Foamed polysiloxanes synthesis

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

Not all copolymers which are produced by step-growth processes are random in nature. Block copolymers are also of major interest. An example of the synthesis of elastic polyurethane fibers was given in Section 1.5.4. Block and graft copolymers of polysiloxane-poly(alkylenc ethers) with segments like5-9 are used as surfactants in the production of polyurethane foams with uniform cell sizes. 

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