| Abstract: | 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 × 107 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 amount of the syndiospecific and nonspecific catalytic species, C ] and C ] respectively, correspond to 79 and 13% of the CpTi(OBu)3. The rate constants of propagation for C and C at 45°C are 10.8 and 2.0 (M s)?1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 × 10?4 and 4.3 × 10?4s?1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 × 10?2 (M s)?1; the spontaneous β-hydride transfer rate constant is 4.7 × 10?2 s?1. The polymerization activity and stereospecificity of the catalyst are highest at 45°C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, M?w/M?n = 2.8–5.7, and up to three crystalline modifications. The Tm of the s-PS polymerized at 0–90°C decreased from 261.8 to 241°C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium. |
