Chlorinated poly dehydrochlorination

The chlorinated polymer is soluble in low-boiling solvents such as acetone, it is resistant to dehydrochlorination and is thermally more stable than poly(vinyl fluoride), chlorinated poly(vinyl fluoride), poly(vinyl chloride), or chlorinated poly(vinyl chloride). 

When chlorinated poly(vinyl chloride) (3.72) is exposed to UV radiation of wavelength > 250 nm (from a mercury lamp), dehydrochlorination proceeds rapidly along the polymer chain leading to the formation of chlorinated polyene sequences (3.73) according to the following reaction [558, 563] ... 

The dehydrochlorination chain reaction is 10 times more eflBcient in chlorinated poly(vinyl chloride) than in non-chlorinated polymer, with a quantum yield of 0.12mol/photon in the absence of oxygen [564], There may be two possible explanations for this ... 

In the photolysis of chlorinated poly(vinyl chloride), the radical evolved by C—Cl photocleavage still possesses chlorine atoms in the P and P positions (—CHCl—CH—CHCl—) it will thus be able to initiate a second zip-dehydrochlorination, as well as the former initiated by the chlorine radical, with formation of twice the amount of HCl as in poly(vinyl chloride). This is illustrated by the overall reaction scheme shown in Fig. 3.42. 

Jamieson and McNeill [142] studied the degradation of poIy(vinyI acetate) and poly(vinyI chloride) and compared it with the degradation of PVC/PVAc blend. For the unmixed situation, hydrogen chloride evolution from PVC started at a lower temperature and a faster rate than acetic acid from PVAc. For the blend, acetic acid production began concurrently with dehydrochlorination. But the dehydrochlorination rate maximum occurred earlier than in the previous case indicating that both polymers were destabilized. This is a direct proof of the intermolecular nature of the destabilizing effect of acetate groups on chlorine atoms in PVC. The effects observed by Jamieson and McNeill were explained in terms of acid catalysis. Hydrochloric acid produced in the PVC phase diffused into the PVAc phase to catalyze the loss of acetic acid and vice-versa. 

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... 

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]. 

Dehydrochlorination of poly vinylidene chloride and chlorinated polyvinyl chloride was carried out. High chlorine content in the polymers (more than 60%) provides the formation of chlorinated conjugated polymers, polychlorovinylenes. The reactivity of chlorinated polyvinylenes contributes to the sp carbon material formation during heat treatment. Synthesis of porous carbon has been carried out in three stages low-temperature dehydrohalogenation of the polymer precursor by strong bases, carbonization in the inert atmosphere at 400-600°C and activation up to 950°C. 

The leading derivative of ethylene dichloride is vinyl chloride [75-01-4] monomer (VCM), which is subsequently used to produce poly(vinyl chloride) and chlorinated hydrocarbons. Vinyl chloride is obtained by dehydrochlorination of ethylene dichloride in the gas phase (500-600°C and 2.5-3.5 MPa). 

The synthetic methods for carbyne employed so far have involved the dehydrohalogenation of polyvinylidene halides [7], dehydrochlorination of chlorinated polyacetylene [8], defluorination of poly(tetrafluoroethylene) [9], and phase transition from carbon materials, such as graphite, under severe conditions. 

In fact, the mediator, i.e. t-BuOH, is electrochemically reduced to the t-BuO anion that nucleophilically attacks PVDF, in much the same way as potassium tert-butylate, to yield elimination products. The authors also studied electrochemical dehydrochlorination of oriented poly(l,2-dichloro-ethylene) films under heterogeneous conditions [9]. The starting polymer was produced by chlorination of polyacetylene [10,20]. The elimination product, however, was found to be predominantly polychlorovinylene with a small proportion of carbynoid moieties. The authors came to that conclusion because of very low intensity of the IR absorption peak attributable to triple C=C-bonds. On the other hand, its low frequency at 2145 cm could... 

Moreover, poly(trichlorobutadiene)s are known to undergo allylic rearrangements with migration of allylic chlorine (14%) and hydrogen (3-10%) atoms under the action of solvents [38]. This accounts for remarkable similarity of the IR spectra of dehydrochlorinated poly(l,l,2-trichloro-butadiene) and poly(l,2,3-trichlorobutadiene) (Figure 12.1). 

At a temperature above 80 °C, poly (vinyl chloride) eliminates hydrogen chloride and allylic chlorinated structures appear, with 4-chloro-2-hexene being considered as a model. At the processing temperature (180-200°C), the main problem of poly (vinyl chloride) stabilization is preventing the zip dehydrochlorination that induces discoloration and cross-linking of the polymer. 

Polyaniline (PANI) is a nonconductive polymer that could be rendered conductive by HCl doping. Several methods exist to accomplish such a doping. One of them is the incorporation of a chlorine-containing polymer into a polyaniline matrix and the irradiation of the resultant blend. Ionizing radiation (e-beam or y-irradiation) leads to the dehydrochlorination of the second polymer and the subsequent doping of the PANI (Figure 9.9). Several chlorine-containing polymers were tested in this approach, PVC, chlorinated polyisoprene, poly(vinylidene chloride-co-vinyl acetate), poly(vinylidene chloride-co-vinyl chloride). " ... 

The dehydrohalogenation of poly(vinylhalides) is important because of its presumed relationship to thermal stability. Most reports agree that PVC and PVDC dehydro-chlorinate by a Zipper Mechanism but kinetic studies have not followed the implications of that mechanism. The rate of PVC dehydrochlorination has been reported to increase, decrease, and remain constant with time and the catalytic effect of hydrogen chloride has not always been observed. PVDC has been reported to follow first order kinetics, but the acceleratory phase of the dehydrochlorination was not adequately accounted for. 

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. ... 

The zip dehydrochlorination basically proceeds in a cage reaction, which explains why long polyenes are mostly found in poly(vinyl chloride) photo-lyzed in the solid state. In solution, where the chlorine radical (Cl ) can more easily diffuse out of the cage, growth of polyene sequences is less favoured and discoloration is much less pronounced [169]. 

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