Poly(diethylsiloxane) and its copolymers with various kinds of R 1 R 2 SiO (R 1 ϭ R 2 ϭ methyl or phenyl, or R 1 ϭ methyl and R 2 ϭ phenyl) units have been prepared by the equilibrium polymerization of cyclosiloxanes. All the polymers have been characterized by 1 H and 29 Si NMR, gel permeation chromatography, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) measurements. The results indicate that a random distribution of different units has been obtained in the structures of copolymers containing 50 mol % diethylsiloxane units content. DSC and DMA show that the presence of 2.5 mol % diphenylsiloxane units or 5.0 mol % methylphenylsiloxane units in the copolymer can disrupt the crystallinity and lead to noncrystalline copolymers with low glass-transition temperatures (ranging from Ϫ133 to Ϫ137°C according to DSC).

No abstract