Little_2020_ACS.Sustain.Chem.Eng_8_14471

Furandioate-adipate copolyesters are an emerging class of bio-based biodegradable polymers with great potential to replace fossil-derived terephthalic acid-based copolyesters such as poly(butylene adipate-co-terephthalate) (PBAT). Furandioate-adipate polyesters have almost exclusively been prepared with conventional primary (1deg) alcohol diols, while secondary (2deg) alcohol diol monomers have largely been overlooked until now, despite preliminary observations that using methyl-branched diols increases the T (g) of the resultant polyesters. Little is known of what impact the use of 2deg alcohol diols has on other properties such as material strength, hydrophobicity, and rate of enzymatic hydrolysis-all key parameters for performance and end-of-life. To ascertain the effects of using 2deg diols on the properties of furandioate-adipate copolyesters, a series of polymers from diethyl adipate (DEA) and 2,5-furandicarboxylic acid diethyl ester (FDEE) using different 1deg and 2deg alcohol diols was prepared. Longer transesterification times and greater excesses of diol (diol/diester molar ratio of 2:1) were found to be necessary to achieve M (w)s > 20 kDa using 2deg alcohol diols. All copolyesters from 2deg diols were entirely amorphous and exhibited higher T (g)s than their linear equivalents from 1deg diols. Compared to linear poly(1,4-butyleneadipate-co-1,4-butylenefurandioate), methyl-branched, poly(2,5-hexamethyleneadipate-co-2,5-hexamethylenefurandioate) (0:7:0.3 furandioate/adipate ratio) displayed both higher modulus (67.8 vs 19.1 MPa) and higher extension at break (89.7 vs 44.5 mm). All other methyl-branched copolyesters displayed lower modulus but retained higher extension at break compared with their linear analogues. Enzymatic hydrolysis studies using Humicola insolens cutinase revealed that copolyesters from 2deg alcohol diols have significantly decreased rates of biodegradation than their linear equivalents synthesized using 1deg alcohol diols, allowing for fine-tuning of polymer stability. Hydrophobicity, as revealed by water contact angles, was also found to generally increase through the introduction of methyl branching, demonstrating potential for these materials in coatings applications.