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1H-NMR spectra of the chain extended samples UP2-DI-0.74, UP2-TRI-0.74, UP2-PEN-0.74 and UP2-BUT-0.74, and the sketched chemical structure for the chain extended hard segments. The multiple peaks at 4.9–5.1 ppm range were enlarged and shown in Figure 3(2a–2d).
