Thermal dynamic relaxation and enthalpy distribution of an aromatic polyimide film: 6FDA-PFMB

Abstract

An aromatic polyimide, 6FDA-PFMB, was synthesized from 2,2'-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2'-bis(trifluoromethyl)-4,4'-diamino biphenyl (PFMB), in refluxing m-cresol at high temperature. The polyimide film possesses two relaxation processes (α and β ) above room temperature. The α-relaxation process is attributed to the glass transition, and the β -relaxation is the result of a sub-glass transition involving rotational motion in the PFMB diamine. An Arrenhius relation was utilized to investigate the β -relaxation and an activation energy E a, of 130kJmol −1 was determined. This value of the activation energy is close to the value calculated based on the relationship derived from absolute reaction-rate theory assuming a zero-entropy contribution to the relaxation process proposed by Starkweather. The distribution of relaxation times, or rather enthalpies, for the β -relaxation is obtained. The α-relaxation, however, obeys a WLF-type equation.