Influence of thermal history on morphology and viscoelastic behavior of ethylene-1-octene copolymers synthesized with metallocene catalysts

The relationships among structure and properties have been established in c opolymers of ethylene and 1-octene, synthesized by a particular metallocene catalyst system. The most important factor affecting the structure and pro perties of these copolymers is, evidently, the comonomer content. However, the cooling treatment from the melt has been found to be also a very signif icant factor and. although its influence on the thermal properties is rathe r small, some structural parameters and the viscoelastic behavior are clear ly dependent upon thermal history. These parameters include the degree of c rystallinity, lattice constants, relaxation processes, stiffness. and micro hardness of the samples. Regarding the viscoelastic behavior, the beta rela xation is shifted to lower temperatures and its intensity is increased as 1 -octene content raises. On the other hand, the or mechanism, associated wit h motions within the crystalline regions, is also moved to lower temperatur es. Such a relaxation is only observed up to a certain 1-octene content in the copolymer.