Relation between properties and molecular morphology of semicrystalline polymers

Abstract

The analysis of experimental data for linear polyethylene fractions is directed to the relationship between the molecular morphology and properties of homopolymers crystallized from the melt. Although the problem has been a matter of deep controversy, clarification is achieved by reviewing the fundamental principles involved and indicating the a priori assumptions that have been made in arguing for a regularly folded, adjacent re-entry interfacial structure. It is concluded that the basic crystallite consists of a lamella-like three-dimensional ordered structure, a very diffuse and distorted interfacial region and an interzonal or amorphous region wherein the chain units in non-ordered conformations connect crystallites and possess liquid-like properties. This crystallite model is the same as that needed to satisfy the small angle neutron scattering data. Higher order crystallite organizations are also introduced with emphasis on the molecular factors and crystallization conditions favouring a particular morphological form. The relationship between properties and these supermolecular structures is also described.