Kinetic Prediction of Functional Group Distributions in Thermosensitive Microgels

Abstract

A kinetic model accounting for the copolymerization of up to four comonomers is applied to predict both chain and radial functional group distributions in carboxylic-acid-functionalized poly(N-isopropylacrylamide) (NIPAM)-based microgels. The model can accurately predict the experimentally observed radial distributions of functional monomers in microgels prepared using a variety of different carboxylic-acid-functionalized monomers with significantly different hydrophobicities, copolymerization kinetics, and reactivities, without requiring the use of adjustable parameters. Multimodal distributions can both be predicted and experimentally generated by copolymerizing two -COOH-containing monomers with widely different reactivities. Chain distributions and monomer block formation can also be probed using the kinetic model, allowing for qualitative predictions of the potentiometric titration behavior of the microgels. The kinetic model reported herein therefore provides the first available analytical method for semiquantitatively predicting and controlling functional group distributions in bulk-polymerized microgel systems.

Interplay between Hydrogen Bonding and Macromolecular Architecture Leading to Unusual Phase Behavior in Thermosensitive Microgels

“…[14] Our small-angle neutron scattering and NMR data suggest that the two repeating units are in fact incorporated statistically in the microgel, which was also reported for other systems. [15] Therefore, we may speculate that hydrogen bonds are formed preferentially between neighboring units, as supported by the strong, cooperative increase of intramolecular bonds at the transition.…”

Semi-batch control over functional group distributions in thermoresponsive microgels

“…Hoare and Pelton have reported extensively on an alternate way to control local compositions in microgels by controlling the copolymerization kinetics of the constituent monomers [42,43]. In the case of thermosensitive PNIPAM-based microgels, monomers that react faster than NIPAM (e.g., methacrylic acid) become localized in the microgel core, monomers with similar propagation rates to NIPAM (e.g., acrylic acid) are distributed throughout the microgel, and monomers with significantly slower propagation rates than NIPAM (e.g., vinylacetic acid or fumaric acid) are concentrated in the microgel shell [42].…”

The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

“…A theoretical model based on the terminal copolymerization kinetics which predicts the microstructure of functionalized microgels was developed by Hoare and McLean. 23,24 Monomer and functional group distribution in multicomponent pNIPAM based microgels can be predicted by linking it to the copolymerization kinetics of the respective comonomers. The control over microgel morphology and its proper characterization is a key area of research.…”