Kinetic isolation of persistent radicals and application to polymer–polymer reactions

Abstract

We analyze the transient kinetics of a mixture of two radicals (M and P), one of which (P) has very low, or zero self-reactivity ͑i.e., P is a ''persistent'' radical͒. For the case where the self-reactivity of the persistent radical is zero, we find a critical value for the initial concentration ratio rϵ P 0 /M 0 , above which the persistent radicals are isolated at long reaction times after all of the M 's react. If r is below its critical value the surviving fraction of P is zero. An experiment employing virtually zero self-reactivity nitroxide radicals is proposed to test the predicted critical behavior. If the self-reactivity of the M is stronger than the cross-coupling reactivity, then the critical value of the ratio r is negative, and a finite fraction of the persistent P radicals are always isolated, regardless of the initial concentration ratio r. For the case where the self-reactivity of the persistent radicals is finite but small, we find similar behavior, except now the P radicals react with one another on a much longer time scale following their isolation. The isolation process facilitates the measurement of P-P reaction kinetics in situations where it is difficult to generate the P radicals by themselves. An experiment to measure fundamental polymer-polymer reaction kinetics in concentrated solutions or melts is proposed based on these ideas.

Interfacial Reactions: Mixed Order Kinetics and Segregation Effects

“…These numerical results are all consistent with our theoretical predictions. On the experimental side, we hope this work will motivate future studies of, for example, interfacial polymer systems involving laser-induced macroradicals [15]. These can help to to resolve fundamental issues in interfacial science.…”

Reaction kinetics in polymer melts

“…( 8)), which subject to the constraints satisfied by the real µ, eqs. (10) and (11), maximizes ϕ t (0). We consider each of the 4 regions in figs.…”

“…Times t l ≪ t ≪ τ . In this case we consider both constraints (10) and (11). Now clearly from its definition in eq.…”

“…We imagine that at t = 0 a certain fraction of the chains randomly and uniformly distributed in a monodisperse polymer melt carry chemically reactive end-groups. Experimentally this can be realized for example by attaching photocleavable groups to the ends of a certain fraction of the melt chains [10]. A laser pulse then cleaves these groups into radical pairs (fig.…”

“…It was shown in ref. [10] that after a transient the small radicals disappear, leaving behind a fraction of order unity of the macroradicals. The reaction kinetics of these kinetically isolated macroradicals will then follow the kinetics developed in the following.…”