Poly vinyl chloride and related polymers

In this chapter the homopolymer, poly(vinyl chloride) (PVC) is considered together with vinyl chloride-vinyl acetate copolymers and other vinyl chloride copolymers of lesser importance. Also discussed are the commercially important copolymers of vinylidene chloride. 

There are two principal industrial routes for the preparation of vinyl chloride, namely from acetylene and from ethylene. 

Acetylene itself is manufactured in two ways. The first method is based on calcium carbide, which is obtained by heating a mixture of coke and lime at about 3000°C in an electric furnace treatment of the carbide with water yields acetylene  

Depending on the purity of the carbide used, the acetylene contains impurities such as ammonia, arsine, hydrogen sulphide and phosphine. Scrubbing with water removes all these impurities except phosphine which is removed with acid dichromate. 

The second method of production of acetylene is based on the cracking either of methane in natural gas or of higher hydrocarbons in, for example, a naphtha feedstock. Various processes have been devised for these cracking operations, which in the case of methane, may be represented as  

In terms of tonnage, poly(vinyl chloride) is (with polyethylene, polypropylene and polystyrene) one of the four most important plastics currently in use. It is extremely widely used in such applications as bottles, building accessories, cable insulation, flooring, packaging film and pipe. 

There are two principal industrial routes for the preparation of vinyl chloride (often designated as VCM for vinyl chloride monomer), namely from acetylene and from ethylene. Ethylene is cheaper than acetylene and although some vinyl chloride is still manufactured from acetylene, new capacities are unlikely to be based on this feedstock (except in countries such as South Africa which have coal-based economies). 

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Radiation-induced Degradation.—There have been several reports on radiation effects in polymers,288 including single crystals,287 fluoropolymers,288 polyamides,289 polysiloxanes,270 polyethylene and its copolymers,271 polypropylene,272 polyolefins,273 polystyrene and its copolymers,274 poly(vinyl chloride) and related polymers,275 rubbers,278 polysulphones and other sulphur-containing polymers,277 polycarbonate,278 nylon,279 poly(vinylpyridines),280 and wool.281... 

These effects are not limited to synthetic polymers and resins (note silk, above) Scandola and Pezzin [13] note the lowering of Tg of elastin by water and describe other aspects of the interaction that are closely related to the plasticization of poly-(vinyl chloride) and polycarbonate. 

Closely related to PVC, but with distinct properties of its own, is chlorinated poly(vinyl chloride) (CPVC), a polymer produced by postchlorination of PVC. The effect of adding more chlorine to the PVC molecule is to raise the Tg of the base resin to 115-135°C (239-275°F) range and the heat deflection temperature under load to around 115°C (239°F). CPVC also has higher tensile strength, higher modulus, and greater resistance to combustion and smoke generation. 

Polymers of Vinyl Chloride and Related Compounds, and Poly "Halogenated" Ethylenes... 

Conformation and Chemical Shifts.—Chemical shifts have been correlated with conformation for H shifts in polystyrene and poly(vinyl chloride) and C shifts in model compounds of polypropylene. In all these papers, the chemical shift is related empirically to the occurrence of three- and four-bond steric interactions, similar to those used in the rotational isomeric state treatment of polymer statistical mechanics, " and the shift is expressed as a sum of compositional and conformational increments. The origin of the shielding contributions (magnetic anisotropy, electric field effects, etc.) is not stated, except for polystyrene in which the magnetic anistropy of the aromatic rings are incorporated... 

A more recent application of ultrasonics has been the characterization of the extent of polymerization in a condensation or radical process. The first observations were made by Sokolov, and subsequent reports of measurements on polystyrene, poly(vinyl chloride) and poly(vinyl acetate) " have confirmed the utility of the method. It is clear that this type of study is still in its infancy however, certain facts emerge which demonstrate the importance of this method. The compressibility of a solution containing monomer and polymer is directly related to the proportion of each component present. It is therefore possible to quantitatively estimate the extent of conversion from the observed velocity of sound. In a suspension polymerization, the glass transition of the polymer forming the bead is itself a function of the extent to which unreacted monomer is retained in the system. In this case, observation of the attenuation can indicate the extent to which polymerization has occurred in the system. Unfortunately the data are not sufficiently extensive to estimate the general validity of the method for the monitoring of polymerization in reactors, although the potential has been clearly demonstrated. 

Materials that are constructed from organic polymers such as polyethylene, polystyrene, polyisoprene (natural rubber and a synthetic elastomer) and poly(vinyl chloride) are common features of our daily lives. Most of these and related organic polymers are generated from acyclic precursors by free radical, anionic, cationic or organometallic polymerisation processes or by condensation reactions. Cyclic precursors are rarely used for the production of organic polymers. 

The incorporation of vitamin B12 derivatives into plasticized poly(vinyl chloride) membranes has resulted in the development of several ion-selective electrodes (ISEs). The response of the electrodes has been related to principles of molecular recognition chemistry. In addition, ISEs have been prepared by electropolymerization of a cobalt porphyrin. These electrodes have selectivity properties that are controlled by both the intrinsic selectivity of the metalloporphyrin and the characteristics of the polymer film (e.g., pore size). 

In a related patent (46) Amagi et al. synthesized a triple latex IPN. In brief, polymer 1 was a crosslinked SBR, polymer 2 was a crosslinked styrene-methyl methacrylate copolymer, and polymer 3 was a crosslinked poly (methyl methacrylate). All three were sequentially synthesized on the same latex particle. The latex material was then mechanically blended with linear poly (vinyl chloride). Also, Torvik (47) blended together four polymers that had different glass transition temperatures. 

Molecular weights are not often measured directly for control of production of polymers because other product properties are more convenient experimentally or are thought to be more directly related to various end uses. Solution and melt viscosities are examples of the latter properties. Poly(vinyl chloride) (PVC) production is controlled aceording to the viscosity of a solution of arbitrary concentration relative to that of the pure solvent. Polyolefin polymers are made to specific values of a melt flow parameter called melt index, whereas rubber is characterized by its Mooney viscosity, which is a different measure related more or less to melt viscosity. These parameters are obviously of some practical utility, or they would not be used so extensively. They are unfortunately specific to particular polymers and are of little or no use in bringing experience with one polymer to bear on problems associated with another. 

Solution viscosities are involved in quality control of a number of commercial polymers. Production of poly(vinyl chloride) polymers is usually monitored in terms of relative viscosity (tj/tjo) while that of some fiber forming species is related to IV [inherent viscosity, c ln(> /)/ )]. The magnitudes of these parameters depends primarily on the choices of concentration and solvent and to some extent on the solution temperature. There is no general agreement on these experimental conditions and comparison of such data from di I ferent manufacturers is not always straightforward. 

Organic polymers can also be incinerated as a means of disposal, (a) What products are formed on combustion of polyethylene (b) What products are formed on combustion of polyethylene terephthalate (c) Are these reactions exothermic or endothermic (See Sections 6.4 and 29.3 for related reactions.) (d) Propose a reason why HOPE and PET must be separated from poly(vinyl chloride) prior to incineration. 

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