Characterization of comonomer distributions in ethylene diene copolymers by C-13-NMR, and using the segregation fractionation technique by DSC and DMTA

Ethylene and linear, nonconjugated dienes were copolymerized with the catal yst system Cp,Cp2ZrCl2/methylaluminoxane (MAO). The comonomer incorporation and the relationships between structure and properties were evaluated by N MR and by thermal techniques, especially the segregation fractionation tech nique (SFT) using DSC and dynamic mechanical thermal analysis (DMTA). The e thylene- 1,5-hexadiene (HD) copolymers showed different behavior than the o thers and it was possible to incorporate as much as 7 mol % of the hexadien e comonomer into soluble polymer compared with only 2.4 mol % of the 1,7-oc tadiene (OD) and 7-methyl-1,6-octadiene (MOD). The melting endotherms of th e HD copolymers obtained after segregation fractionation were very much lik e corresponding endotherms of high-density polyethylene (HDPE) and a popula tion with nearly one lamellar thickness was postulated. This is in agreemen t with cyclic structure formation and absence of branching with crosslinkin g for these copolymers. The OD and MOD copolymers, on the other side, showe d 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 measureme nts confirmed the absence of branches in the HD copolymers and the presence of branches in the OD and the MOD copolymers. (C) 1999 John Wiley & Sons, Inc.