WATER RESISTANCE OF POLY(IMIDE-SILOXANE) ADHESIVES - DIFFUSION-COEFFICIENTS BY GRAVIMETRIC SORPTION

Diffusion coefficients of water vapor in a polyimide homopolymer and p oly(imide-siloxane) multi-block copolymers of different siloxane conce ntration were determined from gravimetric sorption experiments. Diffus ion coefficients were of the order of magnitude of 10(-8) cm(2)/sec. H igher levels of siloxane incorporation caused a definite increase in t he diffusion coefficient, indicating a decreased resistance to water i ngression. The increase in diffusion was found to be influenced by sil oxane block length and was interpreted in terms of free volume and mor phology. The diffusion coefficient of the 10-weight-percent PDMS copol ymer, however, was found to be the same within error as that of the po lyimide. This and a previous surface study suggested that an increased surface water resistance may be achieved at low siloxane concentratio ns without greatly increasing the bulk diffusive properties to undesir able levels.