Ring-opening polymerization polysiloxanes

Base and acid catalyzed ring opening polymerization of cyclotri-siloxane, -[Me2SiO]3- [e.g. reaction (10)], is a well-known method of generating high molecular weight polysiloxanes. 

Ring-opening polymerization of cyclic siloxanes with cationic initiators allows the possibility of introducing stable end groups by the use of suitable chain transfer agents. Thus, polysiloxanes with trimethylsilyl end groups are formed when the cationic polymerization of octamethylcyclotetrasiloxane is carried out in the presence of hexamethyldisiloxane as transfer agent ... 

Ring-Opening Polymerization of a Cyclic Oligosiloxane to a Linear, High-Moiecuiar-Weight Polysiloxane with Hydroxy End Groups Curing of the Polymer... 

There are several reports in recent literature on the application of silicon-containing compounds as the initiators of cationic ring-opening polymerization. This apparently is related to the attempts to prepare block copolymers containing polysiloxane or polysilane segments. (CfL SiCFAgClCL system was used to initiate cationic polymerization of tetrahydrofuran... 

Elastomers and nonsilanol terminated fluids are produced by base-catalyzed polymerization of low-molecular weight siloxanes. Polydimethylsiloxanes are also produced by ring opening polymerization of D3, D4, and D5. In the presence of MM or MDDM (endcapper), silicones MD M are formed otherwise, silanol terminated polysiloxanes may be obtained. 

The living polysiloxanes having various densities of vinyl groups were obtained by anionic living ring-opening polymerization of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane (V3) or by copolymerization of this monomer with hexamethylcyclotrisiloxane (D3) or with 2-vinyl-2,4,4,6,6-... 

In addition to step and chain polymerizations, another mode of polymerization is of importance. This is the ring-opening polymerization of cyclic monomers such as cyclic ethers, esters (lactones), amides (lactams), and siloxanes. Examples of commercially important types are given in Table 10.1. Of those listed, only the polyalkenes are composed solely of carbon chains. Those that have enjoyed the longest history of commercial exploitation are polyethers prepared from three-membered ring cyclic ethers (epoxides), polyamides from cyclic amides (lactams), and polysiloxanes from cyclic siloxanes. 

The proposed scheme includes liberation of polysiloxanes from the growing chain ends. At the time when this result was published, but more frequently much later, other examples of such behaviour were observed in ring-opening polymerization [321] and the effect was named back-biting reaction. 

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