Vinyl chloride moiety

During the late 1930s, Otto Wichterle was working at the Czech Technical University in Prague when he first encountered l,3-dicholo-2-butene, a byproduct in the production of the synthetic rubber monomer chloroprene. The compound, which contains a reactive allylic chloride and an inert vinylic chloride, was first used in the bis-alkylation of diethyl malonate. When this compound was dissolved in sulfuric acid, evolution of HCl gas began immediately. The product obtained from this reaction was identified as being diethyl 3-acetyl-4-methyl-3-cyclohexene-l,l-dicarboxylate, which is the net result of the hydrolysis of the vinylic chloride moiety followed by a subsequent intramolecular aldol condensation. 

Amino acid derivatives containing a vinyl chloride moiety can be prepared by adding HCl to an alkynyl amino acid precursor. The reaction of 4-chloro-2-butyn-l-ol (1.45) with potassium phthalimide was followed by Jones oxidation27 to give phthalimidoyl acid 1.46. In this particular case, HCl was added to convert the phthalimide moiety to the requisite amine (-NH2), but HCl also added to the alkyne moiety to give a vinyl chloride, as seen in 1.32. The yield of this latter process was... 

Such copolymers of oxygen have been prepared from styrene, a-methylstyrene, indene, ketenes, butadiene, isoprene, l,l-diphen5iethylene, methyl methacrjiate, methyl acrylate, acrylonitrile, and vinyl chloride (44,66,109). 1,3-Dienes, such as butadiene, yield randomly distributed 1,2- and 1,4-copolymers. Oxygen pressure and olefin stmcture are important factors in these reactions for example, other products, eg, carbonyl compounds, epoxides, etc, can form at low oxygen pressures. Polymers possessing dialkyl peroxide moieties in the polymer backbone have also been prepared by base-catalyzed condensations of di(hydroxy-/ f2 -alkyl) peroxides with dibasic acid chlorides or bis(chloroformates) (110). 

Investigation of the kinetics of the reaction of 4-chloro-2-pentene, an allylic chloride model for the unstable moiety of polyfvinyl chloride), with several thermal stabilizers for the polymer has led to a better understanding of the stabilization mechanism. One general feature of the mechanism is complexing of the labile chlorine atom by the metal atom of the stabilizer. A second general feature is substitution of the complexed chlorine atom by a ligand (either carboxylate or mercaptide) bound to the metal. Stabilization requires that the new allylic substituent (ester or sulfide) be more thermally stable than the allylic chlorine. The isolation of products from stabilizer-model compound reactions supports the substitution hypothesis of poly(vinyl chloride) stabilization. 

The head-to-tail structure of poly (vinyl chloride) permits the continuous regeneration of an allylic chloride moiety as hydrogen chloride elimination proceeds along a chain. Thus, once initiated, loss of hydrogen chloride may proceed along a polymer chain without abatement. 

Allylic Chloride vs. tert-Chloride Reactivity. There is some question in the literature as to whether the allylic chloride moiety or ferf-chloride group is more responsible for the thermal instability of poly (vinyl chloride) (I, 2). To shed some light on this problem we compared the relative reactivities at 100 °C. in chlorobenzene of 4-chloro-2-pentene and 2-chloro-2-methylbutane with dibutyltin -mercaptopropionate. Data are summarized in Table I. The half-time for the reaction of the allylic chloride with the stabilizer mercaptide group was less than 15 minutes, whereas the half-time for the tert-chloride was nearly 20 times longer. The greater reactivity of the allyl chloride suggests that it is the more important functionality in polymer degradation. However, these results on rates of chlorine substitution are not necessarily an exact measure of thermal instability. 

The data in Table II demonstrate that the effectiveness for poly (vinyl chloride) stabilization of dibutyltin salts of maleic acid or monoesters of maleic acid is caused by a high rate of reaction with allylic chloride moieties. Thus, it is not necessary to postulate, as has been done several times in the literature, that these compounds are effective because they are dieneophiles and therefore capable of disrupting the long chains of unsaturation responsible for color formation. It is gratifying that the performance of the maleate stabilizers is consistent with the Frye-Horst substitution hypothesis. 

The work reported here shows that the allylic chloride model is a good one for the unstable moiety of poly (vinyl chloride). 

Poly(styrene)s containing acylperoxide groups are thus obtained by selective photolysis of the azo moieties at 350 or 371 nm. These prepolymers are successively used as macronitiators for the free radical polymerization of vinyl chloride at 70 °C. Styrene/vinyl chloride block copolymers are thus produced [55] by the above two-step route, although relevant amounts (50-60%) of poly(styrene) and poly(vinyl chloride), due to both low peroxide content ( 0.6 groups per macromolecule of polystyrene) and chain transfer with solvent and monomer, are also pre t. 

Summary AIBN-type radical polymerization initiators have been grafted onto poly-ciystalline titanium surfaces allowing synthesis of polymer films covalently bound to the surfaces. Vinylic monomers such as styrene, methyl methacrylate, and 4-chloromethyl-styrene have been used the pendant benzyl chloride moiety present at the outer surface of the polymer film obtained fi om the latter monomer has allowed further functionalization of the system. In the case of polystyrene films on Ti, molecular weights of the polymer have been estimated to be A/w == 25 000 A/ = 10 000 (Pd = 2.5). 

Inorganic macroinitiators can also be used for graft copolymerizations. Pendant vinyl functional pDMS was subjected to hydrosilation with 2-(4-chlorometh-ylphenyl)ethyldimethylsilane to prepare a multifunctional ATRP macroinitiator by Matyjaszewski et al. [233,234]. The ATRP of St was carried out using a pDMS macroinitiator with Mn=6600 and Mw/Mn=1.76 to yield a graft copolymer with Mn=14,800 and Mw/Mn=2.10. The increased polydispersity was attributed to the variation in the number of initiating sites on the pDMS backbone. NMR analysis showed that less than 5% of the total number of benzyl chloride moieties were left unreacted and that the weight ratio of pSt/pDMS was 1.18 [234]. 

By Chemical Modification. Stabilization by chemical pretreatment with organotins (22,23,24,25) has been discussed already. Pretreatment studies with other reagents have been reviewed briefly (22), and improved stability is now also said to result from the prior reaction of PVC with maleic anhydride (92). Kennedy s interesting work on stabilization reactions of organoaluminums (93) has been continued by a report of enhanced stability (compared with that of ordinary PVC) for poly (vinyl chloride-g-styrene) obtained from the Et2AlCl-induced reaction of PVC and styrene monomer (94). Selective destruction of defect sites seems a plausible explanation for this result (94), but improved stability has been observed also for the PVC parts of PVC-polystyrene blends (53,95,96) and for the PVC moieties of poly (vinyl chloride-g-styrene )s prepared by alternative methods (95,96,97). 

Fig. 31.10 Oxidative alkylation of a guanine moiety by vinyl chloride.

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