Nadimide substituted fluorinated polyphosphazenes: synthesis and characterizations

Abstract

Synthesis of nadimide substituted fluorinated polyphosphazenes, i.e., PPZ (viz. PPZ-1 containing N-(4-hydroxyphenyl) chlorendimide, PPZ-2 containing N-(4-methylphenyl) nadimide and PPZ-3 containing N-(4-hydroxyphenyl) methyl nadimide) was carried out by substituting the chlorine atoms of polydichlorophosphazene by sodium salts of different nadimide derivatives and trifluoroethanol, and then their structural properties were corroborated by gel permeation chromatography, FTIR and NMR analysis. Their thermal analysis was performed with the help of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC showed the initiation in the decomposition of uncured PPZ resins after their melting which might be due to the commencement of retro-Diels–Alder reaction in the norbornene moieties present in the structure of uncured resins. Moreover, the TGA of uncured PPZ resins inferred that their decomposition temperatures were in the order of PPZ-1 < PPZ-2 < PPZ-3 because of the relative stabilities of differentiating bonds or groups present in their structures. The curing of PPZ resins was further done using AIBN to enhance their thermal stabilities. The TGA of cured resins showed rise in their onset decomposition temperatures range from 240–294 °C to 405–455 °C, and final decomposition temperatures range from 350–415 °C to 555–598 °C due to the formation of cross-linked networks. Curing also enhanced the % char yield of PPZ resins by 45 ± 3%. Similar trend in the stability of PPZ resins, i.e., PPZ-1 < PPZ-2 < PPZ-3 was shown by the isothermal aging analysis. Besides this, water uptake properties of PPZ resins were investigated to study the extent of water absorption by them which exposed the highest water uptake for PPZ-1 and lowest for PPZ-3. The wettability of PPZ resins was also evaluated by calculating their water contact angles which supported the trend of their water uptake behavior.