Crystallization rate minima of sustainable aliphatic polyesters

Bio-sourced polyethylene-like polyesters have been synthesized as possible substitutes for commodity polymers derived from fossil fuel feedstocks. Their crystalline and mechanical properties are of interest in the path to developing a more sustainable, circular plastics economy. Symmetric (PE-X,X), and asymmetric (PE-X,Y) long-spaced polyesters are also excellent models to understand the manifestation of crystallization rate minima in polydisperse polyethylene-like systems in which a moiety, such as the ester group, is placed at a precise distance along the polyethylene backbone. Recent studies will be presented of the overall crystallization and linear growth rates of asymmetric polyesters PE-X,Y with a fixed methylene length in the diacid (Y =18) and the carbons in the diol changing from 2 to 18. Excluding the longest-spaced PE-X,Y polyester, all are layered and display two or three discrete crystallization rate minima with increasing crystallization temperature. The rate minima are more pronounced in the odd-spaced polyesters. The rate minima are uncorrelated with the polymorphism observed in the lowest-spaced PE-X,Y polyesters, but correlate with transitions between lamellar structures with the same crystal form differing in a monomer step-increase in crystal thickness. The role of the crystalline layer in the manifestation of the rate minima will be discussed.