Polyisoprene (PI) and saturated mid-vinyl polybutadiene (hPB) form a polydiene-polyolefin system, and are expected to show limited compatibility (high interaction energy density, X, proportional to Flory-Huggins interaction parameter, χ). The regular mixing model suggests that styrene units (S), given the higher solubility parameter of polystyrene, can boost inter-block compatibility when incorporated in small amounts into the hPB chain via random copolymerization. This behavior is also predicted by the three-component copolymer equation model. Mixing thermodynamics in symmetric polydiene-polyolefin block-random copolymers composed of PI and a selectively saturated random copolymer of mid-vinyl polybutadiene and styrene (hSBR) were investigated via location of the order-disorder transition (ODT) temperature by dynamic mechanical thermal analysis. Block and “block-random” copolymers were prepared by anionic polymerization, followed by selective saturation of the butadiene units with a homogeneous ruthenium catalyst (hRu1). The true value of X was determined from the measured value of X by employing the multi-component copolymer equation to account for the presence of minor structures due to the imperfect selectivity of hRu1. ODT temperatures showed that diblock copolymers with no S (PI-hPBs) exhibited a true X of 0.74 MPa. Selectively saturated block-random copolymers with ~10, ~20 and ~60 wt% S in the hPB block exhibited a significant decrease in true X relative to PI-hPB. At ~30 wt% S, the diblock was disordered at all temperatures, indicating X &lt; 0.14 MPa. This indicates a strong enhancement in compatibility with low levels of S incorporation. X at various levels of styrene incorporation (low and high) exhibited the parabolic behavior predicted by the copolymer equation model.

Miscibility enhancement in polyisoprene-polyolefin block copolymers by styrene incorporation

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.