Macroradicals, occluded acrylonitrile

Seymour and coworkers (27,28,29,30) actually used these composition gradients to prepare block copolymers by swelling particles containing occluded (i.e., living) macroradicals with a second monomer. Such block copolymers were prepared from occluded vinylacetate, methyl methacrylate, and acrylonitrile macroradicals, and the yield of block copolymers was studied as a function of the solubility and rate of diffusion of the swelling monomer in the particles. 

Charge transfer complexes of styrene and acrylonitrile have been shown to exist when in the presence of zinc chloride. Proton nuclear magnetic resonance spectroscopy has been used to establish this effect. In the proper solvents styrene and acrylonitrile will form occluded macroradicals which may then be used to form block copolymers. These block copolymers occur both in the presence and absence of zinc chloride. Pyrolysis gas chromatography, differential scanning calorimetry, and solubility studies show the properties of the two copolymers and their various block copolymers to be quite similar. Differences in the copolymers may be seen from carbon-13 nuclear magnetic resonance spectroscopy. Yield data for the block copolymers is reported. 

These occluded macroradicals have been used to prepare block copolymers of styrene (17,19), acrylonitrile (20), vinyl acetate (21), and methyl methacrylate (22). This principal may be extended to binary monomer systems as well. An interesting example of this is shown by the highly alternating copolymers synthesized by charge transfer complex (CTC) copolymerization. 

Monomer pairs, one electron rich, the other electron poor, have been shown to form (CTC) s. Typical CTC s are formed from styrene and maleic anhydride and styrene and acrylonitrile in the presence of Lewis acids (23-25). These CTC s are known to rapidly polymerize in the presence of free radical initiators to form copolymers with a high degree of alternation (26,27). If the copolymerization is conducted in a poor solvent for the polymer, occluded macroradicals will be produced. 

While most copolymers of vinyl acetate are random copolymers, alternating copolymers are formed when the reactivity ratios for the two monomers are suitable. This occurs spontaneously when vinyl acetate is polymerized with electron-poor monomers such as maleic anhydride [273]. Alternatively, it has been reported that acrylonitrile which has been precomplexed with zinc chloride gives alternating polymers with vinyl acetate [274]. Block polymers of vinyl acetate with methyl methacrylate, acrylonitrile, acrylic acid, and n-vinyl pyrrolidone have been prepared by the strategy of preparing poly(vinyl acetate) macroradicals in poor solvents in which the macroradicals are occluded. Addition of a second monomer swells the polymer coils, and polymerization continues with the addition of the new monomer [275]. 

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