Diacyl peroxides polymerization agents

In the polymerization of acrylic monomers by bulk, suspension, or in organic solution, the most common initiators are diacyl peroxide (e.g., dibenzoyl peroxide supplied as a paste in water) or azo compounds (e.g., 2,2 -azobisisobutyronitrile). For emulsion or aqueous solution polymerizations, sodium persulfate by itself or in combination with bisulfites or a host of other reducing agents may be used. 

Some characteristics of initiators used for thermal initiation arc summarized in Table 3.1. These provide some general guidelines for initiator selection. In general, initiators which afford carbon-ccntcrcd radicals e.g. dialkyldiazcncs, aliphatic diacyl peroxides) have lower efficiencies for initiation of polymerization than those that produce oxygen-centered radicals. Exact values of efficiency depend on the particular initiators, monomers, and reaction conditions. Further details of initiator chemistry are summarized in Sections 3.3.1 (azo-compounds) and 3.3.2 (peroxides) as indicated in Table 3,1. In these sections, we detail the factors which influence the rate of decomposition i.e. initiator structure, solvent, complexing agents), the nature of the radicals formed, the susceptibility of the initiator to induced decomposition, and the importance of transfer to initiator and other side reactions of the initiator or initiation system. The reactions of radicals produced from the initiator arc given detailed treatment in Section 3.4. 

Some initiators (e.g., dibenzoyl peroxide and potassium per-oxydisulfate) and the derived radicals may oxidize RAFT agents to sulfme or other products. Other initiator radicals may react with the RAFT agent to form a stable thiocarbonylthio compound. It is important that the initiator-derived radical is a good leaving group with respect to the propagating radical. For example, use of an aliphatic diacyl peroxide (e.g., dilauroyl peroxide) will provide a relatively stable RAFT agent with R = primary alkyl. Similarly, azobis(methyl isobutyrate) (AIBMe) is not a suitable choice for RAFT polymerization of MMA. ... 

Gaylord et al. [231] described the bulk or suspension polymerization of ethylenically unsaturated monomers, particularly vinyl chloride, using a catalyst system consisting of a monomer-soluble peroxyester or diacyl peroxide and a reducing agent which is a stannous or antimony(III) mercaptide. 

Ascorbic acid has also been used as a complexing agent in the polymerization of vinyl chloride [240] in the presence of a diacyl peroxide and various water-soluble metal salte. Similarly 6-O-polmitoyl-L-ascorbic acid has been used as a reducing agent in the polymerization of vinyl chloride in the presence of hydrogen peroxide [241] and methyl ethyl ketone peroxide [242]. 

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