Macromolecules, Vol.35, No.21, 8045-8055, 2002
Effect of saturation of polydienes with varying microstructures on the phase behavior of poly(vinyleyclohexane)/poly(ethylene-alt-propylene) and poly(vinyleyclohexane)/poly(ethylene-co-1-butene) blends
The effect of saturation of polydienes with varying microstructures on the phase behavior of poly(vinyleyclohexane) (PVCH)/poly(ethylene-co-1-butene) (PEB) and PVCH/poly(ethylene-alt-propylene) (PEP) blends was investigated. For the study, a series of polyisoprenes (PI) and polybutadienes (PB) with varying microstructures and molecular weights and polystyrenes (PS) with varying molecular weights were synthesized via anionic polymerization. Subsequently, they were saturated, yielding PVCH, PEB, and PEP, respectively. Binary blends of PVCH and PEB and binary blends of PVCH and PEP with blend compositions varying from 10 to 90 wt% were prepared from solvent casting in toluene. Laser light scattering was used to take cloud point measurements, which were then used to construct phase diagrams. For comparison, the phase behavior of PS/PI and PS/PB; blends was also investigated. It was found that the PVCH/PEB and PVCH/PEP blends exhibit upper critical solution temperature, similar to the PS/PI and PS/PB blends. The interaction parameter for each polymer pair chosen was determined by curve-fitting the experimental phase diagram to a theoretical phase diagram predicted from the Flory-Huggins theory. The interaction parameters thus obtained were used to predict, via the currently held mean-field theory, the order-disorder transition temperature (T-ODT) of the PVCH-bloch-PEB and PVCH-bloch-PEP copolymers reported in the literature. It has been found that the predicted T-ODT of the PVCH-block-PEP and PVCH-bloch-PEB copolymers is higher than that of the unsaturated precursors having PI or PB blocks with predominantly 1,4-addition. These findings are in agreement with the experimental results reported in the literature. It is concluded that the experimentally observed increase in TODT after complete saturation of SI or SB diblock copolymers having PI or PB blocks with predominantly 1,4-addition is due to the substantial increase in the repulsive segment-segment interactions between PVCH and PEP and between PVCH and PEB.