The co-crosslinked products and the entrapping phenomenon that may exist in a poly(vinyl chloride)/ low density polyethylene/dicumyl peroxide (PVC/LDPE/ DCP) blend were investigated. The results of selective extraction show that unextracted PVC was due to not being co-crosslinked with LDPE but being entrapped by the networks formed by the LDPE phase. SBR, as a solid-phase dispersant, can promote the perfection of networks of the LDPE phase when it is added to the PVC/LDPE blends together with DCP, which leads to more PVC unextracted and improvement of the mechanical properties of PVC/ LDPE blends. Meanwhile, the improvement of the tensile properties is dependent mainly on the properties of the LDPE networks. Finally, the mechanism of phase dispersion-crosslinking synergism is presented. (C) 2003 Wiley Periodicals, Inc.