Copolymers, vinyl chloride

Copolymers of vinyl chloride with vinyl acetate (VAC) prepared by granular polymerization are the most important. As crystallinity of the PVC is almost certainly eliminated by copolymerization, a typical copolymer with 13% VAC has a lower Tg and much improved flow properties, compared with the homopolymer. 

The copolymer is blended with several additives to improve the performance of the record. For example, static charge can accumulate on the record surface, impairing the sound reproduction antistatic agents such as quaternary ammonium salts have some limited value in solving this problem. Fillers cannot be tolerated in this application, although pigment is included, and stabilizers and lubricants are chosen to produce minimum surface noise. A typical formulation for records is  

Vinyl chloride/vinyl acetate copolymer (VC/VA, 87 13) Dibasic lead stearate (lubricant/stabilizer) 

Records are moulded using pre-heated extruded compound (dough) at 130-140°C the cycle time varies from 20-30 seconds. It is possible to mould records in an injection/compression sequence on an injection machine. The machine operates in the conventional way, except that the mould is not completely closed (about 6 mm clearance), the melt is injected into the cavity 

The main use of the vinyl chloride - vinyl acetate copolymer is in the production of flooring tiles. Typically, tiles contain 30-40 phr of plasticizer and 300-400 phr of filler (e.g. chalk, asbestos, pigments). The mix is dry-blended in an internal mixer and calendered. 

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Acrylic Resins. The first synthetic polymer denture material, used throughout much of the 20th century, was based on the discovery of vulcanised mbber in 1839. Other polymers explored for denture and other dental uses have included ceUuloid, phenolformaldehyde resins, and vinyl chloride copolymers. Polystyrene, polycarbonates, polyurethanes, and acryHc resins have also been used for dental polymers. Because of the unique combination of properties, eg, aesthetics and ease of fabrication, acryHc resins based on methyl methacrylate and its polymer and/or copolymers have received the most attention since their introduction in 1937. However, deficiencies include excessive polymerization shrinkage and poor abrasion resistance. Polymers used in dental appHcation should have minimal dimensional changes during and subsequent to polymerization exceUent chemical, physical, and color stabiHty processabiHty and biocompatibiHty and the abiHty to blend with contiguous tissues. 

By copolymerising the vinylidene chloride with about 10-15% of vinyl chloride, processable polymers may be obtained which are used in the manufacture of filaments and films. These copolymers have been marketed by the Dow Company since 1940 under the trade name Saran. Vinylidene chloride-acrylonitrile copolymers for use as coatings of low moisture permeability are also marketed (Saran, Viclan). Vinylidene chloride-vinyl chloride copolymers in which the vinylidene chloride is the minor component (2-20%) were mentioned in Chapter 12. 

The polymer may be prepared readily in bulk, emulsion and suspension, the latter technique apparently being preferred on an industrial scale. The monomer must be free from oxygen and metallic impurities. Peroxide such as benzoyl peroxide are used in suspension polymerisations which may be carried out at room temperature or at slightly elevated temperatures. Persulphate initiators and the conventional emulsifying soaps may be used in emulsion polymerisation. The polymerisation rate for vinylidene chloride-vinyl chloride copolymers is markedly less than for either monomer polymerised alone. 

Properties and Applications of Vinylidene Chloride-Vinyl Chloride Copolymers ... 

Since some properties of the vinylidene chloride-vinyl chloride copolymers are greatly dependent on crystallisation and orientation it is convenient to consider the applications of these copolymers and then to discuss the properties of the products. 

Bowmer and Tonelli [161] have also studied the thermal characteristics of the whole range of ethylene-vinyl chloride copolymers prepared by partial reductive dechlorination of PVC using tri-n-butyltin-hydride. Naqvi [162] has substantiated further his explanations for the thermal stability characteristics of ethylene-vinyl chloride copolymers reported by Braun et al. [159] using the results of Bowmer and Tonelli [161] as a basis. 

Uses Solvent for uncured rubber, polyvinyl chlorides, vinyl chloride copolymers, 1,1-dichloro-ethylene copolymers, polyurethane coatings natural resins topcoating solutions cellophane magnetic tapes adhesives printing inks organic synthesis. 

Vinylite is the most widely used vinyl chloride copolymer. This copolymer is not as strong nor as resistant to corrosives as rigid PVC but is more readily processed. PVC is flexibilized by blending it with elastomers (impact modifiers). These ductile blends of PVC and impact modifiers are more widely used when impact resistance is essential. 

The gas molecules produced in the 88% poly (vinyl chloride) copolymer (probably primarily HC1) have much higher molecular weight and would be expected to show much lower diffusion rates than hydrogen. The gas molecules liberated in poly (methyl methacrylate) are sim-... 

D.P- Moore, USP 3463683 (1969) CA 71, 114823s (1969) Division of USP 3409708 (CA 70, 21466s) (A solid propellant used as substitute for Dynamite was prepd by mixing 7—20% starch with 4.05—16% vinyl chloride copolymer, heating to 80°, and mixing with 60—90% AN, and a perchlorate, chlorate or an alkali nitrate)... 

RIS theory is used to calculate mean-square unperturbed dimensions 0 and dipole moments

of ethylene-vinyl chloride copolymers as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the vinyl chloride sequences. As was previously found for several other copolymeric chains, is much more sensitive to chemical composition and chemical sequence distribution than is 0. The present calculations also indicate that both and are most strongly dependent on chemicel sequence distribution for ethylene-vinyl chloride chains having vinyl chloride sequences which are significantly syndiotactlc in structure. 

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