Himeji 671 -22, Japan, and 3Kobe City College of Technology, Maikodai, Tarumi-ku, Kobe 655, Japan SYNOPSISAfter the reaction of polypropylene by ozone oxidation, methyl methacrylate was graftcopolymerized onto the polypropylene. The active species determined by ESR spectroscopy as a peroxyl radical was converted t o hydroperoxide, and the hydroperoxide was broken by heating, giving alkoxyl and hydroxyl radicals, the former of which initiated graft copolymerization. The effect of the ozone-oxidation time and polymerization time on the graft copolymerization was investigated. At the constant polymerization time, the total conversion and the degree of the grafting increased with the ozone-oxidation time, while the graft efficiency decreased. On the other hand, at the constant oxidation time, the total conversion and the degree of grafting increased with the polymerization time, while the graft efficiency decreased. These results were compared with a polyethylene case. The mechanism of the ozone oxidation and the initiation of the graft copolymerization were also discussed. I NTRO D U CTI 0 NWith graft copolymerization onto polypropylene or polyethylene, it has been found that when using benzoyl peroxide or azobisisobutylonitrile radical polymerization would not be initiated and, also, that the introduction of functional groups by means of a polymer reaction would be very difficult. I t has been reported that the introduction of active species onto polymers by using radiation 1-5 or oxidation 6-9 was very useful for this purpose. Since those methods using radiation are very expensive and not easy to handle, the introduction of the active species using the oxidation reaction is commercially hopeful. Moreover, the methods using oxidation have the merit that fewer homopolymers are produced, because the active species are formed on the trunk polymer in these methods. As one of the most advantageous methods, ozone oxidation would be applicable to graft copolymerization onto polyethylene or polypropylene. Recently, we have reported graft copolymerization of methyl methacrylate onto polyethylene oxidized with ozone." The results were discussed in terms of the ozone-oxidation and polymerization times, and the oxidation mechanism was investigated. In the present paper, polypropylene was oxidized with ozone, followed by graft copolymerization with methyl methacrylate. The effect of the ozoneoxidation and polymerization times on the graft copolymerization was also investigated and compared with the polyethylene case. Previously, we have confirmed active species by ESR in the cases of polyethylene lo and polypropylene, l1 that is, peroxyl radicals were formed on those polyolefins when they were treated with ozone.

In a previous study of graft copolymerization of methyl methacrylate onto polyethylene oxidized with ozone, we clarified that ozone-oxidation reactions produce peroxyl radicals in polyethylene and that the graft copolymerization is assumed to start upon heating, through the decomposition of hydroperoxides which are converted from the peroxyl radicals. A series of reaction processes proposed for the ozone oxidation were examined from the viewpoint of the reaction rate. The time–dependent content of the peroxyl radicals was pursued by observing in situ ESR; the initial evolution rate of the peroxyl radicals and the decay rate after the ozone-stop were discussed on the basis of the proposed ozone-oxidation mechanism, leading to a good agreement between the experiment and theory. The amounts of hydroperoxide and carbonyl species determined from iodometry and the IR spectra, respectively, were also discussed with regard to the oxidation time, showing reasonable linear dependences.

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.

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