Ethylene/1-pentene copolymers were prepared using a [(CO)(5)W=C(Me)OZr(Cp)(2)Cl] (1)/MAO catalyst system. 1-Pentene incorporation in the copolymer was monitored using C-13-NMR spectroscopic methods. The weight average molecular weights (M-w) of the copolymers were between 142,000 and 629,000 g/mol, with polydispersity indexes (PDIs) ranging from approximate to 2 to 90, as analyzed by size exclusion chromatography (SEC). Melting and crystallization temperatures, determined using differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF), decreased linearly as the amount of 1-pentene in the copolymer increased. SEC-FTIR revealed that the 1-pentene is predominantly incorporated in the low molecular weight fraction. (C) 2004 Wiley Periodicals, Inc.