Poly allylic chlorine

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. 

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. 

Theoretically the decomposition of the azido group in a linear PAA should have resulted in a mass loss of 33.7%. The PAA thus had a lower azido content. This may be due to the branched structure of poly(allyl chloride) (PAC), which resulted in lower chlorine content, and since poly(allyl azide) was prepared by azidation of PAC therefore the azido content will be decreased. 

It may be noted here that unsaturated terminal groups containing allylic chlorine are also thought to contribute to the instability of poly(vinyl chloride). Such groups can arise by disproportionation during polymerization ... 

Commercially available poly(vinyl chloride) contains small amounts of different abnormal structures (defects) which may originate from synthesis. Such groups are random unsaturation (allylic chlorines) [316, 317,710,956,957] chain end groups [2, 3, 357, 710, 955, 1431, 2052] branch points (tertiary-bonded chlorine atoms) [2,3, 319, 357, 995,1514,2052-2054] head-to-head units [3,309,357,710] and oxidized structures [3,317,357,700]. It has been estimated that the number of defects per 1000 monomer units in commercial poly(vinyl chloride) samples are [357] 4-6 chloromethyl branches, 0.4-2.4 chloroethyl branches, 0.4-1.6 butyl branches (value uncertain), 0.18-2.4 long branches (value uncertain), 6-7 head-to-head structures (values uncertain), 1.4-3 total double bonds and 0.08-0.27 internal double bonds. Labile chloride atoms have been estimated at 0.6-2.5 per 1000 monomer units of which 0.5-2.5 are allylic chlorine or ketochloroallylic chlorine and 0.16-1.0 are chlorine at tertiary carbon (value uncertain). The possible structures of these defects are given in Table 3.12. 

Using radiotracer techniques it has been shown that stabilizer ligands are attached to the polymer during the degradation of poly(vinyl chloride). In most cases, allylic chlorine appears to be the reactive site in the polymer. For example, dibutyl tin mercaptides react as follows ... 

If the same grafting reaction is attempted with poly(vinyl chloride) (PVC) as backbone, grafting occurs only onto the few allylic chlorines of the chain, which originate from the slight dehydro-halogenation that PVC always undergoes. 

The principal kinds of thermoplastic resins include (1) acrylonitrile-butadiene-styrene (ABS) resins (2) acetals (3) acrylics (4) cellulosics (5) chlorinated polyelliers (6) fluorocarbons, sucli as polytelra-fluorclliy lene (TFE), polychlorotrifluoroethylene (CTFE), and fluorinated ethylene propylene (FEP) (7) nylons (polyamides) (8) polycarbonates (9) poly elliylenes (including copolymers) (10) polypropylene (including copolymers) ( ll) polystyrenes and (12) vinyls (polyvinyl chloride). The principal kinds of thermosetting resins include (1) alkyds (2) allylics (3) die aminos (melamine and urea) (4) epoxies (5) phenolics (6) polyesters (7) silicones and (8) urethanes,... 

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. 

A number of chlorinated poly(ethers) have practical uses. A common compound from this group is polyepichlorohydrin, [-CH(CH2CI)CH20-]n. Polyepichlorohydrin has practical applications as an elastomer and is used in copolymers with propylene oxide, ethylene oxide, allyl glycidyl ether (1-allyloxy-2,3-epoxypropane), etc. Another example is poly oxy[2,2 -bis(chloromethyl)-1,3-propandiyl] or poly[oxy-1,3-(2,2 -dichloromethyl)propylene], CAS 25323-58-4, which can be used as inert lining material for chemical plant equipment, as adhesive, coating material, etc. This macromolecule can be prepared starting with pentaerythritol in the sequence of reactions shown below ... 

POLY(ETHYLENEIMINE) or POLY-ETHYLENEIMINE or POLYETHYLENE POLYAMINES (26913-06-4) Combustible liquid (flash point 207°F/98°C). Violent reaction with strong oxidizers, strong acids. Incompatible with organic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted allyls, cellulose nitrate, cresols, caprolactam solution, chlorine oxyfluoride, epichlorohydrin, ethylene dichloride, isocyanates, ketones, glycols, nitrates, phenols, vinyl acetate. Exothermic decomposition with maleic anhydride. Increases the explosive sensitivity of nitromethane. Attacks aluminum, copper, magnesium, zinc, and other nonferrous metals. 

If the allylic chloride group is particularly favourable to such elimination (and aflylic chlorine is highly reactive in heterolytic reactions because of the stability of the carbonium ion formed) then an unzipping process can be envisaged for poly (vinyl chloride). 

The effect of polymer composition on secondary reactions is easily seen in rubber mastication. The greater tendency for gelation and branching in styrene rubber is related to the radicals involved. The radicals from styrene rubber have a greater reactivity than allyl radicals [7] toward a-methylenic hydrogen atoms and double bonds. This behavior has been attributed previously to the pendant vinyl groups in certain synthetic rubbers [8,9]. Poly-chloroprene also forms a gel by addition of radicals to double bonds, whose activity is increased by the chlorine substituent [10]. 

PMR spectroscopy has been applied to the characterisation of a wide range of homopolymers including PMMA [286-289], PVC [290-294], PS [293, 295, 296], polyvinyl ethers [297-300], polyacrylic acid [301], poly(methyl-a-chloroacrylate) [302], carboxy terminated polybutadiene [303], poly(a-methyl styrene) [304], natural rubber [305-307], chlorinated polyisobutylenes [308], sulfonated PS resins [309, 310], polyvinyl phenyl ether [311], lactone polyester [312], chlorinated PVC [313], PC [314], poly 1,3 butadiene [315], poly-2-allyl phenyl acrylate [316], poly(4-methyl-pentene-1) [317], polymethacrylic acid [318], PP [296], cyclic ethers [319], polymethacrylonitrile [320], poly(a-methyl styrene) tetramer [321], PEG [322], PE [289], polyacrylamide [311], polymethylacrylamide [323], polypyrrolidone [324], polychloroprene [325], phenol formaldehyde resins [326, 327], Nylon 66 [328], polyvinylidene fluoride [329], polyvinyl formate [330], polyacrylonitrile [331], epoxy resins [332], allyl biguanide [333], poly(2-isopropyl-2-oxazollines) [334] and trehalose vinyl benzyl ether [335]. 

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