Kinetic study of free volume changes occurring in films during thermal imidization of polyamic acid

The positron annihilation method has been used to evaluate free volume changes in films prepared from polyamic acid by thermal imidization. The method proved to be fruitful as a means of determination of the size of micropores, and for evaluating fluctuation free volume in the polymers. The positron annihilation method is also suitable for use in studies of the mechanism of formation of polyimides at the supermolecular level.