Peroxy radicals produced in polypropylene through oxidation with ozone

Abstract

Preirradiated polymers react with some conjugated monomers like methyl methacrylate or styrene. The graft polymerization is considered to be a radical process, and the presence of the radicals was unambiguously confirmed by electron spin resonance (ESR) observation. ESR studies of irradiation oxidation of polypropylene have been developed in detail, one of the most interesting problems being the effect of oxygen on the primary radicals formed'). Quite stable peroxy radicals can easily be produced after the admission of oxygen to preirradiated polymers. On the other hand, graft polymerization is attainable by the method of the thermal decomposition of the hydroperoxide and peroxide groups, created by the treatment of polymers with ozone at room temperature". Polypropylene oxidized with ozone reacts with some conjugated monomers at 7G8O0C3'. The radicals produced in this graft polymerization process have so far rarely been detected or identified. Their detection and identification will be described in this paper. Experimental PartThe ESR measurements were carried out using a conventional X-band ESR spectrometer of "JES-ME3X" type with 100 KHz field modulation.The sample of fibrous polypropylene was filled in a quartz tube, 10mm in diameter, which was inserted in the ESR cavity. An ozone current was introduced into the quartz tube during the ESR measurements. The ESR signals increased rapidly at the beginning and then gradually. When the admission of ozone was broken off, the intensities of the ESR signals were reduced to some extent. Immediately after stopping the ozone treatment, the polypropylene fiber was enclosed in a quartz sample tube, 3mm in diameter, which was supplied for the ESR measurements at liquid nitrogen temperature. The radicals were found to be indefinitely stable at 77 K. Results and DiscussionThe ESR spectra obtained are depicted in Fig. 1. The lineshapes with no hyperfine structure are quite asymmetric and the anisotropic features in the ESR spectra become more obvious at 77 K. These may be because motional averaging is stopped at low temperatures. The theory for a random orientation of radicals with a cylindrical symmetric g tensor developed by Kneubiih14) gives values of g//=2,0317, and g1 =2,00967*) at room temperature and those *) The subscripts // and 1 refer to the relative orientations of the directions of the applied magnetic field and the symmetric axis of the free electron distribution.

Electron spin resonance study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent. V. Comparison with polypropylene and ethylene-propylene copolymer

“…This technique was extended to PP, EPM including tertiary carbons, and EPDM including the double bond molecular structure. Most studies on free radicals in PP concentrated on trapped radicals induced by ionizing radiation or mechanical breakdown at a low temperature 5–14. We tried to observe the polymer radicals during crosslinking reactions at a molten state using ESR.…”

Graft copolymerization of methyl methacrylate onto polypropylene oxidized with ozone

“…The 0-0 bond of the hydroperoxide given in reaction ( 9 ) is broken by heating, and thus the hydroperoxide gives alkoxyl and hydroxyl radicals as follows: (11) The alkoxyl radical and the hydroxyl radical thus obtained would initiate polymerization as active sites and give graft copolymer and homopolymer, respectively.…”

“…This result surely supports reactions ( 7 ) -( 10). Because the alkoxyl radical formed in reaction ( 11) is proportional to the ozone-oxidation time, both TC and DG increased with the oxidation time. propylene with oxidation time and the intensity change of the carbonyl group, respectively.…”

Electron spin resonance study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent. V. Comparison with polypropylene and ethylene‐propylene copolymer

“…Most studies on free radicals in PP concentrated on trapped radicals induced by ionizing radiation or mechanical breakdown at a low temperature. [5][6][7][8][9][10][11][12][13][14] We tried to observe the polymer radicals during crosslinking reactions at a molten state using ESR.…”