The polymers such as polyvinyl alcohol, polyvinyl butyral, copolymers of hydroxyethyl methacrylate, copolymers of methacrylic acid, copolymers of maleic anhydride and similar polymers containing reactive sites along the polymer backbone or on pendent groups are crosslinkable by condensation and addition reactions such as esterification, urethane formation, amide formation, imide formation, when th