Structure–Property Relationships in Low-Density Polyethylene

Modern techniques were adopted and utilized for molecular-weight characterization of commercial low-density (branched) polyethylenes. The index of long-chain branching was uniquely related to that of molecular-weight dispersion, Dn . Two groups of low-density polyethylenes were visualized, differing in width of MW distribution and in the branching index. An attempt was made to relate the flow properties, melt-flow index (MFI) and intrinsic viscosity [n], as well as some physical properties–density, tensile strength, ultimate elongation and resistance toenvironmental stress cracking–toatypical molecular parameter. In all correlations, the two groups are represented by two distinctly different curves. By combining the parameter g for long-chain branching with the weight average molecular weight, [Mbar]γ , the flow parameters are unified into single curves. The mechanical properties studied were found to improve increasing [Mbar]γ and with narrowing of the molecular-weight distribution.