Free-radical polymerization kinetics

Assuming that the concentration of free radicals remains relatively constant during polymerization (the pseudo-steady-state assumption), the rate of polymerization Rp) for bulk or solution polymerization can be expressed as 

Figu re 1.2. (a) Monomer conversion as a function of time, (b) Weight-average molecular weight as a function of conversion for free radical polymerization. 

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German, A.L., Ed. Macromol. Symp., Free Radical Polymerization Kinetics and... 

R.A. Hutchinson, M.C. Grady and WJ. Simonsick, Preprints International Symposium on Free Radical Polymerization Kinetics and Mechanism, II Ciocco, Italy (2001). 

Here, gt takes into account one interesting feature of the free radical polymerization kinetics the auto acceleration in the rate of reaction (better known as the Trommsdorff or gel effect). The gel effect is taken into account in the model (42) by including the experimental correlation developed in [18] for the termination rate ... 

As a consequence of the free radical polymerization kinetics, the termination rates are extremely fast in comparison to the slow initiation rates. This results in the formation of high molar mass chains at the initial stage of the polymerization and decreasing molar masses in the latter stages due to the decrease in the monomer concentration. Under these circumstances, broad molar mass distributions are inevitable. 

Free Radical Polymerization Kinetics of Immobilized Chains... 

Polystyrene and poly(methyl methacrylate) polymerizations are typical of homogeneous bulk chain-growth reactions. The molecular weight distributions of the products made in these reactions are broader than predicted from consideration of classical, homogeneous phase free-radical polymerization kinetics because of autoacceleration (Section 6.13.2) and temperature rises at higher conversions. 

Computational Aspects of Free Radical Polymerization Kinetics with Chain Length Dependent Termination... 

Comprehensive Models. This class of detailed deterministic models for copolymerization are able to describe the MWD and the CCD as functions of the polymerization rate and the relative rate of addition of the monomers to the propagating chain. Simha and Branson (3) published a very extensive and rather complete treatment of the copolymerization reactions under the usual assumptions of free radical polymerization kinetics, namely, ultimate effects SSH, LCA and the absence of gel effect. They did consider, however, the possible variation of the rate constants with respect to composition. Unfortunately, some of their results are stated in such complex formulations that they are difficult to apply directly (10). Stockmeyer (24) simplified the model proposed by Simha and analyzed some limiting cases. More recently, Ray et al (10) completed the work of Simha and Branson by including chain transfer reactions, a correction factor for the gel effect and proposing an algorithm for the numerical calculation of the equations. Such comprehensive models have not been experimentally verified. 

Pierik, B. Masclee, D. Vollmerhaus, R. van Herk, A. German, A. L. In Free Radical Polymerization. Kinetics and Mechanism, Macromolecular Symposia Series, Buback, M., Ed. Wiley-VCH Weinheim, 3rd IUPAC-Sponsored International Symposium on Free Radical Polymerization Kinetics And Mechanism, II Chioccho/Lucca, Italy, June 3—8, 2001. 

Free-radical Polymerization Kinetics. A general scheme for these reactions is the following ... 

Over 200 references describing spontaneous, and chemically initiated styrene polymerization chemistry are reviewed with special emphasis on advances taking place in the past decade. The review is limited to chemistry useful for making amorphous high molecular weight polystyrene in solution polymerization processes. Chemical initiators have been categorized into three basic groups as follws 1) anionic 2) mono-radical and 3) diradical. Analytical techniques used for determination of free radical polymerization kinetics and mechanisms are also discussed. 

Veregin, R.P.N., Odell, P.G., Michalak, L.M., and Georges, M.K., 1996, Molecular Weight Distributions in Nitroxide-Mediated Living Free Radical Polymerization Kinetics of the Slow Equilibria between Growing and Dormant Chains, Macromolecides, 29 3346... 

The polymerization rate is directly proportional to the monomer concentration for ideal free radical polymerization kinetics. Deviations from this first-order kinetics can be caused by a whole series of effects which must be checked by separate kinetic experiments. These effects include cage effects during initiator free radical formation, solvation of or complex formation by the initiator free radicals, termination of the kinetic chain by primary free radicals, diffusion controlled termination reactions, and transfer reactions with reduction in the degree of polymerization. Deviations from the square root dependence on initiator concentration are to be primarily expected for termination by primary free radicals and for transfer reactions with reduction in the degree of polymerization. 

Strategies for controlling the copolymer composition and MWD of latices based on linear and non-linear copolymers, such as styrene/butyl acrylate copolymers and methyl methacrylate/n-butyl acrylate copolymers, are described. These strategies involve on-line procedures based on calorimetric measurements and open-loop processes employing a mathematical model for determining the trajectories of the manipulated variables, such as monomer feed flow rates and chain transfer agent. 35 refs. (3rd lUPAC-Sponsored International Symposium on Free-Radical Polymerization Kinetics and Mechanism, II Ciocco (Lucca), Tuscany, Italy, 3rd-9th June, 2001)... 

O Driscoll, K. F., and Russo, S., eds. (1996). 2nd International Symposium on Free Radical Polymerization Kinetics and Mechanisms, held in Santa Margherita Figure, Genoa, Italy, 26-31 May 1996, 328 pp. 

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