Incorporation of Styrene into a Model Polyolefin for Enhanced Compatibility with Polyisoprene

Polydienes like polyisoprene (PI) and polyolefins like hydrogenated medium-vinyl polybutadiene (hPB) generally show limited compatibility (high interaction energy density, X). Both the regular mixing model and the copolymer equation suggest that styrene units (S) should boost inter-block miscibility when incorporated in minor amounts into hPB, up to 40 wt% S, via random copolymerization. Mixing thermodynamics in symmetric polydiene-polyolefin block-random copolymers composed of PI and a selectively saturated random copolymer of medium-vinyl polybutadiene and styrene (hSBR) were investigated via location of their order-disorder transition (ODT) temperatures. Block and “block-random” copolymers were prepared by anionic polymerization, followed by selective saturation of the butadiene units. At 100°C, X = 0.72 MPa at 0 wt% S, decreasing to below 0.28 MPa at 27 wt % and generally exhibiting a parabolic variation with wt% S, with a minimum near 40 wt% S. While both the regular mixing model and the copolymer equation qualitatively predict this parabolic behavior, the copolymer equation—with all three binary interaction energies determined independently—provides a better quantitative description of how S incorporation tunes X.