Photocatalyzed ring-opening polymerization of 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB) by Pt(acac)(2) is reported. Excellent conversion and high molecular weight polymers are produced in the absence of O-2. Inhibition experiments reveal the coexistence of both homogeneous and heterogeneous catalytic species. The relative activity of these is discussed and a tentative polymerization mechanism proposed. Pt colloid is proved to be the heterogeneous catalyst by a TEM study.