Metal catalyzed polycondensation reactions

Metal catalyzed polymerizations are chain reactions necessitating a constant valence of the metal. In contrast to that metal catalyzed polycondensations are step growth reactions involving a change of the valence of the metal. Tuning of the reaction by structural variations of the metal catalyst are demonstrated with the Pd-catalyzed vinyl polymerization of norbornene, the alternating copolymerization of ethylene with carbon monoxide and the Heck reaction as examples. One and two electron processes can be involved in metal catalyzed polycondensations. The oxidative polymerization of 2,6-dimethylphenol, the Heck reactions as well the Ni-catalyzed synthesis of polyphenylenes are discussed.