The nonlinear change in conformation of polyelectrolyte macromolecules in saltless water-organic solvent

High molecular weight polyelectrolyte: poly(dimethylaminoethyl methacrylate) [PDMAEMA] with molecular weights M(W)=28.0x10(6), 20.0x10(6), 15.0x.10(6) was investigated in dilute solution by light scattering, flow birefringence and viscometry (at different rate gradients) in a water-acetone system by varying the weight fraction of acetone gamma in the mixture. At T=0.76 the polymer undergoes a reversible coil-globule transition accompained by a drastic decrease in intrinsic viscosity [n], mean-square radius of gyration <R(2)>(1/2)(z) and second virial coefficient A(2), with no change in molecular weight. The coil asymmetry parameter p (p=2.5 at gamma=0.50) decreases with increasing gamma and attains unity (completely symmetrical particle) at the transition point (gamma=0.76). The anomalous behavior of the viscosity of PDMAEMA-water-acetone solutions, detected near the transition point (gamma=0.6+0.7), is interpreted by formation of local knots of compactization on the molecular chain under the influence of a hydrodynamic field.