TEMPERATURE-INDUCED MICELLE FORMATION OF A DIBLOCK COPOLYMER OF STYRENE AND TERT-BUTYLSTYRENE IN N,N-DIMETHYLACETAMIDE

Static and dynamic light-scattering studies are presented on the tempe rature-induced associating behavior of a polystyrene-poly(tert-butylst yrene) block copolymer in a selective solvent N,N-dimethylacetamide. O n cooling from 65-degrees-C down to room temperature, three temperatur e regions of unimer, transition, and micellar particles appeared seque ntially. The molecular weight and the hydrodynamic radius of the polym eric micelles formed at 25-degrees-C were found to be 1 X 10(7) g mol- 1 and 50 nm, respectively, whereas those of unimers examined at 60-deg rees-C were 2 x 10(5) g mol-1 and 10 nm, respectively. In both cases, a narrow size distribution was observed. In the intermediate transitio n region, dynamic light-scattering measurements have clearly demonstra ted a temperature- and concentration-dependent equilibrium between sin gle polymer chains and polymer micelles. From the concentration depend ence of the critical micelle temperature, the standard enthalpy of mic ellization was estimated to be -240 kJ mol-1. A closed association mod el with the enthalpy factor as the driving force is discussed. On the basis of the mass action law model of micelle formation and the time-a veraged scattered intensity results or the results of bimodal relaxati on rate distributions in the transition region obtained by the CONTIN analysis, we were able, for the present system, to estimate the critic al micelle concentration and related standard thermodynamic functions of micellization.