Polysiloxanes living

Block copolymers containing polysiloxane segments are of great interest as polymeric surfactants and elastomers. Polycondensation and polyaddition reactions of functionally ended prepolymers are usually employed to prepare well-defined block copolymers. The living polystyrene anion reacts with a,co-dichloropoly(dimethyl-siloxane) to form multiblock copolymers398. ... 

Pyun, J. Xia, J. Matyjaszewski, K. Organic-Inorganic Hybrid Materials from Polysiloxanes and Polysilsesquioxanes Using Controlled/ Living Radical Polymerization. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 273—284. 

Polysiloxanes also possess a variety of other useful properties such as hydro-phobicity and exceptionally high permeability to gases. Indeed, snails can live submerged beneath the surface of low molecular weight poly(dimethylsiloxane)... 

This is a very important polymerization mode. Usually these polymerizations can be made to proceed by the living mechanism, even cationic. Important polymers are produced in this way (some polyamides, polysiloxanes, polyacetals, polyethers, polyimines, etc.). 

Cationic polymerizations are not only important commercial processes, but, in some cases, are attractive laboratory techniques for preparing well-defined polymers and copolymers. Polyacetal, poly(tetramethyl-ene glycol), poly(e-caprolactam), polyaziridine, polysiloxanes, as well as butyl rubber, poly(N-vinyl carbazol), polyindenes, and poly(vinyl ether)s are synthesized commercially by cationic polymerizations. Some of these important polymers can only be prepared cationically. Living cationic polymerizations recently have been developed in which polymers with controlled molecular weights and narrow polydispersity can be prepared. 

Half-lives (t g) were taken as estimates of catalytic effectiveness. The order of catalytic activity was 5 > 4 > 3b > 3a > 3c > 6, which is quite similar to the order for catalysis of hydrolysis of DPPC suspended in 0.5 M aqueous sodium bicarbonate (5 > 4 > 3b > 6 > 3a) (3). Clearly, the I-oxypyridinyl-substituted polysiloxane 5 was the most effective catalyst of those studied under both sets of conditions (1) DPPC and catalyst in dichloromethane-0.5 M aqueous sodium bicarbonate suspensions and (2) DPPC and catalyst in... 

In addition to the termination of living poly(dichlorophosphazene) with phos-phoranimine-terminated poly(dimethylsiloxane), another method has been presented to synthesize poly(phosphazene-siloxane) block copolymers. Hydrosilyla-tion reactions of hydride-terminated poly(dimethylsiloxane) and allyl-terminated polyphosphazenes (210a, 210b) have been shown to yield polyphos-phazene-h/ocfc-polysiloxane-h/oc/c-polyphosphazene polymers (21 la, 21 Ib). ... 

Grafting of Linear Functionalized Living Polysiloxane onto the SiOi-Particle Surface and onto Silica Hybrids... 

The hybrids were prepared by a coupling reaction between the living polysiloxane-bearing vinyl or diphenylphosphinoethyl groups bonded to silicon and having the lithium silanolate group at one chain end and the chloride group at the silica surface. 

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-... 

The grafting of the living vinylated polysiloxanes to the reactive groups (Si-Cl) on the silica sur ce occurs with a yield fiom 12 to 20%. In the same conditions, the polysiloxane bearing the phosphine groups is attached to the surface with a still low yield, about 14%. The characteristics of selected hybrids are presented in Table 1. Full details are described in Ref. [5]. 

Tetraalkoxysilanes can be converted to polysiloxanes in 1 h at 20°C, using a siloxane polymerase from a marine sponge.334 Many living organisms use such enzymes to produce shape-controlled silica skeletons. 

Other bifunctional initiators are the di-l,3-dioxolan-2-ylium cation 127) dicationic living polysiloxane 119) and ditetrahydrofuranium cations 128). 

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