Synthesis and Nonisothermal Crystallization Kinetics of Poly(Butylene Terephthalate-co-Tetramethylene Ether Glycol) Copolyesters

Poly(butylene terephthalate-co-tetramethylene ether glycol) (PBT-co-PTMEG) copolymers with PTMEG ranging from 0 to 40 wt% were synthesized through melt polymerization. The structure and composition were supported by Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (¹H NMR). All samples had excellent thermal stability at a T_d-5% around 370 °C. Crystallization temperature (T_c) and enthalpy of crystallization (ΔH_c) were detected by differential scanning calorimetry (DSC), revealing a decrement from 182.3 to 135.1 °C and 47.0 to 22.1 J g^-1, respectively, with the increase in PTMEG concentration from 0 to 40 wt%. Moreover, nonisothermal crystallization was carried out to explore the crystallization behavior of copolymers; the crystallization rate of PBT reduced gradually when PTMEG content increased. Hence, a decrement in the spherulite growth rate was detected in polarizing light microscope (PLM) observation, observing that the PTMEG could enhance the hindrance in the molecular chain to lower the crystallinity of PBT-co-PTMEG copolyester. Moreover, thermal properties and the crystallization rate of PBT-co-PTMEG copolymers can be amended via the regulation of PTMEG contents.

The effect of crystallization properties influenced by 2-methyl-1,3–propanediol units on the optical properties of modified poly(ethylene terephthalate)

In this study, the preparation and properties of poly(ethylene terephthalate-co-2-methyl-1,3-propanediol) copolyester (PEMT) were reported. The PEMT crystallization properties, optical properties, thermal properties, rheological properties, and other properties were characterized by nuclear magnetic resonance (1H NMR), differential scanning calorimetry, thermo gravimetric analysis, ultraviolet visible near-infrared (UV-VIS-NIR) spectroscopy, polarizing microscope crystal culture, X-ray diffraction (XRD), and rheometer. It was proved that the crystallization abilities and crystallization rate of PEMT copolyesters were significantly affected by the content of 2-methyl-1,3-propanediol (MPO) units; the copolyester becomes amorphous when the content of MPO units exceeded 20 mol%. According to the XRD data, the diffraction peaks of PEMT remained unchanged compared with those of poly(ethylene terephthalate). The transmittance of copolyesters displayed a tendency of increasing at first and then declining with the increase in MPO. In addition to the crystallization properties, the transmittance of copolyesters was also affected by the extent of yellowing. When the MPO addition was less than 20 mol%, PEMT can maintain good thermal decomposition performance and processability.