Aliphatic-aromatic copolyesters containing monophenyl terephthalic acid and biphenyl 4,4′-oxybisbenzoic acid: Influence of composition and chemical microstructure on thermal and mechanical properties

In order to compare the effect of the monophenyl ring terephthalic acid (TPA) and biphenyl rings 4,4′-oxybisbenzoic acid (OBBA) with ether bond on poly(butylene adipate) (PBA)-based copolyesters properties, two copolyester series poly(butylene adipate-co-butylene terephthalate)s (PBATs) and poly(butylene adipate-co-butylene oxybisbenzoate)s (PBAOs) were synthesized, and comparatively investigated. All the synthesized copolyesters had satisfactory number-average molecular weights in the range of 26,500–73,000 g/mol. For PBATs copolyesters, the crystalline structure gradually transitioned from the monoclinic crystal structure of poly(butylene adipate) to poly(butylene terephthalate) (PBT) with increasing TPA because of the crystalline segments transformation from butylene adipate to butylene terephthalate, while PBAO copolyesters progressively shifted from the crystalline structure of PBA to the amorphous structure of poly(butylene oxybisbenzoate) (PBO) as increasing content of OBBA. The incorporation of either TPA or OBBA comonomers with rigid cyclic structure into PBA chain noticeably increased the glass transition temperature (T_g). With the same monomer molar ratio, PBAOs because of incorporation of the bicyclic comonomers presented higher T_g (range from −24.2 to 49.5°C) than that of PBATs (range from −56.5 to 22.4°C). It was found that copolyesters with bicyclic and ether bond OBBA comonomers exhibited a better flexibility in property than that with monocyclic TPA comonomers.