SynopsisThis paper reviews our current understanding of the kinetics and mechanisms of free-radical chain polymerization of methyl methacrylate. A mathematical model previously proposed to describe the bulk polymerization of MMA is here extended to cover solution polymerization. This extended model is validated by comparing its predictions with experimental data over a range of conversions and product molecular weights.
SynopsisSeveral control strategies for the free-radical polymerization of methyl methacrylate are analyzed with a detailed constitutive model incorporating the gel and glass effects. Optimal temperature history, photoinitiation intensity variation, and programmed monomer and solvent additions, employed alone and in combination, represent cases simulated by this model. Solvent addition is selected for further experimental studies, due to some attractive features. The product molecular weight distribution is narrowed, while the molecular weight averages are maintained high. Model predictions of the solvent injection history exhibit a strong sensitivity to the constitutive equations for describing the gel and glass effects.
We report and model a linear increase in the thermal conductivity (κ) of polymer composites incorporated with relatively low length/diameter aspect ratio multiwalled carbon nanotubes (CNTs). There was no evidence of percolation-like behavior in the κ, at/close to the theoretically predicted threshold, which was attributed due to the interfacial resistance between the CNT and the polymer matrix. Concomitantly, the widely postulated high thermal conductivity of CNTs does not contribute to the net thermal conductivity of the composites. Through estimating the interfacial resistance and the thermal conductivity of the constituent CNTs, we conclude that our experimental and modeling approaches can be used to study thermal transport behavior in nanotube–polymer composites.
SynopsisProgrammed solvent injection was previously proposed and analyzed in the first part of this twepaper series as a viable alternative for controlling the average molecular weight and narrowing the polydispersity of products from a free-radical polymerization process with an inherent tendency to exhibit strong gel and glass effects. Here, methyl methacrylate is chosen for experimental verification of this idea. The product molecular weight distribution is indeed narrowed.
SynopsisOxygen injection has been proposed as a n effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model is developed to describe the system behavior with and without oxygen injection. Because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight.
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