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Khudyakov I.V.,Bomar Specialties | Turro N.J.,Columbia University
Designed Monomers and Polymers | Year: 2010

The efficiency of photoinitiators depends upon the quantum yield of photogeneration of reactive free radicals and the cage effect value. Only radicals that escape the cage can initiate free radical polymerization. The modern concept of the cage effect is presented. Dependencies of the cage effect upon increasing of solvent viscosity in the course of polymerization are discussed. Cage effect dynamics or kinetics of geminate recombination is of special interest. Results of a kinetic study on the cage effect using ns laser flash photolysis are described. © Koninklijke Brill NV, Leiden, 2010.

Khudyakov I.,Bomar Specialties | Zharikov A.A.,TU Munich | Burshtein A.I.,Weizmann Institute of Science
Journal of Chemical Physics | Year: 2010

The kinetics of recombination/dissociation of photogenerated radical pairs (RPs) is described with a generalized model (GM), which combines exponential models (EMs) and contact models (CMs) of cage effect dynamics. The main assumption of EM is the irreversible dissociation of RP as a first-order reaction. CM takes into account repetitive contacts of radicals in the pair or reversible diffusional separation of radicals. The present GM accounts for both the recombination of RP within the cage of outcome and their diffusional separation in a free space. GM predicts that a short initial time RP decay is described by EM, and RP kinetics at longer times of observation is described by CM. This theory successfully describes available experimental data. Solvent viscosity effect on the cage effect values is also analyzed. © 2010 American Institute of Physics.

Khudyakov I.V.,Bomar Specialties | Khudyakov I.V.,Solutia Inc.
Research on Chemical Intermediates | Year: 2013

The majority of free radicals are highly reactive species which participate in bimolecular reactions with each other. Validation of the theory of molecular diffusion and reactivity in the liquid state requires knowledge of rate constants of radical-radical reactions (recombination, disproportionation) and their viscosity dependencies. An accurate comparison of theory and experiment has become available due to experimentally measured diffusion coefficients of reactive radicals by transient grating technique. Initial distribution of radicals in solution can be not random but pair-wise as in photo- or thermoinitiation of free radical polymerization reactions. Probability of a radical escape of a partner (cage escape) characterizes the initiator efficiency. Despite decades of measurement of cage effect values, cage effect dynamics with free radicals have only been investigated quite recently. The present tutorial review considers the effect of viscosity of Newtonian liquid on two types of recombination - in the solvent bulk and in a cage. Further, since radicals are paramagnetic species, external magnetic field affects probability of their reactions in pairs. These effects are also observed in viscous liquids, and reasons for such observations are explained. The recently discovered low magnetic field effect is also observed on radical pairs in viscous liquids. © 2012 Springer Science+Business Media B.V.

Aerykssen J.H.,Bomar Specialties | Khudyakov I.V.,Bomar Specialties
Industrial and Engineering Chemistry Research | Year: 2011

Dendritic oligomers were prepared using the Michael reaction of thiol with acrylates taken in excess. Liquid oligomers A-D demonstrate exceptional shelf life. When cured, the oligomer produces a coating with relatively high tensile strength and hardness that is akin to high viscosity dendritic urethane acrylates. Oligomers A-C demonstrate a balance of properties in between the developed in our lab earlier dendritic polyester acrylates, BDE-1025 (low viscosity, lower hardness) and the dendritic urethane acrylates D and XDR-1416 (high viscosity, high hardness). © 2010 American Chemical Society.

Swiderski K.W.,Bomar Specialties | Khudyakov I.V.,Bomar Specialties | Boynton L.R.,Bomar Specialties
PCI-Paint and Coatings Industry | Year: 2010

This brief review article did not aim to cover the most recent advances in the area of radiation cure and thermal cure of urethane prepolymers (oligomers) but rather briefly describe the current status of this technology. UV processors are affordable, with a starting price of $5 k. A simple, inexpensive processor fits inside the trunk of a car. Although not necessarily UV, cure with visible light can be rather efficient. An excellent example is a cure by visible light (l 450-480 nm) of dental restorations, which are methacrylates and urethane methacrylates in particular. Formulations cured by visible light are colored; that color may decrease or disappear due to the partial or complete consumption of PI with the formation of colorless products.

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