Thermal properties of ethylene/long chain alpha-olefin copolymers producedby metallocenes

Metallocene type copolymers of ethylene with the alpha -olefins 1-octene, 1 -tetradecene and 1-octadecene were characterized by dynamic scanning calori meter (DSC) and by dynamic mechanical analysis (DMA). At a similar comonome r content above 3 mol%, the higher alpha -olefins gave lower melting points , crystallinities and densities than 1-octene. In DSC a separation techniqu e sorting the crystalline sequence lengths of the polymer into groups was a pplied, and DSC index, DI, which gave a semiquantitative idea of the chemic al homogeneity of the comonomer compositional distributions. By DMA the sto rage modulus as an indicator of stiffness and loss modulus and loss tangent as a measure of the effect of branching on the beta relaxations were studi ed. The DMA measurements showed the loss modulus maximum to be a more sensi tive value than the loss tangent maximum for the characterization of the co monomer distribution. The intensity of the beta\ transition of 1-octadecene did not increase with increasing branching in contrast to the situation fo r 1-octene and 1-tetradecene copolymers. (C) 2001 Elsevier Science Ltd. All rights reserved.