The homogeneous copolymerization of acrylamide (AM) and sodium 2-acrylamido-tetradecane sulfonate (NaAMC14S)

which is a kind of acrylamide-type anionic surface-active monomer

was carried out in aqueous solutions.The concentrations of NaAMC14S were controlled above and below the critical micellar concentration (CMC)

respectively

and the copolymers with two types of chain structures

random and microblocky were obtained.The structures of the copolymers were characterized by FTIR spectra

and their molecular weights were correspondingly expressed by the intrinsic viscosities obtained with an Ubbelohde viscometer.The hydrophobically associating properties of the copolymers and rheological characters of their aqueous solutions were studied mainly by using the fluorescence probe method and apparent viscosity measurements.The experimental results show that the copolymers with microblocky structure have strong hydrophobically associating properties

and the apparent viscosities of their aqueous solutions increase rapidly as their concentrations are over 0.2 wt%.The shear thinning behavior of their aqueous solutions is obviously reversible

and they exhibit strong shearing resistance.There is a special finding about a positive salinity sensitivity of the aqueous solution viscosity of the microblocky copolymers.For those copolymers with microblocky structure the apparent viscosity of their brine solution is much higher than that of their pure water solution.The apparent

viscosity of the salt solution is enhanced actually by three orders of magnitude as the concentration of the copolymer is 0.3 wt% and the concentration of CaCl2 is 2 wt%

and a unique positive salt sensitivity

i.e.salinity thickening

is displayed.