DYNAMIC MECHANICAL THERMAL ANALYSIS ON ZIEGLER-NATTA AND METALLOCENE TYPE ETHYLENE COPOLYMERS

Abstract

Commercial linear low density polyethylenes (LLDPE) and linear very low density polyethylenes (VLDPE) produced with traditional high activity Ziegler-Natta (Z-N) and metallocene (single site) catalysts, respectively, have been characterized by dynamic mechanical thermal analysis (DMTA). The results demonstrated that particularly the study of the β relaxations from the tan δ and the loss modulus curves may give valuable information of differences in branching amounts and distributions of different types of polyethylenes.The intensity of the tan δ maximum peak increased with the incorporation of more comonomer (more amorphous species, more branching and lower density). The metallocene polymers, with the exception of the metallocene LLDPE studied, gave the highest tan δ intensity values which demonstrated the ease of incorporating higher comonomer amounts in the case of single site polymers. The studied metallocene LLDPE polymer showed a behaviour very close to that of low density polyethylenes (LDPE). For the metallocene polymers correlations between the tan δ maxima values and the melting points, densities and comonomer contents, respectively, were obtained. In many cases the study of the maxima of the loss modulus curves gave still more exact information of the smaller amounts of branching present in the polymer. © 1997 Elsevier Science Ltd. All rights reserved