Abstract: | Poly(diethylsiloxane) and its copolymers with various kinds of R1R2SiO (R1 = R2 = methyl or phenyl, or R1 = methyl and R2 = phenyl) units have been prepared by the equilibrium polymerization of cyclosiloxanes. All the polymers have been characterized by 1H and 29Si 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 ?133 to ?137 °C according to DSC). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2722–2730, 2003 |