The interaction of cetyl trimethylammonium bromide (CTAB)and an anionic copolymer derived from 3-sulfopropylmethacrylate

potassium salt (SPMS) and styrene (St) in aqueous solutions has been studied. It was found that the viscosity of the anionic copolymer-CTAB solution rises suddenly in a specific molar ratio of CTAB/anion. For instance

the viscosity of polymer (No.1) solutions increases to about 20 times at CTAB/-SO3K=1.0～1.05

and increases to about 100 times at CTAB/-SO3K=1.4～1.5. In the caseof polymer samples No.2 and No.3

the changes of solution viscosity are similar to that of sample No.1

but the gelation takes place at CTAB/-SO3K=1.4～1.5 region because of the lower negative charge density on No.2 and No.3 polymer chains.It is proposed that the dramatical change of the P(SPMS-co-St) aggregates. This consideration was verified by fluorescence determination and laser light scattering experiments.Using DMAF as fluoresscent probe

the hydrophobic microdomain existed in P(SPMS-co-St)/CTAB aqueous solutions in the viscosity rising region has been confirmed and it is in agreement well with the results obtained by laser light scattering determination.