Reactivity ratios have been determined for the monomer
pair methyl methacrylate and
n-butyl methacrylate under a range of polymerization
conditions. The value of using reactivity ratios as
a mechanistic probe is discussed. Reactivity ratios determined
where M1 = MMA and M2 = n-BMA are
1.04, 0.81, classical anionic; 1.10, 0.72 ,
alkyllithium/trialkylaluminum initiated; 1.76, 0.67, group
transfer
polymerization; 0.98, 1.26, atom transfer radical polymerization; 0.75,
0.98, catalytic chain transfer; and
0.93, 1.22, classical free radical polymerization. The data
suggest ATRP and CCTP proceed via radical
type propagation. Li/Al-initiated polymerization undergoes an
anionic mechanism, while strong evidence
is found for an associative, catalyst dependent mechanism for GTP.
Galvinoxyl is demonstrated to inhibit
GTP as well as free radical polymerization, and it is suggested that
neither the use of inhibition nor
polymer stereochemistry can be used to distinguish between anionic and
radical processes.