synopsisRandom copolymers of eisand trans-1,4-cyclohexylenedimethylene terephthalate were permitted to undergo ester-interchange reorganization a t temperatures just below the melting point. As predicted from the principles of crystallization-induced reactions of semicrystalline copolymers proposed in the first two papers of this series, the copolymers were observed to undergo changes in physical properties which are associated with the conversion of a random to a block copolymer. The driving force for this antiequilibrium ordering hrocess is believed to be the irreversible expansion of the crystalline regions following replacement of cis by trans glycol units. Solubility, crystallinity, and crystallization properties were monitored to determine the effects of copolymer composition, temperature, catalyst, and molecular weight on the reorganization rate. This type of process is also believed to be responsible for the direct preparation of block copolymers by a solid-state polycondensation reaction used in this study. 2927

Small‐angle light scattering experiments were conducted on thin films of linear polyethylene fractions over a very wide range of molecular weights. Spherulitic structures were found in all samples with molecular weight 9 × 105 or less. A rodlike morphology predominates for molecular weights between 1 × 106 and 2 × 106. Still higher fractions yield a very disordered superstructure. These results can be correlated with previous studies of the overall crystallization rates and the resulting properties.

Electron microscope studies are reported for crystals of linear polyethylene formed in dilute solution from very sharp low molecular weight fractions. Emphasis is placed on molecular weights in the range of 1.1 × 103 to 15.1 × 103. The dependence of the crystal habit on the crystallization temperature is very similar to that which has been found for the higher molecular weight species. However, the demarcation temperature for the crystallization of the different morphological forms is very molecular weight‐dependent. The conditions under which interfacial dislocation networks form can be clearly defined. The molecular weight must be less than 3000, so that these structures are restricted to very small chain lengths. However, not all crystallization conditions within this allowable molecular weight range yield such dislocations. The formation of interfacial dislocation networks are shown to occur only under very special circumstances. Their occurrence clearly cannot be offered as evidence, as has been done in the past, for a regular, chain‐folded interfacial structure.

Previous work on the small‐angle light scattering of polyethylene films, to determine the supermolecular structure, has been continued. One of the main efforts has been the study of a binary mixture whose low molecular weight component forms well defined spherulites and whose high molecular weight component yields a poorly defined rod‐like morphology. The addition of the high molecular weight fraction causes a progressive deterioration of the initial spherulitic morphology; a relatively small amount of the high molecular weight species causes a major decrease in the spherulitic size. However, there are no indications of any spherulitic structures when the weight fraction of the high molecular weight species is 0.5 or greater. The isothermal crystallization of a fraction M = 6.6 × 105 was also studied. Spherulites were formed at low crystallization temperatures while at the higher crystallization temperatures the morphology became nondistinct. Preliminary studies with solvents indicate that high molecular fractions, which do not form spherulites when crystallized in the pure state, do so when crystallized from highly swollen solutions.

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