Molecular design of multicomponent polymer systems. VII. Emulsifying effect of poly(ethylene–b–styrene) copolymer in high‐density polyethylene/polystyrene blends

Poly(butadiene–b–styrene) copolymers containing a pure, 1,4‐PB block have been synthesized by a “living” coordination process. The complete hydrogenation of the PB chain leads accordingly to a high‐density polyethylene (HDPE) block. The emulsifying efficiency of such a copolymer (H‐7) in HDPE/PS blends is compared with that of a previously reported poly(ethylene–butene–b–styrene) copolymer (SE‐7) obtained by the PB hydrogenation of an anionically prepared PB–b–PS. Microscopy examinations demonstrate unambiguously the interfacial activity of both copolymers in HDPE/PS blends. The tensile mechanical properties of the blends are significantly but also differently modified by the two emulsifiers. The copolymer H‐7 gives rise to the highest strengths, but, contrary to the copolymer SE‐7, provides a poor ductility to the blends. This different behavior is assumed to result in part from the different characteristics of the hydrogenated PB blocks. The elastomeric HPB chain of SE‐7 should form at the interface a more or less extended soft zone whereas a rigid interface would result from the cocrystallization of the HPB chain of H‐7 with the HDPE homopolymer.