Hydrogen bonded supramolecular elastomers: correlating hydrogen bonding strength with morphology and rheology

A series of six low-molecular-weight elastomers with hydrogen bonding end groups have been designed, synthesized, and studied. The poly(urethane)-based elastomers all contained essentially the same hard block content (ca. 11%) and differ only in the nature of their end groups. Solution-state 1H NMR spectroscopic analysis of model compounds featuring the end groups demonstrates that they all exhibit very low binding constants in the range of 1.4 to 45.0 M-1 in CDCl3, yet the corresponding elastomers each possess a markedly different nanoscale morphology and rheology in the bulk. We are able to correlate small variations of the binding constant of the end groups with dramatic changes in the bulk properties of the elastomers. These results provide important insight into the way in which weak noncovalent interactions can be utilized to afford a range of self-assembled polyurethane-based materials that feature different morphologies.