Termination and Transfer Kinetics of Acrylamide Homopolymerization in Aqueous Solution

The single pulse–pulsed laser polymerization–electron paramagnetic resonance (SP–PLP–EPR) method affords the detailed kinetic analysis of acrylamide polymerization in aqueous solution. Highly time-resolved SP–PLP–EPR experiments for 10 and 20 wt % AAm were first carried out at −5 °C, where only secondary propagating radicals (SPRs) occur. In a second step, the time evolution of midchain radicals (MCRs), produced from SPRs by backbiting, was measured at higher temperatures. The termination kinetics, including chain-length dependent termination of SPRs, the backbiting rate of SPRs, and the propagation rate of MCRs were determined. The rate coefficients from SP–PLP–EPR in conjunction with the known propagation rate coefficient of SPRs, enable the simulation of the kinetics and product properties of AAm radical polymerizations in aqueous solution

Termination, Transfer, and Propagation Kinetics of Trimethylaminoethyl Acrylate Chloride Radical Polymerization in Aqueous Solution

The SP–PLP–EPR (single pulse–pulsed laser polymerization–electron paramagnetic resonance) method has been used to measure the rate coefficients of termination, intramolecular transfer, and propagation for the radical polymerization of 20 wt % trimethyl­aminoethyl acrylate chloride (TMAEA) in the temperature range 0–90 °C. The high complexity of this acrylate system is due to water being the solvent, to the monomer being a strong electrolyte, and to both secondary chain-end radicals and tertiary midchain radicals being simultaneously present. The termination kinetics, which was analyzed by a chain-length-dependent scheme, largely differs from the situation met with nonionized radicals. The reliability of the rate coefficients obtained from the SP–PLP–EPR experiments has been demonstrated by the almost perfect agreement of TMAEA conversion vs time data from simulation, on the basis of these coefficients, and from the chemically initiated TMAEA polymerization experiment at 70 °C

Propagation and Chain-Length-Dependent Termination Rate Coefficients Deduced from a Single SP–PLP–EPR Experiment

The laser single pulse (SP)–pulsed laser polymerization (PLP)–electron paramagnetic resonance (EPR) technique allows for deducing propagation (<i>k</i>_p) and termination (<i>k</i>_t) rate coefficients, including the chain-length dependence of <i>k</i>_t, from a single pulsed-laser experiment. The method, which is particularly well suited for slowly terminating radicals, e.g., sterically hindered and ionic radicals, is illustrated for di­(<i>n</i>-butyl) itaconate in bulk at temperatures from 30 to 60 °C. The time evolution of the DBI radical concentration is measured with a high time resolution at constant magnetic field. Propagation is associated with a relatively low pre-exponential <i>A</i>(<i>k</i>_p), which is responsible for the small <i>k</i>_p value of 6.8 L mol^–1 s^–1 at 30 °C. The chain-length dependence (CLD) of <i>k</i>_t, deduced from the same SP–PLP–EPR signal as is <i>k</i>_p, turns out to be adequately represented by the composite model. Whereas typical numbers are found for the power-law exponents for short and long radicals and for the crossover chain length, the parameter <i>k</i>_t(1,1), which represents mutual termination of two radicals of chain length unity, is by 2 orders of magnitude below <i>k</i>_t(1,1) of monomers without significant steric hindrance

Chain-Length-Dependent Termination of Sodium Methacrylate Polymerization in Aqueous Solution Studied by SP-PLP-EPR

Via the single pulse–pulsed laser polymerization–electron paramagnetic resonance (SP-PLP-EPR) technique, the chain-length-dependent termination of 5 and 10 wt % sodium methacrylate (NaMAA) in aqueous solution was measured from 5 to 60 °C. The rate coefficients <i>k</i>_t(<i>i</i>,<i>i</i>) for termination of two ionized radicals of identical size <i>i</i> were analyzed by the composite model. Three out of the four composite-model parameters behave similarly to nonionized monomers, whereas the fourth parameter, the rate coefficient for termination of two radicals of chain length unity, <i>k</i>_t(1,1), exhibits a distinctly different behavior. The temperature dependence of <i>k</i>_t(1,1) is significantly below the one of fluidity (inverse solution viscosity). Moreover, absolute <i>k</i>_t(1,1) increases with NaMAA concentration, i.e., toward higher viscosity. Both observations indicate that the termination kinetics of ionized radicals largely differs from the Smoluchowski-type behavior