Single crystals of linear polyesters

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Abstract
The influence of chemical groups regularly spaced along a polymer chain on structure and behaviour of chain folded single crystals was studied on linear aliphatic polyesters with different lengths of repeating unit. Poly(oxytetramethyleneoxysebacoyl) (or polyester 4,10), poly(oxyhexamethyleneoxysebacoyl) (or polyester 6,10), and poly(oxydecamethyleneoxysebacoyl) (or polyester 10,10) single crystals were grown from solution and their structure and annealing behaviour were examined. Chain folded lamellae with two different structures were formed depending on the chemical composition of polyester. Although in both structures the chains are perpendicular to the lamella surface, the ester group planes {00l} are parallel to the lamella surface in polyester 4,10 as opposed to the polyester 10,10 where the ester group planes are inclined.In spite of the fact that the chain folded lamellae are of about 100Å thick and can accommodate only few crystallographic repeats along, the lamella thickness of all three polyesters increases continuously with crystallization temperature. A picture of chain folded lamellae containing folds of different but quantized lengths mixed in different proportions is proposed in order to explain the continuous increase of lamella thickness.On annealing, the lamella thickness of polyester 4,10 and 6,10 increases in discrete steps suggesting that a rearrangement of folds leading to a more uniform fold length mixture takes place. In contrast, in polyester 10,10 the lamella thickness increases continuously on annealing which is attributable to the inclination of the ester group planes to the lamellar surface and to the ensuing non‐equivalence of the folds which distinguishes it from the other two polyesters. Some generalizations about fold length changes are being made.

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