Among the many polymers with which the invention may be practiced are polyolefins such as low, medium and high density polyethylenes and polypropylene, polybutene-l, poly(dodecamethylene pyromellitimide), ethylene-propylene copolymers and terpolymers with non-conjugated dienes, polyvinylidine fluoride, polyvinylidine fluoride-tetrafluoroethylene copolymers, etc.