Vapor pressure and mean adsorption time of pyromellitic dianhydride and 4,4 '-oxidianiline

Thermogravimetry (TG) measurements taken at pressures ranging from 10(-1) t o 10(-3) Pa are used to calculate the vapor pressure of pyromellitic dianhy dride (PMDA) and 4,4'-oxidianiline (ODA). The vapor pressure calculated for PMDA is closely agrees with to those reported by Pethe et al., Elshazly an d Salem. For ODA, the calculated vapor pressure fits exactly on the curve o btained by Salem. The enthalpy is also calculated. The activation energy of desorption is found to be nearly equal to the enthalpy. The adsorption and desorption rates for both PMDA and ODA at various substrate temperatures a re also observed. The mean adsorption time, tau calculated for ODA is sever al orders of magnitude larger than that for PMDA. 1:1 doses of ODA and PMDA therefore produce imine bonds which lead to the formation of thermally uns table films.