Poly , dehydrochlorination

Resistance to weathering. Zinc oxide and magnesium oxide stabilize poly-chloroprene against dehydrochlorination. Further, zinc oxide helps vulcanize the rubber, and magnesium oxide reacts with /-butyl phenolic resin to produce a resinate which improves heat resistance of solvent-borne polychloroprene adhesives. 

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. 

PCSs obtained by dehydrochlorination of poly(2-dilorovinyl methyl ketones) catalyze the processes of oxidation and dehydrogenation of alcohols, and the toluene oxidation207. The products of the thermal transformation of PAN are also catalysts for the decomposition of nitrous oxide, for the dehydrogenation of alcohols and cyclohexene274, and for the cis-tnms isomerization of olefins275. Catalytic activity in the decomposition reactions of hydrazine, formic acid, and hydrogen peroxide is also manifested by the products of FVC dehydrochlorination... 

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... 

A PPV derivative which is twofold phenylsubstituted at the vinylene unit, poly(l,4-phenylene-l,2-diphenylvinylene DP-PPV), (71b) (see also the discussion of dehydrochlorination of unsymmetrically substituted para-xylylene dichlorides in Section 3.1) was first synthesized by Smets et al., using acid-catalyzed elimination of nitrogen from l,4-bis(diazobenzyl)benzene 83 [106]. The yellow products obtained are fully soluble in common organic solvents (toluene, chloroform, ethylene chloride, DMF, THF). 

I.4.2.I. Synthesis and Modification of Polymers Unstable bis(nitrile oxide), generated by dichloroglyoxime dehydrochlorination, polymerizes in solution to give poly(furoxan) or (in the presence of 1,3-dienes) gives rise to their being cross-linked (500). Polymerization of terephthalonitrile dioxide and its... 

It is evident that reactions of unsaturated polymers with bisnitrile oxides lead to cross-linking. Such a procedure has been patented for curing poly(butadiene), butadiene-styrene copolymer, as well as some unsaturated polyethers and polyesters (512-514). Bisnitrile oxides are usually generated in the presence of unsaturated polymers by dehydrochlorination of hydroximoyl chlorides. Cross-linking of ethylene-propylene-diene co-polymers with stable bisnitrile oxides has been studied (515, 516). The rate of the process has been shown to reduce in record with the sequence 2-chloroterephthalonitrile oxide > terephthalonitrile oxide > 2,5-dimethylterephthalonitrile oxide > 2,3,5,6-tetramethylterephthalo-nitrile oxide > anthracene-9,10-dicarbonitrile oxide (515). 

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. 

Guyot and coworkers have also noted that monomers stabilize poly(vinyl chloride) during mastication, probably because they act as free radical scavengers with the exception of basic monomers, such as vinyl pyridine, B. In this case dehydrochlorination reaction... 

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 degradation reactions of polymers have been widely reviewed 525). In the absence of air, thermal reactions are the important degradation route. They may involve reactions of functional groups on the chain without chain scission, typified for example by the dehydrochlorination of PVC, or reactions involving chain scission, often followed by depropagation and chain-transfer reactions to yield complex mixtures of products. This latter route would be typical of the degradation of poly(methyl methacrylate), which depolymerizes smoothly to its monomer, and of polystyrene, which produces a wide range of tarry products. 

The thermal and photochemical dehydrochlorination of the vinyl chloride—CO copolymer have been studied by two different groups56,57). The decomposition rate for the copolymer was significantly higher than that for poly(vinyl chloride), the rate increasing with increasing CO content of the copolymer. In addition, the thermal decomposition of the copolymer was accelerated in the presence of molecular 02 while the photodegradation was slowed down 57). As with poly(vinyl chloride), the dehydrochlorination of the copolymer resulted in the formation of polyene sequences. There was no appreciable decrease in molecular weight. 

In the presence of hydroquinone the rate of dehydrochlorination of poly (vinyl chloride) in oxygen is reduced considerably (20, 24). The presence of an oxygen scavenger in lieu of a radical scavenger or antioxidant would be expected to have an even greater effect. 

This hypothesis has been confirmed by the greatly improved thermal stability of PVC as a result of the formation of a graft copolymer of d -l,4-polybutadiene onto poly (vinyl chloride). The improved thermal stability is demonstrated by the almost total absence of discoloration on molding the graft copolymer into a film at 200°C in air, the reduced rate of dehydrochlorination on heating in an inert atmosphere at 180°C, and higher onset and peak temperatures for hydrogen chloride evolution as determined by differential thermal analysis. 

Milled rigid sheets of poly (vinyl chloride) on heating at 185°C. lose weight at a rate which increases with time. By polymer fractionation procedures, it was shown the rate of hydrogen chloride loss increases as the content of tetrahydro-furan-insoluble resin increases. The insoluble resin content accumulates at a rate which depends, in part, on the additive present. This insolubilization reaction is catalyzed by cadmium compounds. The increased dehydrochlorination rate of the insoluble crosslinked resins may result from the susceptibility of the crosslinked structures to oxidation and from the subsequent thermal degradation of the oxidation products. The effects of various common additives on the rates of insolubilization and weight loss are described. 

The principal reactions which have been studied in thermally degraded poly (vinyl chloride) are (1) the dehydrochlorination reaction ... 

Virtually all previously published opinions on thermally degraded poly (vinyl chloride) regarded the dehydrochlorination process as being in the first instance, a monomolecular process resulting in conjugated polyene structures, and that all oxidation and cross-linking reactions... 

Milled rigid sheets of poly (vinyl chloride) on oven aging at 185 °C. undergo a slow initial dehydrochlorination which, if continued long enough, results in the formation of a tetrahydrofuran-insoluble fraction. This insoluble polymer dehydrochlorinates much more rapidly than the soluble polymer fractions. 

Although aramid fiber is by far the most successful fiber made via the liquid crystal route, there are some other important fibers that have been made by this process. For example, poly(p-phenylene benzobisthiazole) (PBT) (Wolfe et al, 1981a, 1981b) is synthesized from terephthalic acid and 2,5-diamino-l,4-ben-zenedithiol dihydrochloride (DBD). The DBD is first dissolved in poly-phosphoric acid (PPA), followed by dehydrochlorination. Terephthalic acid and more PPA are then added and the mixture is heated to 160°C to make a solution. The solution is heated to 180 C and reacted for 18 hours to obtain the... 

The formation of tri- and especially tetrasilanes which are already branched (tertiary Si-units) as the first reaction products (described elsewhere [4]) suggests the appearance of intermediate silylene species which could enter in insertion reactions of Si-Si as well as Si-Cl bonds. The tri- and tetrasilanes undergo thermal crosslinking reactions at reaction temperatures of 165-250 °C. In addition dehydrochlorination reactions initiated by acid H-abstraction of methyl groups cause the formation of carbosilane (methylene) units in the polymer framework. Table 1 shows the gross compositions of poly(methylchlorosilanes) which are determined by the reaction temperature. 

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