Study on the crystallization of poly(alkylene dicarboxylate)s derived from 1,9-nonanediol and mixtures with different ratios of azelaic acid and pimelic acid units

Abstract

Polyalkylene dicarboxylates derived from 1,9-nonanediol and mixtures with different ratios of pimelic acid and azelaic acid were synthesized by thermal polycondensation. All samples had a high degree of crystallinity although it was found to decrease with the comonomer content. Crystallization kinetics of the two homopolymers and the copolymer with the eutectic composition was studied by calorimetric and optical microscopy techniques. Similar Avrami parameters were determined for the three samples and a spherulitic growth with heterogeneous nucleation was deduced. Spherulites showed negative birefringence and a fibrillar or ringed texture depending on the sample. Furthermore, clear differences were found in the primary nucleation density, the spherulitic growth rate and even in the secondary nucleation constant deduced from the Lauritzen-Hoffman treatment. The three studied samples had a similar arrangement of molecular chains, and consequently their WAXD patterns showed the same strong reflections related to the molecular packing. SAXS data revealed that a lamellar insertion mechanism was characteristic for non-isothermal crystallization from the melt. In addition, significant differences were found between the crystal lamellar thicknesses of the homopolymer and copolymer samples. Diffraction and spectroscopic data suggested that the lamellar crystals of the eutectic copolymer were mainly constituted by azelate units whereas the pimelate units were preferentially located in the amorphous regions including the interlamellar amorphous layer associated with the chain folds.