Synthesis and fractionation of syndiotactic-polystyrene/polyethylene copolymers with C₅H₅TiCl₃ catalysts

Highly stereoregulated syndiotactic-polystyrene/polyethylene (s-PS/PE) block copolymers with variable ethylene block lengths are synthesized using the sequential monomer feed scheme with C₅H₅TiCl₃ catalyst. The copolymer, after removing the atactic portion, is separated into two fractions by tetrahydrofuran (THF). The insoluble fraction contains a highly stereoregulated s-PS block linked with PE blocks, while the soluble fraction also contains a highly stereoregulated s-PS block but separated randomly by a shorter or isolated ethylene unit. For the I-fraction, r(E) = 25 ± 5 and r(S)= 1.9 ± 0.3, and for the S-fraction r(E) = 0.4 ± 0.1 and r(E) = 0.34 ± 0.15. These results are compared with prior studies, where mainly random type PS/PE copolymers with low styrene stereoregularity and rigio-irregular styrene and polyethylene are produced. Apparently, both the sequential feed scheme coupled with the use of a lower reactivity metallocene catalyst facilitated the switching of catalytical sites with the majority product being of block nature. (C) 2000 Elsevier Science Ltd.