E.S.R. Spectra of Free Radicals Relevant to Methacrylate Polymerization

Abstract

Carbon-based free radicals were generated by thermal cleavage of the tetraester Me2C(COOME)-CH2-CMe( COOMe )- CMe ( COOMe )-CH2-C( COOMe )Me2 which is a model for head-to-head units in a poly(methyl methacrylate ) chain. The resulting electron spin resonance spectrum had higher resolution than the 'nine-line' spectrum previously reported; this enabled identification of the component radicals. In the present case, the spectrum was well matched by a summation of spectra of the Me2C(COOME)-CH2-CMe( COOMe ) radical and the 1-methoxycarbonyl-1-methylethyl radical Me2-C-COOMe derived from it by loss of methyl methacrylate. Both of these radicals were generated in separate experiments. Radicals were also generated from starting materials containing a CD3 group in place of the single CH3.

Conformational Structure of Methacrylate Radicals as Studied by Electron Spin Resonance Spectroscopy: From Small Molecule Radicals to Polymer Radicals

“…The temperature dependence was similar to that of 1 rather than those of 5 and 6 (Table ). This spectrum is the same as that reported in 1992 by Keah et al ) in a fashion similar to the assignments for several radicals ever reported in literature, as described in detail in section 6.…”

“…The precursor 7Br was prepared with methyl 2-lithioisobutyrate and MMA followed by the reaction with bromine. Adamantyl 2-bromoisobutyrate ( 3bBr) was prepared from 1-adamantanol and 2-bromoisobutyryl bromide.…”

“…For the enolate radicals with more complicated structure, the magnitude of the equivalent or unequivalent β-CH 2 couplings has been reported to depend on the structure of the substituents. Typical examples are summarized in Table . ,,− …”

“…Flash chromatography (pentane/ether = 10/1) followed by recrystallization gave colorless prisms: mp 54.0−55.0 °C (pentane) (lit. mp 53.1−54.8 °C); yield 0.24 g (2%); R f 0.45. 1 H NMR (CDCl 3 , 300 MHz) δ 3.78 (s, 3H, OCH 3 ), 3.68 (s, 3H, OCH 3 ), 2.80 (d, J = 14.6 Hz, 1H, CH 2 ), 2.74 (d, J = 14.6 Hz, 1H, CH 2 ), 1.85 (s, 3H, CH 3 ), 1.23 (s, 3H, CH 3 ), 1.08 (s, 3H, CH 3 ); 13 C NMR (CDCl 3 , 75.5 MHz) δ 177.36 (CO), 171.81 (CO), 58.86 (CBr), 52.98 (OCH 3 ), 51.94 (OCH 3 ), 50.80 (CH 2 ), 42.55 (C q ), 28.20 (CH 3 ), 27.03 (CH 3 ), 22.99 (CH 3 ).…”

Stable Free Radicals Produced in Acrylate and Methacrylate Free Radical Polymerization: Comparative EPR Studies of Structure and the Effects of Cross-Linking

“…A three-line spectrum was observed from the acrylate or acrylic acid samples. All spectra were assigned to the propagating free radical. − A variety of explanations of these spectra, especially focusing on the methacrylate or methacrylic acid polymerizations, involve different rotational configurations of the polymer end group radical , or a dynamic equilibrium between the configurations . The latter has been widely accepted, invoking a dynamic equilibrium between two conformations of the two C β −H bonds, which make projections of 55° and 65° on the normal to the C α −C β bond with respect to the axis of the p-orbital of the unpaired electron .…”