Figure 3.

Introduction of reversible bonds enhances the stiffness and extensibility of polymer networks. (a) Representative optical image of an LAL polymer (sample TV 1, Table 1). Scale bar: 10 mm. (b) Radially averaged 1D SAXS intensity I as a function of the magnitude of wavevector q. The triblock polymers have nearly the same end block volume fraction, f ≈ 10%, but various fractions of amide groups, λ = 0, 0.09, and 0.25. Dashed lines: melts of middle block polymer; solid lines: polymer networks self-assembled by triblock copolymers. The primary scattering peak, q*, is associated with the average center-to-center distance between two neighboring glassy domains (green spheres in Figure 1): d = 2π/q*. (c) Frequency dependence of storage (solid symbols, G′) and loss (empty symbols, G″) moduli of the self-assembled polymer networks measured at 20 °C at a fixed strain of 0.5%. The slope 1/2 corresponds to the Rouse dynamics of the network strands. The arrow represents the trend of the crossover frequency ω_c below which G′ becomes greater than G″. (d) Contribution to shear storage modulus from reversible bonds, (G′ – G^′_x)/G^′_x, in which G^′_x is the shear storage modulus of the polymer without reversible bonds. (e) Dependence of engineering stress, σ_eng, on strain, ϵ, at a fixed strain rate of 0.01/s. (f) Dependence of the tensile toughness on the fraction of amide bonds. Error bar: standard deviation from measurements for the same sample reprocessed using solvents (n = 3).