Miscibility Enhancement in Polyisoprene-Polyolefin Block Copolymers

Polydienes and polyolefins generally show limited compatibility (high interaction energy density, X). We investigate the thermodynamic interactions in symmetric amorphous polydiene-polyolefin block copolymers composed of polyisoprene (PI) and hydrogenated medium-vinyl polybutadiene (hPB). The regular solution model suggests that styrene units (S), given the higher solubility parameter of polystyrene, can boost inter-block miscibility when incorporated in small amounts into the hPB block via random copolymerization (hSBR). Block and “block-random” copolymers were prepared by anionic polymerization, followed by selective saturation of the butadiene units. Diblock copolymers with no S (PI-hPBs) exhibited an interaction energy density of 0.81 MPa, after correcting the measured value of X for the imperfect selectivity of the hydrogenation catalyst. A selectively saturated block-random copolymer with ~10 wt% styrene in the random block (PI-hSBR10) exhibited a measured X of 0.30 MPa, which is lower than the measured X (uncorrected) of a PI-hPB diblock copolymer (0.52 MPa) with identical levels of block saturation, indicating a strong enhancement in compatibility. Further work delineating the effect of S content on inter-block miscibility is underway.