Crosslinking peroxide bridges

Special methods of incorporation alkyl peroxide bridging to vinyl containing siloxane polymers used for conductive applications improved curing characteristics decreased by the presence of carbon black crosslinking based on platinum catalyzed polyvinylmethyl siloxane and polymethyl hydrogen siloxane is not inhibited by carbon black in situ silica formation in fonnation of PDMS nanocomposite, montmorillonite was delaminated in polymer prior to crosslinking ... 

In the presence of oxygen and oxy radicals produced, the crosslinking may involve the formation of oxygen or peroxide bridges. 

Free radical crosslinking. Peroxide curing is through the methylene bridge in a diphenylmethane diisocyanate urethane prepolymer. 

The concentration of hydroperoxides can often be determined by infrared analysis or by chemical titration. Diperoxides are more difficult to detect experimentally. If both substituents of the peroxide are polymeric radicals, P, the corresponding peroxide POOP can actually be considered as an oxygen bridge between two macromolecules and should therefore behave like a crosslink ... 

The vulcanizing agenl, which supplies the bridge between the polymer chains, is furnished predominantly by the sulfur molecule m commercial formulations. Peroxide vulcanizers that produce carhon-to-carbon crosslinks are also important. 

As a preliminary step in the manufacture of unsaturated polyester thermoset plastic one uses low molecular weight linear polyester (Mr 10,000) obtained by a polycondensation of polyglycols with saturated and unsaturated dicarboxylic acids. The precondensate can then be dissolved and stored in the stabilized comonomer, e.g. styrene, with which it will be crosslinked later. The crosslinking polymerization reaction between the polyester chains and the styrene bridges is initiated with the help of organic peroxides which are added dispersed in plasticizers. The reaction begins at 60-90 °C and then proceeds exothermally. In addition to this a cold hardening reaction can also be carried out. For this reaction cold accelerators are necessary, e.g. tertiary amines or cobalt naphthenate. 

Another method of compatibihzation involves crossUnkingbetween the phases of a phase separated system. This method is employed in one of the most common of commercial polymer blends, i.e., elastomer blends utilized in tire construction. In order to achieve the proper balance of properties for tire applications, crosshnked blends of phase separated elastomers are often employed. Sulfur (or peroxide) crosslinking will lead to covalent bridges between the phases, thus assuring proper translation of mechanical stress from one phase to the other. 

The LP polymers are usually cured by oxidation using higher-valence-state metal oxides or peroxides. (Dichromate and manganese dioxide cure systems are used in aircraft systems.) Oxides such as lead dioxide react with the mercaptan groups to form higher polymers as well as crosslinks through disulfide bridges. Cure is accelerated by sulfur and water, and retarded by stearic acid. 

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