Dendronized Polymers with Ureidopyrimidinone Groups: An Efficient Strategy To Tailor Intermolecular Interactions, Rheology, and Fracture

A library of poly­(methyl methacrylate)-based dendronized polymers with generation numbers <i>g</i> = 1–3 was prepared, which contain different degrees of dendritic substitution (0–50%) with strongly hydrogen bonding 2-ureido-4­[1<i>H</i>]­pyrimidinone (UPy) moieties at their respective <i>g</i> = 1 levels. Our rheological and thermal studies demonstrate that the strong intermolecular UPy interactions are suppressed for <i>g</i> = 2 and essentially eliminated for <i>g</i> = 3. Focusing on samples with short backbone degrees of polymerization (<i>P</i><sub>n</sub> ≈ 40), the linear viscoelastic response alters from liquid-like in the absence of UPy to gel-like with ever increasing moduli as the UPy content increases. Nonlinear rheological measurements indicate a transition from ductile to brittle behavior and, in parallel, a transition from shear strain thinning to shear strain hardening. This unique behavior makes UPy-DPs promising candidates for the design of new functional materials.