Marco Dossi

Investigation of Free-Radical Copolymerization Propagation Kinetics of Vinyl Acetate and Methyl Methacrylate

The free-radical copolymerization propagation kinetics of vinyl acetate (VAc) and methyl methacrylate (MMA) at 50 degrees C were investigated through an experimental study combined with a computational analysis based on quantum chemistry. Copolymer composition data, obtained using pulsed laser polymerization followed by size exclusion chromatography (PLP-SEC) and proton nuclear magnetic resonance (NMR), were well represented by the terminal model using monomer reactivity ratios obtained with the computational approach (r(VAc) = 0.001 and r(MMA) = 27.9). Concerning the composition-averaged copolymerization propagation rate coefficient k(p,cop), the differences between the terminal model and the implicit penultimate unit effect (IPUE) model (s(MMA) = 0.544 and s(VAc) = 0.173) are small for VAc/MMA, with the terminal model sufficient to describe the experimental k(p,cop) data measured by PLP-SEC. Monomer and radical charge distributions determined computationally are used to explain the reactivity exhibited by the VAc/MMA system.

Density functional theory study of addition reactions of carbon-centered radicals to alkenes.

Addition reactions of carbon-centered radicals to unsaturated compounds have been studied using quantum chemistry. Following the review by Fischer and Radom (Angew. Chem., Int. Ed. 2001, 40, 1340.), the radicals were grouped in four different families, and the alkenes were selected from among those typical of polymer productions. All of the kinetic constants were calculated using density functional theory and classic transition state theory. Geometries of reactants, products, and transition states were determined at the B3LYP/6-311+G(d,p) level of theory, whereas reaction enthalpies, activation energies, and kinetic constants were estimated using different basis sets. By comparative evaluation of the results obtained with different basis sets, the best computational approach for each kinetic step was identified. As a result of this study, a computational methodology suitable for investigating a large number of kinetic pathways typical of free-radical polymerization processes is proposed.

Quantum chemistry investigation of fluorinated polymer systems of industrial interest.

In this work, the free-radical polymerization (FRP) of widely used fluorinated monomers was investigated. Computational studies were conducted to assess the FRP kinetics of each binary copolymerization between vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). More specifically, all calculations were performed using density functional theory (DFT), and the B3LYP level of theory was used to optimize structures and determine absolute minimum energy geometries, whereas the electronic energies were estimated using B3LYP/6-31G(d,p) as well as a higher level of theory, MPWB1K/6-31G(d,p). Transition state theory was employed to determine kinetic parameters according to the terminal model of copolymerization. The homopolymerization of VDF and all of its corresponding copolymerizations were investigated by taking into account every possible propagation reaction (head to head, head to tail, tail to tail, head to monomer, tail to monomer, etc.) to estimate the Arrhenius parameters for each system. This study provides the estimation of a large set of rate coefficients, which gives detailed pictures of the specific copolymerization systems examined and is highly valuable to generate a comprehensive overview of the polymerization kinetics of relevant fluorinated monomers.