page_title: Radical polymerization
section_title: Initiator efficiency
hierarchical_section_title: Radical polymerization / Initiation / Initiator efficiency
caption_attribution_description: English: Recombination of phenyl radicals from the initiation of BPO outside the solvent cage.
context_page_description: Free-radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks. Free radicals can be formed by a number of different mechanisms, usually involving separate initiator molecules. Following its generation, the initiating free radical adds monomer units, thereby growing the polymer chain.
  Free-radical polymerization is a key synthesis route for obtaining a wide variety of different polymers and material composites. The relatively non-specific nature of free-radical chemical interactions makes this one of the most versatile forms of polymerization available and allows facile reactions of polymeric free-radical chain ends and other chemicals or substrates. In 2001, 40 billion of the 110 billion pounds of polymers produced in the United States were produced by free-radical polymerization.
  Free-radical polymerization is a type of chain-growth polymerization, along with anionic, cationic and coordination polymerization.
context_section_description: Due to side reactions and inefficient synthesis of the radical species, chain initiation is not 100%. The efficiency factor f is used to describe the effective radical concentration. The maximal value of f is 1, but typical values range from 0.3 to 0.8. The following is a list of reactions that decrease the efficiency of the initiator.
  Primary recombination
  Two radicals recombine before initiating a chain (Figure 8). This occurs within the solvent cage, meaning that no solvent has yet come between the new radicals.
  Other recombination pathways
  Two radical initiators recombine before initiating a chain, but not in the solvent cage (Figure 9).
  Side reactions
  One radical is produced instead of the three radicals that could be produced (Figure 10).
caption: Figure 9: Recombination of phenyl radicals from the initiation of BPO outside the solvent cage
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