Effect of Structure and Additives on Thermal Stability of Silicone Fluids

A series of polydimethylsiloxane (PDMS) polymers and poly(dimethyl-diphenyl siloxane) (PDMS-PMPS) copolymers were synthesized by the anionic ring-opening polymerization method and then blended with titanium isooctoate as thermal additives. Their thermal stabilities have been investigated by TGA in an inert gas atmosphere. The temperature for 10% conversion, 50% conversion, and the temperature for the maximum rate of decomposition (MRDT) initiated from TGA curves recorded at a heating rate of 5, 10, 15, and 20 degrees C min(-1) and the apparent activation energy E(a) using the FWO method as a function of conversion alpha indicated that the thermal stabilities of the polysiloxanes could be enhanced either by modifying the structure of the polymer or by introducing a certain amount of a thermal additive. PDMS-PMPS copolymers with a MePhSiO segment content of 10.2 mol % and terminated by diphenylmethylsiloxyl groups exhibited optimal heat resistance. The thermal stabilities of the polysiloxanes could be further improved by introducing homogenous titanium additives and with the addition of 1550 ppm content of titanium additives, the temperature for 10% conversion, the temperature for 50% conversion, and MRDT have been found to be increased by 20.11, 71.28, and 98.67 K, respectively, relative to the unmodified PDMS-PMPS copolymer. Fourier transform infrared (FTIR) analysis has proven the formation of a Si-O-Ti bond in the titanium-modified PDMS-PMPS copolymer, which may be responsible for the efficient enhancement of its thermal stability. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2530-2537,2010