Block copolymer compatibilization of cocontinuous polymer blends

The effect of block copolymers on the cocontinuous morphology of 50/50 (w/w) polystyrene (PS)/high density polyethylene (HDPE) blends was investigated using symmetric polystyrene–polyethylene block copolymers (PS–PE) with molecular weights varying from 6 to 200 kg/mol. The coarsening rate during annealing was compared to the Doi–Ohta theory. An intermediate molecular weight PS–PE, 40 kg/mol, showed remarkable results in reducing the phase size and stabilizing the blend morphology during annealing. Mixing small amounts of 6, 100 or 200 kg/mol PS–PE in the blend did not reduce the phase size significantly, but did decrease the coarsening rate during annealing. In stabilizing the morphology, 6 kg/mol PS–PE was inferior to 100 and 200 kg/mol. The existence of an optimal molecular weight block copolymer is due to a balance between the ability of the block copolymer to reach the interface and its relative stabilization effect at the interface.