Electron spin resonance study of the photooxidation mechanism in poly(n-butyl acrylate): photochemical processes in polymeric systems. 11

Abstract

Kinetics of the reactions of the principal radical species, the tertiary alkyl and peroxy radicals, generated on photooxidation of poly(n-butyl acrylate) (PnBA) were studied at room temperature under different oxygen pressures. A simplified mechanism of photooxidation, similar to that proposed earlier (Liang, R. H.; Tsay, F.-D.; Gupta, A. Macromolecules 1982,15,974), was used to interpret the data. The kinetic rate parameters as well as the radical concentrations developed under steady-state illumination conditions were estimated by a least-squares fit to the observed data by using kinetic equations based on such a mechanism. It was found that at least two different types of tertiary alkyl radicals (i.e., radicals of different reactivities) were being formed during photooxidation of PnBA.

Termination, Transfer, and Propagation Kinetics of Trimethylaminoethyl Acrylate Chloride Radical Polymerization in Aqueous Solution

“…Second, the remaining signal, which is entirely due to MCR3 and MCR5 species, has been analyzed on the basis of the associated hyperfine coupling constants listed in Table S2. The presence of two such coexisting MCR conformers is in agreement with literature data and constitutes a general feature of MCRs in acrylate polymerizations. ,, Hyperfine coupling constants (hfc’s) deduced from the experimental spectra are listed in Table S2. The hfc’s of the SPR and MCR3 species are insensitive toward temperature throughout the entire experimental range, from −5 to 95 °C, whereas the hfc pattern of the MCR5 conformer changes with temperature and has been adjusted for each temperature (see Figure and Table S2).…”

The role of mid‐chain radicals in acrylate free radical polymerization: Branching and scission

“…On the basis of the observation by Kim et al, 57 they simulated the MCR and found the overlap of such spectrum with the one identified for the SPR to match the experimental observation. As an example, the experimental and the simulated spectrum obtained from PLP of butyl acrylate in toluene solution at 60 C is shown in Figure 2.…”

“…After the spectrum of the SPR was clarified, Willemse et al came to the conclusion that the additional lines observed at elevated temperatures by themselves as well as in the spectra of Yamada and coworkers can only be explained by presence of large amounts of MCRs, even more than were reported before. On the basis of the observation by Kim et al,57 they simulated the MCR and found the overlap of such spectrum with the one identified for the SPR to match the experimental observation. As an example, the experimental and the simulated spectrum obtained from PLP of butyl acrylate in toluene solution at 60 °C is shown in Figure 2.…”

“…However, for the MCR one would expect coupling with all four hydrogen atoms in direct vicinity to the MCR center and essentially only with three hydrogen atoms for the SPR as all other hydrogen atoms would require long‐distance coupling. In fact, Kim et al57 observed an increase in the number of lines in the ESR spectra taken from polyBA films (from three to seven). Thereby, the spectrum taken at 100 °C resembles largely the spectra taken in the previously discussed work on acrylate solution polymerizations.…”

PLP−ESR Monitoring of Midchain Radicals in n-Butyl Acrylate Polymerization

“…The authors attributed this effect to the coupling of the radical functionality with two sets of slightly nonequivalent protons. 38 Kajiwara and Kamachi 19 reported on changes of the ESR spectra in the solution polymerization of tertbutyl acrylate at temperatures between -30 and 60 °C. In the initial stage of the polymerization at -30 °C, a six-line spectrum was observed.…”