照射したポリ(フッ化ビニリデン)のESR

The radical species trapped in irradiated poly (vinylidene fluoride)(PVdF) were assigned by electron spin resonance(ESR). The films of PVdF were drawn by 400% at 45 C. The samples thus obtained had a crystal structure of the zigzag chain conformation, where the chains were aligned parallel to the drawing direction (Fig.2). The samples, which were sealed in ESR sample tube and evacuated, were irradiated with g -rays from Co-60 at 77 K. The ESR spectra were recorded at 77 K and room temperature. The ESR spectra obtained at 77 K after irradiation showed broad an, d diffuse pattern with several shoulders (Fig.10). After annealing the sample at room temperature for an hour, a resoluble pattern (Fig.3 and 4) consisting of a double sextet appeared. The radical responsible for the double sextet was assigned to the alkyl-type radical, -CH2-CF-CH2-, and the conformation was presumed (Fig.6). Upon annealing at 195 K after irradiation, the chain scission radical, -CH2CF2, was observed as a small portion of the trapped radicals.When the sample irradiated at 77 K was stored for a long time at room temperature or annealed for a short time at high temperature in vacuo, the siglet spectrum remained (Fig.9). The singlet was stable in vacuo and was assigned to polyenyl radicals, -(CF=CH)-CH-.The alkyl-type radicals and polyenyl radical easily reacted with oxygen to form peroxy radicals. Oxygen, molecules diffused into the crystalline regions and reacted with the trapped radicals. Therefore, when irradiation was performed in air at low does rate, these radicals were converted into peroxy radicals, which hindered the crossliaking reaction. The stability of the alkyl-type radicals and the reactivity with oxygen had relations to crosslinking and degradation.