Foamed polysiloxanes with poly

An important route to the production of foamed polysiloxane rubbers relies on the use of a low molecular weight silicone gum and on a series of tin catalysed cure and gas formation reactions. Normally, a dihydroxy terminated poly dimethylsiloxane containing a small amount of silica filler, together with a polyfunctional crosslinking agent (e.g. tetrapropylsilicate), is used as the starting material. 

Surfactants based on block copolymers of dimethylsiloxane with poly(ethylene oxide) are unique in regulating the cell size in polyurethane foams. One route to such polymers uses reaction I.E in Table 17.6 between a polysiloxane and an allyl ether of polyethylene oxide [11], Increasing the silicone content makes the surfactant more lipophilic (oil-loving), whereas increasing the poly(ethylene oxide) content makes it more hydrophilic (water-loving). 

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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