Chlorine Containing Polymers

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

Whilst such stabilisers have found use in many chlorine-containing polymers their main application has been with polyfvinyl chloride). These additives will be considered in Chapter 12. 

Of these various groups there was extensive interest for some years in polyalkenamers such as frani -polypentenamer which has now abated whilst interest in polynorbomene is steadily increasing. Since the chemistry and technology of the two types is somewhat different each type will be dealt with separately. A third group comprises the chlorine-containing polymers announced by Goodyear in 1980. 

Kaplan78 studied the X-ray radiolysis of poly(a>-chloroolefin sulfone)s and found that the chlorine-containing polymers are less sensitive to radiation than the non-chlorine containing species. He found that dehydrochlorination is a significant reaction in the radiolysis of poly(to-chloroolefin sulfone)s, but it is not a necessary one in order to lose... 

Widespread chlorine-containing polymers would include, 1) stable molding material for practical use such as polyvinyl chloride (PVC), polyvinylidene chloride and poly(epichlorohydrin)(PECH) and, 2) reactive polymers capable to introduce additional functional groups via their active chlorines such as chloromethyl polystyrene, poly (3-chloroethyl vinyl-ether) and poly (vinyl chloroacetate). While the latter, especially the chloromethyl polystyrene, has been widely used recently for the synthesis of variety of functional polymers, we should like to talk in this article about the chemical modification of the former, mainly of PVC and PECH, which was developed in our laboratory. 

Chlorine-containing polymers such as poly(vinyl chloride) PVC undergo an autocatalytic dehydrochlorination reaction under the influence of elevated temperature and UV radiation. Since the HCl originating from the dehydro chlorination of the PVC chains is believed to sustain this autocatalytic process, stabilizers that irreversibly bond HCl can thus inhibit the degradation. Heavy metal compounds such as cadmium stearate or lead stearate are currently used for this purpose. However, alternatives are required due to environmental problems associated with the use of heavy metals. Indeed, the largest current application of LDH materials is in the polymer industry, mainly to stabilize PVC [3,229-232]. 

Coupling of polymers to form graft copolymers is accomplished by nucleophilic reaction between living polystyryl carbanion and various chlorine-containing polymers such as... 

Polymeric carbocations have been formed from a chlorine-containing polymer such as chlorinated SBR and polystyrene, poly(vinyl chloride), and polychloroprene, by reaction with (C2Hs)2A1C1, for example... 

In addition to the free-radical chain degradation described for polyolefins, another type of degradation (dehydrohalogenation) also occurs with chlorine-containing polymers, such as PVC. As shown by the following equation,... 

The combustion of polyacrylonitrile produces hydrogen cyanide. Any of the chlorine-containing polymers will produce hydrogen chloride upon combustion. This would include polyvinyl chloride and polyvinylidene chloride. 

Their relatively high solubility in polymer matrices have led to the use of perchlorate salts as dopants in polymers in order to obtain antistatic behavior. As dopants in polyvinylchloride (PVC) and other chlorine-containing polymers, they improve heat stability and fire retardation characteristics. 

One example in this category is the case of one polymer in two stereoregular forms Other examples are of two polymers which are chemically very similar such as poly(methyl acrylate) with poly(vinyl acetate) A series of systems which have been studied in some detail are various mixtures of chlorine containing polymers. Blends of chlorinated PVC with PVC have been studied It has been suggested that at 65.2 % wt.- % chlorine they are miscible and at 67.5 wt.- % they are not. Chlorinated polyethylene with 45 wt.- % chlorine has also been found to be miscible with PVC In this case it was suggested that phase separation occurs on heating. 

Chlorine-containing Polymers. Polymers containing one chlorine atom in various environments (other sustituents) were studied by XPS poly(vinyl chloride) PVC, poly(chlorotrifluoro-ethylene) PCTFE, an (ethylene-chlorotrifluoroethylene) copolymer, and poly(epichlorohydrine) PEPI, were chosen because besides carbon atoms they contain chlorine in presence of hydrogen, fluorine, and oxygen atoms. The valence band spectra of these compounds (see Figure 9) show that features can be easily and unambiguously assigned to a contribution from the chlorine molecular orbitals. 

M. Blazso, B. Zelei, andE. Jakab, Thermal decomposition of low-density polyethylene in the presence of chlorine containing polymers, J. Anal. Appl Pyrol, 35, 221-235 (1995). 

Under a variety of conditions, COClj and polycaprolactam gave insoluble chlorine-containing polymers [1392],... 

In many cases a favorable interaction between the chains is known to exist. For example, in the case of mixtures of chlorine containing polymers with polyesters, hydrogen bonds of the type... 

Figure 9.2. The structures of three of the chlorine-containing polymers considered in developing the correlation for the dielectric constant e at room temperature, (a) Poly(vinyl chloride), (b) Poly(vinylidene chloride), (c) Poly(oxy-2,2-dichloromethyltrimethylene).

Test for polyivinyl chloride). Specific tests for chlorine containing polymers are performed only when the presence of chlorine is confirmed by preliminary test. The simplest method of chlorine determination is the Beilstein test, described previously. Plastidzers are removed from the test material by ether extraction and the Beilstein test for chlorine is repeated to make certain that chlorine is still present. The material is then dissolved in tetrahydrofiiran, filtered and the polymeric product reprecipitated by adding methanol. 

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