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Primary processes in pulse irradiated poly(ethersulphone)
PERGAMON
Radiation Physics and Chemistry Radiation Physics and Chemistry 54 (1999) 187±188
Primary processes in pulse irradiated poly(ethersulphone) S. Karolczak a, *, S. Wysocki b, R.A. Fouracre c a
Institute of Applied Radiation Chemistry, Technical University, WroÂblewskiego 15, 93-590 LoÂdz, Poland Institute of Fundamental Food Chemistry, Technical University, Stefanowskiego 4/10, 90-924 LoÂdz, Poland c Department of Electronic and Electrical Engineering, The University of Strathclyde, Glasgow, G1 1XW, Scotland b
Poly(ethersulphones) (PES) represent an important group of commercially useful polymers because of their high thermal stability, excellent electrical properties and remarkable radiation resistance. Numerous reports on the eect of g-radiation, high energy electrons and particle beams on polyarylsulphones can be found in the literature (Web, 1996). In these reports, the extent of radiation-induced degradation and relevant mechanisms for poly(ethersulphones) were evaluated on the basis of an analysis of ®nal, stable products, yields of chain scission and crosslinking, and changes of mechanical, physical and chemical properties. Recent ESR studies (Faucitano 1996) provided new valuable data on the type of radical species, their formation and subsequent reactions. There is still no information on primary processes following ionization and excitation of PES by ionizing radiation. In this paper, time-resolved spectroscopic studies on the simplest PESÐpoly(oxy1,4-phenylsulfonyl-1,4-phenylene) (±O±C6H4±SO2± C6H4±)nÐfollowing irradiation are very brie¯y reported. Films 50±100 mm thick were irradiated with short (1±4 ms) pulses of 6 MeV electrons. The pulse radiolysis system has been described elsewhere (Karolczak, 1992). Samples of PES were mounted in a cryostat or a thermostat and irradiated in vacuum, nitrogen or oxygen atmosphere. In separate experiments PES foil presaturated with water was also examined. Decay of transient absorption measured at selected wavelengths and time resolved spectra were recorded over a wide temperature range namely from 77 K to 500 K. The transient species were formed upon excitation with an electron pulse. As a result, broad absorption spectra with three bands were produced, with peaks around 370, 440 and 550 nm. At 77 K these bands
* Author for correspondence: Fax: (48-42)-360-246; E-mail: [email protected]
were well resolved, whereas at ambient and higher temperatures two latter peaks are barely seen on the shoulder of the dominating 370 nm band. As seen from Figs. 1 and 2, at 77 K absorption decays are in seconds, while at room temperature this process goes to completion in tens of microseconds. The kinetics of overall decay is complex but second order processes seem to be dominant. Simple kinetic analysis showed that absorption at all peak wavelengths decay with very similar rates. Whether this indicates single species is not yet clear. The change of relative amplitude of the aforementioned peaks with temperature could indicate that more than one transient is involved. No stable or transient absorption was observed in the near IR region which would con®rm the presence of trapped electrons. Arrhenius-like plots using the reciprocal of the ®rst half-life time, i.e. (1/t 11/2) vs T ÿ 1, as presented in Fig. 3, exhibit two interesting features. Two sections of the plot with the break point at 290 K represent decay processes with activation energies diering by nearly one order of magnitude. Most likely, such a change indicates that two very dierent mechanisms are responsible for the decay of transients in vacuum-irradiated PES. No relevant phase transition in the temperature range near the break point has so far been reported for this polymer. Transients formed by irradiation of PES in the presence of oxygen decay with activation energy about three times lower than that for the vacuum-irradiated material. A change of mechanism due to the contribution of oxygen molecules in the samples is the most plausible explanation. The rate of absorption decay in the presence of oxygen is higher than for samples irradiated in vacuum or in nitrogen atmospheres. Even higher rates are observed for water saturated samples. Detailed kinetic analysis and radiolysis of model (monomeric) compounds should allow for unambigous identi®cation of the observed transients and mechanisms.
0969-806X/99/$19.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 8 ) 0 0 2 3 9 - 4
188
S. Karolczak et al. / Radiation Physics and Chemistry 54 (1999) 187±188
Fig. 1. Time evolution of absorption spectra for PES irradiated at 77 K in vacuum.
Fig. 3. Arrhenius plots for PES irradiated in vacuum (w), and in the atmosphere of oxygen (). O2 pressure at 295 K was equal to 400 mm Hg. Rate constant was approximated as k = (t 11/2) ÿ 1. Where t 11/2 is ®rst half-life time.
References
Fig. 2. Time evolution of absorption spectra of PES irradiated at 331 K in vacuum.
Faucitano, A., Buttafava, A., 1996. ESR study of gamma radiolysis of polyethersulphones. Radiat. Phys. Chem. 48, 122. Karolczak, S., Hodyr, K., PolowinÄski, M., 1992. Pulse radiolysis system based on ELU-6E Linac. IIÐDevelopment and upgrading the system. Radiat. Phys. Chem. 39, 1. Web, site, 1996. http://allen.rad.nd.edu
Radiation Physics and Chemistry Radiation Physics and Chemistry 54 (1999) 187±188
Primary processes in pulse irradiated poly(ethersulphone) S. Karolczak a, *, S. Wysocki b, R.A. Fouracre c a
Institute of Applied Radiation Chemistry, Technical University, WroÂblewskiego 15, 93-590 LoÂdz, Poland Institute of Fundamental Food Chemistry, Technical University, Stefanowskiego 4/10, 90-924 LoÂdz, Poland c Department of Electronic and Electrical Engineering, The University of Strathclyde, Glasgow, G1 1XW, Scotland b
Poly(ethersulphones) (PES) represent an important group of commercially useful polymers because of their high thermal stability, excellent electrical properties and remarkable radiation resistance. Numerous reports on the eect of g-radiation, high energy electrons and particle beams on polyarylsulphones can be found in the literature (Web, 1996). In these reports, the extent of radiation-induced degradation and relevant mechanisms for poly(ethersulphones) were evaluated on the basis of an analysis of ®nal, stable products, yields of chain scission and crosslinking, and changes of mechanical, physical and chemical properties. Recent ESR studies (Faucitano 1996) provided new valuable data on the type of radical species, their formation and subsequent reactions. There is still no information on primary processes following ionization and excitation of PES by ionizing radiation. In this paper, time-resolved spectroscopic studies on the simplest PESÐpoly(oxy1,4-phenylsulfonyl-1,4-phenylene) (±O±C6H4±SO2± C6H4±)nÐfollowing irradiation are very brie¯y reported. Films 50±100 mm thick were irradiated with short (1±4 ms) pulses of 6 MeV electrons. The pulse radiolysis system has been described elsewhere (Karolczak, 1992). Samples of PES were mounted in a cryostat or a thermostat and irradiated in vacuum, nitrogen or oxygen atmosphere. In separate experiments PES foil presaturated with water was also examined. Decay of transient absorption measured at selected wavelengths and time resolved spectra were recorded over a wide temperature range namely from 77 K to 500 K. The transient species were formed upon excitation with an electron pulse. As a result, broad absorption spectra with three bands were produced, with peaks around 370, 440 and 550 nm. At 77 K these bands
* Author for correspondence: Fax: (48-42)-360-246; E-mail: [email protected]
were well resolved, whereas at ambient and higher temperatures two latter peaks are barely seen on the shoulder of the dominating 370 nm band. As seen from Figs. 1 and 2, at 77 K absorption decays are in seconds, while at room temperature this process goes to completion in tens of microseconds. The kinetics of overall decay is complex but second order processes seem to be dominant. Simple kinetic analysis showed that absorption at all peak wavelengths decay with very similar rates. Whether this indicates single species is not yet clear. The change of relative amplitude of the aforementioned peaks with temperature could indicate that more than one transient is involved. No stable or transient absorption was observed in the near IR region which would con®rm the presence of trapped electrons. Arrhenius-like plots using the reciprocal of the ®rst half-life time, i.e. (1/t 11/2) vs T ÿ 1, as presented in Fig. 3, exhibit two interesting features. Two sections of the plot with the break point at 290 K represent decay processes with activation energies diering by nearly one order of magnitude. Most likely, such a change indicates that two very dierent mechanisms are responsible for the decay of transients in vacuum-irradiated PES. No relevant phase transition in the temperature range near the break point has so far been reported for this polymer. Transients formed by irradiation of PES in the presence of oxygen decay with activation energy about three times lower than that for the vacuum-irradiated material. A change of mechanism due to the contribution of oxygen molecules in the samples is the most plausible explanation. The rate of absorption decay in the presence of oxygen is higher than for samples irradiated in vacuum or in nitrogen atmospheres. Even higher rates are observed for water saturated samples. Detailed kinetic analysis and radiolysis of model (monomeric) compounds should allow for unambigous identi®cation of the observed transients and mechanisms.
0969-806X/99/$19.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 8 ) 0 0 2 3 9 - 4
188
S. Karolczak et al. / Radiation Physics and Chemistry 54 (1999) 187±188
Fig. 1. Time evolution of absorption spectra for PES irradiated at 77 K in vacuum.
Fig. 3. Arrhenius plots for PES irradiated in vacuum (w), and in the atmosphere of oxygen (). O2 pressure at 295 K was equal to 400 mm Hg. Rate constant was approximated as k = (t 11/2) ÿ 1. Where t 11/2 is ®rst half-life time.
References
Fig. 2. Time evolution of absorption spectra of PES irradiated at 331 K in vacuum.
Faucitano, A., Buttafava, A., 1996. ESR study of gamma radiolysis of polyethersulphones. Radiat. Phys. Chem. 48, 122. Karolczak, S., Hodyr, K., PolowinÄski, M., 1992. Pulse radiolysis system based on ELU-6E Linac. IIÐDevelopment and upgrading the system. Radiat. Phys. Chem. 39, 1. Web, site, 1996. http://allen.rad.nd.edu