Amphiphilic block copolymers have many unique physical and chemical properties

especially stronger self-assembling ability

because of amphiphilic property and microphase separation of their molecules．In this investigation

the amphiphilic block copolymers of acrylamide(AM) and styrene(St) were prepared in microemulsion medium．One series of copolymers PAM-b-PSt was synthesized by changing the feed ratio under remaining other copolymerization conditions invariable．The apparent viscosity of the aqueous solutions of copolymers samples were measured using a rotational rheometer．The effects of various factors on apparent viscosity

such as concentration of polymer

composition of copolymer

shear rate

temperature and salt concentration

were investigated in detail．The studying results show that there is strong hydrophobic interaction between the block suctions of PSt in the macromolecules of PAM-b-PSt

so that stronger intermolecular hydrophobic associations are formed in aqueous solution and above a critical polymer concentration(about 0.2％

wt％)．The intermolecular association leads to network structures and the hydrodynamic size of chains is increased

so the amphiphilic block copolymer PAM-b-PSt exhibits good thickening property．The another reason leads to good thickening property of PAM-b-PSt is that introducing of phenyl groups of styrene significantly enhanced the viscosity．Besides

under increasing shear

the physical links between chains are disrupted

but recover with decreasing shear

and also the associations are enhanced by the application of shear．The reversibility of the rheological property can to avoid the irreversible mechanical degradation．Therefore

the reversible association／dissociation process gives rise to particular rheological behaviors for PAM-b-PSt．Because hydrophobic association is endothermic

the intermolecular association is favoured by increasing the temperature

and so PAM-b-PSt has the withstanding temperature property．The containing of salt in aqueous solution of polymer can increase the polarity of the solvent

and the effect favoured the intermolecular association．As a consequence

the solution of the block copolymer PAM-b-PSt has salt resistance．Above described excellent properties of amphiphilic block copolymer PAM-b-PSt will leads to its wide commercial application．