Trans-2-Butene-1,4-Diol as an Olefinic Building Block to Prepare Biobased Unsaturated Copolyesters with High Molecular Weight: Synthesis, Characterization, and Physical Properties

A series of biobased poly(butylene succinate-co-trans-butene succinate) (PBStBS) was prepared by copolymerizing biobased trans-2-butene-1,4- diol(tB), succinic acid, and 1,4- butanediol via a two-step polycondensation. NMR and gel permeation chromatography characteristics indicated that the isomerization and branching side reactions were prevented in PBStBS synthesis. Random copolyesters with high number average molecular weights (Mn) over 40 kDa were achieved. Despite being random, these PBStBS can crystallize in the whole composition range, exhibiting a eutectic region on the copolyesters with around 70-76 mol % trans-butane succinate (tBS) content. In combination with WAXD analysis, PBStBS showed an unexpected isodimorphism, in which the crystallization rate of PtBS was very slow, but could also show typical isodimorphism with PBS after isothermal crystallization for a long time. The isodimorphism between PBS and PtBS was further investigated by thermodynamics. The tensile test result demonstrated that PBStBS copolyesters had excellent mechanical properties, considering their satisfactory thermal and crystal properties; thus, PBStBS was promising as linear biobased unsaturated polymers for a wide range of applications. This work suggested that tB is a suitable diol for the direct synthesis of linear unsaturated copolyesters, and the fully biobased PBStBS can potentially replace the common packaging materials of PBAT and PE from fossil resources.