Polyvinyl chloride initiation

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. 

Polyvinyl chloride can also be produced in emulsion. Water is used as the emulsion medium. The particle size of the polymer is controlled using the proper conditions and emulsifier. Polymers produced by free radical initiators are highly branched with low crystallinity. 

When many molecules combine the macromolecule is termed a polymer. Polymerization can be initiated by ionic or free-radical mechanisms to produce molecules of very high molecular weight. Examples are the formation of PVC (polyvinyl chloride) from vinyl chloride (the monomer), polyethylene from ethylene, or SBR synthetic rubber from styrene and butadiene. 

In the production of polyvinyl chloride by the emulsion process, the percentages of catalyst, wetting agent, initiator, and solvent all affect the properties of the resultant polymer. They must be carefully metered into the reaction vessel. The vinyl chloride used must also be very pure. Either the scope must specify that the purchased raw material shall meet certain specifications, or some purification equipment must be installed so that the required quality can be obtained. 

In suspension polymerization, the monomer is agitated in a solvent to form droplets, and then stabilized through the use of surfactants to form micelles. The added initiator is soluble in the solvent such that the reaction is initiated at the skin of the micelle. Polymerization starts at the interface and proceeds towards the center of the droplet. Polystyrene and polyvinyl chloride are often produced via suspension polymerization processes. 

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

Figure 22.4 Radical chain mechanism for the degradation of polyvinyl chloride a) initiation, b propagation and c) termination...

On commercial scale this technique is used to obtain polyvinyl chloride, polyvinyl acetate, etc. In this the free radical initiators are used. 

Suspension polymerization. In this process, monomers and initiator are suspended as droplets in water or a similar medium. The droplets are maintained in suspension by agitation (active mixing). Sometimes a water-soluble polymer like methylcellulose or a finely divided clay is added to help stabilize or maintain the droplets. After formation, the polymer, is separated and dried. This route is used commercially for vinyl-type polymers such as polyvinyl chloride and polystyrene. 

The initial halogenated polymeric materials were obtained from the polyvinyl chloride-polyvinylidene chloride, PVC-PVDC (Rovil fiber) and chlorinated polyvinyl chloride, PVC. Dehydrochlorination was performed in the presence of a base solution in a polar organic solvent (dimethylsulfoxide, acetone or tetrahydro-furane). The products were filtered and extracted with water in a Soxhlet apparatus until all chloride ions were removed. Thermal treatment was performed in a tubular furnace in CO flow at 10 cm min". ... 

A more detailed study of transport processes in solvent polymeric membranes was initiated recently.72 One aim was to get information on the distribution within the membrane of the carrier and the cation transported after a steady state has built up during an electrodialysis experiment. A further objective was the demonstration of a relaxation of the concentration gradients of both carrier and cation. To this end the transport properties of solvent polymeric membranes containing the carrier l4C-valinomycin (66 wt.% dioctyladipate, 33 wt.% polyvinyl chloride, 1 wt.%, JC-valinomycin) in contact with aqueous solutions of -,H-a-phenylethylammonium chloride were studied. 

Vinyl chloride (VC) is the monomer from which the common polymer, polyvinyl chloride, is produced. Hence, VC is produced on a very large scale. Not surprisingly, occasional releases of the rather toxic VC to the environment occur. What initial biodegradation product would you expect from VC if it were released into an oxic environment ... 

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). 

While initial aging did cause some loss in volume resistivity, it was no more severe in unstabilized than in stabilized compositions. The most startling effect was the marked increase in volume resistivity under severe aging conditions. This may be due to volatilization loss of DOP or cross-linking of polyvinyl chloride, both of which could reduce migration of ionic impurities, or it may involve adsorption of ionic impurities by the dark-colored, conjugated, polyene structure which forms by loss of hydrogen chloride. In any case it deserves further study. 

Previous work hod shown that low temperature coke is formed from cools hooted to between 450° and 500° C. by a process of nudeation and growth of spherical bodies in the plastic vitrinite. An essentially similar process has now been found to occur with coke-oven and petroleum pitches, with polyvinyl chloride, and with some polynuclear hydrocarbons, all of which yield carbons which grophitize readily at high temperatures. The process is probably general for the initial stages of formation of such carbons from the liquid phase. Some control of the solidification process has been achieved on the laboratory scale, and the physical and chemical structure of the spherulites has been investigated. 

Active sites created by an electric discharge method were being used for graft copolymerization by Akutin et al. (130). When a solution of a polymer in a suitable monomer is subjected to high voltage electric discharge polymerization of monomer is initiated as a result of the pressure impulses acting on the system. The authors studied the copolymerization of methyl methacrylate onto polyvinyl chloride, and of vinyl chloride onto ethylcellulose. 

Bofors Detonating Cord or Bonocord. It consists of a core of PETN contained within a woven tube of cotton threads protected by an outer covering of a plastic compn which is based on polyvinyl chloride or polyethene. Its outer diam is ca 5-5mm and the quantity of expl is ca 12g per meter. Bonocord is usually examined for appearance,resistance to cold, sensitivity to initiation, propagation of detonation and velocity of deton, as described in Ref... 

Coal Mine Fires. Fires in coal mines are particularly dangerous not only because a naked flame may ignite firedamp (or coal dust) and initiate an expln, but also because coal itself provides a virtually unexhaustible supply of fuel. Every precaution should be taken to prevent such fires and the use of combustible materials in mines should be avoided. As an example of fire caused by a combustible article, may be cited the disastrous fire in 1950 at Creswell Mine, England, responsible for the death of 80 people. It was caused by flammable rubber conveyer belting. To prevent a repetition of such disaster, the British National Coal Board ordered replacement of all underground rubber belting by non-flammable polyvinyl chloride belting... 

Swedish detonating cord consists of a PETN core, covered with braided cotton threads, and protected by an outer coating of a plastic which is based on polyvinyl chloride or polyethylene. The quantity of PETN is 12g/m the total wt of Bonocord is 30g/m, and its outer diameter is 5.5mm. It has a deton vel of 6000—7000m/s, is initiated with a No 6 Exploder, and is used for direct detonation of all types of expl charges... 

Plesh (188) treated polyvinyl chloride and vinyl chloride-vinylidene chloride copolymers with aluminium chloride or titanium tetrachloride for initiating the carbonium polymerization of styrene. As expected (218)... 

Volkheimer further demonstrated resorption of particles as large as 65 xm (polyvinyl chloride) and initially referred to this process as persorption . 

As the shear rate increases, the viscosity of some dispersions actually increases. This is called dilatancy, or shear-thickening. Dilatancy can be due to the dense packing of particles in very concentrated dispersions for which at low shear, the particles can just move past each other but at high shear they become wedged together such that the fluid cannot fill (lubricate) the increased void volume, and the viscosity increases. An example of this effect is the apparent drying of wet beach sand when walked on, the sand in the footprint initially appears very dry and then moistens a few seconds later. Other examples include concentrated suspensions (plastisols) of polyvinyl chloride (PVC) particles in plasticizer liquid and the commercial novelty product Silly Putty (which is a silicone material). 

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. 

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