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 ( ¹ H 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.