Synthesis and mechanism of formation of syndiotactic polystyrene using a (tert-butylcyclopentadienyl)titanium complex

Polymerization of styrene in the presence of [Ti(eta(5)-C(5)H(4)(t)Bu)Cl-3]-methylaluminoxane has been investigated. The resultant polymer is essentially 100% syndiotactic polystyrene (SPS; by NMR and differential scanning calorimetry measurements) and of narrow polydispersity (ca. 2.0-2.2). Analysis of SPS using matrix-assisted laser/desorption ionization time-of-flight mass spectrometry demonstrates that polymer chains have both methyl and ethyl end groups, indicating that the SPS is formed by both ''Ti+-H'' and ''Ti+-Me'' initiators. These mass spectral data, together with NMR data, confirm that the major mode of chain growth termination is via beta-H transfer. The polymer molecular weight is dependent on the temperature of polymerization: at 0 degrees C, M(n) = 26 x 10(3) (by NMR and size exclusion chromatography), whereas at 65 degrees C, M(n) = 4 x 10(3). Semilogarithmic plots of consumption of styrene with time are linear over the initial part of the polymerization, indicating that the number of active titanium centers remains constant during this time. Increasing the quantity of styrene results in an identical conversion (percentage), suggesting that propagation is favored over termination processes.