Vinyl acetate solid-state polymerization

Vinyl acetate, frozen to a glassy state or a crystallized form, has been subjected to solid-state polymerization with UV radiation. The rate of polymerization was foimd to vary with the physical state [183]. On the other hand at — 195°C, vinyl acetate did not polymerize when exposed to a dosage rate of... 

A unique feature of high-energy-radiation apphcations relates to solid-state polymerizations [27-31]. In this case, a catalyst is not required and the irradiations can be performed at deliberately chosen temperatures, because the absorption of radiation is temperature-independent. Of particular interest in this context are compounds such as trioxane, hexamethylcyclotrisiloxane, P-propiolactone and diketene, all of which polymerize readily in the solid state but slowly, or not at ah, in the hquid state. Other compounds such as styrene, acrylonitrile and formaldehyde polymerize faster in the crystalline state than in the liquid state just above the melting point Compounds that undergo solid-state polymerization upon y-hradiation are listed in Table 5.1. In contrast, vinyl chloride, vinyl acetate and methyl methacrylate do not polymerize in the solid state. 

Fluorescence optical microscopy (FOM) of poly(vinyl alcohol) and poly(vinyl acetate) blends in compositions 9/1,1/1, and 1/9 (w/w) showed that these blends present phase separation in the solid state. Each domain of the solid samples was identified by FOM as poly(vinyl alcohol)-richer domains by green fluorescence of fluorescein and poly(vinyl acetate)-richer domains by the blue fluorescence of anthracene. The dimensions, shapes, and distributions of these domains were dependent on the initial composition of the polymeric mixtures in solution. Specific interactions between both homopolymers were studied using FTIR microspectroscopy, which allowed the obtaining of spectra for both poly(vinyl alcohol)-richer and poly(vinyl acetate)-richer domains. 24 refs. 

Radical polymerization is initiated by a free radical, which subsequently adds to a vinyl or diene monomer to produce a propagating radical. To obtain information about the structure and concentrations of initiating and propagating radicals in radical polymerizations, use of ESR spectroscopy has called the interest of physical or polymer chemists. However, ESR measurements on these radicals in solution poly merizati on were found to be difficult, except for the case where polymers precipitated, because otherwise the concentrations of the radicals were too low. Thus, these measurements had to be limited to polymerization systems in highly viscous solutions or in the solid state, where the disappearance of free radicals by bimolecular reactions is suppressed. Bresler et al. -i7) succeeded for the first time in obtaining ESR spectra of free radicals which were produced in homogeneous bulk polymerization of methyl methacrylate (MMA), methyl acrylate (MA) and vinyl acetate (VAc) at conversions of 50-60% (in the gel state). 

A number of ethylenic monomers and cyclic monomers undergo chain polymerization in the solid state when exposed to high-energy radiation (e.g. y-radiation). Examples include acrylamide, acrylic acid, acrylonitrile, vinyl acetate, styrene, 1,3,5-trioxane, propriolactone and hexamethylcyclo-trisiloxane. These polymerizations may involve free-radical and/or ionic species, but in most cases the precise mechanisms operating are not known. 

Flame retardance of ethylene-vinyl acetate copolymer can be achieved using magnesium hydroxide incorporated in the polymeric matrix. The adduct of a small amount of zinc borate as synergistic agent in the formulation increases the fire-proofing properties. Multinuclei solid-state NMR appears as a means to characterise materials before and after combustion. It was shown that endothermic dehydration, water vapour evolved and formation of a glassy coating provided the flame retardancy of interest to the polymer matrix. 12 refs. EUROPEAN COMMUNITY EUROPEAN UNION FRANCE WESTERN EUROPE... 

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