The preparation of cyclic ethylene and butylene 2,5-furandicarboxylate oligoesters and their conversion to furan-based polyesters poly(ethylene furanoate) (PEF) and poly(butylene furanoate) (PBF) by ring-opening polymerization (ROP) are described. The cyclic oligoesters were obtained in high yields by both high dilution condensation and thermal cyclodepolymerization methods, and they consisted of mixtures of small size species. Cyclic dimer, trimer and tetramer oligoesters were isolated by semipreparative chromatography and found to be crystalline compounds melting within the 140–200 °C range. ROP catalyzed by Sn(Oct)2 of both mixtures and individual species afforded PEF and PBF with weight-average molecular weights between 50,000 and 60,000 g mol-1. Polymerization rate was found to be higher for butylene than for ethylene cyclic oligofuranoates, and also to increase slightly as cycle size decreased. The thermal properties of PEF and PBF prepared by ROP were in full agreement with those reported for these polyesters obtained by melt polycondensation.Peer ReviewedPostprint (author's final draft

2,4:3,5-Di-O-methylene-d-mannitol, abbreviated as Manx, is a d-mannitol-derived compound with the secondary hydroxyl groups acetalized with formaldehyde. The bicyclic structure of Manx consists of two fused 1,3-dioxane rings, with two primary hydroxyl groups standing free for reaction. A homopolyester made of Manx and dimethyl terephthalate as well as a set of copolyesters of poly(butylene terephthalate) (PBT) in which 1,4-butanediol was replaced by Manx up to 50% were synthesized and characterized. The polyesters had M_w in the 30 000–52 000 g mol^–1 range and a random microstructure and were thermally stable up to nearly 370 °C. They displayed outstanding high T_g with values from 55 to 137 °C which steadily increased with the content in Manx. Copolyesters containing up to 40% of Manx were semicrystalline and adopted the crystal structure of PBT. Their stress–strain parameters were sensitively affected by the presence of carbohydrate-based units with elongation at break decreasing but tensile strength and elastic moduli steadily increasing with the degree of replacement.

Carbohydrate-based bicyclic compounds, isohexides and diacetalized alditols and aldarates, are suitable polycondensation monomers to prepare partially renewable aromatic copolyesters displaying a satisfactory pattern of basic properties and enhanced T _g and hydrodegradability.

Three carbohydrate-based bicyclic diols, 1,4:3,6-dianhydro-D-glucitol (isosorbide, Is), 2,3:4,5-di-O-methylene-galactitol (Galx) and 2,4:3,5-di-O-methylene-D-mannitol (Manx), were made to react in the melt and under the same conditions with dimethyl terephthalate and 1,4-butanediol to produce respectively three series of PB_xIs_yT, PB_xGalx_yT and PB_xManx_yT random copolyesters. Five different copolymerizations, with molar feed ratios of 1,4-butanediol to sugar-based diols of 90 : 10, 80 : 20, 70 : 30, 60 : 40 and 50 : 50, were carried out for each bicyclic diol in order to make a comparative study on their reactivity and properties of the resulting copolyesters. Molecular weights and compositions data of the copolyesters revealed the greater facility of diacetalized diols to react under these conditions compared to isosorbide. The three bicyclic diols contributed to increase the thermal stability and also the glass-transition temperature of PBT. The replacement of 40% of 1,4-butanediol by sugar-based diols increased the glass transition temperature of PBT from 31 °C to ∼60 °C in the case of Galx and up to ∼90 °C regarding Is and Manx. All PB_xGalx_yT copolyesters as well as PB_xIs_yT and PB_xManx_yT ones with contents of Is and Manx of up to 32% and 41%, respectively, were semicrystalline.

Biotechnologically accessible 1,4-butanediol and vegetal oil-based diethyl sebacate were copolymerized with bicyclic acetalized d-glucose derivatives (Glux) by polycondensation both in the melt at high temperature and in solution at mild temperature mediated by polymer-supported Candida antarctica lipase B (CALB). Two series of random copolyesters (PB_xGlux_ySeb and PBSeb_xGlux_y) were prepared differing in which d-glucose derivative (Glux diol or Glux diester) was used as comonomer. The three parent homopolyesters PBSeb, PBGlux, and PGluxSeb were prepared as well. Both methods were found to be effective for polymerization although significant higher molecular weights were achieved by melt polycondensation. The thermal properties displayed by the copolyesters were largely dependent on composition and also on the functionality of the replacing Glux unit. The thermal stability of PBSeb was retained or even slightly increased after copolymerization with Glux, whereas crystallinity and melting temperature were largely depressed. On the contrary, the glass-transition temperature noticeably increased with the content in Glux units. PGluxSeb distinguished in displaying both T_g and T_m higher than PBSeb because a different crystal structure is adopted by this homopolyester. The hydrolytic degradability of PBSeb in water was enhanced by copolymerization, in particular, when biodegradation was assisted by lipases.