Rebekka Siegmann

Free Radical Copolymerization Kinetics of γ-Methyl-α-methylene-γ-butyrolactone (MeMBL)

The propagation kinetics and copolymerization behavior of the biorenewable monomer γ-methyl-α-methylene-γ-butyrolactone (MeMBL) are studied using the pulsed laser polymerization (PLP)/size exclusion chromatography (SEC) technique. The propagation rate coefficient for MeMBL is 15% higher than that of its structural analogue, methyl methacrylate (MMA), with a similar activation energy of 21.8 kJ·mol(-1). When compared to MMA, MeMBL is preferentially incorporated into copolymers when reacted with styrene (ST), MMA, and n-butyl acrylate (BA); the monomer reactivity ratios fit from bulk MeMBL/ST, MeMBL/MMA, and MeMBL/BA copolymerizations are r(MeMBL) = 0.80 ± 0.04 and r(ST) = 0.34 ± 0.04, r(MeMBL) = 3.0 ± 0.3 and r(MMA) = 0.33 ± 0.01, and r(MeMBL) = 7.0 ± 2.0 and r(BA) = 0.16 ± 0.03, respectively. In all cases, no significant variation with temperature was found between 50 and 90 °C. The implicit penultimate unit effect (IPUE) model was found to adequately fit the composition-averaged copolymerization propagation rate coefficient, k(p,cop), for the three systems.

Propagation rate coefficients for homogeneous phase VDF-HFP copolymerization in supercritical CO2.

For the first time, propagation rate coefficients, k(p,COPO) , for the copolymerizations of vinylidene fluoride and hexafluoropropene have been determined. The kinetic data was determined via pulsed-laser polymerization in conjunction with polymer analysis via size-exclusion chromatography, the PLP-SEC technique. The experiments were carried out in homogeneous phase with supercritical CO(2) as solvent for temperatures ranging from 45 to 90 °C. Absolute polymer molecular weights were calculated on the basis of experimentally determined Mark-Houwink constants. The Arrhenius parameters of k(p,COPO) vary significantly compared with ethene, which is explained by the high electronegativity of fluorine and less intra- and intermolecular interactions between the partially fluorinated macroradicals.

Chapter 7:Supercritical Carbon Dioxide as Reaction Medium for Fluoropolymer Synthesis and Kinetic Investigations into Radical Polymerizations of VDF and HFP

Fluoropolymers are mostly insoluble in organic solvents. An attractive alternative reaction medium for the synthesis and processing of fluoropolymers is supercritical carbon dioxide, which is non-toxic, abundant, and considered to be environmentally benign. Moreover, supercritical carbon dioxide allows for the shaping of the polymers, e.g. in the preparation of well-defined polymer particles or porous materials. The material properties may be changed by the choice of pressure and temperature, which strongly affect the physicochemical properties of supercritical carbon dioxide. Supercritical carbon dioxide may be considered as a tunable reaction medium for fluoropolymer synthesis and detailed investigations into polymerization kinetics and mechanisms.