Comparing solution and melt-state association of hydrogen bonds in supramolecular polymers

Abstract

Mono- and bifunctional poly(n-butyl acrylate)s (PnBAs) bearing different hydrogen bonding motifs (thymine (THY) or 2,6-diaminotriazine (DAT)) were prepared by a combination of atom transfer radical polymerization (ATRP) and azide/alkyne “click”-reaction to investigate the association of hydrogen bonding motifs in solution (toluene-d₈) and in the melt state. THY and DAT functionalized PnBAs (3a, 4a,b, 5a and 6a,b) with molecular weights of ∼4000 up to ∼25 000 g mol⁻¹ were synthesized and they exhibit complete end group transformation as proven by NMR and MALDI-MS methods. The association of end groups in solution was studied by NMR-titration experiments and compared to the association in the melt state, investigated via frequency dependent rheology experiments. Association of THY and DAT functionalized PnBAs (3a, 4a,b, 5a and 6a,b) in solution is strikingly different when compared to the association in the melt state. Whereas association in solution follows this order in association strength: DAT–DAT < THY–THY ≪ THY–DAT, association in the melt state was found to display the order THY–THY < DAT–DAT ≲ THY–DAT, thus stressing the different dynamics of hydrogen bonds due to restricted movement of polymer chains in the melt state.