Hydrophobically associating polymers solubilization with surfactant

Hydrophobically associating polymers consist primarily of water-soluble monomer units with a small number of water-insoluble monomer units. Synthesis of high-molecular-weight random copolymers of acrylamide and alkylacrylamides required a novel aqueous surfactant micellar solution polymerization (2-4) because of the mutual immiscibility of the water-soluble and hydrophobic monomers. The use of surfactant micelles enabled solubilization of the hydrophobic monomer (alkylacrylamide [R]) into the aqueous phase containing the water-soluble monomer (acrylamide [AM]). The resulting RAM polymer after isolation provided homogeneous aqueous solutions. 

In the presence of a polymer, the surfactant chemical potential is lowered with respect to the situation without polymer (Figure 20.6). There are several interactions which can be responsible for surfactant binding or a polymer-induced micellization. We note that in many respects (variation with surfactant alkyl chain length, solubilization, micelle structure and dynamics) there is a close similarity to the micellization of the surfactant alone. The normal hydrophobic interaction between the alkyl chains must therefore still be a dominating contribution to the free energy of association. However, it is modified by mainly one of the following two factors. 

Strauss and Jackson [4] were the first to synthesize associated hydro-phobically modified poiyelectrolytes. In 1951, they partially quartemized poly(2-vinylpyridine) with n-dodecyl bromide, and showed that the polymers formed a compact conformation in aqueous solution, through hydrophobic association of the n-dodecyl groups, if the degree of quarter-nization was higher than a certain value. They called these hydrophobically modified poly(2-vinylpyridine)s polysoaps [4]. The compact conformation of these amphiphilic polycations showed an analogy with surfactant micelles in that the polymers solubilized hydrophobic small molecules in dilute aqueous solutions. Later, Strauss et al. [5,6] synthesized a series of... 

The opposite effect on quenching by neutral molecules when small amounts of detergent are added to aqueous solutions of 3 could be attributed to several possible factors. First, the addition of detergent to the polymer may help in affording a more hydrophobic environment in its vicinity that may enhance the polymer-small molecule association. Also, since surfactants such as DTAB are well known to solubilize organic molecules in water, it appears reasonable that clusters of the detergent may combine with the neutral quenchers and function as chaperones to increase their effective solubility and thus enhance the complex formation with the polymer. 

Rheological studies of solutions of these polymers in distilled water clearly identified viscosity enhancement due to the presence of the hydrophobic tert butylstyrene endblocks. Comparison with homopolymer and random copolymers of similar composition and molecular weight demonstrated the increased viscosification with the block configuration. The block polymer solutions were also observed to solubilize toluene with a marked increase in the solution viscosity. These results are interpreted as the result of polymer intermolecular association through the hydrophobic blocks similar to micellization of surfactants. 

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