Under a variety of circumstances commonly encountered in practice linear macromolecules crystallize into the form of thin platelets whose large upper and lower surfaces consist of an array of molecular folds. We refer to these as “chain-folded crystals” or “chain-folded lamellae,” the latter term usually being reserved for folded structures in polymers crystallized from the melt. The theory of the rate of formation of these platelets will be outlined, and the prediction and origin of the thin dimension given. The thin dimension of the crystal platelets is determined by kinetic factors, and the elucidation of the kinetics of growth is therefore of importance in polymer morphology on both a molecular and a macroscopic scale.

The Rate of Crystallization of Linear Polymers with Chain Folding

The melting behaviour of heat crystallized poly(ethylene terephthalate)

Multiple melting behaviour of poly(ethylene terephthalate)

The effect of high-energy radiation on n-alkanes and polyethylene (PE) are reviewed. The article includes a description of (a) primary radiation events, formation, spatial distribution and decay of free radicals and radical migration mechanisms, (b) formation of cross-links and other stable products, (c) the effects of crystallinity, crystalline modifications and morphology on radiation cross-linking, and (d) radiation-induced changes in the crystal lattice and the destruction of crystallinity at high irradiation doses. An attempt is made to bring together conflicting views on various unsolved problems of the radiation physics and chemistry of these important and much studied substances. Long-chain paraffins are given considerable attention since their radiation behaviour often provides a link between that of PE and its short-chain analogues.

Radiation effects in polyethylene and n-alkanes

Isotacticity effect on crystallization and melting in polypropylene fractions: 3. Overall crystallization and melting behaviour

Melting and annealing of polyethylene single crystals

Chain folded polyethylene single crystals grown from dilute solutions at undercoolings of 20–40°C are metastable. It is well known that under certain conditions the crystals begin to thicken rapidly at elevated tempera-tures.1, 2, 3 In fusion studies of polyethylene in our laboratory, the observed melting temperature of solution grown crystals (where the crystallization temperature is 77°C or lower) has been found to increase by nearly 10°C as a result of thickening while the crystals were being heated at 10°c/min. Thus, it was impossible to correlate the melting results with structural data which had been obtained on the original crystals prior to heating.

H. E. Bair

Papers

Melting and annealing of polyethylene single crystals

The Equilibrium Melting Temperature and Surface Free Energy of Polyethylene Single Crystals