(2015). Enzymatic synthesis and preliminary evaluation as coating of sorbitol-based, hydroxy-functional polyesters with controlled molecular weights. European Polymer Journal, 67, 459-475. DOI: 10.1016/j.eurpolymj.2014 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. By using a combination of bio-based monomers (sorbitol, 1,10-decanediol and a range of dicarboxylic acids), a series of novel sorbitol-based polyesters was prepared by solvent-free enzymatic polycondensation using an immobilized form of Candida antarctica lipase B (Novozyme 435). The aim was to prepare linear polyesters with pendant, curable hydroxyl groups along the polymer backbone. To achieve this, the polyester molecular weight was controlled by tuning the reaction time, enzyme loading and reaction stoichiometry. Extensive molecular and thermal characterization was performed, showing that the obtained polyesters were semi-crystalline materials with a low T g . The presence of sorbitol in the polyesters was confirmed through a qualitative investigation using MALDI-ToF-MS. The quantification of the sorbitol content in the polymers was achieved by inverse-gated decoupling 13 C NMR spectroscopy, while 31 P NMR provided information regarding the selectivity of CALB for the primary vs. the secondary hydroxyl groups. Moreover, 31 P NMR and potentiometric titration were utilized for the quantitative determination of the amount of carboxylic groups and hydroxyl functional groups present in the polyesters. The obtained hydroxyl-functional polyesters had suitable properties to be applied as solvent-borne coatings in terms of their molecular weight, functionality and thermal characteristics. Cross-linked coatings were prepared using different conventional curing agents, including two renewable diisocyanates (ethyl ester L-lysine diisocyanate and dimer fatty acid-based diisocyanate). The resulting poly(ester urethane) coatings were tested in terms of solvent resistance, hardness and resistance against rapid deformation, showing the beneficial effect of the implemented sorbitol on network formation.

Enzymatic catalysis is an attractive approach toward the synthesis of sustainable polyesters, which also provides advantages in terms of selectivity compared to conventional methods. Furthermore, the use of immobilized enzymes allows for solvent-free, ecofriendly polycondensation routes, but also leads to some limitations in terms of applicability to certain systems. A systematic study has been performed on the synthesis of close to linear aliphatic polyesters from biobased, commercially available sorbitol, 1,10-decanediol, and dimethyl adipate. Polycondensation reactions were carried out in the melt using SPRIN liposorb CALB (trade name for the immobilized form of Candida antarctica lipase B) as catalyst, targeting a number-average molecular weight between 4 and 6 kg/mol, and an amount of pendant and terminal hydroxyl groups within the range commonly used for coating applications. The efficacy with which the increasing amounts of sorbitol were built into the polyester backbone was studied in detail via 13C NMR spectroscopy. In addition, the particular selectivity for primary vs secondary hydroxyl groups of the biocatalyst was confirmed via 31P NMR spectroscopy. Extensive structural characterization was carried out via MALDI-ToF-MS analysis, which also provided further insights into limitations of the system related to sorbitol incorporation. Differential scanning calorimetry and X-ray diffraction analysis revealed that the melting temperature and crystallinity of the materials are lower when increased amounts of sorbitol are incorporated into the polyesters.

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