Supramolecular interactions (hydrogen-bonding) are ubiquitous in both synthetic and natural macromolecules. Hydrogen-bonding in mono-vinyl (meth)-acrylates has been proposed as an explanation for the unexpectedly fast rates of bulk photopolymerization1-3. The fast rates in mono-vinyl acrylates were shown not to be due to chain-transfer, but rather to an effect of hydrogen-bonding on the propagation and termination kinetics1. Moreover, linear polymers arrange in a more syndiotactic morphology with hydrogen-bonding mono-vinyl (meth)acrylates2. A few researchers showed that these monomers also allow for extension in conversions by up to 40%4after irradiation pulses, i.e. no more primary radicals are being produced and polymerization is not expected to continue. Despite these efforts, a comprehensive explanation for this advantageous and fundamentally interesting phenomenon is still elusive.We discuss the potential for the formation of a unique equilibrium formed between the methacrylate-based propagating radicals and the neighboring hydrogen-bonding sites. We found a series of hydroxylated mono-methacrylates that prolong monomer consumption in more than 40-50% after light-cessation with conventional photoinitiators. We show how this dark polymerization disappears when we 'break' the hydrogen bonding with increase in temperature, as does their fast reactivity. We utilized kinetic models with previously calculated kinetic5constants to support the long-lived polymerization, and compared it to the effects of covalent crosslinks on the polymerization kinetics.Using Electron paramagnetic resonance spectroscopy (EPR), we found that the line-shape of the propagating radicals is broadened as expected due to radical delocalization effects by supramolecular interactions (hydrogen bonding). Additionally, EPR signals for propagating radials lasted for minutes after light cessation, whereas non-hydrogen-bonding monomer analogs showed a rapid extinction of the corresponding EPR line-structure. We provide more in-depth molecular mechanics to answer this long-standing inquiry. Ultimately we want to utilize this mechanism rationally towards the design of controlled high-performance supramolecular polymers with faster rates, improved mechanical properties and targeted molecular architectures.References (1) Lee, T. Y.; Roper, T. M.; Jonsson, E. S.; Guymon, C. A.; Hoyle, C. E. Macromolecules 2004  , 37, 3659�3665.(2) Jansen, J. F. G. A.; Dias, A. A.; Dorschu, M.; Coussens, B. Macromolecules 2003  , 36, 3861�3873.(3) Deepak, V. D.; Rajan, J.; Asha, S. K. J. Polym. Sci. A Polym. Chem. 2006  , 44, 4384�4395.(4) Kilambi, H.; Reddy, S. K.; Schneidewind, L.; Stansbury, J. W.; Bowman, C. N. J. Polym. Sci. A Polym. Chem. 2009  , 47, 4859�4870.(5) Goodner, M. D.; Bowman, C. N. Chemical Engineering Science 2002  , 57, 887�900.

Supramolecular hydrogen bonding in monovinyl hydroxylated methacrylates leading to long-lived propagating radicals

248th National Meeting (2014)

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