Chapter 4: Base Catalysts for Organopolymerization

The application of organobases is one of the fundamental approaches to achieving metal-free polymerization. The wide range of potential catalysts has generated a surprisingly rich chemistry with an extensive scope of suitable monomers, various catalytic mechanisms and polymer architectures. The major classes of amidines, guanidines, phosphazenes, N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) will be discussed from this perspective. Each family of organobase is presented, including properties, pK_a data and synthesis. Special emphasis is put on the polymerization behaviour and how it is influenced by the catalyst structure. Relevant polymerization mechanisms are discussed in detail, also encompassing examples where the operation as base is accompanied by alternative or cooperating mechanisms, such as H-bonding or nucleophilic ring-opening. The organobases described in this chapter are employed to prepare, among others, poly(ester), poly(carbonate), poly(ether), poly(amide), poly(phosphoester), poly(siloxane) and acrylic polymer.