Magnetic and Electrostatic Effects on the Polymerization of Water Soluble Monomers
Editorial Ecole Polytechnique Federale de Lausanne
Lugar: Lausanne, Suiza; Año: 2006 p. 211
Free radical polymerization is the most frequently used technique to produce synthetic polymers. They represent more than 25% of the total volume of materials made by the mankind. 3% thereof correspond to water soluble polymers with annual growth rates estimated as 8%. Therefore, everything contributing to progress of the radical polymerization of water soluble monomers may be evaluated as signicant. This thesis was devoted to identify the influence of magnetic (MF) and electrostatic interactions on the kinetics and mechanism of the radical polymerization of water soluble monomers. Acrylamide (AM), acrylic acid (AA), its ionized species, acrylate (A-), and diallyldimethylammonium chloride (DADMAC) were selected for homo and copolymerization case studies. Thermal and photochemically initiated polymerizations were performed varying the MF intensity, pH, ionic strength, monomer and initiator concentration, conversion degree, viscosity and temperature of the polymerization medium. The thesis reports the experiments, results, and conclusions thereof, increasing gradually the complexity of the polymerization system. It was demonstrated that an hybrid mechanism rules the persulfate initiated polymerization of AM also at 0.05<[AM]<0.15 mol/L. The influence of pH on the AM-AA copolymerization, was quantified for 2<pH<12. The reactivity ratios of AM (rAM) and AA (rAA) increased from 0.54 to 2.95 and decreased from 1.48 to 0.42, respectively, when the pH changed from 2 to 8, and remained almost constant in the range 8<pH<12. When the total monomer concentration was varied from 0.2 to 0.6 mol/L at pH=12, rAM decreased from 4.01 to 2.13 and rAA increased from 0.25 to 0.47. A novel analytical approach to predict the composition of copolymers obtained from monomers with variable reactivity was developed. It applies terpolymerization mathematical treatment to binary systems combining the actual reactivity constants with the electrochemistry of monomers and growing radicals. The criteria for the observation of MF effects on radical polymerization were established. The effects can be observed at MF intensities below 0.5 Tesla only when primary radicals are generated and quenched in the T+ spin state. The MF effects on the kinetic parameters involved in the homopolymerization of AM, AA, A-, and DADMAC were quantified. The MF increased the initiator efficiency up to 60% while decreasing the termination rate coefficients up to 40% without altering propagation rate coefficients and reaction orders of the monomers. Studing the synergism between magnetic and electrostatic fields on the radical polymerizations of AA polymerization, magnetic and electrostatic fields influenced separately the initiation and propagation steps, while coupled effects on the termination step were observed. The selectivity of MF to modify the termination but not the propagation steps was proposed to elucidate a reaction mechanism in radical polymerization. Purposely, the effect is proposed to investigate the odd functionality of the kp/kt0.5 ratio with the monomer concentration in case of DADMAC polymerization. Copolymerizing AM/AA, AM/A-, AM/DADMAC, and AA/DADMAC under the influence of MF, revealed significantly higher monomer consumption rates than without MF. Despite this effect, the copolymer composition remained unchanged. Overall, the work contribute to better understanding of the radical polymerization of water soluble monomers. In addition, it may be useful to improve polymerization processes and product properties by selective magnetic and electrostatic adjustment of the kinetic parameters for initiation, propagation, and termination steps without modifying actual recipe formulations, temperature profiles and classical mass and heat transfer. Furthermore, it is suggested to investigate the polymerization conditions needed to generate primary radicals in S-T- states, as well as the influence of the cage dimension on the MF effects. Such research may be useful to extend the MF effects to thermally initiated reactions, and to identify the optimal combination of initiator-monomer-solvent sets for the effectiveness of MF.