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Polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate in the presence of tri n butylboron and butyl p benzoquinone or 2,5 di tert butyl p benzoquinone occurred with no induction period. The yields and molecular masses of the polymers linearly increased with an increase in the conversion degree, which suggests the free radical mechanism of "living" chain polymerization. The poly(methyl methacrylate) macrochains of the prepolymers contained sterically hindered aromatic structures with labile C-O bonds. The latter underwent reversible homolytic dissociation to give a growth inducing radical and steri cally hindered aryloxyls. Pseudoliving free radical polymerization in the presence of the prepolymer (macroinitiator) was studied at 45, 60, and 80 °C.Key words: polymerization, methyl methacrylate, p benzoquinone, 2 butyl p benzo quinone, 2,5 di tert butyl p benzoquinone, prepolymer, pseudoliving polymerization.When studying the polymerization of methyl meth acrylate (MMA) at 30 °C initiated by dicyclohexyl peroxydicarbonate (1) in the presence of tri n butylboron (2) and a number of quinones, we have obtained for the first time reliable data on the elementary steps of reac tions of poly(methyl methacrylate) radicals with some quinones. 1 We have found that these growth inducing radicals react with p benzoquinone (3) mainly at the C=C bond to give quinonoid structures and with 2,5 di tert butyl p benzoquinone (4) at the C=O bonds result ing in the insertion of aromatic structures into the macrochain.The polymerization of MMA has no induction period and its initial rate is higher than the rate of the polymer ization initiated by organic peroxide 1. The polymeriza tion rate depends on the molar ratio of p quinones to trialkylborane. For quinone 3, the initial polymerization rate increases to a maximum value at a molar ratio of 1 : 1 and then drops virtually to zero. In the presence of quinone 4, the rate increases only slightly and remains virtually unchanged at its high concentrations. To explain the observed fact, we have assumed that the sterically hindered aromatic fragments incorporated in the macro chain can act as macroinitiators inducing free radical pseudoliving polymerization. 1With the foregoing in mind, here we studied the poly merization of MMA initiated by peroxide 1 in the pres ence of tributylboron (2), quinones 3, 4, and butyl p benzoquinone (5) to collect additional data and sub stantiate the peculiar features of the polymerization of MMA in the presence of p quinone 4 and monosubsti tuted p quinone 5. We have shown 2 that the latter adds to poly(methyl methacrylate) radicals at both the C=O and C=C bond. ExperimentalOrganic solvents were purified according to known proce dures. 3 Methyl methacrylate was distilled under reduced pres sure (22 Torr, 25 °C). Commercial peroxide 1 was recrystallized from aqueous methanol. Tri n butylboron (2) was prepared from BF 3 •Et 2 O and n butylmagnesium bromide in ether 4 and dis tilled under reduced pressure (8 Torr, 90 °C). Quinone 3 was...

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