DSC studies of linear low density polyethylene. Insights into the disrupting effect of different comonomers and the minimum fold chain length of the polyethylene lamallae

This paper reports a DSC examination of a series of linear low density polyethylenes (LLDPE) prepared variously with propylene, 1-butene or 4-methyl-1-pentene comonomers. The enthalpy of fusion of the crystalline regions of the LLDPE decreases progressively with increasing comonomer content and is effectively independent of the comonomer type. Disruption of polymer crystallinity is thus determined principally by the number and distribution of the chain irregularities. A sequence length of n = 14 was calculated as the critical chain dimension below which polyethylene segments cannot be readily packed into a stable crystal lattice.