On the origin of ionic liquid‐induced variations in hydroxypropyl methacrylate propagation rate coefficients

Abstract

Pulsed laser polymerizations were used to study the propagation kinetics of hydroxypropyl methacrylate (HPMA) in ionic liquids (ILs) and common organic solvents. The functional monomer was chosen to investigate the complex interplay of all interactions between monomer molecules and between monomer and solvent molecules and to obtain a deeper understanding of the impact of these interactions. The solvent effect on the HPMA propagation rate coefficient (kp) was examined using a linear solvation energy relationship (LSER) based on Kamlet‐Taft solvatochromic parameters π*, α, and β. The results suggest that dipolarity/polarizability, associated with π*, and hydrogen bond–donating ability of the solvents, accounted for by α, majorly contribute to variations in kp. Hydrogen bond–accepting (electron pair donating) ability of the solvents (β parameter) is of much lesser importance. In addition, LSER enables the prediction of HPMA kp based on solvatochromic parameters of the solvents. The results suggest that interactions between the hydroxyl group of the monomer and the anion are dominant compared with classical hydrogen bonding between carbonyl and hydroxyl groups of the monomer units. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3188–3199, 2010

Toward the Description and Prediction of Solvent Induced Variations in Methacrylate Propagation Rate Coefficients on the Basis of Solvatochromic Parameters

“…(1) for BzMA, THF, and [BzMIM][Tf 2 N] are listed in Table 1. Previously, it was seen for HPMA systems that ideal mixing occurs 21. Thus, here ideal mixing of BzMA and solvents is assumed.…”

“…In addition, the method allows for detailed investigations into the impact of the solvent environment on k p 12. Particularly strong influences on the propagation kinetics were seen for aqueous phase polymerizations of water‐soluble monomers11, 13–16 and for methacrylate polymerizations in ILs 17–21…”

“…Detailed investigations into the propagation kinetics of methyl methacrylate (MMA), 2‐ethoxyethyl methacrylate (EEMA), and 2‐hydroxypropyl methacrylate (HPMA) homopolymerizations in solution with ILs revealed that for each combination of monomer and IL a very unique solvent effect occurs 17–21. Studies into polymerizations of MMA, the monomer with the smallest ester group, showed that the highly polar environment due to the presence of ILs leads to an increase in k p by up to a factor of 4.…”

“…HPMA polymerizations in ILs constitute considerably more complex systems, because of the hydroxyl group that has the ability to undergo strong classical H‐bonding. It was shown that the occurrence of hydrogen bonding in HPMA/organic solvent mixtures has a strong impact on HPMA propagation kinetics 21, 22. Similarly, propagation kinetics in 2‐hydroxyethyl methacrylate polymerizations are strongly affected by H‐bonding 23.…”

“…Similarly, propagation kinetics in 2‐hydroxyethyl methacrylate polymerizations are strongly affected by H‐bonding 23. Although H‐bond formation between HPMA and IL molecules was not detected by IR spectroscopy, the solvent effect on HPMA k p was mostly stronger than for organic solvents 21. LSER analysis of HPMA/solvent systems without classical H‐bonding suggested again that dipolarity and polarizability have the strongest contribution to the solvent‐induced variations in HPMA k p , whereas, contributions from the H‐bond donating ability of the IL was of lesser importance.…”