Second-overtone carbonyl bands at 1918 and 2036 nm in the near-infrared (NIR) spectrum are used to monitor the phase separation of poly(ether urethane urea) (PEUU) block copolymers at 100°C. Exact positions of urea and urethane carbonyl bands are determined by NIR spectroscopic analyses of model compounds in bulk and in dilute solution. Results indicate that the carbonyl groups in the copolymers are affected by two different structural processes that occur with annealing. A faster process causes an increase in the number of free urethane groups, and a slower process causes a decrease in the number of free urea and urethane carbonyl groups. Although several structural mechanisms can be used to describe these trends, more information is necessary to identify exact structural changes that occur with annealing.

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