Synthesis and characterization of new polyesters based on renewable resources

Abstract

A series of non-crosslinked biobased polyesters were prepared from pentaerythritol and aliphatic dicarboxylic acids, including fatty acids grafted as side-chains to the backbone of the polymer. The strategy utilized tends to create linear polymers by protecting two of the hydroxyl groups in pentaerythritol by esterification with fatty acids before the polymerization reaction. The solvent-free syntheses were performed under vacuum and catalyzed by the ion-exchange resin Amberlyst 70. The maximum yield was around 98%. Pristine polyesters had average molecular weights of about 104 g/mol according to SEC-MALLS analysis. Melting temperatures and extent of crystallinity were determined by differential scanning calorimetry. By using relatively short fatty acids, such as lauric acid, soft materials were obtained with low crystallinity and a melting point below room temperature, whereas longer side-chains, such as behenic acid, gave brittle polymers with higher melting temperatures and crystallinity. The use of a short chain dicarboxylic acid, such as succinic acid, resulted in closer side-chains and promoted higher crystallinity and melting temperatures. In order to improve the thermal properties of these materials, a series of copolyesters were designed by developing synthetic methods to approach a random- and a block-copolymerization. A wide range of properties was thus obtained according to the composition of these novel copolyesters.