Octamethylcyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane were ring opening polymerized to prepare vinyl terminated poly(dimethyl-co-methylvinyl)siloxane and the effect of the reaction conditions on the molecular weight, the reaction yield, the structure, and the composition of the copolymer was studied. When excess end capping agents are added and the reaction is carried out under a condition where its reaction is favorable, ring opening occurs rapidly and high reaction yield and low molecular weight products can be obtained. When the reaction temperature is set far from the activation temperature of the end capping agent, relatively high molecular weights can be obtained, however, the time required for ring opening increases and the reaction yield decreases significantly. At 120 °C where the ring opening occurs relatively stably, minimizing the amount of end capping agent increased the molecular weight and the reaction yield simultaneously. Due to the lower reactivity of octamethyl-cyclotetrasiloxane relative to 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, at lower copolymerization temperatures the content of dimethyl siloxane block in the copolymer is lower than the feed composition and the product is mainly random copolymers.

八甲基环四硅氧烷与 1,3,5,7-四甲基-1,3,5,7-四乙烯基环四硅氧烷开环聚合制备乙烯基封端聚（二甲基-共聚）-甲基乙烯基)硅氧烷以及反应条件对共聚物的分子量、反应产率、结构和组成的影响。当加入过量封端剂并在有利反应条件下进行反应时，开环速度快，反应收率高，分子量低。当反应温度远离封端剂的活化温度时，可以获得较高的分子量，但开环所需的时间增加，反应产率显着下降。在开环相对稳定的 120 °C 下，最小化封端剂的量可同时增加分子量和反应产率。