SynopsisBenzaldehyde (PhCHO) is found to be able to initiate the radical polymerization of methyl methacrylate (MMA). The rate of polymerization is expressed by the following equation: R, = const[PhCH0]0.5[MMA]1.5. The overall activation energy is estimated to be 56.3 kJ mole-'. The mechanism of polymerization is discussed.(PhCHO) will be reported. It was concluded that PhCHO is able to initiate the homogeneous radical polymerization in benzene. Styrene (St) could not be polymerized, while acrylonitrile (AN) gave a little conversion under the same condition with the case of MMA. The results obtained is surprising in view of the fact that such a simple compound having aldehyde group as PhCHO can generate the free radicals in benzene solution. = 0 is much more unstable than CsH5-C = 0. O---CH,\ c, CH, \H----O@c\mH, -I // CH,CH,,-C complex "C"