Phenylmaleimide-containing PET-based copolyester: cross-linking from 2π + π cycloaddition toward flame retardance and anti-dripping

• Published in: Polymer chemistry Vol. 7; no. 15; pp. 2698 - 2708
• Main Authors: Dong, Xue, Chen, Li, Duan, Rong-Tao, Wang, Yu-Zhong
• Format: Journal Article
• Language: English
• Published: 21.04.2016
• Subjects: Calorimetry; Combustion; Crosslinking; Cycloaddition; Gas chromatography; Mass spectrometry; Networks; X-ray photoelectron spectroscopy
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/C6PY00183A

The concept of incorporating cross-linkable precursor as the copolymerizing monomer has been proved efficient for polyesters to achieve low flammability and anti-dripping property. Adapting this concept, in our latest paper, a new co-monomer named 5-(2,5-dioxo-3-phenyl-2,5-dihydro-1 H -pyrrol-1-yl) isophthalic acid (DPDPI) was synthesized and incorporated into PET chain. Results from limiting oxygen index (LOI), UL-94 and the cone calorimetric test demonstrated that these PET- co -DPDPI copolyesters possess excellent flame retardance and anti-dripping performance. UL-94 V-0 rating could be achieved with a DPDPI content of as low as 10 mol% (PET- co -DPDPI10). Results from thermogravimetry-differential scanning calorimetry (TG-DSC) and dynamic oscillatory rheology proved the existence of the cross-linking behaviour during heat. The cross-linked polymer structures were stable at high temperature and could promote the char formation during burning. According to the results of Raman spectroscopy, X-ray photoelectron spectrometry (XPS) and pyrolysis/gas chromatography-mass spectrometry (Py/GC-MS), the cross-linking and flame-retardant mechanism were proposed for PET- co -DPDPI X , that during combustion, 2π + π cycloaddition which occurred between the phenylmaleimide groups as the cross-linking reaction. Afterward, the cross-linked networks promoted aromatization and carbonization, which resulted in self-extinguishing and anti-dripping.