Characterization hydrophobically associating polymers

Y. Feng, L. Billon, B. Grassl, A. Khoukh and J. Francois, Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post-modification. 1. Synthesis and characterization, Polymer, 2002, 43, 2055-2064. 

The dynamics of intact lime cuticle and its two major component polyesters, cutin and wax, have been studied by the MAS NMR experiment [134]. By the measurements of spin-lattice relaxation times and spin-lattice relaxation times in the rotating frame which characterize respectively the megahertz- and kilohertz-regime motions, it is indicated that motional restrictions are present at the crosslinks of the cutin polymer and along the alkyl chains of the wax. The values of relaxation times, which differ for analogous carbon sites of cutin and wax individually, approach common values for the two materials in the intact lime cuticle. These results are considered to provide evidence for hydrophobic association within the plant cuticle of the long aliphatic chains of cutin and wax. 

The nature of hydrophobic interactions and their effects on the structure and properties of water have been extensively studied, particularly for small molecules (i 3). In contrast, the introduction of hydrophobic associations into synthetic water-soluble polymers to control solution rheology has received rather limited and recent study (4-7). To better understand the relationships between polymer structure and solution properties, we have synthesized and characterized a series of copolymers of acrylamide and N-substituted alkylacrylamides and terpolymers containing anionically charged carboxyl groups. Solution properties of these systems have been obtained in both the dilute and semidilute concentration regime, to probe the influence of intra- and intermolecular interactions. In addition, the influence of the shear field and solvent quality on the associations was studied. 

The same process of hydrophobic association, observed in solution and characterized by the phase diagram in Figure 5.3, occurs in the elastic matrix where hydrophobic association displays as a visible contraction. The parallel process of cloudy formation of polymers in solution transforms in the elastic matrix into a contraction capable of performing mechanical work. 

Synthesis and Characterization of Hydrophobically Associating Water-Soluble Polymers... 

Nevertheless, hydrophobically associating water-soluble polymers present challenges to both the synthetic and characterization chemists. Hydrophobically associating water soluble polymers are often difficult to synthesize because of problems associated with mixing oil-soluble and water-soluble reagents/ monomers. Similarly, since only small levels of hydrophobe are needed for rheology control, characterization of hydrophobe contents often stretch the detection limits of conventional polymer characterization methods. 

The Ej(30) has also been used to explore polymer association as a function of the hydrophobe level. As shown in Fig. 2.15, the increase in A(max) tracks the increase in hydrophobe content in the polymer. This indicates increased hydrophobe character for the microdomains and stronger polymer association with increasing hydrophobe levels. It is noteworthy that the increase in A(max) dovetails the increase in solution viscosity (Fig. 2.16). Thus, the dye probe provides microscopic domain information which complements the macroscopic solution viscosity characterization of the polymer system. 

A new class of water soluble cellulosic polymers currently receiving attention Is characterized by structures with hydrophobic moieties. Such polymers exhibit definite surface activity at alr-llquld and liquid-liquid Interfaces. By virtue of their hydrophobic groups, they also exhibit Interesting association characteristics In solution. In this paper, results are presented on the solution and Interfaclal properties of a cationic cellulosic polymer with hydrophobic groups and Its Interactions with conventional surfactants are discussed. 

Because the main driving force for surfactant self-association in polymer-surfactant mixed systems is the hydrophobic effect, the binding of surfactants to polyelectrolytes exhibits a similar dependence on the length of the alkyl chain as known for free micellization. Surfactants with longer hydrocarbon chains bind more strongly to polyions than those with shorter chains, and the binding starts a lower surfactant concentrations. In this context, a convenient parameter to characterize polyelectrolyte-surfactant systems is the critical aggregation concentration, cac, which is a counterpart of the well-known critical micellization concentration, cmc, but applies to solutions of surfactants in the presence of a polymer. It is defined as the... 

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