One-pot synthesis of precise polyisoxazoles by click polymerization: Copper (I)-catalyzed 1,3-dipolar cycloaddition of nitrile oxides with alkynes

摘要

This article reports a new one-pot method for polymer preparation, which involves double click chemistry. In one pot, two click reactions take place sequentially by adding the reactants step by step. The first click reaction is to produce the monomer for the second click reaction for polymerization. The click polymerization differs from the general click polymerization with the reaction of diazides and dialkynes. Nitrile oxides, produced in situ by the first click reaction of the formation of aldoxime, instead azides, avoiding the poisonousness and explosiveness of azides and being much safer and easy to operate. And 3,5-disubstitute polyisoxazoles are produced by the copper(I)-catalyzed the 1,3-dipolar cycloaddition of nitrile oxides with alkynes in high yields by our one-pot method. The resulting polyisoxazoles agree well with the structural assignment obtained by the ~1H NMR and IR analyses, with high molecular weights, narrow molecular weight distribution (M_w/M_n < 1.2) and high regioregularity. The poor solubility of these polymers is found to be caused by their crystallization. Improvement of solubility is achieved by modifying the structures of alkyne monomers. All the polymers are thermally stable, losing little of their weights when heated to ～350 °C.