Silicone polymers reactions

The reaction shown is important in the industrial preparation of dichlorodimethylsilane for eventual conversion to silicone polymers... 

In addition, silicone polymers in both gel and elastomer forms have been shown to induce a typical subcutaneous foreign body reaction and fibro sarcoma development in rats. The lower-molecular weight silicone polymers may migrate into the adjacent tissues or stimulate other cellular and immunological response. 

C21-0050. Write the reactions that generate a silicone polymer starting from ethyl chloride (C2 H5 Cl), and draw a portion of the stmcture of the resulting polymer. Show at least four repeat units of the polymer. 

C21-0051. Write the reactions that generate a silicone polymer starting from a 1 1 mixture of... 

Employing a molar excess of the alkyne over the active hydrogen of only 12 percent the selectivity (determined by proton NMR after work-up) may be expressed as the ratio of Si-C=CH- to Si-CH2-CH2-CO-, which is about 100 1 [16]. The same reaction, carried out with silicone polymers with 10 or more pendant silicon-bonded hydrogen atoms, proceeds similarly cleanly without noticeable crosslinking by acrylic hydrosilylation. A slight excess of triple bond over Si-H groups is mandatory to suppress this side reaction as well as hydrosilylation of the olefinic group of the 2-silylalkene isomer product (see Table 2.). 

Si-H bonds add across olefins over platinum catalysts. This reaction (hydrosi-lation) is used in silicone polymer manufacture, when the silane is a hydrogen bearing oligo(alkylsiloxane). With some types of olefin there have been reports of runaways to explosion because of unexpectedly fast reaction. Dangerous substrates recorded are 2-allylphenols and ethenylsiloxanes. Very low levels of catalyst (ppm) and good cooling are recommended. 

Silicon (Si) forms silicone polymers similar to hydrocarbon polymers. Though both the heat of reaction and the density of Si are higher than those of C, the ignihon temperature of Si is much higher than that of C. 

Catalysis. Platinum-catalyzed hydrosilation is used for cross-linking silicone polymers and for the preparation of functionally substituted silane monomers (250). The most widely used catalyst is chloroplatinic acid (Spier s catalyst), H2PtCl6. Other compounds that catalyze the reaction include Pt(II)... 

POLYDIMETHYLSILOXANE. A silicone polymer developed for use as a dielectric coolant and in solar energy installations, It also may have a number of other uses. It is stated to be highly resistant to oxidation and biodegradation by microorganisms. It is degradable when exposed to a soil environment by chemical reaction with clays and water, by which it is decomposed to silicic acid, carbon dioxide, and water. 

The formulation ofmoisture-ujriiig silicones includes a silicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. A newer class of silicone sealants are known as the silicone latex sealants. These sealants are silicone-in-water emulsions that cure by evaporation of the emulsifying water. Addition-curing silicones in general are two-part systems that cure by the platinum-catalyzed reaction of a silicone hydride with typically a vinyl group attached to silicon. Because no by-products are generated by the cure, there are few volatiles and no shrink in thick sections. 

Silicone polymer technology rests in practice upon the preparation of reactive substituted silanes from silicon metal and the subsequent conversion of these reactive substances, usually through stepwise hydrolysis and condensation reactions, into polysiloxanes. Thus the hydrolysis of these reactive intermediates is a fundamental process, the nature and implications of which have demanded increasing attention as organo-silicon chemistry and technology have developed. 

Hydrosilylation (the addition of R3SiH to a double bond) is an important reaction in the silicone polymer industry. It is used for curing silicone rubber, by cross-linking polymer chains. The reaction is catalyzed by Pt and Rh complexes, following the cycle shown in Figure 3.45. 

Moran et al. have also reported the preparation of hyperbranched ferrocenyl. S7-based polymers (Figure 8.1). The construction of ferrocenyl —silicon polymers 40 and 41 was effected by the reaction of dilithioferrocene-TMEDA with the tetrachlorosilane 35 (see Scheme 8.10) and the Pt-mediated hydrosilylation of l,l -divinylferrocene with tetrasilyl-hydride 38. The 3-dimensional motif exhibited by hyperbranched polymers 40 and 41 is analogous to that depicted by the ferrocenyl — silicon network structures 38,43 42 and 43 (Figure 8.2). 

Polymerization, polycondensation, polyaddition and other reactions Thermoplastic polyurethranes, silicone polymers... 

The cross-linking reaction can take place at room temperature and thus these silicone polymers are useful for the fabrication of monolithic matrix systems for thermosensitive drugs. 

Certain adhesive formulations have been developed by reaction of silicone polymers containing amine termination with epoxy resins. The resulting products exhibit good flexibility while still maintaining good chemical and thermal stability.27... 

The addition of a silicon compound such as R3SiH to alkene functionality, as shown by reaction 7.25, is used widely in silicone polymer manufacture and is called the hydrosilylation reaction. Although hydrosilylation was discovered in 1947, the first homogeneous catalyst, H2PtCl6 (1-10%), in 2-propanol was reported in 1957 from the laboratories of Dow Coming. 

Dimethyldichlorosilane. Because dimethyldichlorosilane has been polymerized to a silicone polymer on cotton fabrics to impart stain and water resistance and can be applied as a vapor, this agent was examined as a possible consolidant. This treatment also improves fabric hand, resistance to chemicals and weathering, resistance to abrasion (by reducing friction), and reduces the tensile strength loss when resin finishes are applied all factors that should make the material a desirable and effective consolidant. The reactions involved are as follows ... 

Scheme 1 General procedure of silicone polymer synthesis by cross-coupling reaction...

---