Monomer-solvent complexes

Upon dilution in solvents which may associate via hydrogen bonds (water, methanol, dioxane) the situation is more complex. I.R. and Raman spectroscopy indicate the formation of various monomer-solvent complexes (4, 6). The corresponding absorption bands are in the same range as the characteristic bands for open dimers and oligomers and the latter cannot therefore be determined quantitatively. However, the viscosity of carboxylic acids was found to rise upon addition of water or methanol (4, 7) suggesting that these solvents bind together "oligomers". The persis-... 

Auto-acceleration was observed in the homopolymerization of methacrylic acid solutions over limited concentration ranges in methanol and in water. Perhaps under such conditions swelling of the polymer favors monomer diffusion leading to a larger amount of pre-oriented structures III. Alternatively, a monomer-solvent complex may arise which favors a pre-oriented structure and thus, may be responsible for the onset of a matrix effect (9). 

Based upon the above studies, it may be concluded that there is strong evidence to suggest that Bootstrap effects arising from preferential solvation of the polymer chain operate in many copolymerization systems, although the effect is by no means general and is not likely to be significant in systems such as STY-MMA. However, this does not necessarily discount a Bootstrap effect in such systems. As noted above, a Bootstrap effect may arise from a number of different phenomena, of which preferential solvation is but one example. Other causes of a Bootstrap effect include preferential solvation of die chain end, rather than the entire polymer chain, or the formation of non-reactive radical-solvent or monomer-solvent complexes. In fact, the Bootstrap model has been successfully adopted in systems, such as solution copolymerization of STY-MMA, for which bulk preferential solvation of the polymer chain is unlikely. For instance, both Davis and Klumperman and O Driscoll adopted die terminal Bootstrap model in a reanalysis of die microstructure data of San Roman et al. for the effects of benzene, chlorobenzene and benzonitrile on the copolymerization of MMA-STY. 

This form of the model is for monomer—solvent complexes generally. Under the MCD model, the complexing agent C is the other monomer (Mj). As with all of the solvent effects models, variations are possible by making a different assumption as to which units can affect radical reactivity. 

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