Vinyl chloride reactivity ratios

The data in Table 7.6 list the mole fraction of methyl acrylate in the feedstock and in the copolymer for the methyl acrylate (Mi)-vinyl chloride (M2) system. Use Eq. (7.54) as the basis for the graphical determination of the reactivity ratios which describe this system. 

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacryhc fibers (23,24). Dynel, a staple fiber that was wet spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus acrylonitrile is much more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain-transfer agent. To make the Dynel composition of 60% vinyl chloride, the monomer composition must be maintained at 82% vinyl chloride. Since acrylonitrile is consumed much more rapidly than vinyl chloride, if no control is exercised over the monomer composition, the acrylonitrile content of the monomer decreases to approximately 1% after only 25% conversion. The low acrylonitrile content of the monomer required for this process introduces yet another problem. That is, with an acrylonitrile weight fraction of only 0.18 in the unreacted monomer mixture, the low concentration of acrylonitrile becomes a rate-limiting reaction step. Therefore, the overall rate of chain growth is low and under normal conditions, with chain transfer and radical recombination, the molecular weight of the polymer is very low. 

GopolymeriZation. The importance of VDC as a monomer results from its abiHty to copolymerize with other vinyl monomers. Its Rvalue equals 0.22 and its e value equals 0.36. It most easily copolymerizes with acrylates, but it also reacts, more slowly, with other monomers, eg, styrene, that form highly resonance-stabiHzed radicals. Reactivity ratios (r and r, with various monomers are Hsted in Table 2. Many other copolymers have been prepared from monomers for which the reactivity ratios are not known. The commercially important copolymers include those with vinyl chloride (VC),... 

Vinyhdene chloride copolymerizes randomly with methyl acrylate and nearly so with other acrylates. Very severe composition drift occurs, however, in copolymerizations with vinyl chloride or methacrylates. Several methods have been developed to produce homogeneous copolymers regardless of the reactivity ratio (43). These methods are appHcable mainly to emulsion and suspension processes where adequate stirring can be maintained. Copolymerization rates of VDC with small amounts of a second monomer are normally lower than its rate of homopolymerization. The kinetics of the copolymerization of VDC and VC have been studied (45—48). 

Kunitake, Yamaguchi and Aso149 studied the copolymerization of 2-furaldehyde with olefins and vinyl ethers using BF3 Et20 in methylene chloride or toluene at —78 °C. No copolymers were obtained with olefins, but p-tolyl vinyl ether or 2,3-dihydropyran gave polyethers. With the former co-monomer the values of the reactivity ratios were rx = 0.15 0.15 and r2 = 0.25 0.05 (Mj = 2-furaldehyde). 

For the remaining three systems, styrene-vinyl acetate, vinyl acetate-vinyl chloride, and methyl acrylate-vinyl chloride, one reactivity ratio is greater than unity and the other is less than unity. They are therefore nonazeotropic. Furthermore, since both ri and 1/7 2 are either greater than or less than unity, both radicals prefer the same monomer. In other words, the same monomer—styrene, vinyl chloride, and methyl acrylate in the three systems, respectively—is more reactive than the other with respect to either radical. This preference is extreme in the styrene-vinyl acetate system where styrene is about fifty times as reactive as vinyl acetate toward the styrene radical the vinyl acetate radical prefers to add the styrene monomer by a factor of about one hundred as compared with addition of vinyl acetate. Hence polymerization of a mixture of similar amounts of styrene and vinyl acetate yields an initial product which is almost pure polystyrene. Only after most of the styrene has polymerized is a copolymer formed... 

The best test for functionality would be in a copolymerization study. A polystyrene with a methacrylate terminal functional group was prepared. A review of relative reactivity ratios indicated that vinyl chloride reacts very rapidly with methacrylates. Therefore, a copolymerization of the polystyrene terminated with a methacrylate functional group in vinyl chloride would be a good test case, and one should observe the disappearance of the MACROMER if the reaction is followed by using GPC analysis. 

A second test was done by using butyl acrylate as the comonomer as shown in Figure 11. The reactivity ratios in this case are such that the methacrylate functionality would react slower with acrylates than with vinyl chloride. As predicted the butyl acrylate is at 62% conversion before the MACROMER peak is significantly diminished. These data add validity to the hypothesis that the placement of side chains in the backbone is dependent on the terminal group of the macromonomer and the relative reactivity of its comonomer. 

The work with l-bromo-2-chloroethane allowed the influence of the nature of the halogen on its reactivity to be observed as either vinyl bromide or vinyl chloride are formed. The ratio of the chloride to the bromide in the products changed with the nature of the catalyst, being around 0.1 for sulphates of Ni, Co, Mn, Cu, Zn and for silica—alumina, 0.6 for alumina and 5 for KOH—Si02 [179]. 

Copolymers. Vinyl acetate copolymenzes easily with a few monomers, e g, ethylene, vinyl chloride, and vinyl neodecanoate, which have reactivity ratios close to its own. Block copolymers of vinyl acetate with methyl methacrylate, acrylic acid, acrylonitrile, and vinyl pyrrolidinone have been prepared by copolymerization in viscous conditions, with solvents that are poor solvents for the vinyl acetate macroradical,... 

The vinyl chloride and vinyl bromide copolymer samples were prepared as polymer analogs of PVC. Cleavage of the carbon-halogen bond at LNT should result in the same radical for these polymers. Since secondary C-Cl and C-Br bond dissociation energies are 73 and 59 Kcal/mole respectively, a copolymer of vinyl chloride and vinyl bromide could be regarded as a PVC chain with weak points. The feed ratio of VC/VB was 10/1 by volume. Since the reactivity ratios are (in solution, at 40°C), r = 0.825 for VC and r2 = 1.050 for VB (22), the copolymer composition should be 15 units of vinyl chloride for one unit of vinyl bromide on the average. In addition, the values for r and... 

More industrial polyethylene copolymers were modeled using the same method of ADMET polymerization followed by hydrogenation using catalyst residue. Copolymers of ethylene-styrene, ethylene-vinyl chloride, and ethylene-acrylate were prepared to examine the effect of incorporation of available vinyl monomer feed stocks into polyethylene [81]. Previously prepared ADMET model copolymers include ethylene-co-carbon monoxide, ethylene-co-carbon dioxide, and ethylene-co-vinyl alcohol [82,83]. In most cases,these copolymers are unattainable by traditional chain polymerization chemistry, but a recent report has revealed a highly active Ni catalyst that can successfully copolymerize ethylene with some functionalized monomers [84]. Although catalyst advances are proving more and more useful in novel polymer synthesis, poor structure control and reactivity ratio considerations are still problematic in chain polymerization chemistry. 

In the copolymerization of vinyl chloride and vinyl acetate, what monomer feed composition is needed to produce a copolymer containing 5 mol % vinyl acetate (The reactivity ratios are listed in Table 7-1.)... 

Recent investigations [259] have indicated that the polymerization is not conventional free radical in character but is likely to be coordinated anionic. In support of this view are the reactivity ratio coefficients in copolymerization of vinyl chloride with vinyl acetate and methyl methacrylate, which are different from those found with free radical initiators. 

The reactivity ratios, although numerically different for the Ziegler and free radical catalysts, do show the same orders of monomer reactivity, vinyl acetate being less reactive and methyl methacrylate much more reactive than vinyl chloride. With the rather wide scatter in literature values for reactivity ratios — particularly with coordination systems — the data on VC/MM A cannot be regarded as completely indicative of a non-radical reaction however, the very low value of rj in the VA/VC system is more definitive. 

If two of the three monomers belong to the group described above and one is weakly conjugated, i.e. of the group of vinyl chloride, vinyl esters, olefins and the like, the product probabilities are approximately 0.006. It is evident that knowledge of the product probabilities permits to predict relative reactivity ratios for a wide variety of monomers. 

Table III. Reactivity Ratios and Q and e Values for Ethylene-Vinyl Chloride and Ethylene-Vinyl Acetate Copolymerizations...

Some data recently obtained on high pressure ethylene copolymerizations illustrate the quantitative aspects of an ethylene-based Q-e scheme (6). In Figures 3 and 4 copolymer composition curves for the ethylene-vinyl chloride and the ethylene-vinyl acetate copolymerizations are given. The monomer reactivity ratios for these two systems are tabulated in Table III along with Q values and e values for vinyl chloride and vinyl acetate calculated using ethylene as the standard (Q = 1.0 and g = 0). These Q and e values may be compared with those obtained using styrene as the standard. 

These ethylene-based Q and e values may be used to calculate the reactivity ratios for the copolymerization of vinyl acetate with vinyl chloride. Agreement is good when these values are compared with experimental values. In Table IV reactivity ratios calculated from ethylene- and styrene-based Q and e values are shown. 

Table IV. Reactivity Ratios for Vinyl Chloride(M )-Vinyl Acetate(M2)...

Synthesis. The copolymers were prepared by suspension polymerization using a 1 gal stainless steel reactor operating at the autogenous pressure of vinyl chloride at 50° C. The vinyl chloride (Matheson) was purified by passing the gas over KOH pellets. A 9 1 ratio of water to vinyl chloride was used, the suspending agent being methyl cellulose (Methocel 25 cps, Dow Chemical). Percadox 16 (Noury Chemical Corp.) was the catalyst. Because the calculated reactivity ratios indicated that... 

Unsaturated alkyl halides, alcohols and ethers can also act as alkylating agents to give products derived by alkylation at one or more reactive sites. Tsukervanik and Yuldashev examined the reaction of vinyl chloride with toluene and anisole in the presence of AICI3 by varying the ratio of reactants. For example, with anisole (equation 90) two products were formed. The diarylated product resulted from reaction of anisole with both reactive centers in vinyl chloride. 

Some commercially important examples of random free-radical copolymerizations include styrene (ri = 0.8)-butadiene (r2 = 1.4) for which rir2 = 1.1 and vinyl chloride (ri = 1.4)-vinyl acetate (r2 = 0.65) for which rir2 = 0.9. In these products the proportion of a given monomer in the copolymer depends on the feed concentrations and reactivity ratios [Eq. (7.11)]. 

If rj and r2 are less than 1, the polymers tend to alternate. If r is greater than 1 and r2 is less than 1, M predominates in the polymer. To prevent forming a polymer with a wide distribution of composition, it is necessary that the more reactive monomer be added during the course of the polymerization. The reactivity ratios for vinyl chloride (Mp and other monomers (M2) are shown in Table VI. 

The composition of a vinyl chloride-vinyl acetate copolymer produced from a mixture of monomers Is shown in Figure 9. Because r-, the monomer reactivity ratio, is greater than one, and r2 is less than one, the copolymer is richer in Mj (vinyl chloride). Thus, if one were to copolymerize a mixture of monomers comprising 60% vinyl chloride, the resultant copolymer would contain approximately 75% vinyl chloride. 

Table VI. Monomer Reactivity Ratios, = Vinyl Chloride...

Disulfide Formation in Polystyrene Networks. Polymer-bound thiols were prepared by copolymerizations of bis -vinylbenzyl)disulfide with other divinyl monomers followed by diborane reduction (Scheme 5) (fiS). The initially formed thiols were juxtaposed for reoxidation to disulfides. Polymer-bound thiols were prepared also by copolymerization of p-vinylbentyl thiolacetate with divinyl monomers followed by hydrolysis (Scheme 6). llie latter thiols were distributed randomly throughout the polymer network. The copolymer reactivity ratios for p-vinylbenzyl thiolacetate and styrene are unknown, but should be similar to those of styrene (Mi) and p-vinyl-bentyl chloride (M2) ri = 0.6, r2 = 1.1 (fifi). Copolymeiizations with equal volumes of monomers and 1/1 acetonitrile/toluene product macroporous 40-48% DVB-cross-linked networks (651. 

Example 8.1 The reactivity ratios for the copolymerization of methyl methacrylate (1) and vinyl chloride (2) at 68°C are rj = 10 and r2 = 0.1. To ensure that the copolymer contains an appreciable quantity (>40% in this case) of the vinyl chloride, a chemist decided to carry out the copolymerization reaction with a feed composed of 80% vinyl chloride. Will the chemist achieve his objective ... 

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