Synthesis, swelling behavior, and viscoelastic properties of functional poly(hydroxyethyl methacrylate) with ureidopyrimidinone side-groups

Abstract

In this report the swelling and linear viscoelastic behavior of a hydrophilic polymer containing reversibly associating hydrogen bonding side-groups will be examined. Ureidopyrimidinone (UPy) moieties self-associate to form hydrogen-bonded dimers (DDAA) in non-polar media; however, UPy behavior in water-swollen hydrogel environments is unclear. A series of technologically important, poly(hydroxyethyl methacrylate) (poly(HEMA)) polymers, with varying UPy side-group content, were prepared using a reversible addition–fragmentation chain transfer (RAFT) polymerization. Water swelling experiments revealed that UPy side-groups retard early time (<24 h) Fickian-like swelling and lead to two-stage, temperature-dependent, water sorption. At longer times UPy side-groups promote water swelling. Rheological studies show that the material's viscosity and viscous relaxation time both increase with increasing UPy-content. The activation energy of the shear-induced flow scales linearly with UPy-content, suggesting cooperative dynamics. These results are similar to observations made for hydrophobic polymers bearing hydrogen-bonding side-groups and suggest some UPy hydrogen-bonding occurs in hydrated poly(HEMA), despite competitive H-bonding with water. Experimental observations can be explained by reversible association of UPy side-groups within water-excluded domains of poly(HEMA)'s secondary structure.