Polymers of monolefins and diolefins, for example polypropylene, polyisobutylene, polybut-1-ene, polymethylpent-1-ene, polyisoprene or polybutadiene, and polymers of cycloolefins such as cyclopentene or norbornene, and also polyethylene, e.g. high density polyethylene (HDPE), low density polyethylene (LDPE) or linear low density polyethylene (LLDPE).