Solvent Effects in Thermal Curing of Poly(4,4'-oxybis(phenylenepyromellitamic acid))

Abstract

Thermal curing of poly(4,4'-oxybis(phenylenepyromellitamic acid)) (PAA) films prepared from PAA solutions using a novel solvent system composed of tetrahydrofuran (THF) and methanol (MeOH) has been investigated. In the drying process of casted PAA films, MeOH was entirely evaporated, while a significant amount of THF remained in the dried film. The progress of thermal imidization was observed during the process of drying at 80 °C. NMR measurements for the dried film revealed that the thermal imidization of trans-amidized PAA predominated over that of cis-amidized PAA. Dynamic mechanical thermal analyses (DMTA) pointed out that the dried PAA film containing THF showed no significant plasticization during the thermal cure. This indicates the mobility of polymer chain would be low during the thermal cure so that the resulting polyimide film has a higher in-plane orientation. The coefficient of thermal expansion (CTE) of the polyimide film was found to be low compared with a film obtained from a PAA solution using NMP.

Preparation of Polyimides by Using Mixtures of Tetrahydrofuran and Methanol and Their Properties

“…1 These monomers were also frequently employed in studies devoted to PI synthesis using THF/MeOH mixed solvent. [3][4][5] Concentrations of solutions of polyimide precursors (PAA) in NMP for commercial and research purposes usually range from 10 to 15 wt%. Echigo 3,4 describes the preparation of a 15 wt% PAA solution based on the above mentioned monomers using THF/MeOH mixtures with composition ratio 4:1 (w/w).…”

“…[3][4][5] Concentrations of solutions of polyimide precursors (PAA) in NMP for commercial and research purposes usually range from 10 to 15 wt%. Echigo 3,4 describes the preparation of a 15 wt% PAA solution based on the above mentioned monomers using THF/MeOH mixtures with composition ratio 4:1 (w/w). During our polymerization tests PAA precipitated from the solution at concentrations higher than 5 wt% regardless of the THF/MeOH ratio of the two solvents.…”

“…It is thus apparent that PAA(THF/MeOH) retains these agents less tenaciously. Echigo 4 showed that THF remains in PAA films even after drying at 80 • C for 24 h, while a major part of MeOH is evaporated upon drying at 40 • C for 30 min.…”

“…2 From this point of view the preparation of PAA in the tetrahydrofuran/methanol mixed solvent (THF/MeOH) appears to be promising. [3][4][5][6][7][8] However, in our preliminary tests we were unable to reproduce the preparation of 15 wt% solutions of PAA based on pyromellitic dianhydride (PMDA) and 4, 4 -oxydianiline (ODA) in THF/MeOH with component ratio 4:1 (w/w) as described by Echigo et al 3,4 The reaction conditions of the preparation of PAA solutions (based on PMDA and ODA) in THF/MeOH mixtures and the transformation of the resulting PAA into PI are studied in this work. The properties of final films are compared with those prepared by using NMP as the solvent.…”

Polyimide-Epoxy Composites

“…These problems have been largely circumvented by employing a low boiling point solvent system developed by Echigo et al [82][83][84] containing tetrahydrofuran (THF) and methanol (MeOH) for the synthesis of polyamic acid. As seen by Gaw et al, THF/MeOH easily solvates both the polyamic acid and epoxy monomers forming stable solutions and is easily removed prior to cure [73].…”