Phase behavior of I2S single graft block copolymer/homopolymer blends

This work is part of an extensive study of model nonlinear block copolymer/ homopolymer blends. Effects of graft molecular architecture on the morpholo gy of block copolymer/homopolymer blends have been examined. The single gra ft Y-shaped block copolymers used in the study are I2S block copolymers, wh ich have two low polydispersity (PDI) polyisoprene arms and one low PDI pol ystyrene arm joint at a single junction point. Previously reported linear d iblock copolymer/homopolymer blend systems showed that the order-order tran sitions (OOTs) occur at about the same volume fractions as in pure linear d iblock copolymers. The OOT occurs at the same volume fraction regardless of the direction from which it is approached, i.e., blending homopolymer A wi th a diblock which forms A cylinders in a B matrix to push it toward lamell a or blending B homopolymer with a lamellar diblock to push it back toward cylinders. This study shows that when a homopolymer is blended with an I2S block copolymer, the OOTs split so that they occur at different volume frac tions depending up whether they are approached by blending homopolymer into the two-arm or the one-arm side of the block copolymer interface. A perfor ated lamellar morphology is obtained in a blend of homopolystyrene (hPS) an d a lamella forming single graft block copolymer, and it is found to be sta ble to thermal annealing.