Abstract: Three series of the amphiphilic block copolymers of acrylamide(AM) and styrene(St) were prepared in microemulsion medium by using sodium dodecyl sulfate(SDS) as the surfactant. One of the copolymer PAM-b-PSt series had a variation of the amount of the hydrophobic block segments PSt by changing the feed ratio in copolymerization at fixed amount of initiator and at constant level of St/SDS,the second had different lengths of the hydrophobic block section PSt by changing the ratio St/SDS which decides the length of the hydrophobic blocks,under fixed amount of initiator and at constant level of feed ratio of monomers,and the third had a variation of molecular weight by changing the amount of initiator at constant level of feed ratio of monomers and constant level of St/SDS. The hydrophobic associating behavior of amphiphilic block copolymers can be revealed at a macroscopic level by the formation of hydrophobic microdomains in aqueous solution and its surface activity can be displayed by the ability to decrease surface tension of aqueous solution. So the relationship between the microstructue and the hydrophobic associating property and surface activity of the amphiphilic block copolymer PAM-b-PSt was investigated by florescence probe technology and measuring of surface tension of aqueous solution. The experiment results showed that the hydrophobic associating property of PAM-b-PSt was dependent on its microstructue strongly. In aqueous solution,above a critical associating concentration,intermolecular hydrophobic interactions lead to the formation of polymolecular associations and the formation of hydrophobic microdomains. When the content of PSt blocks and molecular weight are constant for copolymers PAM-b-PSt, the hydrophobic associating extent varies with the change of the length of the hydrophobic blocks. The longer the hydrophobic blocks are,the stronger the hydrophobic association degree is. But the length of the hydrophobic blocks does not influence its surface activity nearly. When the length of the hydrophobic blocks and molecular weight are constant,the hydrophobic associating extent varies with the change of the content of PSt blocks,at a appropriate level of the content of PSt in the PAM-b-PSt molecular chains there are the strongest hydrophobic associating effects. When the length and content of the hydrophobic blocks are constant for copolymers PAM-b-PSt,the hydrophobic associating extent does not vary with the change of the molecular weight nearly. But,the molecular weight influences the surface activity of PAM-b-PSt obviously. The lower the molecular weight is,the stronger the surface activity is. Thus after clarifying the relationship between the aqueous solution properties and the microstructue for PAM-b-PSt,it is possible to control its association degree and surface activity for some purpose.

Key words: Amphiphilic block copolymer, Acrylamide, Styrene, Microstructur, Hydrophobic association, Surface activity