Pulsed NMR study of radiation polymerization and crosslinking of N-isopropylacrylamide

The T2 spin-spin relaxation time curves were used to monitor the network formation during the radiation-induced polymerization of N-isopropylacrylamide (NIPAAm) in solution. Before irradiation, a single long exponential decay curve is observed (T2L, about 1 sec). After irradiation with doses in the range of 0.03 - 0.1 kGy, T2L decreases to about 100 msec, and there appears a shorter component, T2s, of the order of tens of milliseconds, indicating the presence of a network. From solubility measurements the gel dose was 71 Gy. At doses above 0.1 kGy the decay curve always consist of two components, a longer of the order of tens of milliseconds, and a shorter of the order of milliseconds. The temperature dependence of the relaxation time for samples irradiated with different doses is in good agreement with swelling data. (Author)