Prediction of Chain Propagation Rate Constants of Polymerization Reactions in Aqueous NIPAM/BIS and VCL/BIS Systems

Abstract

Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.

Monitoring Microgel Synthesis by Copolymerization of N‐isopropylacrylamide and N‐vinylcaprolactam via In‐Line Raman Spectroscopy and Indirect Hard Modeling

“…This behavior is in accordance with off‐line kinetic studies using quantitative 1 H‐NMR spectroscopy of VCL and NIPAM copolymerization from Balaceanu et al From samples taken during reaction at 70 °C, they identified a PVCL:PNIPAM composition of 0.4–0.55 mol mol −1 before 10 min of reaction time and a composition of 0.9–1.2 mol mol −1 after, which supports faster NIPAM than VCL conversion . A recent simulation of chain propagation rate constants calculated higher rate constants for NIPAM than for VCL . Hence, slower conversion of NIPAM in homopolymerization is due to rate limiting effects, which are different from the kinetics of chain reaction.…”

“…Copolymerization is substantially more complex to control than homopolymerization due to cross-reactions between both monomers. [15] In view of the functional applications mentioned above, accurate control of conversion of each individual monomer is crucial, which requires accurate knowledge of the conversion of individual monomers. Raman spectroscopy was found to be applicable to monitor microgel syntheses since the monomer CC bonds are Raman active.…”

“…[27] A recent simulation of chain propagation rate constants calculated higher rate constants for NIPAM than for VCL. [15] Hence, slower conversion of NIPAM in homopolymerization is due to rate limiting effects, which are different from the kinetics of chain reaction. Possible limiting effects include monomer diffusion to radicals, steric effects, or termination effects.…”

“…Synthesis of copolymers allows more degrees of freedom such as the choice of monomers, their ratio and time of monomer dosing. Copolymerization is substantially more complex to control than homopolymerization due to cross‐reactions between both monomers . In view of the functional applications mentioned above, accurate control of conversion of each individual monomer is crucial, which requires accurate knowledge of the conversion of individual monomers.…”

Carbon2Polymer – Conceptual Design of a CO2‐Based Process for the Production of Isocyanates

“…The latter is the barrier in Gibbs free energy that the reaction must overcome to achieve product formation. This barrier can be predicted from ideal gas and solvation properties , .…”