SYNTHESIS OF POLYAMIC-ACIDS WITH CONTROLLED MOLECULAR WEIGHTS.

Abstract

A series of polyamic-acid polymers with varying molecular weight have been prepared by condensation of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) in N-methylpyrrolidone (NMP). Polyamic-acid solutions between 10-20 wt% total solids content were prepared under highly controlled conditions. Molecular weights, which were determined by light scattering, were in good agreement with those calculated from the monomer stoichiometric imbalance according to classical step growth behavior. This behavior held for polymerizations carried out at solids contents of less than 10 wt% and was unaffected by the monomer addition sequence, provided the functionality used in excess was initially present as a homogeneous solution. At higher solids contents, noticeable deviation from the theoretically calculated molecular weights were observed. Possible mechanisms for this behavior are discussed along with ways to remedy this problem.