Abstract
The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P21ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9) crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface.
Highlights
Poly(alkylene dicarboxylate)s constitute a family of biodegradable polymers with growing interest since the limitations caused by the moderate molecular weight usually attained by conventional thermal polycondensation methods [1] have been overcome by using chain extenders [2,3], new highly efficient catalysts [4,5,6] or even ring opening polymerizations [7,8]
Morphology of Single Crystals of PES 9,7, PES 9,9, and COPES 9,7/9 Samples. Lamellar crystals of both PES 9,7 and PES 9,9 homopolyesters were obtained by isothermal crystallization in dilute diol solutions and a narrow temperature range (i.e., 30–50 ̋ C)
The crystalline structure is similar to other polyesters constituted by long diol and dicarboxylate units
Summary
Poly(alkylene dicarboxylate)s constitute a family of biodegradable polymers with growing interest since the limitations caused by the moderate molecular weight usually attained by conventional thermal polycondensation methods [1] have been overcome by using chain extenders [2,3], new highly efficient catalysts [4,5,6] or even ring opening polymerizations [7,8]. The present work is focused on the study of the crystalline structure of poly(nonamethylene azelate) and poly(nonamethylene pimelate) homopolymers and the related copolymer constituted by an equimolar ratio of the two dicarboxylic units as examples of bio-based odd-odd poly(alkylene dicarboxylate)s. Distribution of comonomer units in the crystalline phase of the random copolymer is evaluated as well as the repercussions on the single crystal morphology and the degradation behavior
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