Studies of comonomer distributions and molecular segregations in metallocene-prepared polyethylenes by DSC

This paper is devoted to the study of crystallization and melting of two metallocene polyethylenes (m-PEs). A metallocene linear low density polyethylene (m-LLDPE) and a metallocene very low density polyethylene (m-VLDPE) were used consisting of 3.3 mol% butyl and 6 mol% ethyl branches, respectively. Several melt endotherms after stepwise crystallization revealed that the two m-PEs consisted of molecular fractions with different molecular weight and branch distribution. More segregation was observed for the m-VLDPE comparing with m-LLDPE. Using the relationships proposed by Hosoda, the short chain branching distribution (SCBD) and the average methylene groups in the lamella thickness were also calculated for the two polymers. These values were compared with the values obtained from theory of rubber elasticity. There was a very good correlation between the data.