Aggregation Behavior of Mono-endcapped Hydrophobically Modified Poly(sodium acrylate)s in Aqueous Solution

Abstract

Titration microcalorimetry and steady-state fluorescence spectroscopy have been used to study the aggregation of mono-endcapped hydrophobically modified poly(sodium acrylate)s in aqueous solution. Polymers with molecular weights varying between 800 and 31,700 were synthesized by radical polymerization using an initiator and chain transfer agent. The resulting polymers form hydrophobic microdomains in aqueous solutions. The following conditions were applied: no salt and pH 5 and 9, respectively; 1 M sodium citrate and pH 9. At pH 5 the critical aggregation concentration (CAC, the concentration at which microdomains are formed) increases with increasing molecular weight of the polymers. The concentration range for aggregation is about 0.2-2.4 mM. At pH 9 the carboxylic acid groups are deprotonated and electrostatic repulsions are introduced; therefore the concentration for aggregation rises to about 80 mM. Interestingly, in case of polymers having M(n)<1400 the CAC decreases with increasing molecular weight due to a counterion-concentration gradient toward the hydrophobic microdomain. Near the microdomain the counterion binding is increased, reducing the electrostatic repulsions and allowing for lower aggregation concentrations. In the presence of 1 M sodium citrate this anomalous trend is suppressed to a large extent; since the overall counterion binding is increased and the CAC is lower. The concentration for aggregation is then in the same range as at pH 5 in the absence of salt. Copyright 2000 Academic Press.

The association of octadecyl-end-capped poly-(sodium 2-acrylamido-2-methylpropanesulfonates) in water and salt solutions: A study by fluorescence spectroscopy and isothermal titration calorimetry

“…A similar observation has been reported in a recent study of the micellization of endcapped poly(sodium acrylates) (M n ∼ 30 000) [9]. The effect was attributed to a "self-salting-out effect", which consists of a concentration gradient of sodium counterions toward the hydrophobic core of the aggregates and takes place in water for polyelectrolytes of sufficiently high molecular weight.…”

“…106 The European Physical Journal E This was demonstrated, for example, in early studies of amphiphilic derivatives of poly-(N-isopropylacrylamide) (PNIPAM) consisting of a PNIPAM chain substituted at one end with a di-(n-octadecyl) group or a N-(noctadecyl)-N- [4-(1-pyrene)]butyl group [7,8] and, more recently, in investigations of mono-endcapped poly(sodium acrylates) [9] and of cholesterol-end capped PAMPS [10]. In the latter case, a detailed analysis of the solution properties of the polymers demonstrated that unimers of cholesterol-PAMPS coexist with multipolymeric micelles.…”

A concise analysis of the effect of temperature and propanediol-1, 2 on Pluronic F127 micellization using isothermal titration microcalorimetry

“…Curves that did not present clear sigmoidal features were analyzed by a data treatment analogous to the one suggested by many authors [12,21,23,29]. Linear fits of the data sets in the lower and upper concentration domains were performed.…”

Evaluation of the Micellization Mechanism of an Amphipathic Graft Copolymer with Enhanced Solubility of Ipriflavone

“…Under this experimental condition, thermodynamic reactions derived from the phase of (ii) and (iii) may be observed. The non-sigmoidal thermograms were analyzed according to a method that has been reported by many authors 23,29,30) and enables a rough estimation to be made of the start of transition (ST) and end of transition (ET) corresponding to the start and end of the micellization process. As shown in Fig.…”