Mechanophore cross-linking enhances ballistic energy dissipation of polymers

(a) E p *(MJ/kg) as a function of polymer dispersity for h 0 ≈ 160 nm films at a projectile impact velocity of v i ≈ 750 m/s. (b) E p * as a function of projectile impact velocity for h 0 ≈ 160 nm films. (c) E p * as a function of cross-link density for h 0 ≈ 160 nm films at v i ≈ 750 m/s. Samples were prepared as described in the Methods. Each condition was measured across 3 to 5 separate samples. The number of impact measurements analysed was: a, high-dispersity films, n = 7 for PS, n = 7 for N1, and n = 6 for N2; low-dispersity films, n = 11 for PS, n = 9 for N1, and n = 12 for N2; b, v i ≈ 350 m/s, n = 12 for PS, n = 12 for N1, and n = 13 for N2; v i ≈ 550 m/s, n = 9 for PS, n = 7 for N1, and n = 8 for N2; v i ≈ 750 m/s, n = 11 for PS, n = 9 for N1, and n = 12 for N2; c, 0.2 mol% cross-link density, n = 11 for PS, n = 7 for N1, and n = 6 for N2; 2 mol% cross-link density, n = 11 for PS, n = 9 for N1, and n = 12 for N2. The low-dispersity data in a, the v i ≈ 750 m/s data in b, and the 2 mol% cross-link density data in c are the same dataset as shown in Fig. 1e and are replotted in each panel for parallel comparison. Box plots show the median as the centre line, the 25th and 75th percentiles as the box bounds, and the minimum and maximum data points as whiskers. Statistical significance was assessed using two-sided unpaired t-tests with Welch’s correction. Exact P values for N1 versus PS and N1 versus N2, respectively, were: a, high-dispersity films, P = 0.00424 and P = 0.0101; low-dispersity films, P = 5.89 × 10−6 and P = 5.85 × 10−7; b, v i ≈ 350 m/s, P = 0.261 and P = 0.0560; v i ≈ 550 m/s, P = 4.14 × 10−5 and P = 2.44 × 10−5; v i ≈ 750 m/s, P = 5.89 × 10−6 and P = 5.85 × 10−7; c, 0.2 mol% cross-link density, P = 0.565 and P = 0.969; 2 mol% cross-link density, P = 5.89 × 10−6 and P = 5.85 × 10−7. Significance is indicated as ns, not significant (P > 0.05); *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; and ****P ≤ 0.0001.