Studies on Radiation Crosslinking of Polysulfone
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JP0050427 JAERI-Conf 2000-001 Studies on Radiation Crosslinking of Polysulfone Xiaoguang Zhong Jiazhen Sun Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 130022, China Polysulfone is a kind of high temperature-resistance and radiation-resistance engineering plastic. The chemical structure is as follows: Brown (1), Lyon (2), Sasuga (3), et al have already studied its radiation effect. We studied CH3 radiation crosslinking effect of polysulfone by using of XPS, ESR, and CG methods and got some new results. Results and Discussions 1. Study radiation crosslinking of polysulfone by XPS method Because of conjugate system of benzene ring, polymer material which contains of benzene ring will appear shake-up peak in XPS spectra. Wanxi Zhang (4) shows that during radiation crosslinking of polystyrene increases with radiation dose and the intensity of shake-up peak decreases gradually with increase of radiation dose and crosslinking degree. This suggests that radiation crosslinking destroyed conjugate system of benzene ring. During radiation crosslinking of polysulfone, we find rules of shake-up peaks in the XPS spectra are different at different radiation crosslinking temperature. At lower temperature the intensity of shake-up peak decreases with the increase of radiation dose. This rule is similar to that of radiation crosslinking of polystyrene. The results are shown in Fig. 1. 183- JAERI-Conf 2000-001 Fig. 1. The spectra of radiation crosslinking of polysulfone at 70"C Comparing with radiation crosslinking at lower temperature, the intensity of shake-up peak increases with radiation dose when radiation crosslinking reaction takes place at temperature above glass transition temperature of polysulfone. The results are shown in Fig. 2. 203"C Fig.2. The XPS Spectrum of radiation crosslinking of polysulfone at 203"C It means that the mechanisms of radiation crosslinking of polysulfone at different radiation temperature are different above or below their glass transition temperature. The conjugate effect of polysulfone also increases during radiation crosslinking at high temperature. The relationship between shake-up peak and radiation dose is shown in Fig. 3. R Dose, KGy Fig. 3. Relative intensity of shake-up peak—Dose relationship of irrad. Polysulfone -184- JAERI-Conf 2000-001 We find that the point of intersection of the two straight lines is the dose of gelation in the figure of P~R relationship from Fig. 3. P is the ratio of area of Cls and the area of shake-up peak. The dose of gelation of polysulfone Rgel that got from the change of shake-up peaks is 279KGy, but the dose Rgel that got from gel method is 270KGy and the results are very similar. Thus we can obtain a new method to characterize the degree of radiation crosslinking by the change of shake-up peaks. 2. Studies of the mechanism of radiation crosslinking of polysulfone We measured the changes of free radical of polysulfone during radiation crosslinking. ESR spectra at low temperature are shown in Fig. 4. (i) Fig. 4. ESR spectra of polysulfone after Y-radiation at -196"C. The structures of multi-peak on the both sides in the ESR spectra are belong to free radicals( I ). (I) The hyperfine coupling constants a (CH2)=51G and a (cyclic H)=10G are close to those in the literature. The free radicals (I)are unstable when temperature is rising. The multi-peak structures on the both sides disappear in the ESR spectra when temperature rises near 50°C. This shows the free radicals cannot exist stably near 50°C. Thus, when radiation crosslinking reactions take place at the room -185- JAERI-Conf 2000-001 temperature, the free radicals join the reactions and thus destroy the conjugate system of benzene ring, which make the intensity of shake-up peak smaller. This phenomenon agrees with the results measured by XPS spectra. Fig. 5a and Fig. 5b are the ESR spectra of polysulfone at different temperatures. 25"C Fig. 5a Radical at different temperature 50G 1L5TC 95-C ( TT +TTD Fig. 5b Radical at differerrt -temperature -186- JAERI-Conf 2000-001 From the figures, we can see the peaks which denote free radicals(II and III) tends to decrease weakly at 75°C. It means that these two kinds of free radicals are beginning to join the radiation crosslinking reactions. (ID (III) In the RSR spectra, g value of free radicals (II) equal 2.007 is close to that of free radicals (III) which is 2. 005. Therefore, the peak of g=2. 007 we got from ESR spectra maybe is the results of overlap of free radicals(II)and (III). The concentration of the free radicals in the ESR spectra decreases gradually with raising of irradiation temperature. The concentration of free radicals changes rapidly near the glass transition temperature of polysulfone. The results are shown in Fig. 6. [K.-] 40 60 80 100 120 Fig. 6. The relationship between the free radicals and temperature When radiation crosslinking takes place at high temperature, the lives of the free radicals are very short, so the chance to join to the crosslinking is relatively less. Because the free radicals(II) and(III)begin to join the reactions, the mechanism of radiation crosslinking reactions at high temperature is different to which of at low temperature. The free radicals(IV)and(V)maybe exist, Lyon had reported the existence of the free radicals(IV). But we have not found in the ESR spectra. (V) -187- JAERI-Conf 2000-001 The g value of the free radicals(V)which equals 2.006 is very close to that of the free radicals (II) and (III) so may be overlap by free radicals (II). It seems that phenyleneoxy and phenylene sulfone radical join the reactions at high temperature of radiation crosslinking. Therefore, the possibility of reactions between the free radicals (II) and (III) and the free radicals (IV)and(V) is increased. Certainly, we can not exclude the free radicals(IV)and(V)to form crosslinking bond of H type. However, the main ones must be recombination of (II) and (III) and (IV) and (V). Therefore, we consider the radiation crosslinking of polysulfone takes place by the reaction mechanism of the T type. This agrees with the concept of the reaction mechanism of T type or Y type of the polymers has rigid chains. References 1 J.R.Brown , J.Polym. Sci. Part B ,8,121 (1970) 2.A.R.Lyons , N.C.R.Symons and J.K. Yandell, Die Markromol.Chem. 157,103(1972) 3.T.Sasuga and Haya Kawa, J.Polym.Sci., Phys.Ed. 22,529(1984) 4.W.X.Zhang, J.Z.Sun etal, Kexue Tongbao 30(6)750(1985) -188-.