ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 9, pp. 1393!1402. + Pleiades Publishing, Inc., 2006.
Original Russian Text + V.N. Salimgareeva, S.V. Kolesov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 9, pp. 1409!1418.
Principles of Radiation Protection of Poly(Methyl Methacrylate)
V. N. Salimgareeva and S. V. Kolesov
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences,
Ufa, Bashkortostan, Russia
Received July 15, 2005
Abstract-Mechanisms of radiation aging of poly(methyl methacrylate) and methods for enhancing its resis-
tance to high-energy radiation are considered.
Poly(methyl methacrylate) (PMMA) is one of the
most important materials in production of structural-
decorative elements in building, of machines and de-
vices, of items for medicine, of consumer’s goods,
and also as structural material in nuclear and space
engineering where it is exposed to ionizing radiation.
Poly(methyl methacrylate) is also exposed to radiation
in the course of radiation sterilization of medical
equipment, which is a widely used procedure.
High-energy radiation induces changes in physical,
physicomechanical, and chemical properties of poly-
meric materials, resulting in deterioration of their ser-
vice characteristics [1, 2]. The radiation resisance of
PMMA items requires enhancement. This goal can be
accomplished by introducing special protecting addi-
tives (antirads) preventing the development of unde-
sirable radiation-chemical reactions and this prevent-
ing or considerably reducing changes in the structure
and properties of the polymer upon irradiation.
As radiation protectors are used aromatic hydrocar-
bons and aromatic amines, urea and thiourea deriva-
tives, alkyl mercaptans, and organophosphorus and
sulfur-containing heterocyclic compounds . The
range of compounds used for radiation protection of
PMMA steadily expands; various methods are used
for their introduction into polymeric items or incor-
poration into macromolecules . Development
of new approaches to the radiation stabilization of
PMMA remains an urgent problem.
This review summarizes and correlates published
data on the search for high-performance radiation-
chemical inhibitors of PMMA aging and on the devel-
opment of scientific principles of their choice and
introduction into the polymer.
RADIATION AGING OF PMMA
Irradiation of a substance results in generation of
free electrons, cations, and excited molecules. Trans-
formations of these intermediates yield the second
generation of active intermediate species (excited
molecules, cations and anions, free radicals, radical
ions) according to the scheme 
AB 6 AB
+e,AB6 AB*, AB
AB + e 6 AB
, AB* 6 A
, AB* 6 AB
where the asterisk denotes electronically excited state.
Free-radical reactions make the major contribution
to radiation-chemical transformations of polymers.
The generation of primary radicals and subsequent
radical chain processes are responsible  for the
chemical cross-linking and degradation of macromole-
cules under g-irradiation.
Irradiation of PMMA causes random cleavage of
the backbone; the number of breaks is proportional to
the radiation dose . The contribution of depolymer-
ization to the radiation-induced degradation is very
small compared to pyrolysis involving the depolymer-
ization by the radical-chain mechanism. The mono-
mer, methyl methacrylate (MMA), is not released
until the polymer is heated to 398 K and higher tem-
peratures . Simultaneous action of heat and radia-
tion (irradiation with an electron beam at 4983598 K)
causes thermal and radiation degradation. The gaseous
products released in the process mainly consist of
MMA . The activation energy of the thermal de-
gradation of PMMA decreases from E = 140 without
irradiation to E =5kJg
under irradiation .
The mechanism of radiation aging of PMMA was
studied at low temperatures (<100 K) with the aim to
elucidate the primary events in the interaction of the
radiation with the substance [10, 13, 14]. At these
temperatures, the effect of secondary processes associ-
ated with the migration and diffusion of the primary
active species is reduced to a minimum. At 77 K, low-