POLYISOBUTYLENE-BASED THERMOPLASTIC ELASTOMERS .3. SYNTHESIS, CHARACTERIZATION, AND PROPERTIES OF POLY(ALPHA-METHYLSTYRENE-B-ISOBUTYLENE-B-ALPHA-METHLSTYRENE) TRIBLOCK COPOLYMERS

The first efficient synthesis of poly(alpha-methylstyrene-b-isobutylene-b-alpha-methylstyrene)(P alpha MeSt-PIB-P alpha MeSt) triblock copolymer thermoplastic elastomers (TPEs) has been accomplished by living cationic polymerization using sequential monomer additions. Living PIB was prepared by the 5-tert-butyl-1,3-bis(1-chloro-1-methylethyl)benzene (tBuDiCumCl)/TiCl4/Hex:MeCl 60:40 v:v/-80 degrees C polymerization system. The living ends were capped by 1,1-diphenylethylene (DPE). TiCl4 was replaced by SnBr4, followed by the addition of alpha MeSt. Triblock copolymers with close to theoretical molecular weights and narrow molecular weight distributions (M(w)/M(n) similar to 1.1) were obtained. Homopolymer and diblock contamination have been found to be negligible. The thermal stability of the triblock copolymer was characterized by thermogravimetric analysis. Microphase separation was evidenced by the two glass transitions (at -65 and +180 degrees C) observed by differential scanning calorimetry and in dynamic mechanical analysis. Triblock morphology was examined by transmission electron microscopy. Compression-molded samples with 16-45 wt % P alpha MeSt exhibited similar to 12-24.5 MPa tensile strength, apparently directly related to the P alpha MeSt content and independent of the PIB molecular weight.