Radical Chain Polymerization

This chapter describes the characteristics of radical chain polymerization, with emphasis on the parameters that control polymer molecular weight. The rate and molecular weight in both reversible and irreversible polymerizations are discussed together with the process conditions needed for producing different polymers. Various methods of initiation are discussed–thermal decomposition of peroxides and azo compounds, redox, and photolysis. Molecular weight control depends on initiation rate, temperature, and chain transfer reactions. Chain transfer to polymer is responsible for short and long branching. Temperature alters the polyerization rate, polymer molecular weight, and reversibility of polymerization. Various additives inhibit or retard polymerization. Polymerization is autoaccelerated because of large changes in viscosity during polymerization. Living polymerization by atom transfer, nitroxides, and addition-fragmentation transfer allow the synthesis of block, graft, star, and other polymer architectures. Increased pressure alters polymerization rate and polymer molecular weight. The synthesis and uses of polyethylene, polystyrene, poly(vinyl chloride), acrylic polymers, fluoropolymers, and other commercial polymers are discussed.