Polyvinyl chloride peroxides

Experimental evidence is available to show that at room temperature diperoxides are formed in polyethylene, whereas polypropylene and polyvinyl chloride generate hydroperoxides. The temperature at which the peroxides decompose and initiate grafting depends on the type of polymer used. 

Figure 22.2 Chemical structure of monomer soluble initiators for polyvinyl chloride a) dilauryl peroxide, b) benzoyl peroxide and c) azobisisobutyronitrile...

A number of polymers, in particular teflon, polyvinyl chloride and, to a lesser extent, polyethylene do not provoke the decomposition of peroxide. 

When handling large quantities of hydrogen peroxide it is necessary to wear protective goggles, overalls made of protective fabric (an apron of polyvinyl chloride), rubber gauntlets and boots, since severe burns are caused if it comes into contact with the skin. 

To learn more about the possible effects of ionic impurities on volume resistivity, we added known quantities of various impurities which are frequently present in polyvinyl chloride. Lead chloride is postulated as the end-product when lead compounds are used to stabilize polyvinyl chloride. Laurie and benzoic cids probably result from wasteful decomposition of the lauroyl and benzoyl peroxides used to initiate the polymerization reaction. Of these impurities, only benzoic acid had any noticeable effect on volume resistivity (Table III). 

Polyvinyl chloride. Organic peroxides are used to catalyze the free radical polymerization of vinyl chloride monomer in water. The organic peroxide is selected to generate free radicals thermally at the temperature of polymerization. 

Vinylene carbonate is one of the few 1,2-disubstituted ethylenes that is known to undergo facile radical initiated homopolymerization. Initiation may be by oxygen, peroxides or cobalt-60 y-radiation. Such polymers are reportedly useful as coatings and films. Vinylene carbonate also copolymerizes with ethylene under high pressure to yield a material with about 10% vinylene carbonate content. This polymer, when blended with polyvinyl chloride, is suitable for injection molding. 

Journal of Applied Polymer Science 77, No.12, 19th Sept. 2000, p.2657-66 PEROXIDE CROSSLINKING OF UNPLASTICISED POLYVINYL CHLORIDE... 

Manufacture. The monomer of polyvinyl chloride is gas at room temperature and has a boiling point of -13.9°C. The monomer is manufactured in two ways (1) Acetylene and HCl gas are allowed to pass over active carbon and to react with each other at 150 200 C (2) chlorine gas is allov/-ed to react on ethylene to produce C H CI CEDC) at 200 350 C to produce vinyl chloride and HCl gas. These are separated by distillation. The monomer is then polymerized in a pressure vessel the mixture of water and liquid monomer is stirred violently. Benzoyl peroxide is used as a catalyzer and polyvinyl alcohol as a dispersion agent for the reaction. 

In vinyl compound polymerization of vinyl acetate, alcohol, bromide, chloride, or carbonate, ascorbic acid can be a component of the polymerization mixture (733-749). Activators for the polymerization have been acriflavine (734), other photosensitive dye compounds (737,738), hydrogen peroxides (740,741,742), potassium peroxydisulfate (743), ferrous sulfate, and acyl sulfonyl peroxides (747). Nagabhooshanam and Santappa (748) reported on dye sensitized photopolymerization of vinyl monomers in the presence of ascorbic acid-sodium hydrogen orthophosphate complex. Another combination is vinyl chloride with cyclo-hexanesulfonyl acetyl peroxide with ascorbic acid, iron sulfate, and an alcohol (749). Use of low temperature conditions in emulsion polymerization, with ascorbic acid, is mentioned (750,751). Clarity of color is important and impact-resistant, clear, moldable polyvinyl chloride can be prepared with ascorbic acid as an acid catalyst (752) in the formulation. 

In addition polymerization, monomers react to form a polymer chain without net loss of atoms. The most common type of addition polymerization involves the free-radical chain reaction of molecules that have C = C bonds. As in the chain reactions considered in Section 18.4, the overall process consists of three steps initiation, propagation (repeated many times to build up a long chain), and termination. As an example, consider the polymerization of vinyl chloride (chloro-ethene, CH2 = CHC1) to polyvinyl chloride (Fig. 23.1). This process can be initiated by a small concentration of molecules that have bonds weak enough to be broken by the action of light or heat, giving radicals. An example of such an initiator is a peroxide, which can be represented as R—O—O—R, where R and R represent alkyl groups. The weak 0—0 bonds break... 

Polyvinyl chloride Acids, bases, amines, peroxides... 

Addition polymerization takes place for unsaturated monomers. In the presence of a catalyst, such as a free radical, a pi bond in the monomer is disturbed, and the resulting molecule is. itself, a chemically active free radical. This first step of the process is called initiation. The process may then continue, with the new molecule bonding with additional monomers in the same manner, thus forming a chain. Following this propagation step, free radicals may combine, thus forming a more stable polymer chain. This final step is called termination. Peroxides, such as benzoyl peroxide, are common agents that, when heat is applied, form free radicals that can initiate the polymerization process. An example of addition polymerization is shown below for the monomer vinyl chloride, which forms polyvinyl chloride. 

PVC may be formed by the polymerisation of vinyl chloride emulsion under pressure, using a peroxide catalyst. Polyvinyl chloride is found as UPVC (unplasticised PVC), plasticised PVC or as an impact modified PVC. 

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