2,2,4.4,6,6-Hexamethylcyclotrisiloxane polymerization

The present observations could well be explained on the same basis since hexamethylcyclotrisiloxane polymerizes via both anionic and cationic mechanisms (5). (No evidence exists to date for free radical polymerizations.) The greater activity of H2O as an inhibitor, as compared with NH3, is explained on the basis of a more rapid ion transfer. Since this would be a hydrogen ion rather than a hydride ion, it further suggests an anion as the primary polymerization species in the present polymerization. The authors feel, however, that further work is required before definite conclusions can be drawn regarding the polymerization mechanism or mechanisms. 

Poly (dimethyl siloxane) obtained by anionic ring-opening polymerization of hexamethylcyclotrisiloxane (D3) can also be end-capped with vinylbenzyl bromide or other electrophiles, such as p. (chlorodimethylsilyl)styrene80). 

Boileau and coworkers11 have used a novel trimethylsilylmethyl lithium initiator MesSiCTDLi (1), in combination with a cryptand [211], for the ring-opening polymerization of cyclosiloxanes. Initiation of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) polymerization has been followed by H, 7Li, 13C and 29Si NMR. 

Cyclic siloxanes can undergo a ring-opening polymerization that is a chain-growth process. Free radicals are not useful as initiator species, because of the nature of the siloxane bond, but anionic and cationic initiators are very effective. The reaction is illustrated using the most common cyclic oligomers, the trimer hexamethylcyclotrisiloxane... 

Hexa(—)menthyldistannane, preparation, 3, 856 Hexamethylbenzenes, with titanium, 4, 246 Hexamethylcyclotrisiloxane, in polymerization, 3, 654 Hexamethyldigermane, terminal alkyne reactions, 10, 747 1,1,2,2,3,3-Hexamethylindane, metallation, 9, 15—16 Hexanuclear arenes, in hexaruthenium carbido clusters,... 

Dispersion Polymerization. AB block copolymer stabilizers were prepared using anionic polymerization techniques by the addition of hexamethylcyclotrisiloxane to "living" polystyryl-... 

The macromonomer method was used by Fujimoto et al. for the preparation of (PS)(PDMS)(PtBuMA) stars [53], as described in Scheme 20. The lithium salt of the p-(dimethylhydroxy)silyl-a-phenyl styrene was synthesized and used as initiator for the polymerization of hexamethylcyclotrisiloxane (D3). Living PS chains were reacted with the end double bond of the macromonomer, followed by the anionic polymerization of the f-BuMA. 

Polymerization of hexamethylcyclotrisiloxane with 3-butadienyllithium afforded butadienyl-ended polysiloxane macromonomer,20 [27], Polycondensation of a chiral methyl (3-hydroxyisobutyrate at a temperature higher than 150 °C with Ti(0-nBu)4 afforded directly a biodegradable polyester macromonomer, 21 [28]. 

The exterior of carbosilane dendrimers can also serve as initiator sites for polymerization, in which case the dendrimers serve as cores for star polymers. Vasilenko and coworkers95 synthesized a multilithiated carbosilane dendrimer which they then used as an initiator for the ring-opening polymerization of hexamethylcyclotrisiloxane to yield star polymers of narrow weight distribution (Scheme 7). The researchers later extended this work to polymerize styrene, isoprene and ethylene oxide96,97. Star poly(ethylene oxides) were also prepared using hydroxy-terminated carbosilane dendrimers as the core98,99. 

A system where good evidence exists that oligomers are formed directly from monomer is that of the cationic polymerization of hexamethylcyclotrisiloxane (45). Apart from polymer of molecular weight 10s, a mixture of all cyclic siloxanes with ringsize from 6 (monomer) up to 48 have been detected using gaschromatography. 

Radiation-Induced Polymerization. Polymerization induced by irradiation is initiated by free radicals and by ionic species. On very pure vinyl monomers, D. J. Metz demonstrated that ionic polymerization can become the dominating process. In Chapter 12 he postulates a kinetic scheme starting with the formation of ions, followed by a propagation step via carbonium ions and chain transfer to the vinyl monomer. C. Schneider studied the polymerization of styrene and a-methylstyrene by pulse radiolysis in aqueous medium and found results similar to those obtained in conventional free-radical polymerization. She attributes this to a growing polymeric benzyl type radical which is formed partially through electron capture by the styrene molecule, followed by rapid protonation in the side chain and partially by the addition of H and OH to the double vinyl bond. A. S. Chawla and L. E. St. Pierre report on the solid state polymerization of hexamethylcyclotrisiloxane by high energy radiation of the monomer crystals. 

The solid state polymerization of hexamethylcyclotrisiloxane has been investigated over the temperature range —196° to 60°C. The rates of polymerization have been related to the presence of ion scavengers, H20, NH3, in the monomer and to the size of the crystals. Using large crystals dried over sodium, G values of polymerization of 11 X 103 were obtained at 50°C. This is five times larger than previously reported values. The reaction is concluded to be surface initiated and to be terminated at a crystal face or at a defect. 

In this chapter we report some results from an intensive investigation of the radiation-induced polymerization of a single monomer—hexamethylcyclotrisiloxane—which by virtue of its ease of polymerization and very high solid state vapor pressure affords an opportunity for comment on two of the points mentioned above. 

The syntheses of siloxanes with vinyl groups at the silicon atoms of the chain was performed by anionic ring-opening polymerization of vinyl group-containing cyclotri- or cyclotetrasiloxanes (03, 04 ) with alkyl lithium compounds as initiators. The polymerizations were terminated by chlorosilanes with additional silico- or carbofunctional groups or octyl groups. In the block copolymerizations we used 03 or 04 and hexamethylcyclotrisiloxane (D3) (Scheme 1 and 2). 

It was shown that in the polymerization of hexamethylcyclotrisiloxane in the presence of CF3SO3H the monomer ist mostly consumed by the addition. However, the condensation has strong impact on the kinetics of this process ° ... 

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-... 

Very recently the development of the controlled anionic polymerization of hexamethylcyclotrisiloxane (D3) led to the synthesis of a PDMS(PS)2 miktoarm star,97 according to Scheme 37. A benzene THF (50 50 v/v) solution of the living PDMS arm was added... 

Hexamethylcyclotrisilazane and hexamethylcyclotrisiloxane were purified by rectification in vacuum following which their purity was tested by gas chromatography. Plasma polymerizations were carried out in an electrode system described previously ( ). Thin film were deposited in a 20 kHz glow discharge on the surface of stainless steel electrodes or on gold or silicon electrodes in the case of thin layers intended for further studies of electrical properties. All polymerizations were carried out at constant discharge parameters current density j = 1 mA/cm2, discharge duration t = 30 sec, monomer vapour pressure p = 0.3 Torr. 

The chemical structure of thin films formed by plasma polymerization of hexamethylcyclotrisilazane (HMCTSN) and hexamethylcyclotrisiloxane (HMCTSO) was studied. The investigations were carried out using combined techniques of pyrolysis - gas chromatography - mass spectrometry. The results showed that the pyrolysis products of highly crosslinked plasma polymers contained low-molecular weight compounds trapped in the... 

Siloxanes are another class of cyclic monomers that have been incorporated into CRP copolymers via a transformation reaction. Miller and Matyjaszewski used n-butyllithium to initiate the ROP of hexamethylcyclotrisiloxane (D3), then terminated the polymerization with chlorodimethylsilane [234]. Allyl 2-bromoi-sobutyrate was then incorporated via a hydrosilylation reaction using Karstedt s catalyst. This reaction did not achieve a high end-functionality, but use of 3-butenyl 2-bromoisobutyrate, and the addition of 0.2 mol% of 2-methyl-l,4-... 

The title block copolymers with characteristics ranging from thermoplastic elastomers to polyethylene-like thermoplastics are obtained from ring opening polymerization of hexamethylcyclotrisiloxane with living a,(D-dilithiopoly-styrene. Chain scissions and oligomerizations which usually complicate siloxane polymerization are avoided, and molecular parameters regulating physical and mechanical properties are conveniently controlled to provide a unique family of thermoplastic materials. 

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