Free-Radical Chain-Growth Polymerization - Principles of Polymer Chemistry - page 123

by reaction of free radicals obtained from decomposition of azo-initiators, such as azobisisobutyr-
onitrile or l,1 0 -azobis(cyclohexanecarbonitrile) with selected nitrones:

CN

CN

CN

CN

N

N

O

N

O

O

CN

CN

CN

CN CN

N N

O O

CN

The alkoxyamines were utilized in radical polymerization of acrylates and styrene in bulk or in
solution between 100 and 145 C. Low molecular weight polymers, 3,000-14,000 g/mol formed
rapidly with polydispersity,

M n between 1.2 and 3.4. High styrene conversion was observed
together with a low polydispersity.
Subsequently, nitroxides and parent alkoxyamines were formed directly in the polymerization
medium (in situ NMP ) by reaction of the nitrone with the free radical initiators [ 270 ]. Two types of
reactions were carried out. One was a reaction before monomer addition and the other one after the
addition. In either case, a prereaction was systematically carried out at temperatures ranging from 60
to 80 C. This was followed by polymerizations at 130 C. The in situ-formed nitroxides and
alkoxyamines controlled the radical polymerizations of

M w /

n -butyl acrylate yielding, however, low

molecular weight polymers, of M n equal to 1.65-2.0.

A patent was issued to Wertmer and coworkers [ 271 ] for controlled radical (co)polymerization of
vinyl monomers mediated by nitrones substituted by longer alkyl groups that contained as much as 18
carbon atoms. The nitrone was simply heated in the presence of peroxide and a monomer, such as
styrene at 130 C for 24 h. High-molecular-weight polystyrene, M n ¼ 98,000-146,000 was formed.
The ratio of M w / M n , however, was not disclosed
Recently, Grubbs and coworkers [ 272 ] have synthesized an active alkoxyamine by reaction of 2-
methyl-2-nitrosopropane with 1-bromoethylbenzene, catalyzed by ligated CuBr in the presence of
metallic copper. A purified alkoxyamine was used to initiate the radical polymerization of styrene and
isoprene. Well-defined low polydispersity polymers formed with

M n < 10,000 and M w /

1.14 for polystyrene
and 1.28 for polyisoprene. Subsequently, Grubbs and coworkers [ 273 ] used this alkoxyamine and
successfully controlled the radical polymerization of

M w / M n ¼

-butyl acylate at 125 C. Lower ratio of

M n
was observed when the alkoxyamine was preheated at temperatures up to 125 for 30 mm prior to
adding the monomer. This prereaction was needed for an excess of free nitroxide to be formed in situ
and for polymerization to be controlled.

n M w /