Distribution of chain defects and microstructures of melt crystallized polyethylene. II. Influence of defect size and of plastic deformation

Unit cell expansion data for (a) melt-crystallized polyethylene (PE) containing known amounts of methyl, ethyl, and butyl branches and for (b) plastically deformed samples, are examined in the light of a model which takes into account the penetration of constitutional defects (branches) at interstitial crystal sites by means of a generation of 2g1 step chain defects (kink isomers). The present analysis complements previous results obtained for melt-crystallized PE samples with a widely varying number concentration ? of butyl or longer branches. An estimation of the concentration of chain defects incorporated into the crystal lattice is carried out. The results reveal that the fraction χ_c of defects which are accomodated within the lattice depends on both the amount and size of the chain defects and on the mechanical deformation of the sample. For PE chains with methyl and ethyl groups, χ_c ≈ 50%, whereas for butyl and longer branches, χ_c does not exceed 20% of the total concentration of defects. In addition, after cold drawing, PE with low amounts (? < 1%) of butyl or longer chain branching, χ_c turns out to be zero; i.e., during deformation single molecular chain rearrangements leading to a chain segregation of defects into the amorphous phase must occur.