the organopolysiloxanes of this invention comprise repeating units consisting essentially of a five - membered ethylenically unsaturated heterocyclic ring containing a diorganosiloxane group bonded to the two cyclic carbon atoms adjacent to the hetero atom , which can be nitrogen , oxygen or sulfur . this invention encompasses homopolymers of said repeating units and copolymers comprising said units and diorganosiloxane units such as dimethylsiloxane . the present polymers are characterized by their high resistance to thermally induced degradation , and do not exhibit a significant weight loss at temperatures up to 300 degrees c .