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

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2004-06, Vol.42 (11), p.2698-2704
• Main Authors: Ban, Hoang The, Tsunogae, Yasuo, Shiono, Takeshi
• Format: Article
• Language: English
• Subjects: aluminoxane; Applied sciences; block copolymers; butadiene-styrene; catalysts; Copolymerization; crystallization; Exact sciences and technology; half-metallocene; Organic polymers; Physicochemistry of polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts; stereospecific living polymerization
• ISSN: 0887-624X; 1099-0518
• DOI: 10.1002/pola.20144

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. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2698–2704, 2004 cis‐Polybutadiene/syndiotactic polystyrene (syn‐PS) block copolymers with long crystallizable syn‐PS segments chemically bonded with high cis‐1,4‐polybutadiene segments were prepared and successfully isolated via a sequential block copolymerization of 1,3‐butadiene (BD) with styrene in the presence of a cis‐specific BD living catalyst system (CpTiCl3/modified methylaluminoxane) at ambient temperatures. Although the final product contained a mixture of homopolymers and copolymers, it was possible to isolate the block copolymers through a combination of solvent fractionation and cross‐fractionation. The unique structure of the block copolymers was derived from the existence of highly crystallizable syn‐PS segments, which exhibited extremely high melting temperatures up to 260 °C in comparison with those of commercial BD–styrene block copolymers.