and n are as previously defined; copolymers of the formula: ##STR7## wherein R and n are as previously defined; and copolymers derived from at least two monomers from which the above polymers are derived; and wherein B is a pharmaceutically or veterinarily acceptable hydrophilic polymer selected from the group consisting of polyvinylalcohol, polyvinylpyrrolidone, polyethylene glycol, polyacrylami