Visible light irradiation of N‐bromosuccinimide serves as an effective means to convert methyl 2‐(azidomethyl)‐3‐arylpropenoates and 2‐(azidomethyl)‐3‐arylacrylonitriles to the corresponding iminyl radicals via α‐hydrogen abstraction and subsequent extrusion of dinitrogen. Thus formed iminyl radicals then undergo intramolecular ortho attack on the aryl ring, affording methyl quinoline‐3‐carboxylates and quinoline‐3‐carbonitriles respectively.
Epoxy resin samples with low cross-linking density were prepared, and their shape recovery rate and glass transition were studied. The results showed that the shape fixity ratio was over 99 % for all of the samples. Without constraint, the final recovery ratio was approximate to 100 % for all of the samples. The temperature with rapid recovery rate for different samples changed in accordance with Tg. Under a constant temperature, the folding angle for the samples of EP80 decreased with the increase in time rapidly, at first, and then tended to level off. Curves can be fitted with the formula of $ y + A_{0} = A/(1 + \exp ((t - t_{0} )/\tau )) $ with R2 higher than 99.9 %. The fitting results demonstrated that the value of τ decreased from 15.1 to 6.39 when the temperature increased from 88 to 98 °C for EP80. The recovery rate decreased a little by extending the holding time from 10 to 60 s. By keeping the testing temperature constant, glass transition temperature (Tg) decreased with the increase in curing agents, and the value of τ reduced with the decrease in Tg. Usually, when temperature was close to Tg, segments of macromolecules were idle to move, and then, the relaxation process, τ, was lengthened and the shape recovery rate decreased accordingly. In a word, τ showed the similar change rules with that of relaxation process of polymers; therefore, the shape recovering process could be predicted with the model of relaxation time and modulus according to relaxation formulas. 相似文献