Effect of homopolymer molecular weight on order-order transition in block copolymer and homopolymer blends.

The order-order transition temperature (T(OOT)) in blends of poly(styrene-b-isoprene-b-styrene) (S-I-S) triblock copolymer and polyisoprene (PI) homopolymer was investigated by using synchrotron small-angle X-ray scattering (SAXS). Pure triblock copolymer undergoes an order-order transition (OOT) from hexagonally ordered cylinder (HEX) to body centered cubic (BCC) phases. In order to investigate the effect of the molecular weight of the added homopolymer on T(OOT) of the triblock copolymer, various low-molecular-weight PI homopolymers were studied. The results revealed that T(OOT) was affected by the PI molecular weight. T(OOT) was reduced for blends having low-molecular-weight PI.