A zwitterionic monomer of 4-vinylpyridine propylsulfobetaine (4-VPPS) was prepared by the ring opening reaction of 1

3-cyclopropanesultone (PS) with 4-vinylpyridine (4-VP) at 80℃ for 20 h.Zwitterionic copolymers P(AM-co-VPPS) containing sulfobetaine groups were synthesized by copolymerization of acrylamide (AM) and 4-VPPS in aqueous solutions.The effects of 4-VPPS mole fraction in total monomer

the amount of initiator

total monomer concentration and reaction temperature on intrinsic viscosity of copolymers were investigated.The structure and composition of the copolymers were characterized by FTIR spectroscopy and 1H-NMR.The reactivity ratios of rl (AM)and r2 (4-VPPS) had been determined to be 2.01，8.71 and 1.99

8.44 according to Finemann-Ross equation and Kelen-Tudos equation

respectively.The experimental results showed that the intrinsic viscosity of copolymers reached the maximum value 656.4 mL/g when the reaction took 12 h at 20℃

with 0.03 wt% initiator concentration

2% 4-VPPS mole fraction in total monomer and 30 wt% total monomer concentration.The experimental results from viscometry indicated that copolymers P(AM-co-VPPS) exhibited typical anti-polyelectrolyte behavior

i.e.

the intrinsic viscosity of the zwitterionic copolymer increased with increasing the amount of low molecular weight electrolytes added regardless of NaCl or CaCl2.The increase of the intrinsic viscosity of copolymers P(AM-co-VPPS) in brine compared to that in the deionized water was strongly influenced by species and concentration of salts and the 4-VPPS mole fraction percentage in the copolymer P(AM-co-VPPS).As for copolymer P(AM-co-VPPS) containing 10.2 mol% 4-VPPS

the intrinsic viscosity increased by 47.3%

56.7% and 56.8% respectively in 1 mol/L NaCl

2 mol/L NaCl and 2 mol/L CaCl2 compared to that in deionized water.The zwitterionic copolymers with brine induced viscosifying effect could be used in enhanced oil recovery.