2 results for Alghamdi, M.M.

  • Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

    Taylor, D.R.; van Berkel, K.Y.; Alghamdi, M.M.; Russell, G.T. (2010)

    Journal Articles
    University of Canterbury Library

    A comprehensive and systematic study of overall termination rate coefficients, kt, in low-conversion radical (homo)polymerization of methyl methacrylate and styrene is presented. Values of kt were determined by gravimetric analysis of steady-state experiments, employing 2,2’-azoisobutyronitrile as initiator. The values delivered by this simple method were found to be in qualitative and quantitative agreement with those from more modern and sophisticated techniques for measuring kt. Accordingly, correlations for bulk, low-conversion kt as a function of temperature are given for each monomer. The effects of initiator concentration, cI, and temperature on bulk kt were studied in a controlled way for both monomers. Additionally, ethyl benzene was used as solvent in order to investigate rigorously the effect of monomer concentration, cM, on styrene kt. The trends found by these systematic studies were considered in the light of what is known about the chain-length dependence of termination. Styrene’s behavior was always found to be qualitatively in accord with expectation, although the variations of kt with cI and cM were not as strong as should be the case. However its activation energy, 15 kJ·mol–1, is shown to be almost perfectly in agreement with theory. Methyl methacrylate, on the other hand, is recalcitrant in that its overall kt does not make manifest the chain-length dependent termination that has been directly measured by other techniques. Possible reasons for these discrepancies are discussed, as are reasons for the difference in values between kt for the two monomers. On the latter topic it is concluded likely that the chain-length dependence of termination at short chain lengths is primarily responsible for styrene having kt that is higher by a factor of about 3, with there also being a contribution that arises from styrene’s slower propagation.

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  • How Advances in Polymer Characterization Are Enabling a More Rigorous Understanding of Radical Polymerization Kinetics

    Alghamdi, M.M.; Russell, G.T. (2014)

    Conference Contributions - Other
    University of Canterbury Library

    The advent of reversible-deactivation radical polymerization (RP) has resulted in enormous growth in interest in RP over the last two decades. In the chemical community, this interest has been overwhelmingly focused on synthesis and material properties. However, the marketplace has not yet undergone any sea change, and industrial chemists remain very interested in traditional RP kinetics. As it so happens, major advances in this domain have also occurred. Two recent of these will be outlined in this talk: (1) The characterization of product polymer by large-molecule mass spectrometry (MS) as a window onto the kinetics of chain formation. Such information is yielded by the relative peak heights of the specifically identified products from the various avenues of dead-chain formation. By way of example, new and (for the first time) rigorous results for the disproportionation-to-combination ratio will be presented. (2) The coupling of pulsed-laser polymerization with EPR spectroscopy – the so-called SP PLP EPR technique – to study chain-length-dependent termination (CLDT), which it is now realized is the key to understanding many RP kinetic phenomena. By way of example, results for (meth)acrylate (macro)monomers will be presented. Combining these two strands, it will be shown that MS may be used to study CLDT, as exemplified for methyl methacrylate. Knowledge of the kind furnished by these studies is essential for robust modeling and rigorous understanding of such polymerizations, an obligatory aspect of the design and uptake of advanced materials.

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