Redistribution catalyst, ring/chain

As predicted by theory, the position of the ring/chain equilibrium was found to be independent of the nature of the redistribution catalyst employed (acid or base) (4,13,24- ) and of the specific inert solvent used (26). Russian authors (4,27) equilibrated mixtures of eyelosiloxanes comprised of dimethylsiloxane (75 mole %) and either trifluoropropylmethyl, cyanoethylmethyl, or cyanopropylmethyl siloxane (25 mole %) in acetone at a siloxane repeating unit concentration of 0.833 moles/A. They measured the dipole moments of the respective cyclosiloxanes, [(CH3)9SiO]3[Si(CH3)R0j>, to be 2.76 for R = trifluoropropyl, 3.45 for R cyanoethyl, and 3.58 in the case of R cyanopropyl. The equilibrium weight fraction of rings,... 

The reaction of chlorosilanes produces hydrolyzates consisting of cyclics and linears with hydroxy and/or chlorine ends, depending upon conditions. Silanol functional linears are easily obtained and can be end-capped by silylation. More pertinent to this discussion, however, is the nature of end blocks that result from siloxane redistribution reactions. Conversion of cyclosiloxanes to equilibrium ring-chain distributions affords chains with ends arising from the catalyst i.e., if KOH is used, the chains have ends bearing silanol and K silanolate functionality. Neutralization with CO2 and HjO then converts the silanolates to silanols. Alternatively, the equilibrates, as well as the above hydrolyzates, can be silylated to convert the silanols and silanolates to other kinds of ends. 

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