Novel alpha,w-divinyloligodiphenylsiloxanes (1,9-divinyldecaphenylpentasiloxane, 1,7-divinyloctaphenyltetrasiloxane, 1,5-divinylhexaphenyltrisiloxane, and 1,3-divinyltetraphenyldisiloxane) were prepared and copolymerized by Pt-catalyzed hydrosilylation with a,alpha,w-dihydridopentasiloxanes. The molecular weights of the copolymers were measured with gel permeation chromatography, and their thermal properties were characterized with differential scanning calorimetry and thermogravimetric analysis. The polymers had high thermal stability in air and nitrogen. The oligomer and polymer structures were determined with H-1, C-13, F-19, and Si-29 NMR and IR spectrometry. The molecular weights of the oligomers were measured with high-resolution mass spectrometry. (c) 2005 Wiley Periodicals, Inc.