Preparation, structure characterization, and thermal performance of phenyl-modified MQ silicone resins

Methyl- and phenyl-modified MQ resins have been prepared by cohydrolysis and condensation-polymerization of the prepolymer of sodium silicate with SiO2/Na2O = 3.33 using the ethanol solution of hexamethyldisiloxane (MM), 1,1,3,3-tetramethyl-1,3-divinyldisiloxane (TMDVS), methyldiphenylethoxysilane (MDPES), dimethylphenylethoxysilane (DMPES), or their dimers. The influence of different end-capping agents on the composition and properties of the MQ resins has been investigated. Thermogravimetric analysis and differential scanning calorimetry results indicate that when the MQ resins are end capped with DMPES instead of MDPES, the resins were more easily purified and almost no high boiling point residuals were found in the phenyl MQ resins. The refractive indexes of the MQ resins were significantly affected by the phenyl group and their values could be adjusted by changing the amount of DMPES. The structures of the resins were characterized by 1H-NMR and FTIR spectroscopy. The M/Q ratios in the prepared MQ resins were calculated from the 1H-NMR spectra or from elemental analysis or both. The M/Q values obtained agreed well with the changes of appearance and thermal stabilities of the MQ resins. The thermal stabilities of the MQ resins were greatly enhanced when DMPES was used. Phenyl-modified MQ resins were in the form of white powders due to the rigidity of the phenyl group while methyl MQ resins exhibited a range of appearances, from transparent liquids to white powders, with the reduction of M/Q values. The method developed to calculate the M/Q values is useful for the characterization of MQ resins and their derivatives. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013