Studies On Polysiloxanes Containing Chloromethyl Groups

Polysiloxane has been made very rapid development in recent years, and a series of functional polysiloxanes with special structures have got a major success in both laboratory research and industrial production. Functional polysiloxanes not only maintain the original excellent performance of general polysiloxanes, but aslo have some other special properties. For instance, the functional groups could react with other compounds, some functional polysiloxanes could be cured through the new crosslinking system, and some have biological activities.This paper studied the synthetic methods and thermal stability of the functional polysiloxanes containing chloromethyl groups, including the following three main aspects of work content:1. Through the hydrolysis and polycondensation reaction of dichlorodimethylsilane and chloromethyldichloromethylsilane, we got low molecular weight functional polysiloxanes containing chloromethyl groups. And cyclosiloxanes were obtained by vacuum distillation, whose structures were characterized and analyzed by IR and1HNMR. It was found that controlling the feed ratio of dichlorodimethylsilane and chloromethyldichloromethylsilane to3:1, the proportion of cyclotetrasiloxane containing chloromethyl groups would be the highest among the products. We studied the effect of synthesis method, hydrolysis medium and materials adding order on the yields, and optimized the method of preparation of functional polysiloxanes containing chloromethyl groups through hydrolysis and polycondensation reaction.2. Through the ring opening copolymerization reaction of chloromethylheptamethylcyclotetrasiloane and octamethylcyclotetrasiloxane, we prepared a series of polysiloxanes containing chloromethyl groups with different chloromethyl group contents and molecular weights. Their structures were characterized by IR and1HNMR, molecular weight was determined by GPC, and the viscosity coefficient was measured with Ubbelohde viscosity meter. But in the process of research, It was found that silanolate of tetramethylammonium which is the most commonly used catalyst in the preparation of polysiloxanes was not suitable to the synthesis of functional polysiloxanes containing chloromethyl groups. So we used acidic catalysts trifluoromethane sulfonic acid and Purolite CT-175instead. An effective way for preparing polysiloxane containing chloromethyl groups was found.3. Functional polysiloxanes with different molar content of chloromethyl groups were synthesized by hydrolysis and polycondensation reactions. Thermogravimetric analysis (TGA) of these functional polysiloxanes was carried out in inert atmosphere by using the multiple-heating rate method. The kinetics parameters of thermal decomposition of polysiloxanes containing chloromethyl groups, the apparent activation energy (Ea) and the apparent pre-exponential factor (A) during different temperature ranges were calculated by the single-heating rate technique (Coats-Redfern) and the multiple-heating rate techniques (Kissinger and Flynn-Wall-Ozawa). The effect of the molar content of chloromethyl groups on the thermal decomposition behavior of the polysiloxanes was also investigated. It was found that the thermal stability of the functional polysiloxanes containing chloromethyl groups decreased with the increasing of the molar content of chloromethyl groups.