FROM MEAN-FIELD TO DIFFUSION-CONTROLLED KINETICS - CONCENTRATION-INDUCED TRANSITION IN REACTING POLYMER-SOLUTIONS

We study irreversible interpolymeric reaction rates k in polymer solutions as a function of concentration phi. At high dilution, kinetics obey mean field theory, and screening of excluded-volume repulsions as phi increases results in a growth, k is similar to phi3g/4, where g is the monomer contact exponent. Screening effects cause a transition to diffusion-controlled kinetics at a value phi**, beyond which (for entangled solutions) k decreases as k is similar to phi-(5/8+gamma), gamma being the entanglement exponent. Thus k is peaked at phi** which, in agreement with experiment, is distinct from the overlap threshold.