Thermal properties of ethylene/long chain α-olefin copolymers produced by metallocenes

Metallocene type copolymers of ethylene with the α-olefins 1-octene, 1-tetradecene and 1-octadecene were characterized by dynamic scanning calorimeter (DSC) and by dynamic mechanical analysis (DMA). At a similar comonomer content above 3 mol%, the higher α-olefins gave lower melting points, crystallinities and densities than 1-octene. In DSC a separation technique sorting the crystalline sequence lengths of the polymer into groups was applied, and DSC index, DI, which gave a semiquantitative idea of the chemical homogeneity of the comonomer compositional distributions. By DMA the storage modulus as an indicator of stiffness and loss modulus and loss tangent as a measure of the effect of branching on the β relaxations were studied. The DMA measurements showed the loss modulus maximum to be a more sensitive value than the loss tangent maximum for the characterization of the comonomer distribution. The intensity of the β transition of 1-octadecene did not increase with increasing branching in contrast to the situation for 1-octene and 1-tetradecene copolymers.