Compatibilization of HDPE/PS Blends by Tapered Diblock PE-PS Copolymers

Abstract

Addition of diblock copolymers is a well-known technique for production of polymer blends with enhanced mechanical performance. This paper investigates some of the relationships between the molecular structure of PE-co-PS tapered diblock copolymers and the compatibilization produced by their addition in HDPE/PS blends. The emulsification generated by the addition of a given amount of copolymer molecules was found to be directly related to the block copolymer molecular weight; the higher the copolymer molecular weight, the finer the HDPE dispersion. On the other hand, an optimum molecular weight seemed to exist when the fracture resistance of compatibilized blends is considered. Improvement of blends fracture resistance was only observed upon addition of the intermediate molecular weight copolymer (PS520-PE2320). Both the low (PS480-PE80) and high (PS375-PE6950) molecular weight copolymers did not improve the fracture resistance of 15 wt% HDPE/PS blends. The lack of homopolymer-copolymer molecular entanglement could explain the poor performance of the low molecular weight copolymer while the formation of a dry brush was postulated in blends compatibilized by the high molecular weight material.