The molecular structure of interphases formed by chemically curing the polyamic acid of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) against meta-aminothiophenol (m-ATP)-primed silver substrates was determined using surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR). It was found that m-ATP was adsorbed dissociatively onto silver substrates through the sulfur atoms. When polyamic acid was deposited onto silver substrates pretreated with m-ATP, acid groups of the polyamic acid combined with amino groups of m-ATP to form ammonium carboxylate salts near the interphase. SERS and RAIR results indicated that the structure of the interphase was significantly different from that of the bulk polymer. Chemical curing of the polyamic acids located in the interphase was suppressed because of the formation of ammonium carboxylate salts. However, the bulk of the polyamic acid films was highly cured to form polyimide. It was also found that more isoimide groups were formed when thin polyamic acid films were chemically cured in acetic anhydride/pyridine solutions than in acetic anhydride/triethylamine solutions.