ON AMIDE EXCHANGE-REACTION OF POLYIMIDE PRECURSOR

The reaction of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and oxydianiline (ODA) with 1-aminopyrene (APy) in solution as a model of amide exchange reaction between PAAs was studied in the temperature range of 0-60-degrees-C using viscometry and light-scattering (LS) measurements. The decrease in the weight-average molecular weight (M(w)BAR) of PAA in N,N-dimethylacetamide (DMAc) solution with time and the acceleration of M(w)BAR drop due to the increase in storage temperature or the addition of APy into PAA solution were observed. Apparent activation energies (E(a)) for scission of PAA chains were similar: about 13 kcal/mol in PAA/DMAc and PAA/APy/DMAc, respectively. When stored at 60-degrees-C for a week, the number of scissions per polymer chain in PAA/DMAc is about 2, but is about 5 in PAA/DMAc with a large amount of APy. The result indicates that the M(w)BAR drop accelerated by the addition of APy is attributed to amide exchange reaction between PAA chains and monofunctional APy. It was concluded from the dependence of M(w)BAR drop on APy concentration that the exchange reaction between different PAA molecules during storage of PAA/PAA solution may scarely occur under the conditions (storage time and temperature) used for preparation of PAA/PAA blends.