Hydrogen Bonding Bottlebrush Networks: Self-healing Materials from Super-soft to Stiff

The impact of polymer architecture on network dynamics and self-healing is presented using bottlebrushes containing side chains that are end-functionalized with 2-ureido-4[1H]-pyrimidinone (UPy). The synthesis of these materials is straightforward through a three-step process: (1) synthesizing rubbery poly(4-methylcaprolactone) macromonomers (pMCL−OH) with a norbornene-based initiator, (2) functionalizing the terminal hydroxyl group with UPy−isocyanate (pMCL−UPy), and (3) statistically copolymerizing pMCL−OH and pMCL−UPy via ring-opening metathesis polymerization (ROMP) to form hydrogen-bonding bottlebrushes having a fraction (p) of side chains functionalized with UPy. Attaching UPy to the free end of bottlebrush side chains dilutes the impact of friction from complementary UPy interactions on segmental dynamics, leading to a much weaker dependence of the glass-transition temperature (Tg) on p than observed in linear analogues, while the activation energy to dissociate UPy−UPy bonds (41..., All polymer 1H nuclear magnetic resonance (NMR) spectra were collected using a Varian Unity Inova AS600 600 MHz equipped with a 5 mm Varian triple resonance 1H/13C/15N inverse detection probe with z-axis pulsed field gradient (PFG). Small molecule 1H and 13C NMR were collected using a Bruker Avance NEO 500 MHz equipped with a CryoProbe Prodigy BBO probe with z-axis PFG. Chemical shifts (δ) are reported in ppm relative to residual undeuterated CHCl3 in CDCl3 (7.26 ppm), CD2Cl2 (5.32 ppm), or acetone-d6  (2.05 ppm) for 1H NMR spectra and CDCl3 (77.16 ppm) for 13C NMR spectra. The following abbreviations (or combinations thereof) were used to describe multiplicities: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet). 1H diffusion-ordered spectroscopy (DOSY) experiments were performed on a Varian Unity Inova AS600 600 MHz using bipolar gradient pulses stimulated echo sequence with convection compensation. The sample solution was kept at approximately 20 mg/mL with no spinnin..., All data can be opened with any application that can read .csv files.
An exception is 2D DOSY NMR which needs to be fitted with NMR software that can operate fitting using the Bayesian method.Â