Vinyl acetate polymerization inhibition

Bilimoria et al. investigated the inhibition of radical initiated polymerization of vinyl acetate by tobacco smoke and some PAHs in 1973 (329). Their results indicated that vapor phase of smoke is an efficient inhibitor of vinyl acetate polymerization and that conjugated dienes like isoprene are responsible for the inhibition. There were no free radicals from tobacco smoke specifically identified in this research. Nisbet and Schmeller presented the results of this research at the 27th Tobacco Chemists Research Conference (TCRC) in 1973 (2789a). 

A further important class of retarders, generally less effective than quinones, are the aromatic nitro compounds. They show very different effectiveness toward the retardation of different monomer types the polymerization of vinyl acetate is inhibited, the styrene polymerization is retarded, but there is nearly no influence on the poljunerization rate of acrylates and methacrylates. The effectiveness, however, increases with the number of nitro groups per molecule. 

Many of the examples in the patent literature have applied GCTP to multicomponent copolymerizations where not all of the monomers are methacrylates. CCTP of methacrylates with other monomers has received rather limited attention in the scientific literature. CCT occurs in copolymerizations of styrene with methacrylates and when acrylates are a minor component in the polymerization system. CCT is reduced or ceases in systems containing larger quantities of acrylates or vinyl acetate and inhibition is reported. Thus, CCT can be applied to copolymerizations of vinyl monomers where methacrylates are at least a major component of the monomer feed. 

Ordinary commercial-grade vinyl acetate is redistilled. One gram of hydroquinone per 100 g. of vinyl acetate is added to inhibit polymerization of the latter, which is then stored at 0-4° until needed. 

Fig. 3-10 Inhibition of the benzoyl peroxide-initiated polymerization of vinyl acetate by duroquinone at 45°C. The three lines are for different concentrations of duroquinone. After Bartlett and Kwart [1950] (by permission of American Chemical Society, Washington, DC).

Bartlett and Kwart [81] gave the figures referring to the so-called inhibition constants in the polymerization of vinyl acetate under influence of various substances, and mainly nitro compounds (Table 27). 

As Kite [85] observed, aromatic nitro compounds inhibited the polymerization of vinyl acetate more strongly than that of methyl methacrylate. 

The compatibility of blends of poly (vinyl chloride) (PVC) and a terpolymer (TP) of ethylene, vinyl acetate, and carbon monoxide was investigated by dynamic mechanical, dielectric, and calorimetric studies. Each technique showed a single glass transition and that transition temperature, as defined by the initial rise in E" at 110 Hz, c" at 100 Hz, and Cp at 20°C/min, agreed to within 5°C. PVC acted as a polymeric diluent which lowered the crystallization temperature, Tc, of the terpolymer such that Tc decreased with increasing PVC content while Tg increased. In this manner, terpolymer crystallization is inhibited in blends whose value of (Tc — Tg) was negative. Thus, all blends which contained 60% or more PVC showed little or no crystallinity unless solvent was added. 

The elementary rate constants of the polymerization of vinyl acetate have been determined over a temperature range of 50 degrees (Berezhnykh-Foldes and TiidSs, 1964 Tiidos et al., 1967), and Arrhenius parameter determinations became possible for inhibition processes of radical polymerization of vinyl acetate according to equations (40)-(42)... 

Thus in radical polymerizations, elementary oxygen is always an inhibitor. Its inhibiting effects in the polymerizations of styrene, vinyl acetate, vinyl chloride, the acrylates and methacrylates, were described some years ago [89, 90]. 

A monomer which forms a stable radical can be used to inhibit the polymerization of another monomer which yields a more reactive radical. Styrene inhibits the polymerization of vinyl acetate, for example. 

Dienes via cyciobutanes. In the synthetic sequence formulated, the addition step is carried out by charging a high-pressure autoclave with redistilled vinyl acetate, 1 g. of hydroquinone, and 3 drops of dipentene or terpinolene (to inhibit polymerization of the fluoroolefin). The ves.sel is closed, cooled in dry ice-acetone, evacuated, and charged with chlorotrifluoroethylene (available in 1 -lb. and 5-lb. cylinders from... 

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