Polymer reaction polysiloxane

The efficiency of this process is usually less than one cross-link per peroxide molecule decomposed. To increase the cross-linking efficiency, small amounts of unsaturation are introduced into the polymer structure. We have already discussed EPDM polymers, which are essentially diene monomers copolymerized with ethylene-propylene (EPR) polymers. For polysiloxanes, copolymerization of small amounts of vinyl-methylsilanol greatly enhances cross-linkability (Equation 5.7). The unsaturation introduced into an otherwise saturated structure provides additional sites for cross-linking through chain reaction. 

This later led to the development of the most popular silicone polymers, the polysiloxanes, which, at high molecular weight, exhibit rubbery properties. Such elastomers are generally obtained from a cyclosiloxane monomer by a ring-opening reaction, as shown in Equation (A). Because of the unusual ease of rotation around the silicone-oxygen bond, the polymer chain is much more flexible than carbon-based polymers, so that a semi-liquid material is obtained, even at molecular weights of several hundred thousand. Fine... 

Akutin and co-workers [159] made block and graft copolymer of fluorine-containing polymers or polysiloxanes as one component and poly(methyl methacrylate), poly(vinyl chloride), and ethylcellulose as the second. During the irradiation, samples were withdrawn at regular intervals in order to determine the extent of reaction by the decrease in solution viscosity, rj. In other cases, a recombination of macroradicals into new polymeric species caused an increase in the viscosity. The sign and rate of change of rj was thus different for different systems. 

Cross-linked polymers containing polysiloxanes have been synthesized by reaction of PPO with polyfunctional amine-terminated polysiloxanes. ... 

A novel polysiloxane, containing the isocyanide group pendent to the backbone, has been synthesized. It is observed to react with the metal vapors of chromium, iron and nickel to afford binary metal complexes of the type M(CN-[P])n, where n = 6, 5, 4 respectively, in which the polymer-attached isocyanide group provides the stabilization for the metal center. The product obtained from the reaction with Fe was found to be photosensitive yielding the Fe2(CN-[P])q species and extensive cross-linking of the polymer. The Cr and Ni products were able to be oxidized on exposure of thin films to the air, or electrochemically in the presence of an electron relay. The availability of different oxidation states for the metals in these new materials gives hope that novel redox-active polymers may be accessible. 

The feasibility of bonding pyridinyl groups to silicon which contains a hydrolytically sensitive functional group has recently been demonstrated 15-71. 2-Fluoro-3-(dimethylchlorosilyl)pyridine and 3-fluoro-4-(dimethylchloiosilyl)pyridine as well as 2-, 3-, and 4-(dimethylchlorosilyl)pyridine were prepared by the reaction of the corresponding lithiopyridines with excess Me2SiCl2- Hydrolysis of the pyridinyl substituted chlorosilanes gave disiloxanes which were insoluble in water. In the present report we will describe extension of this work to include pyridinyl dichlorosilanes which can be hydrolyzed to polysiloxanes. These polymers can be N-oxidized and the resultant derivatives have been shown to be effective hydrophobic transacylation catalysts. 

Liese el al. attached a transfer-hydrogenation catalyst to a soluble polymer and applied this system in a continuously operated membrane reactor.[60] A Gao-Noyori catalyst was bound to a soluble polysiloxane polymer via a hydrosilylation reaction (Figure 4.41). 

Polymerization was carried out in NaOH aqueous solution. Table 4 summarizes the reaction conditions and polymer yields. The first step of the polymerization was hydrolysis and oligomerization of the silylethers at low temperatures from 90°C to 150 °C. In order to increase the polymer yield and the softening point of the polymers, the second step was carried out at higher temperatures under reduced pressure, removing alcohol and water, 1H-NMR, 13CNMR and IR spectroscopy of each polymer show that these polymers have the polysiloxane structure substituted with a phenol group. 

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]. 

Peroxide crosslinking of the copolymer is more efficient than that of the homopolymer (Table 9-1). The process becomes a chain reaction (but with short kinetic chain length) involving polymerization of the pendant vinyl groups on the polysiloxane chains in combination with coupling of polymeric radicals. The crosslinking of EPDM rubbers is similarly more efficient when compared to EPM rubbers since the former contain double bonds in the polymer chain. 

There are various routes to vinyl macromonomers [Gnanou and Taton, 2002]. For example, the reaction of an HO-terminated polymer such as polysiloxane, polycaprolactone, or poly-tetrahydrofuran with acryloyl chloride... 

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