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6834405 
Book/Book Chapter 
25 - Polymerization of Cyclosiloxanes 
Kendrick, TC; Parbhoo, BM; White, JW 
1989 
Pergamon 
Amsterdam 
Comprehensive Polymer Science and Supplements 
459-523 
The cyclodiorganopolysiloxanes (1) are one of the two principal classes of siloxane intermediate used in the manufacture of siloxane polymers. The other is short chain linear α,ω-polydisiloxanols (2). Both are formed simultaneously during the hydrolysis of the appropriate diorganodichlorosilane. The cyclosiloxane fraction can be separated from the linear polysiloxanols by simple flash distillation. Ring-opening polymerization of the cyclosiloxanes, which can be effected by both basic and acidic catalysts, produces high molecular weight linear polymers. Molecular weight control is obtained by the use of hexaorganodisiloxanes (3), which act as chain transfer agents. The polymerization with both catalyst systems is a complex equilibrium polymerization and comprises a series of competing reactions involving both cyclic and linear species as represented below (equations 1–5) for octamethylcyclotetrasiloxane (D4) and hexamethyldisiloxane (M2). 
Bevington, John C.