Co- and terpolyesters based on succinic acid and isosorbide in combination with other renewable monomers such as 2,3-butanediol, 1,3-propanediol, and citric acid were synthesized and characterized. Linear polyesters were obtained via melt polycondensation of nonactivated dicarboxylic acids with OH functional monomers. Polymer end functionality (i.e., hydroxyl or carboxylic acid) was controlled by adjusting the monomer stoichiometry. The glass transition temperatures of the resulting polyesters could be effectively adjusted by varying the polymer composition and molar mass. By adding polyfunctional monomers such as trimethylolpropane or citric acid, polyesters with enhanced functionality were obtained. These biobased polyesters displayed functionalities and Tg values in the appropriate range for (powder) coating applications. The polyesters were cross-linked using conventional curing agents. Coatings from branched polyesters--hydroxyl as well as acid functional--showed significantly improved mechanical and chemical resistance compared to those formulated from linear polymers. These renewable polyesters proved to be suitable materials for coating applications with respect to solvent resistance, impact resistance, and hardness.

Here we present a novel series of biobased polyesters solely based on renewable isohexide building blocks, synthesized via melt polymerization. The recently developed isoidide dicarboxylic acid (IIDCA) was polymerized with rigid renewable diols such as isosorbide (IS), isomannide (IM), isoidide (II), and the novel 2,5-methylene-extended isoidide dimethanol (IIDML). Both IIDCA and IIDML were developed to increase the reactivity of the isohexide building block, while retaining rigidity and hence the beneficial effects on T g . Compared to the parent isohexides, IIDML showed a markedly higher reactivity, resulting in three to four times higher weight-average molecular weight (M w ) values of the synthesized polyesters. The molecular structure of the novel polyesters was analyzed by 1 H, 13 C and 2D-COSY NMR techniques, confirming that the stereoconfigurations of the isohexide moieties were preserved under the applied polymerization conditions. The II/IS-based polyesters have high T g values noted of 70 and 85 °C, respectively, while the IIDML-based polyester has a lower T g of approximately 45 °C, yet with an higher degree of crystallinity than the parent isohexide-based polyesters. A systematic study on structure-thermal properties relations comparing these novel polyesters with, e.g., aliphatic polyesters reveals that, when incorporated into polyesters, both IIDCA and IIDML are able to increase the T g by approximately 70 °C, which is comparable to the parent isohexides. Given the enhanced reactivity, high thermal stability and the retained ability to increase the T g , IIDML is a promising renewable building block for performance polymers.

Isohexides, like e.g. isosorbide, are well-known carbohydrate-based rigid diols which are capable of dramatically increasing the glass transition temperature of polyesters. However, their relatively low reactivity has thus far hampered large-scale industrial applications in the polymer field. Recently, with the aim to increase reactivity while at the same time retain rigidity, we have developed a new isoidide dicarboxylic acid (IIDCA) by transforming the secondary hydroxyls into carboxylate functionalities. Here we report the first polymers based on IIDCA and linear α,ω-diols. The novel polyesters were obtained via melt polymerization and exhibited weight-average molecular weights in the range of 13 000−34 000 g/mol and polydispersities close to 2.0. NMR analyses showed that the exo−exo configuration of the isoidide dicarboxylate units was preserved during synthesis. Both differential scanning calorimetry and wide-angle X-ray diffraction analyses showed that the IIDCA polyesters are semicrystalline materials. A systematic study on structure−thermal properties relations among relevant series of polyesters, such as isomeric polymers based on isoidide, revealed several interesting differences in melting and glass transition temperatures, which are thought to be related to variations in chain packing and free volume.