Characterization of comonomer distributions in ethylene/diene copolymers by13C-NMR, and using the segregation fractionation technique by DSC and DMTA

Abstract

Ethylene and linear, nonconjugated dienes were copolymerized with the catalyst system Cp2ZrCl2/methylaluminoxane (MAO). The comonomer incorporation and the relationships between structure and properties were evaluated by NMR and by thermal techniques, especially the segregation fractionation technique (SFT) using DSC and dynamic mechanical thermal analysis (DMTA). The ethylene-1,5-hexadiene (HD) copolymers showed different behavior than the others and it was possible to incorporate as much as 7 mol % of the hexadiene comonomer into soluble polymer compared with only 2.4 mol % of the 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). The melting endotherms of the HD copolymers obtained after segregation fractionation were very much like corresponding endotherms of high-density polyethylene (HDPE) and a population with nearly one lamellar thickness was postulated. This is in agreement with cyclic structure formation and absence of branching with crosslinking for these copolymers. The OD and MOD copolymers, on the other side, showed endotherms with several peaks indicating a distribution of the comonomers along the chain. Lamellar thickness distributions were calculated from the melting endotherms by using the Gibbs–Thomson equation. The DMTA measurements confirmed the absence of branches in the HD copolymers and the presence of branches in the OD and the MOD copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2379–2389, 1999