SYNDIOSPECIFIC POLYMERIZATION OF STYRENE .2. MONOCYCLOPENTADIENYLTRIBUTOXY TITANIUM METHYLALUMINOXANE CATALYST

Syndiospecific polymerization of styrene was catalyzed by monocyclopentadienyltributoxy titanium/methylaluminoxane [CpTi(OBu)3/MAO]. The atactic and syndiotactic polystyrenes were separated by extracting the former with refluxing 2-butanone. The activity and syndiospecificity of the catalyst were affected by changes in catalyst concentration and composition, polymerization temperature, and monomer concentration. Extremely high activity of 5 x 10(7) g PS (mol Ti mol S h)-1 with 99% yield of the syndiotactic product were achieved. The concentration of active species, [C*], has been determined by radiolabeling. The amounts of the syndiospecific and nonspecific catalytic species, [C(s)*] and [C(a)*] respectively, correspond to 79 and 13% of the CpTi(OBu)3. The rate constants of propagation for C(s)* and C(a)* at 45-degrees-C are 10.8 and 2.0 (M s)-1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 x 10(-4) and 4.3 x 10(-4) s-1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 x 10(-2) (M s)-1; the spontaneous beta-hydride transfer rate constant is 4.7 x 10(-2) s-1. The polymerization activity and stereospecificity of the catalyst are highest at 45-degrees-C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, M(w)BAR/M(n)BAR = 2.8-5.7, and up to three crystalline modifications. The T(m) of the s-PS polymerized at 0-90-degrees-C decreased from 261.8 to 241-degrees-C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium.