CATALYST AND PROCESS FOR PREPARATION OF SYNDIOTACTIC POLYSTYRENE

Abstract: Syndiotactic polymers of vinyl aromatic monomers are prepared by conducting the polymerization in the presence of a catalytic amount of the reaction product of polymethylaluminoxane and a specific monocyclopentadienyl/titanium complex.

Description: CATALYST AND PROCESS FOR PREPARATION OF SYNDIOTACTIC POLYSTYRENE The present invention pertains to a catalyst and a process for polymerizing vinyl aromatic monomers, particularly styrene, to produce syndiotactic polymers. The catalyst is the reaction product of polymethyl aluminoxane and a specific monocyclopentadienyl/- titanium complex It has recently been reported by N. Ishihara, T. Seimiya, M. Kuramoto and M. Uoi in "Crystalline Syndiotactic Polystyrene", Macromolecules, pp 2164-5, (1986) that syndiotactic polystyrene having high stereo regularity had been prepared in the presence of a titanium compound and an organoaluminum compound. In EPO 210,615 syndiotactic polystyrene polymers were prepared utilizing titanium tetraethoxide, and cyclopentadienyltitanium trichloride complexes in combination with a polymethylaluminoxane cocatalyst. According to the present invention there is now provided a process for preparing polymers of vinyl aromatic monomers having a high degree of syndiotacticity comprising contacting one or more aromatic monomers under polymerization conditions with a catalytically effective amount of a catalyst comprising the reaction product of polymethyl¬ aluminoxane and a monocyclopentadienyl/titanium complex corresponding to the formula: CpTiXo, wherein Cp is a π-bonded cyclopentadienyl group, a π-bonded substituted or multiply substituted cyclopentadienyl group or a π-bonded monovalent oligomer of cyclopentadiene and X is independently each occurrence halide, OR, or NR£ > wherein R is independently each occurrence an aliphatic, cycloaliphatic or aromatic hydrocarbon group having from 1 to 12 carbon atoms; and provided further that in at least one occurrence X is OR or NR2«B the term aromatic is included both substituted and unsubstituted aryl groups. Most suitably X is in each occurrence OR and R is selected from the group consisting of phenyl, and C- | _g al yl or cycloalkyl. In a preferred embodiment X is in each occurrence phenoxy. The catalyst is normally formed in the presence of an aliphatic, cycloaliphatic or aromatic solvent or a combination of such solvents. The components are employed in quantities which provide an atomic ratio of Al:Ti suitably from 10:1 to 50,000:1, more suitably from 50:1 to 10,000:1, most suitably from 100:1 to 1000:1. Another aspect of the present invention pertains to a process for preparing syndiotactic polymers of vinyl aromatic monomers which process comprises contacting at least one polymerizable vinyl aromatic monomer under polymerization conditions in the presence of the previously disclosed catalyst. As used herein, the term "syndiotactic" refers to such polymers having a stereo regular structure of greater than 50 percent syndiotactic as determined by C3 nuclear magnetic resonance spectroscopy. Such polymers may be usefully employed in the preparation of articles and objects (eg., via compression molding or other suitable technique) having an extremely high resistance to deformation due to the effects of temperature. Compared to processes employing cyclopentadienyl¬ titanium trichloride containing catalysts, the present invention achieves improved yields. The polymethylaluminoxane may be prepared according to any known technique. One such technique includes the reaction of trimethylaluminum and a hydrated metal salt as disclosed by Kaminsky in U.S. Patent 4,544,762, the teachings of which are herein incorporated in their entirety by reference thereto. • For purposes of calculating the molar ratio of aluminum:titanium 'in the catalysts of the present invention, the polymethylaluminoxane is assigned a repeating unit structure corresponding to the formula: (A1(CH 3 )0). Following preparation of polymethylaluminoxane a cyclopentadienyltitanium complex, as previously defined, is added to the polymethylaluminoxane along with additional diluent if desired. In addition to unsubstituted cyclopentadienyl derivatives, the metal complexes employed to prepare the catalysts of the present invention illustratively include cyclopentadienyl derivatives containing from 1 to 5 alkyl, aryl or silyl substituents having up to 18 carbons, eg., pentamethylcyclopentadienyl derivatives, penta(trimethylsilyl)cyclopentadienyl derivatives, etc. and ring fused derivatives such as indenyl titanium complexes and substituted indenyl titanium complexes. It is understood that the complex may be employed in the form of a precursor that is capable of generating the desired cyclopentadienyl/titanium complex in situ. An example includes such complexes additionally incorporating one - or more molecules of any nature in the crystal structure, such as alcohol molecules associated with the crystal structure via Van der aals forces. In the preparation of the catalyst composition, the cyclopentadienyl/titanium complex and the polymethylaluminoxane can be combined in any order. The catalyst components may be suitably mixed in an inert atmosphere such as nitrogen, argon, xenon, or combinations thereof. The components are mixed at any suitable temperature, preferably from 0°C to 50°C, more suitably 25°C. The polymerization is conducted at temperatures of from 25°C to 100°C, preferably from 30°C to 60°C, for a time sufficient to produce the desired polymer. Typical reaction times are from several minutes to several hours, preferably from 1 to 10 hours. The optimum time will vary depending upon the temperature, solvent and other reaction conditions employed. The polymerization is generally conducted under- slurry polymerization conditions. The polymerization can be conducted at subatmospheric pressure as well as superatmospheric pressure, suitably at reduced pressures such that the lowest boiling component(s) of the polymerization mixture does not vaporize up to about 1000 psig. However, it Is preferable that near atmospheric pressure be employed. Suitable vinyl aromatic monomers which can be polymerized in the process of the present invention include those represented by the formula: HC=CH2 wherein each R is independently hydrogen, an aliphatic, cycloaliphatic or aromatic hydrocarbon group having suitably from 1 to 10, more suitably from 1 to 6, most suitably from 1 to 4, carbon atoms; or a halogen atom. Suitably such monomers include, for example styrene, chlorostyrene, n-butyl styrene, t-butyl styrene and p-vinyl toluene, etc. with styrene being especially suitable. The polymerization is normally conducted in the presence of an inert diluent. Examples include aliphatic, cycloaliphatic, aromatic and halogenated aromatic hydrocarbons, as well as mixtures thereof. Preferred diluents comprise the C__2o alkanes, especially branched chain alkanes, toluene and mixtures thereof. A particularly desirable diluent for the polymerization is isooctane, or blends thereof such as Isopar-E ® , available from Exxon. Suitable amounts of solvent are employed to provide a monomer concentration from 5 percent to 100 percent by weight. During the polymerization, polymer may precipitate from the reaction mixture as it is formed. As in other similar polymerizations it Is highly desirable that the monomers and solvents employed be of sufficiently high purity that catalyst deactivation does not occur. Any suitable technique for monomer purification such as devolitilization at reduced pressures, contacting with molecular sieves or high surface area alumina, deaeration, etc. may be employed. Purification of the resulting polymer to remove entrained catalyst may also be desired by the practitioner. Entrained catalyst may generally be identified by residues of ash on pyrolysis of the polymer that are attributable to aluminum and titanium values. A suitable technique for removing such compounds is by solvent extraction, eg. extraction utilizing hot, high boiling chlorinated solvents, followed by filtration. Having described the invention, the following examples are provided as further illustrative and are not to be construed as limiting. Example 1 In a nitrogen atmosphere glovebox, a dry 2 oz (59 ml) bottle is charged with 32 ml of ISOPAR-E™ (hereinafter IPE), a solution of polymethylaluminoxane (0.325 g., 5.6 mmole, in 7.2 ml IPE), and 220 μl, 22.4 μmole, of a 0.051 M toluene solution of cyclopentadienyltitanium trisphenoxide (formed by the reaction of cyclopentadienyl trichloride and phenol in a 1:3 molar ratio in the presence of an acid scavenger). The molar ratio of styrene:Al:Ti Is 6,000:500:1. The resulting solution is then stirred at room temperature for 30 seconds and is then treated with purified, deaerated styrene (7.0 g., 67.3 mmole). The bottle is then sealed with a sure seal cap which is then sealed again with electrical tape and the thus sealed container is placed in a shaker/hot water bath which is maintained at a temperature of 51°C for 20 hours. The reaction mixture is then hydrolyzed with the addition of 20 ml of methanol, and slurried in 50 ml of 1N aqueous HC1 for 5 minutes. The water is then removed with the use of a separatory funnel. The resultant polystyrene is collected by filtration, washed with methanol and vacuum dried at 110°C for 24 hours. The yield is 6.78 g (97 percent). The resultant polystyrene has a melting point of 246°C, >95 percent syndiotacticity by C13 analysis, and has a weight average molecular weight (Mw) as determined by gel permeation chromatography utilizing atactic polystyrene standards of 166,400. Number average molecular weight (Mn) determined similarly is 50,600. Results are summarized in Table I. Examples 2-13 The reaction conditions of Example 1 are substantially repeated excepting that the titanium complexes, solvents, ratios and reaction temperatures of Table I are employed. Results are contained in Table I. Comparative Examples 14 and 15 These comparative Examples are summarized in Table I. They are not prior art. Note the low yields obtained (in contrast to Examples 1-13. Examples 16-53 These examples are summarized in Table I, and essentially repeated Example 1 except for the different indications listed in Table I. Examples relating to the preparation of syndiotactic tertiary butylstyrene are of particular interest because the polymers obtained had a molecular weight (Mw) that was too high to measure by gel permeation chromatography (Examples 16, 18, 19, 20, 39, 40, 41 and 42). Table 1 __< Complex Ratio Styrene :Al:Ti Solvent! 1 CpTi(OPh) 3 6,000:500: 1 IPE 20 51 20 97 >95 166.4 249 2 CpTi(OPh) 3 6,000:500: 1 IPE 5 51 2.5 56.5 88 60.6 249 3 CpTi(OPh) 3 18,000:500: 1 20 60.3 95 145 250 4 CpTi(OPh) 3 6,000: 500: 1 toluene 40 93.6 84 60.6 253 5 CpTi(OPh) 3 IPE 20 82.1 >94 90.0 250 6 CpTi(OEt) 3 25 67.4 91 123 251 7 CpTi(OEt) 3 51 91.1 — 86.4 251 8 Indenyl- 6,000: 1,000: 1 40 50 20 86.2 >95 160 263 Ti(NMe 2 )3 9 CpTi(NMe 2 )3 6,000:500: 1 51 2.5 71.7 >84 102.9 255 10 CpTi(OPh) 3 6,000: 125: 1 IPE 20 51 20 74.7 95 98.1 — 11 CpTi(OPh) 3 6,000:500: 1 IPE 20 51 2.25 96.7 93 180.9 250 // / 12 Me 5 C 5 Ti(OPh) 3 95.1 >95 343.0 268 // 13 MΘ5C5- 53.3 91 83.0 254 Ti(OPh)CI 2 Table 1 Continued % Mw Melt Ex Complex Ratio temp time syndio¬ Styrene :Al:Ti Solvent 1 styrene! yield % hr_ % tactic x103 pt.°C He 14 Me 5 C 5 TiCI 3 3 6,000:500: 1 IPE 20 51 2.25 30.6 >95 * 333.1 ~ 15 CpTiCI 3 3 6,000:500: 1 20 2.5 27.7 — — 255.4 16 CpTi(NMθ2)3 6,000:500: 1 IPE TBS 20 50 2.25 34.4 >90 — 306 17 CpTi(NMe 2 )3 PVT 20 50 2.25 34.4 >90 — 165 18 Me 5 C 5 Ti (OPH) 3 TBS 20 50 2.25 98 >95 - 308 19 Me5C5Ti(0-i-Pr)3 TBS 20 50 2.25 99.2 >95 -- 308 20 CpTi(OPh) 3 TBS 20 50 2.25 99.8 >90 ~ 291 21 CpTi(OPh) 3 PVT 70 50 2.0 96.9 — 88.9 142 22 Me 5 C 5 Ti (OPH) 3 PVT 20 n 99.6 >95 750.0 167 23 Me 5 C 5 Ti(0-i-Pr)3 PVT 20 99.8 >95 723.0 167 24 Me 5 C 5 Ti (OPH) 3 6,000:500: 1 IPE 20 50 2.25 83.1 >95 509.0 271 » 25 Me5C 5 Ti(0-i-Pr)3 89.8 >95 544.0 271 26 Me CpTi(0-i~Pr) 3 80.9 >93 201.0 271 27 EtMe^sTi- 2.0 76.5 — 556.0 ~ (0-i-Pr) 3 28 [(Me 3 Si)Cp]- 2.0 74.2 — 83.4 -- Ti(0-i-Pr) 3 Table I Continued % Yield % Syndio¬ ix __________ s _ t ι v y r ιS cπe. , l i : . T 1 i 1 50M 1 -^ene2 Temp Time tactic Mw Melt __. X103 pt.°C 29 Me 5 C 5 Ti (OPH) 3 6,000:500: 1 IPE 20 50 2.0 72.0 — 784.0 — 30 // Me 5 C 5 Ti(0-i-Pr) 3 48.2 — 864.0 — 31 EtMe 4 C 5 Ti- 44.0 — 1,070.0 — (0-i-Pr) 3 32 [(Me 3 Si)Cp]- 33.8 ~ 69.8 — Ti(0-i-Pr) 3 33 Me 5 C 5 Ti (OPH) 3 6,000:500: 1 IPE Para-Br 50 2.25 3.3 — — 298 Styene 20 34 Me5C5Ti(0-i-Pr)3 // 3.8 — 296 35 CpTi(OPh) 3 2.3 — -- — 36 Me 5 C 5 Ti (OPH) 3 6,000:500: 1 IPE Para-CI 50 4.0 2.8 — 296 Styrene 20 37 Me 5 C 5 Ti(0-i-Pr) 2.8 38 CpTi(OPh) 3 3.8 292 39 Me 5 C 5 Ti (OPH) 3 6,000:500: 1 MCH 20 50 2 98.6 307 40 Indenyl- 6,000:500/1 MCH 20 50 7 63.0 308 Ti(NMe 2 ) 3 Table I Continued % Syndio¬ Ex Complex Rat Styrene : i I ^o | :T| Solvent St r % enel Te 0 m P τ j e Yield % tactic Mw Melt x103 13 ρt.°C 41 MeCpTi(NMe 2 ) 87.9 300 42 CpTi(NMe 2 ) 3 93.4 291 43 Me 5 C 5 Ti (OPH) 6,000:500: 1 MCH 20 50 2 98.8 158 4 181 44 Indenyl- 7 49.9 165 4 Ti(NMe 2 ) 3 183 t I 45 MeCpTi(NMe 2 )3 38.4 168 " 182 46 CpTi(NMe 2 )3 31.4 155 * 174 47 Me 5 C 5 Ti (OPH) 3 2 99.6 271 48 Indenyl- 2.75 49.6 265 Ti(NMe 2 ) 3 Table I Continued E bxx C coommoplleexx styren a e ti : o AI:Ti So o l l v v e e n n t t~ St tγr e e n n e e2" Te °°cC m P T h im r. e Yi % e,d % te t ^rt t,c ° " x M 1 w 03 p M t e .° l C t — — _ —____ _ —__ He — 49 MeCpTi(NMe 2 ) 3 6,000:500: 1 MCH 20 5500 22..7755 4466..00 - - 264 50 CpTi(NMe 2 ) 3 " " " " " 4444..22 -- -- 266 51 CpTi(NPh 2 ) 3 4 — 52 CpTi(N(Butyl) 2 ) 3 4 — 53 Me 5 C 5 Ti(OPh) 3 " " 0VT 20 4 1 IPE = lsopar - E τu , MCH - Methylcyclohexane 2 Weight Percent of reaction mixture TBS = p-tert butyl styrene PVT = p-vinyl toluene OVT = Ortho-vinyl toluene 3 Comparative examples "" •Two melting peaks

Claims: 1. A process for preparing polymers of vinyl aromatic monomers having a high degree of syndiotacticity comprising contacting one or more aromatic monomers under polymerization conditions with a catalytically effective amount of a catalyst comprising the reaction product of polymethyl¬ aluminoxane and a monocyclopentadienyl/titanium complex corresponding to the formula: CpTiXo, wherein Cp is a π-bonded cyclopentadienyl group, a π-bonded substituted or multiply substituted cyclopentadienyl group or a π-bonded monovalent oligomer of cyclopentadiene and X is independently each occurrence halide, OR, or NPt^ * wherein R is independently each occurrence an aliphatic, cycloaliphatic or aromatic hydrocarbon group having from 1 to 12 carbon atoms; and provided further that In at least one occurrence X is OR or NR2. 2. A process according to Claim 1 , wherein the polymethylaluminoxane and titanium complex are employed in quantities which provide an atomic ratio of Al:Ti of from 50: 1 to 10,000: 1. 3. A process according to Claim 1, wherein the polymethylaluminoxane and titanium complex are employed in quantities which provide an atomic ratio of Al:Ti of from 100:1 to 1000:1. 4. A process according to Claim 1, wherein the monomer is contacted with the catalyst at a temperature from 25°C to 100°C. 5. A process according to Claim 1, wherein an inert diluent is additionally present. 6. A process according to Claim 1, wherein the polymer has a molecular structure containing greater than 70 percent syndiotactic. 7. A process according to Claim 1, wherein X is OR in each occurrence and R is selected from the group consisting of phenyl and Cι_6 al yl. 8. A composition of matter comprising the reaction product of polymethylaluminoxane and a complex corresponding to the formula: CpTiX , wherein Cp is a π-bonded cyclopentadienyl group, a π-bonded substituted cyclopentadienyl group or a π-bonded monovalent oligomer of cyclopentadiene and X is independently each occurrence halide, OR, or NR2 > wherein R is independently each occurrence an aliphatic, cycloaliphatic or aromatic hydrocarbon group having from 1 to 12 carbon atoms and provided further that in at least one occurrence X is OR or NR2. 9. A composition of matter according to Claim 8, wherein X is NR 2 and R is CH .

Inventors: CAMPBELL RICHARD E JR, HEFNER JOHN G, CAMPBELL, RICHARD, E., JR., HEFNER, JOHN, G.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1988
Main classification: C08F4
IPC codes: C08F4, C08F12