Chlorination of PVC

Millan (98) studied the effect of tacticity on the ionic dehydrochlorination and chlorination of PVC. For the dehydrochlorination reaction, both the reaction rate and the polyence sequence distribution depend markedly on the syndiotactic content. Chlorination appeared to be easier through heterotactic parts than through syndiotactic sequences as shown by C-NMR. 

Chlorination of PVC at low temperature gives a polymer which finds use in industrial plumbing for hot effluents. 

CPVC is manufactured by chlorination of PVC polymer thereby raising the chlorine content from 56% to around 66%. Chlorination takes place primarily at the -CH2-groups along the polymer chain so that the resulting structure becomes virtually a copolymer of vinyl chloride with 1,2-dichloroethylene. 

Chlorination of PVC reduces the forces of attraction between the molecular chains. CPVC is also essentially amorphous. Both of these factors allow CPVC to be stretched more easily and to a greater extent than PVC... 

An interesting case of halogenated polyolefin is that of halogenated poly(vinyl chloride). After-chlorination of PVC improves thermal stability of the polymer. The distribution of chlorine atoms in chlorinated PVC has been studi successfully using Py-GC [57]. 

Chlorination. Chlorination of PVC results in a resinous product having about 73% chlorine, which corresponds to the introduction of one chlorine per carbon atom. Such postchlorinated polymers have achieved some industrial importance because they have lower softening temperatures and increased solubility in a variety of solvents. They have been used in synthetic fibers in Germany and in solution coatings. 

Figure 25. Dependence of glass transition temperature on chlorine content in low-temperature chlorination of PVC.

In Germany, a different method was used for the modification of the solubility of PVC, and an acetone-soluble polymer was obtained by the chlorination of PVC. A fiber of this type of polymer was produced for the first time in 1934 and was called the Pe-Ce fiber [145]. 

Although thete have been a number of post- polymerization chemical modificalions of PVC recorded in the literature, the most commercially successful of these has been post-chlorinaliotL Processes for the chlorinalion reaction include a solution method (135 chlorinating a solvent-swollen, PVC resin chlorination of PVC as a dry powder (136-139 or chlorinating the suspended resin in water (140). The process employed can have a dramatic effect on the structure of the CPVC produced because the reaction is heavily depended upon the abihty of the chlorine radical to difiiise into the PVC. The most common reaction scheme is generation of free radicals of chlorine which then react with the PVC chain by ... 

The major benefit of post-chlorination of PVC is the dramatic rise in glass transition temperature as chlorine is added to the molecule. It has been observed that the Tg of chlorinated PVC increases from about 82°C for the starting PVC (chlorine content 57 percent) to about 100°C at 62 to 63 percent chlorine, to above 120°C at about 67 percent chlorine content (146). Fukawa(147)hasdemonstrated thattheTgofa PVC resin, converted to CPVC, follows the relationship ... 

The latest more extensive work on the chlorination of PVC was part of an overall study of the chlorination of polyalkenamers. The chlorinated butadiene polymer (poly-butenamer) was found to be crystalline or at least had crystalline chain segments a unit cell for chlorination products of trans-1,4-polybutadiene was determined and for the crystalline material a structure of a diisotactic poly(erythro-l,2-dichlorobutadiene) was proposed. This proposal required the assumption that the addition of chlorine is stereospecific. It was also mentioned that the number of ordered units of about ten is sufficient to display crystallinity, sufficient to allow the determination of the structure by x-ray analysis. 

Fig. 95. Dependence of the dehydro-chlorination of PVC on the time of heating at 175 C in a stream of air without additives (1) and with additions of 1% lead silicate (2), dibutyltin maleate (3), diphenylolpropane (4), and polyphenyl-acetylene (5).

Chlorinated polyvinyl chloride (CPVC) possess excellent high-temperature performance and other desirable properties. Typical CPVC has about 57% chlorine and is prepared by chlorination of PVC. It has outstanding flame and smoke properties, chemical inertness, and low sensitivity to hydrocarbon feedstocks. The glass transition temperatnre of the polymer, Tg, increases with increase in chlorine content in the polymer. 

Chemical modification of poly(vinyl chloride) (PVQ provided an important feature in a recent symposium devoted to this polymer. Contributions included the effects of tacticity on ionic dehydrochlorination and chlorination of PVC, and chemical methods, such as isotopic chlorine exchange, for the determination of labile chlorine. ... 

Additionally to the procedures described earlier, improvements for thermostabilization is copolymerisation of vinyl chloride with suitable monomers. A great number of monomers were investigated to optimize the properties of resins. But only vinyl acetate, vinylidene chloride, ethylene, propylene, acrylonitrile, acrylic acid esters, and maleic acid esters, respectively, are of interest commercially [305,436,437]. The copolymerization was carried out in emulsion, suspension, and solution in connection with water- or oil-soluble initiators, as mentioned elsewhere. Another possibility for modifying PVC is grafting of VC on suitable polymers [305,438], blends of PVC with butadiene/styrene and butadiene/ methacryl acid esters copolymers [433], and polymer-analogous reactions on the macromolecule [439,440] (e.g., chlorination of PVC). 

Chlorinated Polyvinyl Chloride Resins n CPVC is a plastic produced by the post-chlorination of PVC. 

Chlorination has been carried out on many other polymers as well as PE the chlorinations of PVC, polypropylene, fluorinated polymers, etc, have been the subject of numerous studies. The chlorination of poly(vinylidene fluoride) has been carried out in boiling CCI4 suspension products containing 26% of chlorine were obtained, and exhibit very interesting properties. 

---