Eur. Phys. J. E 5, 105-115

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

M. Mizusaki¹, Y. Morishima¹, B.B. Raju² and F.M. Winnik<sup>2

1</sup>  Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
²  Department of Chemistry and Faculty of Pharmacy, Université de Montréal, C.P. 6128 succursale Centre-ville, Montréal QC H3C 3J7, Canada

francoise.winnik@umontreal.ca

(Received 7 August 2000 and Received in final form 26 October 2000)

Abstract
Steady-state fluorescence spectroscopy and isothermal titration calorimetry (ITC) have been used to study the aggregation in aqueous solutions of poly-(2-acrylamido)-2-methylpropanesulfonic acids, sodium salt mono-endcapped with either N,N-di-n-octadecyl or N-4-[(1-pyrenyl)butyl]-N-n-octadecyl which were prepared by free radical polymerization of 2-(acrylamido)-2-methylpropane sulfonic acid (AMPS) initiated with the azo compounds, 4,4'-azobis{cyano-N,N-di-n-octadecyl}pentanamide and 4,4'-azobis{cyano-N,N-[4-(1-pyrenyl)butyl]-n-octadecyl}pentanamide, respectively. Both techniques indicate the occurrence of multimolecular aggregates in solutions of the polymers in water and in 0.2 M NaCl. The concentration range for aggregation is about 1-14 mmol AMPS l^-1 (0.5-2.7 g l^-1) in 0.2 M NaCl and the enthalpy of micellization, estimated from ITC data, is ~100 J [mol AMPS]^-1. The accessibility of the chromophores to neutral molecules and to cationic species was assessed by quenching of fluorescence with nitromethane and thallium nitrate, respectively. The association of the mono-endcapped polymers is compared to that of PAMPS derivatives carrying hydrophobic groups randomly attached along the chain.

PACS
82.35.Rs - Polyelectrolytes.
65.40.Gr - Entropy and other thermodynamical quantities.
82.30.Nr - Association, addition, insertion, cluster formation.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001