Supramolecular comb polymers featuring aromatic urea receptor pendant units – the effect of aromatic substitution on material properties

Molecular recognition units incorporated in polymer networks can provide a useful avenue for the introduction of dynamic stimuli-responsive properties into bulk materials to permit recovery post-damage. In this study, meta- and para-nitro substitution on pendant urea groups of polymethacrylate comb polymers has been investigated to establish their effect on the bulk-material properties. The effect of supramolecular interactions on bulk properties was assessed through the creation of a series of comb polymers featuring increasing molar ratios of methacrylate monomers that possess urea recognition units, namely 2-(3-(4-(3-(3-nitrophenyl)ureido)phenyl)ureido)ethyl methacrylate (the meta system) or 2-(3-(4-(3-(4-nitrophenyl)ureido)phenyl)ureido)ethyl methacrylate (the corresponding para system) with lauryl methacrylate employed as the comonomer. These monomers are capable of forming multiple supramolecular interactions through hydrogen bonding involving the urea and nitro sites. Varying the ratio of supramolecular monomers yielded materials with increased phase separation, mechanical durability, adhesive shear strength, and improved property recovery. The materials that incorporated the para-substituted urea recognition unit exhibited enhanced mechanical properties when compared to the meta counterparts. The degree of property recovery proved to be comparable across both set of materials: as the supramolecular monomer content was increased in both series, a higher percent of property recovery post-damage was observed.