Hydrophobe content

Fig. 22. Surface activity of closely related cationic polysoaps in dependence on their geometry and on their main chain spacer in water at 25 °C. (Data from [167, 245]). Tail end geometry A = polysoap 53. Head geometry X = copolymer soap 19a (hydrophobe content y = 0.4), + = copolymer soap 19b (y = 0.2), = copolymer soap 19c (y = 0.1)...

A critical concentration for the onset of solubilization (pointing to inter-molecular aggregation), or CMC-like breaks in the surface tension curves have been reported only for oligomeric polysoaps [73, 74, 109,110, 213, 251, 353] or for polymers whose hydrophobe content is below the CAC [212, 214,298, 391],... 

The hydrophobe content of the HMHEC was determined by exhaustive cleavage of the polymer with 57% aqueous hydroiodic acid for 2 h at 18 195 °C followed by analysis of the iodoalkane formed by gas chromatography on a column packed with 10% OV-17 (phenylmethylsilicone) on 80-110-mesh Chromosorb W-HP (diatoma-ceous earth, Alltech Associates) in a Perkin-Elmer 3920B gas chromatograph. All samples were run in triplicate. 

Copolymerization. Synthetic HMWSPs can be prepared according to this approach by the copolymerization of a vinyl or epoxide monomer (4) with a small amount of a specific hydrophobic monomer that is copolymer-izable with the primary monomer as shown in Scheme II. The hydrophobe content of the polymers can be tailored by controlling the amount of the hydrophobic comonomer used in the polymerization process. The nature of the group (i.e., ether, ester, carbamate, etc.) connecting the long-chain... 

As the hydrophobe content of the HMHEC increases, the viscosity first increases, reaches a maximum, and then decreases rapidly. The viscosity finally approaches that of the solvent as the polymer becomes insoluble. A minimum hydrophobe level (discussed in detail later) is necessary to achieve an observable increase in viscosity as compared to that of the unmodified HEC. Above this threshold, viscosity increases rapidly with increase in the hydrophobe content. After reaching the peak viscosity at an appropriate hydrophobe level, the viscosity decreases upon further increase in hydrophobe level. This decrease is not caused by a diminution in the degree of hydrophobic association, but by the incomplete solubility of the sample. That is, a given HMHEC sample has a distribution of polymer chains with different hydrophobe levels. The proportion of insoluble species increases as the overall hydrophobe content of the sample increases. The hydrophobe... 

Figure 10 shows a plot of intrinsic viscosity versus hydrophobe level for two HMHEC samples that have different hydrophobes. As the hydrophobe content at fixed molecular weight increases, the intrinsic viscosity decreases. This behavior is even more striking for CieHMHEC. In dilute solutions, the HMHEC molecules are separate and untangled, and no intermolecular association occurs. However, to minimize the disruption of water structure, hydrophobes on the same chain tend to cluster. This clustering results in a much reduced hydrodynamic volume, and a lower viscosity is observed. Therefore, the dilute solution properties of HMHEC are consistent with intramolecular hydrophobic association (10). Because of intramolecular association and incomplete solubility, the intrinsic viscosity of HMHEC cannot be appropriately correlated with its molecular weight. Hence, to obtain meaningful intrinsic viscosity data, intramolecular association must be com-... 

Figure 10. Aqueous intrinsic viscosity of CaHMHEC (O) and C leHMHEC ( ) vs. their hydrophobe contents. Reproduced with permission from ref. 10. Copyright 1987 TAPPl Press.)...

The data presented in Table IV show that the polymer that formed at the early stages of the polymerization (i.e., about 30% conversion) had a much higher hydrophobe content than polymer produced toward the end... 

ABU Abu-Sharidi, B.F., Hamad, E.Z., and Ah, S.A., Influence of hydrophobe content on phase coexistence curves of aqueous two-phase solutions of associative polyaciyl-amide copolymers and poly(ethylene glycol), J. Appl. Polym. Sci., 89,1351,2003. 

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