Vinyl acetate copolymerization parameters

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Table 4. Copolymerization Parameters of Vinyl Acetate (M ) and Comonomers (M2)...

Hart and de Pauw 98) used this emulsion technique on the system vinyl acetate-acrylic acid. It is well known that the copolymerization parameters rx and r2 are unfavorable in this system therefore the relative solubility of the two monomers exerces only a small influence on the composition of both sequences. The degree of homogeneity of the sequences has been evaluated, after alkaline hydrolysis, by measuring the tendency to lactonization in acid medium. While 72% of the acetate groups could be lactonized in the case of a random copolymer containing 37% vinyl acetate, only 14% are transformed in a block copolymer with the same initial composition. 

Copolymerization. Vinyl chloride can be copolymerized with a variety of monomers. Vinyl acetate [9003-22-9], the most important commercial comonomer, is used to reduce crystallinity, which aids fusion and allows lower processing temperatures. Copolymers are used in flooring and coatings. This copolymer sometimes contains maleic acid or vinyl alcohol (hydrolyzed from the poly(vinyl acetate)) to improve the coating s adhesion to other materials, including metals. Copolymers with vinylidene chloride are used as barrier films and coatings. Copolymers of vinyl chloride with maleates or fumerates are used to raise heat deflection temperature. Copolymers of vinyl chloride with acrylic esters in latex form are used as film formers in paint, nonwoven fabric binders, adhesives, and coatings. Copolymers with olefins improve thermal stability and melt flow, but at some loss of heat-deflection temperature (100). Copolymerization parameters are listed in Table 5. 

Unzueta et al. [18] derived a kinetic model for the emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) employing both the micellar and homogeneous nucleation mechanisms and introducing the radical absorption efficiency factor for micelles, F, and that for particles, Fp. They compared experimental results with model predictions, where they employed the values of Fp=10 and Fn,=10", respectively, as adjustable parameters. However, they did not explain the reason why the value of Fp, is an order of magnitude smaller than the value of Fp. Sayer et al. [19] proposed a kinetic model for continuous vinyl acetate (VAc) emulsion polymerization in a pulsed... 

Recently, copolymerization of vinyl-sulfonate esters was reported with vinyl acetate by Tezuka and coworkers. These monomers have closer solubility parameters and their inherent reactivities are the only operating factors in their copolymerization. More evenly distributed copolymers were thus obtained. These were hydrolyzed, or subjected to nucleophilic substitution of the sulfonate moiety, to produce interesting derivatives22. 

Copolymerization of vinyl acetate with acrylic monomers can lead to the production of latex having a wide range of mechanical and molecular properties depending on the molecular structure of the emulsifier, and also above parameters. 

TABLE IXa Reactivity Ratios and Q-e Parameters for Copolymerization of Allyl Esters (A/ ) with Vinyl Acetate (A/2) [64]... 

Jaisinghani and Ray (40) also predicted the existence of three steady states for the free-radical polymerization of methyl methacrylate under autothermal operation. As their analysis could only locate unstable limit cycles, they concluded that stable oscillations for this system were unlikely. However, they speculated that other monomer-initiator combinations could exhibit more interesting dynamic phenomena. Since at that time there had been no evidence of experimental work for this class of problems, their theoretical analysis provided the foundation for future experimental work aimed at validating the predicted phenomena. Later studies include the investigations of Balaraman et al. (43) for the continuous bulk copolymerization of styrene and acrylonitrile, and Kuchanov et al. (44) who demonstrated the existence of sustained oscillations for bulk copolymerization under non-isothermal conditions. Hamer, Akramov and Ray (45) were first to predict stable limit cycles for non-isothermal solution homopolymerization and copolymerization in a CSTR. Parameter space plots and dynamic simulations were presented for methyl methacrylate and vinyl acetate homopolymerization, as well as for their copolymerization. The copolymerization system exhibited a new bifurcation diagram observed for the first time where three Hopf bifurcations were located, leading to stable and unstable periodic branches over a small parameter range. Schmidt, Clinch and Ray (46) provided the first experimental evidence of multiple steady states for non-isothermal solution polymerization. Their... 

Prior to Harwood s work, the existence of a Bootstrap effect in copolymerization was considered but rejected after the failure of efforts to correlate polymer-solvent interaction parameters with observed solvent effects. Kamachi, for instance, estimated the interaction between polymer and solvent by calculating the difference between their solubility parameters. He found that while there was some correlation between polymer-solvent interaction parameters and observed solvent effects for methyl methacrylate, for vinyl acetate there was none. However, it should be noted that evidence for radical-solvent complexes in vinyl acetate systems is fairly strong (see Section 3), so a rejection of a generalized Bootstrap model on the basis of evidence from vinyl acetate polymerization is perhaps unwise. Kratochvil et al." investigated the possible influence of preferential solvation in copolymerizations and concluded that, for systems with weak non-specific interactions, such as STY-MMA, the effect of preferential solvation on kinetics was probably comparable to the experimental error in determining the rate of polymerization ( 5%). Later, Maxwell et al." also concluded that the origin of the Bootstrap effect was not likely to be bulk monomer-polymer thermodynamics since, for a variety of monomers, Flory-Huggins theory predicts that the monomer ratios in the monomer-polymer phase would be equal to that in the bulk phase. 

The monomer pairs in free radical polymerizations can be arranged in a series according to the products of the copolymerization parameters (Table 22-3). On the left-hand side in this series are monomers with electron-donating groups, such as butadiene, styrene, or vinyl acetate and on the right are monomers with electron-attracting substituents, such as maleic anhydride, acrylonitrile, vinylidene chloride, etc. The product r rg decreases from one to zero in the vertical series, whereas in the horizontal series it increases from low values (left) to values up to unity (right). 

Table 22 5. The Product of the Binary Copolymerization Parameters for the Free Radical Terpolymerization of the Conjugated Monomers Methyl Acrylate, Methyl Methacrylate, Acrylonitrile, and Styrene, as well as for the Nonconjugated Monomers Vinyl Acetate, Vinyl Chloride, and Vinylidene Chloride...

Each of these reactions is characterized by its specific rate constant kg. The composition of the polymer is determined by the copolymerization parameters ri = feii/ki2andr2 = 22/ 21- Ifti = t2 = 1, the comonomer is randomly distributed in the polymer chain. This is largely the case when vinyl acetate is copolymerized with ethylene. 

Vinyl Acetate-Based Copolymers and Derived Polymers. Vinyl acetate units transmit their intrinsic adhesivity to all VA-containing polymers. Thus, vinyl acetate is copolymerized with ethylene, acrylic monomers, and so on. Its reaction behavior can be predicted through parameters Q = 0.026 and e = 0.22 (see Section 8.5.11). 

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