The current explanations of olefin and vinyl monomer polymerization propose that monomer molecules are successively added one by one to the growing polymer chain. This may be true if the monomer molecules exist as individual species in a polymerizing system, e.g. in dilute solutions of monomer. There are cases, however, in which monomer molecules are organized: bulk liquid monomer, solid monomer, a monomer monolayer adsorbed on a support, etc. Various supra-molecular species and particles of monomer exist in such cases. In the 1960-ties, Semenov, Kargin and Kabanov proposed a theory of organized monomer polymerization. In the last 25 years, our research group has further developed and applied that theory to various polymerizing systems: the radical polymerization of compressed ethene gas, the radical polymerization of liquid methyl methacrylate, olefin polymerization by transition metals and by Al-based catalysts. An outline of the main achievements are presented in this article
A series of nanocomposites were prepared by in situ polymerization of styrene with different silica content (1, 3, and 5 wt%) with an average particle size of 7 nm. The influence of nanosilica content on the kinetics of styrene free radical bulk polymerization was studied by isothermal differential scanning calorimetry (DSC) at different temperatures (70, 80, and 908C). Using appropriate kinetic model, describing two reactions observed during styrene polymerization (the first-order reaction and autoacceleration), it was found that silica presence does not affect the apparent activation energies of both processes. The adsorption of styrene on the silica surface caused the formation of interfacial layer in the structure of hybrid materials. Using suggested equation, the thickness of the interfacial layer was determined to investigate its influence on the glass transition temperature of polystyrene (T g ), which was found not to be affected by silica addition. POLYM. COMPOS.,
The free-radical bulk polymerization of many monomers is characterized by a sudden rise in the rate of polymerization, a phenomenon called autoacceleration. Many mathematical models have been developed to describe this phenomenon. In this paper, the development of a new kinetic model is described. The model very successfully describes experimental data obtained by differential scanning calorimetry of the bulk free-radical polymerization of methyl methacrylate. The proposed model is composed of two contributions to the conversion of the monomer, one originating from polymerization according to the classical theory of radical polymerization and the other originating from polymerization during the autoacceleration. The rate constant of the autoacceleration (second contribution) is about eightfold higher than the rate constant of the first-order reaction (first contribution).
The kinetics of styrene-free radical bulk polymerization was studied by differential scanning calorimetry (DSC). The data obtained from DSC thermograms were used to model and predict the autoacceleration during styrene polymerization and to understand how it is influenced by temperature. The experimental data were well described by the estimated kinetic model. The model included two processes (the first-order reaction and autoacceleration), because they occur simultaneously as two parallel reactions rather than being strictly separated. It was found that the autoacceleration activation energy is approximately four times lower than the energy of the first-order reaction. In addition, the first-order reaction followed by the autoacceleration of the styrene-free radical bulk polymerization occurs simultaneously only between 41.7 and 110.5 1C. Keywords: autoacceleration; differential scanning calorimetry; polymerization kinetics; polystyrene; styrene-free radical bulk polymerization INTRODUCTION It is well known that the free radical bulk polymerization of vinyl monomers (derivates of acrylic and methacrylic acids, vinyl acetate, styrene, ethylene and so on) is characterized by the autoacceleration phenomenon. 1-3 The free radical polymerization of these monomers can be explained by classical theory up to definite conversion. After that conversion, autoacceleration of polymerization occurs. The onset of autoacceleration is the moment when the polymerization rate departs from the value anticipated by the classical theory of free radical polymerization. [3][4][5][6][7] The onset and the intensity of autoacceleration are determined by the type of monomer, initiator concentration, temperature and other reaction conditions. Ebdon and Hunt 3 used differential scanning calorimetry (DSC) to follow the course of free radical bulk polymerization of styrene and concluded that autoacceleration is less pronounced at 90 1C than at 80 1C and is absent at 100 1C and above. Autoacceleration appeared at about 2% conversion of styrene polymerized at 20 1C for 252 days in the presence of 2,2¢-azobisisobutyronitrile. 8 To explain this autoacceleration, an equation was applied to the kinetic data obtained under the condition of predominant transfer to the monomer. It was concluded that polymer molecules may move by repetition and the mobility of segments decreases with decrease of free volume. 8 Comparisons of the results obtained for styrene-free radical bulk polymerization with model predictions have quantified the dependence of the gel effect strength on the predominance of chain transfer events. 9 Cioffi et al. 10 performed a rheokinetic study of the bulk-free radical polymerization of styrene with a helical barrel rheometer. The rheokinetic measurements show that autoacceleration in the free radical polymerization of styrene can be reduced when the polymer-
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.