Polylactic acid/ethylene glycol triblock copolymer (LLA(46)EG(46)LLA(46)) was prepared and used in a crosslink process of epoxidized natural rubber (ENR) by employing a ring-opening reaction using Sn(Oct)(2) as a catalyst. The OH-capped copolymer acts as a macromolecular crosslinking agent in the formation of ENR networks, leading to drastic enhancement in tensile properties. Crosslink efficiency and chemical structures of the cured materials are examined by solvent fractionation, swelling experiments, XRD, H-1-NMR, and ATR-FTIR spectroscopy. The efficiency of the curing process is dependent on the ENR/copolymer feed ratios. The degree of property improvement and gas permeability/selectivity behaviors of the cured materials are strongly dependent on the copolymer content and the efficiency of the curing process. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012