Uncontrolled pseudoliving free-radical polymerization of methyl methacrylate in the presence of butyl-p-benzoquinones

Abstract

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...

New method for controlled synthesis of polylactide block copolymers: organoborane/p‐quinone system and reversible‐deactivation radical polymerization

“…The selected p-quinones exhibit different activities in polymerization of vinyl monomers. 50,51,66 With an increase of the inhibition constants of p-quinones their efficiency as agents of controlled polymerization increases.…”

“…14 Besides RAFT agents, a combination of p-quinones with trialkylborane may be used to produce copolymers with desired molecular weight characteristics and microstructures. [49][50][51][52][53] Similar to the systems using atmospheric oxygen, the RDRP mechanism is observed in the presence of p-quinones. However, due to the lack of uncontrolled borane oxidation, a more pronounced control of the polymerization kinetics and molecular weight characteristics of polymers proved to be possible.…”

Synthesis of Copolymers of Methyl Methacrylate and Butyl Vinyl Ether in the Presence of the System Tributylboron – 2,5-di-tert-butyl-p-benzoquinone

“…The macromolecules that are formed in compliance with Scheme 2, are macroinitiators, they are instrumental in re-initiation of the polymerization according to the reversible inhibition mechanism (Sheme 4) [4,8]:…”

Tri-n-butylboron-p-quinone catalytic system in synthesis of block copolymers

“…The main advantage of this approach is control of the molecular weight and composition of the forming macromolecules. One of the ways to implement this approach is the use of the tri-n-butylboron-p-quinone catalytic system [3][4][5][6]. The use of this system allows polymerization of some vinyl monomers to be performed in controlled mode (Scheme 1).…”

“…It has been found that addition of a macroradical to the C=O bond of p-quinone, followed by radical substitution at the boron atom, yields adduct I (macroinitiator), which is capable of reversible homolytic dissociation across the С-О bond [reaction (2)], ensuring the occurrence of the polymerization in the pseudoliving mode [4][5][6][7]. In polymerization of methyl methacrylate (MMA) [3], methyl acrylate, and vinyl acetate in the Scheme 1.…”