Reaction of a low‐molecular‐weight free radical with a flexible polymer chain: Kinetic studies on the OH + poly(N‐vinylpyrrolidone) model

Abstract

This work addresses the issue of kinetics of diffusion-controlled reactions of small radicals with macromolecules in solution. Attack of pulse-generated hydroxyl radicals on poly(N-vinylpyrrolidone)-PVP-chains of various molecular weight in water was used as the model reaction. Pulse radiolysis with spectrophotometric detection was applied to determine the rate constants by competition kinetics. The rate constant depends both on polymer concentration and on its molecular weight. In dilute solutions, a distinct dependence of the rate constant on the molecular weight is observed. In the studied range of molecular weight, the values of reaction radius, calculated using Smoluchowski equation on the basis of experimental kinetic data, are very close to the radius of gyration of polymer coils. We believe that radius of gyration, as an easily determined parameter, could possibly serve for predicting rate constants of diffusion-controlled reactions of polymers with low-molecular-weight compounds in dilute solutions. With increasing polymer concentration and thus increasing spatial overlap of polymer coils the dependence of the rate constant on the molecular weight fades away, and the rate constant values increase with increasing concentration toward the value determined for low-molecular-weight model of PVP. Most steep increase approximately coincides with the

On the origin of functionalization in one-pot radiation synthesis of nanogels from aqueous polymer solutions

“…The general simplication that is oen made when analyzing data from pulsed e-beam irradiations of aqueous polymer solutions, is that all hydroxyl radicals produced upon radiolysis of water are scavenged by the polymeric solute to form carbon-centered macroradicals. 7,8,22 Hence, the average number of macroradical centers formed in a pulse would then simply be determined from the radiation chemical yield of hydroxyl radicals. This may be true at higher polymer concentrations but not necessarily at lower concentrations, where other reactions involving the hydroxyl radical could efficiently compete with the reaction of hydroxyl radicals with the polymer.…”

Temperature Mapping in Hydrogel Matrices Using Unmodified Digital Camera

“…Fortunately, both materials were previously used to trap and image fluorescently labeled proteins, macromolecules, and bacteria. ,− (ii) The probe needs to be smaller than the microporous cavities so it can uniformly distribute and diffuse freely. Agar and agarose matrices are highly porous with a pore size that ranges between 100 and 900 nm when prepared at 0.5%. , The calculated radius of gyration of PVP used in this study with an average molecular weight of 360 K was estimated to be equal to 35 nm . PVP is believed to be efficiently complexing PPE-CO 2 -7 aggregates. , Given the matrix pore size, the probe radius, and its solution dispersity, we expect the nanothermometer to distribute uniformly in the hydrogel.…”

“…34,35 The calculated radius of gyration of PVP used in this study with an average molecular weight of 360 K was estimated to be equal to 35 nm. 36 PVP is believed to be efficiently complexing PPE-CO 2 -7 aggregates. 21,22 Given the matrix pore size, the probe radius, and its solution dispersity, we expect the nanothermometer to distribute uniformly in the hydrogel.…”

On the Mechanism and Kinetics of Synthesizing Polymer Nanogels by Ionizing Radiation-Induced Intramolecular Crosslinking of Macromolecules

“…In parallel to these developments focused on the synthesis of PVP nanogels, the kinetics and mechanism of PVP radiolysis in water has been the focus of many experimental and simulation studies. The kinetics of the • OH reaction with PVP have been studied in some detail by pulse radiolysis employing the competition kinetics approach, indicating the effects of polymer molecular weight and concentration on the apparent values of the rate constants and pointing out that in dilute solutions the factor controlling the reaction rate is the size of polymer coil approximated as R g [124]. Jonsson et al elaborated a numerical simulation model of the radiation chemistry of aqueous polymer solutions and analyzed over 50 different reaction conditions related to the formation and recombination of polymer radicals [61,82,125].…”