Phase diagrams for the blends of a styrene-butadiene diblock copolymer anda styrene-butadiene random copolymer: Theory

The phase diagram of the blends of a diblock copolymer (A-B) and a random c opolymer (ABR) is constructed by the modified confined-chain model develope d earlier where the morphology of A-B block copolymer is lamellae and the c omposition of ABR random copolymer is close to that of A-B. These theoretic al results predict a relatively simple phase behavior for the A-B/ABR blend s in comparison to the A-B/A blends, A being a homopolymer, studied previou sly. Unlike in A-B/A blends, the order-disorder transition temperature in A -B/ABR blends is lowered by the addition of the random copolymer regardless of its molecular weight. It is also found that the fraction of ABR solubil ized into the A-B is very limited due to the endothermic mixing interaction between ABR and each block of A-B.