Figure 2: Dynamic exchange reactions in TBEU-bearing small molecule or polymer.
From: Dynamic urea bond for the design of reversible and self-healing polymers
(a) Exchange reaction between 3c and 2f produces 3f and 2c with isocyanate 1 as the intermediate. (b) 1H NMR spectra after mixing 3c and 2f for different durations at 37 °C. The proton peak intensities of 3c and 2f gradually decreased over time, along with the gradual increase of proton peak intensities of 3f and 2c until an equilibrium of the exchange reaction was reached at ~20 h. The protons subject to analysis from these four compounds were labelled with different colours in a, which correspond to the colours of peaks in b. (c) Conversion of 3c towards reaching equilibrium (conversion ratio=([3c]0−[3c]t)/([3c]0−[3c]eq), [3c]0=initial concentration of 3c, [3c]t=concentration of 3c at time t, [3c]eq=equilibrium concentration of 3c). (d) Poly(4a/5c), TBEU-bearing dynamic polymers, prepared via the polyaddition of 4a and 5c. (e) Dynamic tuning of poly(4a/5c) shown by GPC analysis (signal from light-scattering detector). First, polymer solution was prepared by mixing 4a and 5c with [4a]0:[5c]0=1:1 ([4a]0 (or [5c]0) at 1.0 M in DMF) and the GPC experiment was performed after 2 h incubation at 37 °C (upper curve). One additional equiv 5c was then added to tune the [4a]0:[5c]0 ratio to 1:2 and the GPC experiment was performed after 12 h incubation of the mixture at 37 °C (middle curve). Finally, one additional equiv 4a was added to restore the [4a]0:[5c]0 ratio back to 1:1. DMF was also added to keep [4a]0 (or [5c]0) at 1.0 M. GPC experiment was performed after 2 h incubation of the mixture at 37 °C (lower curve).
