Effect of thermal imidization and curing on fluorescence behavior of a phenylethynyl-terminated poly(amic acid)

Abstract

The imidization and cure reaction of a thermosetting phenylethynyl-terminated amic acid (LaRC PETI-5) in film form have been monitored as a function of temperature by means of a steady-state fluorescence technique using a front-face illumination method. The variation of the fluorescence emission spectra of LaRC PETI-5 can be divided into four temperature regions; Region I: below 150 ο C, Region II: 150-250 ο C, Region III: 250-350 ο C, and Region IV: above 350 ο C. The fluorescence spectra in Region I are largely influenced by residual N-methyl-2-pyrrolidinone in the polymer and also slightly by partial imidization of the polymer. There is a combined effect of imidization and solvent removal on the fluorescence behavior in Region II. The spectra in Regions III and IV are due significantly to the cure reaction of LaRC PETI-5 and to a post-cure effect of the polyimide, respectively. This spectroscopic evidence indicating the transformation of the amic acid imide oligomer into the corresponding polyimide via imidization and cure, agrees well with thermal analysis results obtained previously. The intermediate stage of cure in the range of 250-300 ο C predominantly influences the change of the fluorescence intensity. The later stage above 300 ο C significantly influences the position of the spectrum. This fluorescence study also supports the mechanism proposed in earlier work that the crosslinking reaction takes place at the reaction sites in the conjugated polyene and the phenylethynyl end group in the polyimide chain.

A Universal Study on the Effect Thermal Imidization Has on the Physico-Chemical, Mechanical, Thermal and Electrical Properties of Polyimide for Integrated Electronics Applications

“…The plot of wavelength at maximum intensity vs. curing temperature exhibits a red shift with increasing curing temperature (Figure 3f). As described by Donghwan et al in their study on the effect thermal imidization and curing has on the fluorescence behavior of a phenylethynyl-terminated poly(amic acid) [57], this red shift is most likely related to a decrease in the intermolecular distance due to enhanced CTC formation in the polymers cured at higher temperatures. This is in agreement with the conclusion we drew from the optical properties and UV-Vis spectra of the films investigated in this study.…”

The effect of cure history on the fluorescence behavior of an unsaturated polyester resin with a fluorescence probe

“…Among analytical methods, a fluorescence technique is very powerful to explore the cure behavior based upon molecular and photophysical information involved in changes of local viscosity, chain mobility, micro-environment, and complexation between an intrinsic or extrinsic fluorophore and polymer chains, relying on a time/ temperature profile during cure process. [11][12][13] Fluorescence measurement is also relatively simple, highly reliable, and rapid for data acquisition. In addition, this method is nondestructive and possible to on-line monitor the cure process, which is significantly influenced by a temperature/time profile.…”

“…A number of papers have been reported that the cure behavior of thermosetting resins such as epoxy, 10,14 polyimide 13,15 and polyurethane 16 can be effectively monitored by means of a steady-state fluorescence technique using probed or labeled molecules with fluorescing moieties. This is possible because probed or labeled molecules, which have strong absorption and emission in the ultraviolet region, are very sensitive to the local mobility of molecules that decrease with increasing the degree of cure and viscosity.…”