GENERALIZATION OF THE KINETIC SCHEME FOR A DYE-PHOTOSENSITIZED FREE-RADICAL POLYMERIZATION INITIATING SYSTEM VIA AN INTERMOLECULAR ELECTRON-TRANSFER PROCESS - APPLICATION OF MARCUS THEORY

We present a theoretical description of the kinetics for dye-initiated photopolymerization via an intermolecular electron-transfer process w hich considers the properties of the organic redox pair forming initia ting radicals. An application of the Marcus theory yields a kinetic sc heme, which considers both the thermodynamical and kinetic aspects of the electron-transfer process. The intermolecular electron transfer is the limiting step in the polymerization initiation. The theory is sup ported by:experimental data. Two organic redox pairs forming free radi cals have been tested, (I) a series of pyrazolone azomethine dyes (PAD ) (electron accepters) and N-phenylglycine (NPG) (electron donor) and (2) the Rose Bengal derivative (RBAX) (C2' benzyl ester, sodium salt), serving as an electron acceptor and series of tertiary aromatic amine (TAA) electron donors. The following conclusions are reached: (i) The experimental data demonstrate the inverted region or inverted-region- like kinetic behavior; e.g., the rate of polymerization decreases with an increasing thermodynamic driving force (-Delta G degrees) for elec tron transfer. This behavior allows the use of the Marcus theory for a nalyzing or predicting the ability of organic redox systems for light- induced free-radical. polymerization. (ii) The dependence of the rate of polymerization on Delta G degrees suggests that the dark stability pf the monomer-initiating system mixture may be due to the excited-sta te activation energy (E(00)). (iii) Considering the reorganization ene rgy factor lambda (for the reacting molecules and the monomer), one ma y suspect that the molecular geometry and structure effect the photoin itiation efficiency.