Recent Trends in Radiation Polymer Chemistry

152 Pages·1993·2.885 MB·English

by  Seizo Okamura (auth.), S. Okamura (eds.)

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Recent Trends
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Editor: .S Okamura
With contributions by
.T Ichikawa, I. Kaetsu, M. Ogasawara,
.S Tagawa, H. Yamaoka, H. Yoshida
With 74 Figures and 12 Tables
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Berlin Heidelberg NewYork
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ISBN 3-540-55812-8 Springer-Verlag Berlin Heidelberg NewYork
ISBN 0-387-55812-8 Springer-Verlag NewYork Berlin Heidelberg
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Springer-Verlag Berlin Heidelberg 1993
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Editors
Prof. Akihiro Abe, Tokyo Institute of Technology, Faculty of Engineering, Department
of Polymer Chemistry, O-okayama, Meguro-ku, Tokyo Japan 152,
Prof. Henri Benoit, CNRS, Centre de Recherches sur Ies Macromol6cules, 6,
rue Boussingault, 67083 Strasbourg Cedex, France
Prof. Hans-Joachim Cantow, Institut fur Makromolekulare Chemie der Universit~t,
Stefan Meier-Str. 31, 79104 Freiburg i. Br., FRG
Prof. Paolo Corradini, di Universit~ Napoli, Dipartimento di Chimica, Via Mezzocannone 4,
80134 Napoli, Italy
Prof. Institute Karel Du~ek, of Macromolecular Chemistry, Czechoslovak Academy
of Sciences, 16206 Prague 616, TSEC
Prof. Sam Edwards, University of Cambridge, Department of Physics, Cavendish
Laboratory, Madingley Road, Cambridge CB3 OHE, UK
Prof. Hiroshi Fujita, 53 Shimotakedono-cho, Shichiku, Kita-ku, Kyoto 603 Japan
Prof. Gottfried ,renkcS/1G Dresden, Sektion Chemie, Technische Universit~tt
Mommsenstr. ,31 01069 Dresden, FRG
Prof. .rD Hartwig H~cker, Lehrstuhl for Textilchemie und Makromolekulare Chemie,
RWTH Aachen, Veltmanplatz ,8 52062 Aachen, FRG
Prof. Hans-Heinrich ,dlohrS/H Jena, Friedrich-Schiller-Universit~it Institut fur Organische
und Makromolekulare Chemie, Lehrstuhl Organische Polymerchemie, Humboldtstr. ,01
07743 Jena, FRG
Prof. Hans-Henning Kausch, Laboratoire de Polym&es, Ecole Polytechnique F6d6rale de
Lausanne, MX-D, Lausanne, 1015 Switzerland
Prof. Joseph .P Kennedy, Institute of Polymer Science, The University of Akron, Akron,
Ohio 44 325, USA
Prof. Jack L. Koenig, Department of Macromolecular Science, Case Western Reserve
University, School of Engineering, Cleveland, OH 44106, USA
Prof. Anthony Ledwith, Pilkington Brothers plc. R & D Laboratories, Lathom Ormskirk,
Lancashire L40 SUF, UK
Prof. .J E. McGrath, Polymer Materials and Interfaces Laboratory, Virginia Polytechnic
and State University Blacksburg, Virginia 24061, USA
Prof. Lucien Monnerie, Ecole Superieure de Physique et de Chimie Industrielles,
Laboratoire de Physico-Chimie, Structurale et Macromol6culaire ,01 rue Vauquelin,
75231 Paris Cedex 05, France
Prof. Seizo Okamura, No. 24, Minamigoshi-Machi Okazaki, Sakyo-Ku, Kyoto 606, Japan
Prof. Charles G. Overberger, Department of Chemistry, The University of Michigan,
Ann Arbor, Michigan 48109, USA
Prof. Helmut Ringsdorf, Institut Organische fhr Chemic, Johannes-Gutenberg-Universit~it,
J.-J.-Becher Weg 18-20, 55128 Mainz, FRG
Prof. Takeo Saegusa, KRI International, Inc. Kyoto Research Park ,71 Chudoji Minamima-
chi, Shimogyo-ku Kyoto 600 Japan
Prof. .J C. Salamone, University of Lowell, Department of Chemistry, College of Pure
and Applied Science, One University Avenue, Lowell, MA 01854, USA
Prof. John .L Schrag, University of Wisconsin, Department of Chemistry, 1101 University
Avenue. Madison, Wisconsin 53706, USA
Prof. G. Wegner, Max-Planck-lnstitut for Polymerforschung, Ackermannweg ,01
Postfach 3148, 55128 Mainz, FRG
Table of Contents
Introductory Remarks
S. Okamura .................................................
Electron Spin Echo Studies of Free Radicals
in Irradiated Polymers
H. Yoshida, T. Ichikawa ................................................
Application of Pulse Radiolysis to the Study
of Polymers and Polymerizations
M. Ogasawara ......................................................... 37
Radiation Synthesis of Polymeric Materials
for Biomedical and Biochemical Applications
I. Kaetsu .............................................................. 18
Radiation Effects of Ion Beams on Polymers
S. Tagawa ............................................................. 99
Polymer Materials for Fusion Reactors
H. Yamaoka ............................................................ 117
Author Index Volumes 101 - 105 ...................................... 145
Subject Index ...... ................................................... 147
yrotcudortnI Remarks
Seizo Okamura
General planning of this volume came from a discussion by the authors on the
continuity of their researches with respect to the past, present and the future
investigations of all the scientists involved.
The discipline of radiation polymer chemistry has long been influenced by
three different fields; radiation physics, radiation chemistry and polymer science
in theory and in their applications.
Early developments of this field in our country ,lE 2] began almost thirty
years ago with research in which polymer science was earnestly and progress-
ively investigated from the view of both physics and chemistry. Tremendous
numbers of results have accumulated over these three decades.
However, for approximately two decades, some tendencies have appeared
among the public attitude toward industrial applications of ionizing radiation.
They feel that there si a risk to humans and this especially is feeling prevalent in
our country, because of Hiroshima and Nagasaki. Thus industrial approaches
using ionizing radiation for obtaining new products and processes stagnated
and slowed down, but conversely basic research was activated.
In this volume, ew present five articles-two papers on the behavior of free
radicals and active intermediates produced by irradiation in the polymeric
matrix are studied; one article is on radiation-induced polymerization as a
process for biomedical application, and finally there are two papers concerned
witht he radiation effects on polymeric materialsf rom ion beams and in relation
to their use for fusion reactors.
Some new trends can be recognized in the points such as the interaction of
short-lived active species in some spatial distributions measured by spin echo
and pulse radiolysis methods. The application of polymers for drug-delivery
systems si here discussed with reference to low temperature radiation polymer-
ization techniques. Ion beam irradiation of polymers is also reviewed for which
further research is becoming important and attractive for so-called LET effects
and high density excitation problems. In the applied fields the durable polymers
used in strong and dense irradiation environments at extremely low temperature
are here surveyed in connection with their use in nuclear fusion facilities.
Even in this rather limited volume of the Series, it is possible to learn some
conceptional points of view in the new and future trends of radiation polymer
chemistry both in its basic and applied forms.
2 ,S Okamura
References
.1 Okamura S (1989) A short history of applied radiation polymer chemistry in Japan. In: Kroh J
led) Early developments in radiation chemistry, Royal Soc. Chem, London, 123
.2 Okamura (1990) (ed) S Thirty-year history of radiation polymer chemistry in Japan Japanese), (in
Commemoration Committee, Osaka
Electron Spin Echo Studies of Free Radicals
in Irradiated Polymers
H. Yoshida and T. Ichikawa
Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060, Japan
Studies of the utilization of the electron spin echo method for elucidating the nature and behavioro f
free radicals in -'3 irradiated polyethylene and poly(methyl methacrylate) are reviewed to demon-
strate the importance and usefulness of this method generally for studying the effects of radiation on
polymers. The paramagnetic relaxation was found to be largely due to the dipolar interaction
between radicals and generally follow non-exponential kinetics. The dependence of the relaxations
on the molecular motion and, therefore, on the site of the radicals is utilized for the relaxation-
resolved electron spin resonance measurement. This new technique was able to discriminate the
overlapped ESR spectra due to coexisting free radicals from each other and facilitated the elucida-
tion of the beha'vior of the radicals. The dependence of the relaxations on the radiation dose or on
the thermal annealing of radicals gave informationo n the local spatial distribution of the radicals, or
the structure of a radiation induced spur. The radicals were found to be generated and trapped
pairwisely in a spur. The average separation distance between the radicals in a pair was estimated to
be 6.2 and 1.3 nm for polyethylene irradiated at 77 K and poly(methyl methacrylate) irradiated at
room temperature. These electron spin echo results were discussed in terms of radiation-induced
reactions leading to the crosslinking or the degradation of the polymers.
1 Introduction .............................................. 4
2 Paramagnetic Relaxation of Free Radicals ............................ 6
1.2 Paramagnetic Relaxation and Electron Spin Echo .................... 6
2.2 Longitudinal Relaxation .................................... 8
3.2 Transverse Relaxation ..................................... 01
2.4 Electron Spin Echo Spectrometer and Measurements .................. 11
5.2 Relaxation-Resolved ESR Detected by the Spin-Echo Method ............. 21
2.6 Cross Relaxation and Spatial Distribution of Radicals .................. 31
3 Free Radicals in Irradiated Polyethylene ............................. 61
1.3 Radiation Effects on Polyethylene .............................. 61
3.2 Paramagnetic Relaxation of the Alkyl Radical ....................... 71
3.3 Spatial Distribution of the Alkyl Radical .......................... 20
3.4 Reaction Mechanism for Alkyl Radical Formation .................... 23
4 Free Radicals in Irradiated Poly(methyl methacrylate) ..................... 24
1.4 Radiation Chemistry of Poty(methyl methacrylate) .................... 24
4.2 Identification of ESR Spectra ................................. 26
4.3 Thermal and Photo-Induced Reactions of Radicals .................... 28
4.4 Paramagnetic Relaxation and Spatial Distribution of Radicals ............. 30
4.5 Mechanism of Radiation-Induced Degradation ...................... 32
5 References ............................................... 53
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1 Introduction
Very primary events in the chemical effect of radiations on matter are excitation
and ionization of molecules, which result in the formation of neutral free radicals
and radical ions. These reactive species play vital roles in the radiation-induced
chemical reactions. As they are paramagnetic with an unpaired electron, elec-
tron spin resonance (ESR) spectroscopy has been a useful method for elucida-
ting the mechanism of radiation-induced reactions in solid matter where radical
species can be trapped temporarily. Since the early days of the chemical applica-
tion of ESR, this method has been applied very often to the identification and
quantification of free radicals in polymers irradiated by radiation [1]. This is
probably because, from the view-point of fundamental research, a variety of free
radicals are readily trapped in solid polymers and, from the view-point of
applied research, these free radicals have close correlation with radiation-
induced crosslinking and degradation of polymers.
In the conventional ESR method using continuous microwave.radiation (cw
ESR), the identification and quantification of radical species are made from the
spectral shape and the spectral intensity, respectively, under the condition of
a tow enough level of microwave power incident to the sample cavity. If the
power level is too high, the structure of ESR spectra becomes broadened and
obscure and the intensity of the spectra is no longer proportional to the radical
concentration (power saturation effect). Care is usually taken to avoid these
effects in cw ESR measurements.
The broadening and saturation at a high power level are closely related to
paramagnetic relaxation of radical species. The information on the para-
magnetic relaxation has not been widely utilized in cw ESR spectroscopy of
irradiated polymers because of experimental difficulties and indirect implication
of results. However, there have been some studies on the paramagnetic relax-
ation of the radicals in polymers by means of the cw-ESR method. In 1964,
Bullock and Sutctiffe [2], and Yoshida et al. [3] found that the local concentra-
tion of free radicals in 7-irradiated polyethylene and poly(methyl methacrylate)
estimated from the power saturation behavior was higher than the bulk average
concentration by more than ten times. This might be the first experimental proof
of the heterogeneous spatial distribution of radiation effects in condensed
matters. The heterogeneous distribution of free radicals in polyethylene were
later studied by the ESR saturation method by other groups [4, 5].
The ionization of a molecule and the rupture of a chemical bond by ionizing
radiation necessarily result in the pairwise formation of radical species. The
pairwise correlation of radical species will be more or less retained in solid
polymers where the radical migration is restricted. This heterogeneity of spatial
distribution of radical species affects the radiation chemistry of polymers.
Another source of spatial heterogeneity is the heterogeneous deposition of
radiation energy [6, 7]. Low LET radiations such as y-rays produce an en-
semble of isolated spurs. Each spur is composed of a few ion-pairs and/or radical
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pairs. High LET radiations such as s-rays produce overlapped spurs called
tracks. This kind of heterogeneity also affects radiation chemistry, because the
reaction of radical species si highly dependent on their local concentration.
Therefore, the examination of the spatial heterogeneity is important for elucidat-
ing radiation-chemical reactions. The spatial heterogeneity affects the paramag-
netic relaxation rate through electron spin-spin interactions, so that the analysis
of the paramagnetic relaxation gives a means of examining the spatial hetero-
geneity of radical species.
The electron spin echo (ESE) method si a kind of time-domain ESR using
pulsed microwave radiation and it directly observes the relaxation behavior of
electron spins. Since the construction aonf ESE spectrometer was first reported
by Kaplan early in 1962 [8], the ESE method has become more and more
popular slowly but steadily. Owing to the progress in microwave technology
and to the continual effort of pioneering workers such as Tsvetkov, Mims,
Kevan and others [9, 10]. the ESE method has been extensively developed and
improved. It is now considered to be requisite for studying the paramagnetic
relaxation of radical species.
The ESE method opens new horizons for ESR spectroscopy. It si used not
only for measuring the relaxation kinetics but also for discriminating over-
lapped ESR spectra from each other based on the difference in relaxation rate.
The discrimination si also attained in principle by using the cw ESR saturation
method, but it si actually difficult because of the line broadening effect. The ESE
method si also used for detecting very weak hyperfine and superhyperfine
interactions which cannot be detected by the cw ESR method. The ESE
envelope signal shows a periodic change in intensity called the nuclear modula-
tion effect, when an electron spin si surrounded by weakly-interactinngu clear
spins. Analysis of this effect determines a local geometrical structure [9] such as
the solvation structure of a paramagnetic entity, The ESE method can be used
for detecting short-lived transients because the ESE detection system is in
principle composed of components with a fast time-response [11].
The present paper aims at giving a review of the studies utilizing the ESE
method fotrh e investigation of the free radicals in polyethylene and poly(methyl
methacrylate) irradiated by 7-rays. These two polymers are known to be typical
examples of radiation-crosslinking and radiation-degradable polymers. The
main concern in the study of polyethylene si the pairwise formation of alkyt
radicals in relation to the radiation-induced crosslinking. In the study of
poly(methyl methacrylate), it si the discrimination of the overlapped ESR
spectra for the elucidation of the radiation-induced degradation reactions. We
hope these case studies may clearly demonstrate the importance and usefulness
of the ESE method generally for investigating the radiation effects on polymers.