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ABSTRACT:The effects of both the degree of grafting and ␥ irradiation on the thermal stability and structural characteristic of polypropylene-graft-polyvinylpyrrolidone and polypropylene-graft-polyvinylpyrrolidone modified with ␣-cyano-␦-(2-thienyl) crotononitrile were investigated. The employed techniques were thermogravimetric analysis, differential thermogravimetry, and X-ray diffraction. The thermal stability of various polymeric substrates was investigated through the determination of the degradation temperature and activation energy of degradation. The effects of different parameters on the structural characteristics of different films were investigated through the determination of possible changes in the degree of ordering of the polymeric substrates. The results revealed that the thermal stability of the trunk polymer, grafted polymer, and polymer modified by ␣-cyano-␦-(2-thienyl) crotononitrile increased progressively with an increasing degree of grafting. The increase was, however, more pronounced for the sample undergoing the lowest degree of grafting. The activation energy of the thermal degradation process remained almost unchanged, and this indicated that the degradation processes of the different films followed almost the same mechanism. The ␥ irradiation at a dose of 60 kGy of the sulfur-treated polymeric films [i.e., the polymeric films treated with ␣-cyano-␦-(2-thienyl) crotononitrile] reduced their thermal stability. This conclusion was reached by the consideration of the changes observed in the pre-exponential factor of the Arrhenius equation due to different chemical and ␥-irradiation treatments. The degree of ordering, evidenced by X-ray diffraction measurements of the trunk polymer, grafted polymer, and modified polymer, suffered a significant drop. This drop was much more pronounced for the sulfur-containing polymeric materials. The observed drop in the degree of ordering of the polymeric substrates was taken as a measure of the structure collapse due to a certain treatment (degree of grafting and sulfur inclusion). The ␥ irradiation of the sulfur-containing polymeric materials greatly increased their degree of ordering, which reached a value greater than that measured for the trunk polymer. Therefore, it was concluded that the thermal stability increased as the degree of ordering decreased.

The optical properties of PP thin films of radiation-graft copolymerization of N-vinyl-2-pyrrlidone and the modification of grafted polymer by α, β-unsaturated nitrile are investigated in the UV–visible region. The absorption coefficient (α) is calculated as a function of the degree of grafting and modification copolymerization. The values of the optical band gap (Eg) have been obtained from the indirect allowed transitions in k-space. The width of the tails of localized states in the band gap (Eu) was evaluated from Urbach edges. Both the parameters (Eg) and (Eu) vary with the degree of grafting and the modification of grafting copolymers for irradiated and unirradiated samples.

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