Tabic 6.7 Transfer Constants for Allyl Sulfides at

Allyl sulfonates (35, 36) show analogous behavior. Transfer constants are reported in Tabic 6.8. Other compounds with weak A-R bonds cf. 11) that have the capacity to act as transfer agents are listed in fable 6,9. Allyl bromides 43a, 44, and 45a give predominantly chain transfer whereas, the chlorides (e.g. 45b) 

Peroxyacetals 58106 and peresters such as 61107 are also effective transfer agents, however, at typical polymerization temperatures ( 60 CC) they are thermally unstable and also act as initiators. Compounds such as 62 which may give addition and 1,5-intramolecular substitution with fragmentation have also been examined for their potential as chain transfer agents (l,5-SHi mechanism).108 

The most used transfer agents in this class are the methacrylate macromonomers (e.g. 66-68) and AMS dimer (76). The applications of these compounds are summarized in a review.110 

The rate constants ( add) for addition of the MMA propagating radical30 (and other radicals 9) to 66-68 arc believed to be similar. The transfer constant of 66 is thought to be lower than 67 and 68 by more than an order of magnitude because of 

Tanaka et al,im observed that the adduct 71 from the monomeric MM A radicals adding to dimer was persistent and suggested that 71 may also act as a retarder or inhibitor of polymerization. However, the higher adducts 70 appear to be transient and no retardation beyond that expected from a reduced gel effect is observed.36 

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