Experimental observation of crossover from noncondensed to counterion condensed regimes during free radical polyelectrolyte copolymerization under high-composition drift conditions.

By combining detailed online kinetics of comonomer consumption with light scattering, viscosity, and conductivity data, experimental detection of changing degrees of counterion condensation was achieved by using comonomers of widely separated reactivity ratios that produced large composition drifts during synthesis. Endproducts of such syntheses contained mixtures of chains of widely varying linear charge density. Evidence of a smooth transition from noncondensed to counterion condensed regimes was found during individual synthesis reactions of copolymeric polyelectrolytes, or "copolyelectrolytes", from the changing slope of conductivity versus [ionic comonomer] incorporated in the high-composition drift syntheses. From this, a model was used to connect the latter slope behavior to fractional ionization of counterions. With this modeled fractional ionization versus the instantaneous fractional amount of the charged comonomer incorporated into copolyelectrolyte, which is directly and continuously monitored during synthesis, it was possible to compute linear charge density xi and the corresponding average xi distribution.