| Abstract
| - The dissolution in water of the sodium salts of poly(2-acrylamido)-2-methylpropanesulfonic acid (PAMPS),N,N-di-n-octadecyl-endcapped-poly(2-acrylamido)-2-methylpropanesulfonic acid [(C18)2-PAMPS], cholesteryl-endcapped-poly(2-acrylamido)-2-methylpropanesulfonic acid (Chol-PAMPS), and a random copolymerof AMPS and N-dodecylmethacrylamide (PAMPS-Dod20) was studied by isothermal titration calorimetry(ITC). The endcapped polymers form multimolecular aggregates in aqueous solutions. The concentrationrange for aggregation and the enthalpy of micellization were determined as functions of the electrolyteconcentration (0.01 M < [NaCl] < 0.3 M) and temperature (288 K < T< 308 K) for solutions of (C18)2-PAMPS. At 298 K and 0.2 M NaCl, aggregation of this amphiphilic polyelectrolyte occurs in solutions withconcentrations ranging from about 1 to 14 mmol of AMPS L-1 (0.5−2.7 g L-1) with an enthalpy of micellizationof ∼100 J (mol of AMPS)-1. The effect of the experimental conditions, such as the method of preparationof the polymer stock solution and its concentration, on the ITC results is described in the case of Chol-PAMPS. Titrations performed with poly(sodium-2-acrylamido-2-methylpropane sulfonate) (PAMPS)confirmed that PAMPS does not aggregate in aqueous NaCl, whereas PAMPS-Dod20 forms predominantlyunimolecular micelles. The advantages and limitations of ITC for studying the micellization thermodynamicsof amphiphilic polyelectrolytes are discussed.
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