Synthesis and Non-Isothermal Crystallization Characteristics of Poly[(ethylene)-co-(trimethylene terephthalate)

Abstract

A series of random copolyesters were synthesized by the bulk polycondensation of dimethyl terephthalate with ethylene glycol (EG) and trimethylene glycol (TMG) in various compositions. Their composition, molecular weight, and thermal properties were determined. The copolymers containing 22.2 mol-% ≤ TMG ≥ 46.0 mol-% are crystallizable while the other copolymers containing 32.8 mol-% ≤ TMG ≤ 39.3 mol-% are amorphous. Non-isothermal crystallization exotherms were measured over the cooling rate of 2.5–20.0 K/min by calorimetry and analyzed by the Avrami method. For the crystallization at 2.5 K/min, the Avrami exponent n was estimated to be in the range of 2.91–3.81, depending on the composition. The results suggest that the primary crystallization follows a heterogeneous nucleation and spherulitic growth mechanism. However, when the cooling rate increases and the content of the minor component unit (EG or TMG) increases, the crystallization behavior becomes deviated from the prediction of the Avrami analysis, which is due to the involvement of secondary crystallization and the achievement of relatively low crystallinity. The crystallization rate is accelerated by increasing cooling rate but retarded by incorporating the minor component into the polymer backbone. In addition, the activation energy in the crystallization was estimated.