The effects of styrene content, layer thickness, and temperature on the adhesion of ethylene-styrene copolymers (ES) to low-density polyethylene (LDPE) were examined by measuring the delamination toughness of LDPE/ES microlayers in the T-peel test. Delamination toughness at ambient temperature decreased with increasing styrene content. A linear correlation between delamination toughness and styrene content in ES was observed. Extrapolation predicted that a copolymer with 72.5 wt% styrene would have no adhesion to LDPE. Experiments on microlayers with relatively thin (8-18 mum) ES layers demonstrated that delamination toughness was proportional to ES layer thickness. In situ observations of the damage zone showed stretching throughout the entire thickness of the ES layer. For higher adhesion systems, ES deformation occurred concurrently with localized stretching and crazing of the LDPE layer at the interface. For two representative systems, the effect of temperature on delamination toughness was studied. Major transitions in delamination toughness and fracture mode were observed at the primary thermal transitions of the ES copolymer. The contribution by stretching of the ES layer to measured delamination toughness was approximated by relating the damage zone to the ES engineering stress-strain curve and was estimated to be about half. The remaining contribution to delamination toughness was assumed to be due to LDPE deformation in the damage zone. (C) 2003 Wiley Periodicals, Inc.