FORWARD RECOIL SPECTROMETRY STUDY OF THE DIFFUSION OF PMDA ODA-BASED POLY(AMIC ETHYL-ESTERS)/

The poly(amic ethyl esters) (PAEs) of pyromellitic dianhydride/4,4/-ox ydianiline (PMDA/ODA) were prepared in three isomeric forms, with meta -linkages, para-linkages and randomly alternating meta-and para-linkag es (referred to as mixed PAEs). In addition to the normal PAEs (which contained only hydrogen and which were cast as base layers for diffusi on studies), each of these isomeric PAE was synthesized in two other f orms: (1) labelled with deuterium on the ODA segments, and (2) labelle d with deuterium on the ethyl ester moiety to allow determination of t he imide fraction, f. Forward recoil spectrometry (FRES) was utilized to provide information about the polyimide-polyimide interface by meas uring the depth profile of hydrogen and deuterium for bilayer samples consisting of a thick non-deuterated base layer, and a thin deuterated tracer layer. FRES measurements indicated that the interdiffusion dis tance, w, decreased markedly with increasing imidization temperature, T-i. For base layers prepared from N-methylpyrrolidone, w for the para -and mixed PAE base layers decreased more rapidly with T-i than with w for the meta-PAE base layers. However, these differences were found t o result from the differences in imidization kinetics of the various i somers with I increasing more rapidly with T-i for para-and mixed PAE than for the meta-PAE. Nevertheless, when w was plotted as a function of f, all of the isomers exhibited similar behaviour, i.e. w decreased steadily as the imide fraction f approached 1. Base layers cast from dimethyl sulfoxide did not show differences in either f or w after imi dization at a given T-i. (C) 1997 Elsevier Science Ltd.