Equilibrium and non-equilibrium melting of branched polyethylene relating to defect incorporation within crystals

Abstract

New equilibrium melting point data, for polyethylene containing chain defects, are tested in the light of random copolymer predictions. A simplified expression for the melting point depression of random copolymers containing small amounts of non-crystallizable units is derived. Non-equilibrium melting data for rapidly quenched polyethylene samples are also reported. The fusion enthalpyΔH∘(X), and the surface free energyσ _e for crystals containing defects are evaluated using crystallinity, equilibrium meltingtemperatures and X-ray long period data. It is shown that increasing defect penetration within crystals induces a decrease ofΔH∘(X) withX in accordance with theoretical predictions. Finallyσ _e is, similarly, shown to decrease with increasing number of chain defects attached to the crystal surface.