The above data of substituent effects of the catalyst ligands and phenol monomers strongly support the reaction mechanism of "radical-controlled" oxidative polymerization, in which the coupling of phenoxy radical species would take place from phenoxo-copper(II) complex 2 and/or phenoxy radical-copper(I) complex 3. The "radical-controlled" oxidative polymerization produced not only crystalline PPO, but a new crystalline polymer, P-2,5-DMPO, which showed heat-reversible crystallinity with a high melting point (>300°C). Most of crystalline super engineering plastics were prepared by dehalogenation polycondensation that needs normally high reaction temperature and disposal process of halogenated compounds as by-products. The present polymerization can be taken as a clean, low-loading process, and hence, provides an example of green polymer chemistry.
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