"Initiators, Free-Radical". In: Encyclopedia of Polymer Science and ...

Vol. 6 INITIATORS, FREE-RADICAL 577
Table 5. Commercial Diperoxyketals
CAS 10-h
registry t1/2,
Name number Structure ◦ C a,b
Ethyl 3,3-di(tert-amylperoxy)butyrate [67567-23-1] 112
n-Butyl 4,4-di(tert-butylperoxy)valerate [995-33-5] 109
1,1-Di(tert-butylperoxy)cyclohexane [3006-86-8] 97
1,1-Di(tert-amylperoxy)cyclohexane [15667-10-4] 93
a Temperature at which t1/2 = 10 h.
b In dodecane.
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forming polymers with enhanced molecular weight and enhanced properties due
to the formation of polyradical initiating species.
Diperoxyketals. Some commercially available di(tert-alkylperoxy)ketals
and their corresponding 10-h half-life temperatures (determined in dodecane) are
listed in Table 5 (102). Diperoxyketals thermally decompose by cleavage of only
one oxygen–oxygen bond initially, usually followed by β-scission of the resulting
alkoxy radicals (103–107). For acyclic diperoxyketals, β-scission produces an alkyl
radical and a peroxyester.
Owing to similarity of thermal stability, the peroxyester decomposes,
as discussed previously. Cyclic diperoxyketals such as 1,1-di(tertbutylperoxy)cyclohexane
cleave the cycloalkyl ring during β-scission to give an
alkyl radical with an attached peroxyester group. The effect, after peroxyester decomposition,
is the production of two monoradicals (·OR ′ ), a diradical (·R ′ R·), and
carbon dioxide. Because of the generation of diradicals, cyclic diperoxyketals such
as 1,1-di(tert-butylperoxy)cyclohexane are effective in enhancing polymer molecular
weight or increasing polymer productivity when employed as initiators in
commercial vinyl monomer polymerizations (108,109). Diperoxyketals are used
commercially in styrene polymerizations, curing of elastomers, and in elevated
(27)