Promotion of Thermal Imidization of Semi-Aliphatic Polyimide Precursors by Incorporation of Polyethylene Glycol and Their Modified Solid Structures

Abstract

Thermal imidization reaction of semi-aliphatic poly(amic acid)s (PAAs) prepared from four different semi-aliphatic dianhydrides and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) was effectively promoted by adding a low-Mw polyethylene glycol (PEG) into the PAAs solutions. The noticeable reduction of imidization temperature is attributable to the plasticizing effects of PEG on the PAA chains. The molecular motions of PAA chains are maintained at elevated temperatures owing to the high decomposition and evaporation temperatures of PEG. Moreover, birefringence and refractive index measurement revealed that more isotropic chain-orientation and dense molecular packing were formed in the PI films cured with PEG. The modified solid structures lead to the better physical properties especially for optical and photonic applications.

The Synergistic Effect of Triazine and Phosphaphenanthrene Units on the Physico-Chemical Behavior of Polyimides

“…We presumed that when polyamidic acids were formed, certain intermolecular interactions occurred between the carboxylic acid units from the main chains and DOPO pendant unit (through –OH and P=O), which impeded the formation of a fully-cyclized polyimide, despite the long reaction times and catalyst used in the polycondensation reactions. The incomplete cyclization of the intermediary polyamidic acids to the corresponding fully cyclized polyimide forms is a known phenomenon encountered for polyimides bearing bulky pendant groups where a 100% degree of imidization is rarely found [ 47 , 48 ].…”