A Novel Bio‐Based Isosorbide Polyterephthalate Modified by 1,4‐Naphthalenedicarboxylic Acid With High Heat‐Resistant Performance

To improve the heat‐resistant performance of bio‐based isosorbide polyterephthalate, 1,4‐naphthalenedicarboxylic acid (NDA) was used as a third monomer to prepare poly(isosorbide terephthalate‐co‐isosorbide 1,4‐naphthalenedicarboxylate) (PITN). The properties of PITN were characterized by FTIR, NMR, DSC, TGA, dilute solution viscosity, X‐ray diffraction, saponification value, and degradation rate. The results show that the naphthalate units are successfully introduced into the PITN molecular chain, forming an amorphous structure. The saponification value is decreased from 158.948 mg KOH/g to 119.674 mg KOH/g when the NDA content increases from 0% to 25%. As the NDA content is increased from 0% to 10%, the viscosity‐average molecular weight increases from 28,479 to 35,812 g/mol, while it decreases to 18,458 g/mol for 25% NDA. When the NDA content is 15%, the initial thermal decomposition temperature of PITN reaches 374.8°C, and the maximum thermal decomposition temperature reaches 419.4°C with the residual mass at 550°C of 21.94%, which indicates that thermal stability of PITN is significantly enhanced. When the NDA content is 25%, the acid weight loss rate of PITN is 1.22%, and the alkaline weight loss rate is 1.86% for 15% NDA content, showing good acid and alkali resistance. The rigid structure of the naphthalene ring can significantly improve thermal stability and degradation stability of copolyester.