High Glass Transition PEcBT and PEPecBT Copolyesters Synthesized by Direct Esterification Route

2,2,4,4-Tetramethyl-1,3-cyclobutanediol (CBDO) based copolyesters like poly(cyclohexane dimethylene-co-2,2,4,4-tetramethyl cyclobutylene terephthalate) (PCcBT) has high transparency, heat-resistance and safety and has been commercialized to replace bisphenol A polycarbonate in food contact applications. However, its synthesis and processing suffer from CBDO sublimation, composition deviation and relatively poor thermal stability. In order to obtain transparent heat-resistant CBDO-based copolyesters with improved synthesis robustness and thermal stability, poly(ethylene co-tetramethyl cyclobutene terephthalate (PEcBT)) copolyesters were synthesized from ethylene glycol (EG), CBDO, and terephthalic acid (TPA) via direct esterification route, and the structure–property was studied. It is found that the presence of EG effectively inhibited the sublimation of CBDO, and the resulting PEcBT copolyesters had reasonably good thermal stability so that the melt polycondensation proceeded smoothly without serious foaming. PEcBT copolyesters with intrinsic viscosity ([η]) over 0.60 dL/g were successfully synthesized at copolymer composition ( ϕ cBT ) up to 67 mol%. A quantitative relationship between T g and its influence factors is established. The copolyesters with ϕ cBT of 48–62 mol% displayed T g of 126°C–144°C, flexible tensile behavior, satisfactory tensile properties and reasonably good impact performance. Ternary PEPecBT copolyesters were also synthesized using 1,5-pentanediol as another diol comonomer to improve toughness of the materials.