Polysiloxanes scheme

Polysiloxanes (Scheme 2) can be obtained from commercially available starting materials. Three different types were investigated (22) viz. the addition type Wacker RTV-ME 625 and the condensation types Dow Coming 3140 RTV and Silopren (Bayer). These siloxanes form polymeric membranes by addition or... 

The most common liquid crystal polymers are of the side chain variety (see Chapter 4). In the case of polysiloxanes (Scheme 47), monomer units are prepared with an alkenic moiety (192) that adds to a pre-prepared siloxane backbone (193) to generate liquid crystal polymers (194). 

Thermal cure system. The thermal cure system is based on a hydrosilylation addition reaction between vinyl-functionalized and silicon-hydrido functionalized polysiloxanes [32,33,35], Unsaturated organic groups react with a Si-H functionality in the presence of a platinum-based catalyst (Scheme 10). 

Poly(arylester)-polysiloxane multiblock copolymers have also been synthesized by the interfacial polymerization of aminopropyl terminated polysiloxane oligomers with bisphenol-A and a mixture of isophthaloyl and terephthaloyl chlorides117, 193-1951 as illustrated in Reaction Scheme XV. In these reactions the poly(arylester) blocks are formed in situ during the copolymerization, so the control of their block sizes is not very precise. It is also important to note that since aminopropyl terminated siloxane oligomers are employed, the linkages which connect the arylester and siloxane blocks are amide linkages. 

Hybrid organosilicon-organophosphazene polymers have also been synthesized (15-18) (structure ) (the organosilicon groups were introduced via the chemistry shown in Scheme 11). These are elastomers with surface contact angles in the region of 106°. Although no biocompatibility tests have been conducted on these polymers, the molecular structure and material properties would be expected to be similar to or an improvement over those of polysiloxane (silicone) polymers. 

In this paper, we describe the synthesis and initial reactivity studies of a macromolecule (Scheme 1) containing the isocyanide functional group [Z = -N=C ] tethered to a polysiloxane backbone. 

Polycondensation of difunctional oligomeric cyclodisilazanes with a,co-dihydroxypolysiloxanes proved to be another successful attempt to synthesize silazane modified polysiloxanes of improved thermostability. The cyclodisilazane oligomers IHa (see scheme below) are readily available from common and cheap materials, dichlorodimethylsilane and ammonia (fi). The chlorine atoms in these compounds can be easily exchanged to other functional groups, such as amino, hydroxyl, etc. 

Scheme 2. General Synthesis of "End-Blocked" Polysiloxanes via Equilibration Processes.

Hydrolysis of 1 is carried out at room temperature by the slow addition of aqueous NH3 at 0°C (Scheme 2). The resulting hydroxyl end-functional polysiloxane (2) is dispersed as fine droplets in the aqueous medium and can be separated by centrifugation. When neat, 2 is a colorless fluid with molecular weight ranging from... 

When anti-2 was oxidized with 3 equivalents of MCPBA, the trioxidation product 11 was obtained in 81% yield (Scheme 7). Similarly, the oxidation of anti,anti-3 and anti,anti,anti-4 with 4 and 5 equivalents of MCPBA gave the tetraoxidation product 12 and the pentaoxidation product 13, respectively, in moderate yields. Therefore, these ladder polysilanes were found to be oxidized in a unique manner one of two polysilane main chains was oxidized selectively, and novel ladder compounds consisting of polysiloxane and polysilane chains were formed. 

Asymmetric Diels-Alder reactions have also been achieved in the presence of poly(ethylene glycol)-supported chiral imidazohdin-4-one [113] and copper-loaded silica-grafted bis(oxazolines) [114]. Polymer-bound, camphor-based polysiloxane-fixed metal 1,3-diketonates (chirasil-metals) (37) have proven to catalyze the hetero Diels-Alder reaction of benzaldehyde and Danishefsky s diene. Best catalysts were obtained when oxovanadium(lV) and europium(III) where employed as coordinating metals. Despite excellent chemical yields the resulting pyran-4-ones were reported to be formed with only moderate stereoselectivity (Scheme 4.22). The polymeric catalysts are soluble in hexane and could be precipitated by addition of methanol. Interestingly, the polymeric oxovanadium(III)-catalysts invoke opposite enantioselectivities compared with their monomeric counterparts [115]. 

Scheme 4.22 Camphor-based polysiloxane-fixed metal diketonates in Diels-Alder cycloadditions.

Scheme 7 Synthesis of hyperbranched polysiloxane grafts on silica...

Scheme 12.1.7 Polymerization of polysiloxane in the modification of inorganic particles by a CVD method using 2,4,6,8-tetramethylcyclotetrasiloxane. (From Ref. 46.)...

Scheme 12 Synthesis of crown-containing liquid crystalline polysiloxane poly (23)...

The synthesis of hybrid polysiloxanes is depicted in the following scheme... 

An optimized version of the enantioselective SMB-GC unit was subsequently presented for enflurane enantiomers (chemical structure cf. insert in Figure 24) (Biressi et al., 2002b). It consisted of eight 80 cm x 15 mm (i.d.) stainless steel columns assembled in a home-made SMB-GC unit operated at 35°C (Scheme, cf. Figure 24). Each column with an adsorption bed volume of 140 ml each contained 20 % unpurified Lipodex E in the polysiloxane SE-54 and coated (17 %, w/w) on Chromosorb A (NAW, 20-30 mesh) 0.6 mm). This set-up represented the first gas-chromatographic SMB-GC unit for the preparative-scale separation of enantiomers. 

Masamune et alJ1001 reported the preparation of the first series of high molecular weight, silicon-branching macromolecules by means of the procedure shown in Scheme 4.21. Their iterative procedure utilized two differently branched synthetic equivalents a trifunctional, hydrido-terminated core 71 and a trigonal monomer 72. Syntheses of the polysiloxane core 71 and building block 72 were each accomplished by the treatment of trichloromethylsilane with three or two equivalents of the siloxane oligomers, HO[Si-(Me)20]5Si(Me)2H and H0[Si(Me)20]3Si(Me)2H, respectively. 

Scheme 4.21. Construction of polysiloxane dendrimers prepared by an iterative silane hydroxylation and chloride displacement at silicon.

Scheme 5.38. The convergent preparation of polysiloxane dendrimers also employing silicon as a branching center.

To date, three methods have been described for the synthesis of aldehyde functional polysiloxanes (1) in patent literature, but these are not practiced. The hydroformylation of olefinic siloxanes with carbon monoxide and hydrogen under high pressure and temperature conditions is possible (Scheme 1, eq. (1)), but produces a mixture of... 

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