Synthesis and characterization of cis‐polybutadiene‐block‐syn‐polystyrene copolymers with a cyclopentadienyl titanium trichloride/modified methylaluminoxane catalyst

This article reports a practical method for preparing cis‐polybutadiene‐block‐syn‐polystyrene (cis‐PB‐b‐syn‐PS) copolymers with long crystallizable syndiotactic polystyrene (syn‐PS) segments chemically bonded with high cis‐1,4‐polybutadiene segments through the addition of styrene (ST) to a cis‐specific 1,3‐butadiene (BD) living catalyst composed of cyclopentadienyl titanium trichloride (CpTiCl3) and modified methylaluminoxane (MMAO). The incorporation of ST into the living polybutadiene (PB) precursor remarkably depended on the polymerization temperature. A low temperature (−20 °C) suppressed the rate of ST incorporation, but a high temperature (50 °C) tended to decompose the livingness of the active species and enhance the rate of the aspecific ST polymerization initiated by MMAO. Consequently, temperatures of 0–25 °C seemed to be best for this copolymerization system. Because of the absence of ST livingness, the final products contained not only the block copolymer but also the homopolymers. Attempts to isolate the block copolymer were carried out with common solvent fractionation techniques, but the results were not sufficient. Cross‐fractionation chromatography was, therefore, used for the isolation of the cis‐PB‐b‐syn‐PS copolymer. The presence of long syn‐PS segments was confirmed by the observation of a strong endothermic peak at 260 °C in the differential scanning calorimetry curve.