Polymer-bound substituents, coupling

A wide range of different experimental strategies have been designed to probe this question (2-9). In most cases, evidence has been sought for the occurrence of coupling reactions between pairs of polymer-bound substituents. Superficially, many of the results and conclusions appear to be mutually contradictory. However, they are all in fact compatible with a single model. 

The catalytic activity of copper complexes in oxidative coupling of 2,6-DMP to PPO is significantly improved when polymer-bound 4-aminopyridine is used as ligand [92]. Basic copper-amine complexes also catalyze the oxidative coupling of 2,6-disubstituted phenols [82]. Depending on the size of substituents and the conditions, polymerization or diphenoquinone formation may predominate [83-86]. Small substituents like methyl favor the PPO product. 

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