Polydimethylsiloxanes alkyl groups

Polydimethylsiloxane, hexadimethylsilazane, and polymethylmethacrylate are also added to increase the flexibility and elasticity of polymer. The adhesive can be made plasticizer-free by using a composition of polymers containing a mixture of alkyl groups from Cj to Cg. The use of suitable proportions of different monomers gives the required... 

In Fig. 2.7, Rt and R2 are either simple alkyl or aryl chains (methyl or phenyl) or incorporate functional groups (e.g. cyanopropyl, trifluoropropyl). Combined in different proportions, Ri and R2 modify the polarity and the characteristics of the columns. One of the processes used to obtain a bonded polydimethylsiloxane phase is to allow a solution of tetradimethylsiloxane to flow through the column, then heat to 400 °C after evaporation of solvent and closure of the the extremities (Fig. 2.7). 

The most extensive group of ether surfactants is that of polyethoxylated long-chain alcohols and related ethoxylated products considered, in view of their practical importance, in a separate section. Other ether nonionics of importance are polypropylene glycols, propoxylated alcohols, block-copolymers of ethylene oxide and propylene oxide, block-copolymers of ethylene oxide and butylene oxide [8, 16-20], block-copolymers having a hydrophobic polydimethylsiloxane moiety [19, 21], as well as alkyl polyglycerides, alkyl polyglycosides, derivatives of maltose and other saccarides. 

Substitution of some of the methyl groups of polydimethylsiloxanes by alkyl or aryl groups gives products with somewhat better compatibility but still high surface activity. Figure 4 shows typical structures with z equals zero R can be alkyl or arylalkyl. 

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