (methyl ethoxy) units.
• This molecule is designated herein as LUPEROX ® JWEB 50 and is available from Atofina Petrochemicals, Inc.
• Another commercial product suitable as a multifunctional initiator is 2,2 bis(4,4-di-(tert-butyl- peroxy-cyclohexyl)propane) from Akzo Nobel Chemicals Inc., 3000 South Riverside Plaza Chicago, Illinois, 60606.
• Another commercial product is 3,3' ,4,4' tetra (t-butyl- peroxy-carboxy) benzophenone from NOF Corporation Yebisu Garden Place Tower, 20-3 Ebisu 4-chome, Shibuya-ku, Tokyo 150-6019.
• Monofunctional peroxide initiators can undergo homolytic cleavage to produce monoradicals, each of which can initiate a chain.
• Bifunctional initiators depending on the breakdown patterns, can cause chain extension if biradical formation is possible from a fragment.
• Tri- and tetrafunctional initiators can also cause chain extension. Because of the possible and various complex decomposition patterns, it is not easy to determine a priori how a given initiator will decompose under a given set of conditions; however, by measuring the molecular weight of the resultant polymer, it is possible to determine if the initiators are able to produce chain extension.
• Suitable optional solvents for the polymerization include, but are not nec ⁇ essarily limited to ethylbenzene, xylenes, toluene, hexane and cyclohexane.
• Chain transfer agents and crosslinking agents can be used in applications of this invention as taught by art.
• multifunctional initiators can be used together with chain transfer agents and cross-linking agents to manufacture polystyrene and HIPS that is more highly branched.
• the chain transfer agent and/or cross-linking agent may be added prior to, during or after the initiator is added to the monomer.
• Grafting is also favored by using polybutadiene having a medium or high-cis isomer content.
• Polybutadiene useful in making the composition of the invention is produced, for example, by known processes by polymerizing butadiene in either a hexane or cyclohexane solvent to a concentration of about 12 weight percent, and flashing off the solvent at a temperature ranging from about 80° to 100°C. to further concentrate the polybutadiene solution to about 24 to 26 weight percent, the approximate consistency of rubber cement. The polybutadiene is then precipitated from the solution as a crumb using steam, then dried and baled.
• the copolymerized products of this invention may have a polydispersity of from about 2.2 to 4.5. In another non-limiting [preferred] embodiment, the copolymerized products of this invention may have a polydispersity ranging from about 2.3 to 4.0. In another non-limiting embodiment the polydispersity may range from about 2.3 to 3.2.
• G/R increases as the swell index increases using the multifunctional initiators of this invention, but it has also been found that acceptable G/R can be achieved at increased polymerization rates using these initiators in polymerizations of styrene.
• the rate of polymerization styrene is about 10%/hr at 13O 0 C from 10 to about 50% solids (no initiator).
• the rate (slope of the line) can be increased by a factor of 2 to 7 times that of pure styrene (no initiator) in the range of 10 to 50% PS conversion as the level of initiator increases.
• the slopes are 2.3, 4.3 and 6.6 times that of pure styrene for 200, 400 and 600 PPM of JWEB, respectively as will be seen in FIG. 4.
• batch or continuous polymerizations can be conducted in 97:3 to 91 :9 styrene to rubber, 85:15 to 80:20 typical styrene solvent mixtures to 60-80% styrene conversion to polystyrene and then flashing off the unreacted monomer and the solvent.
• the reactions described can be carried out in continuous units, as the one described by Sosa and Nichols in US 4,777,210, incorporated by reference herein.
• the copolymerizing may be conducted at a temperature between about 8O 0 C to about 200 0 C; in an alternate embodiment of the invention from about 11O 0 C to about 180 0 C.
• components include, but are not necessarily limited to, chain transfer agents, cross-linking agents, accelerators, lubricants, and diluents and the like.
• the first four initiators were chosen for study due to their similarities in half- life temperatures and differences in peroxide functionalities.
• the polymerizations were performed isothermally (11O 0 C), as well as non-isothermally (temperature ramp process), for both crystal and HIPS systems. Further, initiator concentrations were varied to assess rate and molecular weight effects. Isothermal Polymerization Studies - Crystal Polystyrene
• the degree of polymerization (molecular weight) is inversely proportional to the rate of polymerization.
• the molecular weight decreased with increasing initiator concentration. Further, the molecular weight obtained at a given initiator concentration becomes relatively constant after 20-30% conversion.
• Non-isothermal polymerization studies were conducted to assess the effects of initiator type/functionality on crystal PS properties, particularly on molecular weight.
• the reaction profile was 2 hours at 11O 0 C 1 1 hour at 13O 0 C, 1 hour at 15O 0 C, followed by devolatilization at 24O 0 C for 0.5 hours ( ⁇ 2 mmHg; ⁇ 267 Pa).
• a tetrafunctional initiator gave a significantly higher polymerization rate than did any of the other peroxides.
• LUPERSOL 531 a t-amyl peroxyketal, yielded a more rapid rate than does the t-butyl derivative (LUPERSOL 331 ).
• the tetrafunctional initiator yielded the highest molecular weight crystal PS (about 20% higher Mw).
• the bifunctional initiators yielded similar molecular weights and higher rates than does the monofunctional peroxide. Similar results were obtained when the initiators are compared on an equi-peroxide functionality basis. The results further supported the mechanism of polymer chain extension via decomposition of end-group peroxides, followed by propagation.
• FIG. 1 presents graphs of % polystyrene as a function of time for equivalent peroxide functionalities for the four initiators of Table Il where the feed is styrene, such as for Examples 1-4. Generally, the plots are roughly equivalent.
• FIG. 2 provides plots of % polystyrene as a function of time for equivalent peroxide functionalities for the four initiators of Table Il where the feed is styrene and 7% Diene 55, such as for Examples 5-8. Again the results are comparable except that after about two hours the % polystyrene for Perkadox 12-AT25 is somewhat higher.
• the data in FIGS. 1 and 2 are from ramp processes.
• FIG. 3 is a plot of Mw (in thousands) as a function of % conversion for isothermal polymerization at 11O 0 C for equivalent peroxide functionalities for the four initiators of Table II. Interestingly, the monofunctional Trigonox 42S gave relatively lower conversions and somewhat higher molecular weights as compared with the bifunctional Lupersol initiators. The multifunctional Perkadox 12-AT25 provided relatively higher conversions and higher Mw indicative of the greater functionality.
• FIG. 4 is a plot of % solids vs. time for various levels of JWEB 50 tetra- functional initiator for a styrene feed having 4 % Bayer 390 rubber.
• RPS volume median rubber particle size measured by a Malvern Analyzer in methyl ethyl ketone.
• Bi- or multifunctional initiators offer superior rate/molecular weight relationships.
• the developmental tetrafunctional initiator e.g. PERKADOX 12
• tetrafunctional initiators such as alkylperoxy- carbonates, for instance JWEB50 tetra t-butylperoxycarbonate available from ATOFINA Petrochemicals, Inc.
• alkylperoxy- carbonates for instance JWEB50 tetra t-butylperoxycarbonate available from ATOFINA Petrochemicals, Inc.
• FIG. 5 shows the relationship of % gels/% rubber vs. swell index for commercial products.
• the % gels was used a measure of rubber phase volume and was measured by dissolving HIPS in toluene, separating the insoluble gel phase by centrifugation and then reporting the % of insoluble gel of the total sample.
• Swell index (Sl) is measured in the same experiment.
• the swollen gel is weighed, dried under vacuum and then the weight of the dry gel is obtained.
• the swell index is the ratio of the weight of swollen gel to dry gel, and it is a measure of the degree of crosslinking of the rubber phase.
• FIG. 5 shows that some commercial resins have a G/R of 2.2-3.0 at a swell index of 13-9. Note particularly that as the swell index increases the G/R decreases. In one non-limiting explanation, this may be because at higher swell indices the solvent expands the rubber network more and the polystyrene that is trapped inside migrates or diffuses out of the rubber particles, which leads to lower gel values.
• Table Vl shows the data obtained as the level of tetrafu notional initiator is increased. Batch syntheses were carried out isothermally at 127 0 C.
• FIG. 6 compares the results of Examples 27, 28, 29 and 30 of this invention with some of the commercial grades from FIG. 5. It may be noted that JWEB50 shows a surprising, opposing trend that as the level of JWEB50 is increased, the G/R ratio increases, even though the swell index of these materials is very high. The trend of the commercial materials is indicated by the lighter dashed descending line, and this is the trend commonly observed. The trend shown by the darker, ascending line for JWEB50 is surprising and quite unique.
• the resins of this invention are expected to produce HIPS with higher rubber efficiencies, improved impact strength and ductility.
• the styrene-based polymers of the present invention are expected to find use in other injection molded or extrusion molded articles.
• the styrene-based polymers of the present invention may be widely and effectively used as materials for injection molding, extrusion molding or sheet molding.
• the polymer resins of this invention can be used as molding material in the fields of various different products, including, but not necessarily limited to, household goods, electrical appliances and the like.

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• 2004
  • 2004-11-18 WO PCT/US2004/038701 patent/WO2006054995A1/en active Application Filing
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