Furan-based co-polyesters with enhanced thermal properties: poly(1,4-butylene-co-1,4-cyclohexanedimethylene-2,5-furandicarboxylic acid)

Abstract

New co-polyesters of poly(butylene-co-1,4-cyclohexanedimethylene-2,5-furandicarboxylic acid) (PBCFs) were synthesized from 2,5-furandicarboxylic acid (FDCA), 1,4-butanediol (BDO) and 1,4-cyclohexanedimethanol (CHDM) via a two-step esterification–polycondensation procedure. The structure of the synthesized polymers were characterized by ¹H NMR, and the characterization results revealed that the co-polymers had triad components in a random sequential structure. The average sequence length and monomer percentages in the co-polymer could be adjusted by changing the feed molar ratio of BDO to CHDM, however, the easy removal of BDO during the polycondensation procedure facilitates the formation of long chain links containing CHDM units. Co-polyester composition could be calculated from the quantitative ¹³C NMR spectra which are well consistent with the elemental analysis results. The incorporation of CHDM units into poly(butylene-2,5-furandicarboxylate) (PBF) can significantly influence the thermal transition behavior, thermal stability and crystallinity of PBCFs. PBCFs showed T_g monotonously increasing with CHDM content, and the characterized T_g by DSC method is consistent with the calculated value from the Fox equation. As the molar percent of CHDM unit in co-polymers increases from 20 to 70%, T_g changes from 45.7 to 74.4 °C, T_m from 140.1 to 251.9 °C and decomposition temperature from 380.6 to 388.0 °C. XRD results indicated that the crystallinity and crystal structure of the polyester was significantly changed by CHDM incorporation. When the content of CF units increases to 31%, PBC₃₁F is almost amorphous and it is difficult to form long regular segments to form micro-crystals, and this co-polymer shows neither cold-crystallization nor melting behavior. However, multiple melting behaviors are observed in the DSC heating traces of PBC₅₂F, PBC₆₁F, PBC₇₀F and PCF with a shoulder peak on the side of the main melting peak because of partial melting–recrystallization and final melting process taking place successively during the heating scan.