Abstract
Copolyesters derived from 1,4-butanediol and constituted also of aliphatic and aromatic dicarboxylate units in a molar ratio of 3:7 were synthesized by a two-step polycondensation procedure. Succinic, adipic, and sebacic acids were specifically selected as the aliphatic component whereas terephthalic acid was chosen as the aromatic moiety. The second synthesis step was a thermal transesterification between the corresponding homopolymers, always attaining a random distribution as verified by NMR spectroscopy. Hybrid polymer composites containing 2.5 wt % of hydroxyapatite (HAp) were also prepared by in situ polymerization. Hydroxyl groups on the nanoparticle surface allowed the grafting of polymer chains in such a way that composites were mostly insoluble in the typical solvents of the parent copolyesters. HAp had some influence on crystallization from the melt, thermal stability, and mechanical properties. HAp also improved the biocompatibility of samples due to the presence of Ca2+ cations and the damping effect of phosphate groups. Interestingly, HAp resulted in a significant increase in the hydrophilicity of samples, which considerably affected both enzymatic and hydrolytic degradability. Slight differences were also found in the function of the dicarboxylic component, as the lowest degradation rates was found for the sample constituted of the most hydrophobic sebacic acid units.
Highlights
Polyesters are currently among the most competitive biodegradable polymers commercialized as both commodity and speciality products
The present work has been focused on aliphatic/aromatic polyesters derived from 1,4-butanediol, different aliphatic dicarboxylic acids and a high content of terephthalic acid
Weight average molecular weights of purified copolymers varied between 17,100 g/mol and 20,200 g/mol, and the polydispersity index remained in the typical range of polycondensation samples
Summary
Polyesters are currently among the most competitive biodegradable polymers commercialized as both commodity and speciality products. In the range of 30 mol % to 60 mol % of terephthalic acid, which is of particular interest since such materials provide useful material properties; the degradation rate drops linearly with the content of the aromatic acid [9,10] These units may reduce the final cost of the polymer. The present work has been focused on aliphatic/aromatic polyesters derived from 1,4-butanediol, different aliphatic dicarboxylic acids (i.e., succinic, adipic, and sebacic acids) and a high content of terephthalic acid (i.e., a nominal value of 70 molar % with respect to the total dicarboxylic acid content was selected in order to explore the possibility of maintaining the biodegradable characteristics at such a high content) In this case, one should expect a low degradation rate as a result of such high aromatic content and the relatively high degree of crystallinity. Some limitations may be expected as a consequence of the low concentration and reactivity of hydroxyl groups on the nanoparticle surface, which could lead to a reduced number of grafted molecules
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