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for radicals to be lost and then irradiation is renewed, changing from lower intensity to higher
one, then stationary concentration of radicals will increase proportionally to I 0,5 and the rate
of photolysis - proportionally to I 1,5 . Hence, the rate of photolysis is proportional to light
intensity and concentration of radicals. These data show that acetic acid is formed at
photolysis of radicals and in connection with this radical processes at CA photolysis have
been studied.
2.3. K INETICS OF R ADICALS A CCUMULATION
Quantitative study of kinetics of radicals accumulation has required solution of auxiliary
problem - definition of the rate of photoinitiation W in . In the case of solid-phase reactions
there are experimental difficulties in solution of this problem. Measurement of W in according
to consumption of inhibitor is complicated by possible photochemical reactions of inhibitor
itself and specific solid-phase effects of “kinetic stop” type and so on [10]. Measurement of
W in according to initial rate of radicals accumulation is also tactless in solid polymer, as the
latter may be much lower than W in [164].
1,4 - trichlormethylphenylene (TCMP) was chosen as photoinitiator for solution of the
set problem. Under light action TCMP splits atom of chlorine, which possesses high
reactivity and easily breaks hydrogen atom off the polymer [165]. So, macroradical of
polymer and molecule of chlorine hydrogen are formed in primary act of TCMP
photoinitiation. That is why formation of chlorine hydrogen, which is easily measured by
pressure gauge, is peculiar counter of polymer macroradicals being formed.
It has been found that the rate of chlorine hydrogen formation at TCMP photolysis in CA
in the wide range of light intensities and TCMP concentrations (0,01-0,2 mole/kg) is
proportional to light intensity and TCMP concentration. Quantum yield of hydrochloric acid,
defined from these data, was equal to Ф HCL =0,028. Data on kinetics of accumulation of HCl
and macroradicals at CA photolysis with TCMP addition are given in Figure 2.4. The rate of
HCl formation (and also W in ) remains constant during the whole period of films irradiation
that is why, determination of stationary concentration of radicals is caused by determination
of balance between reactions of formation and destruction of macroradicals.
According to the data of Figure 1.4 a, b the rate of photoinitiation decreases by 20 times
at light intensity decreasing by 20 times. This shows that in experiment conditions W in - I, as
it was to be expected. Stationary concentration of radicals (R*) st decreases from 0,001 (Figure
2.4a) to 0,0002 mole/kg (Figure 2.4 b), that agrees with the law (R*) st - I 0,5 which is usually
characteristic in the case of quadratic destruction of radicals. The rate of photoinitiation is
equal to the rate of all radicals formation at polymer photolysis. Initial rate of radicals
accumulation is equal to such one only for those radicals, which in the conditions of
experiments are registrated by EPR method. It may be lower than the rate of photoinitiation,
if it is impossible to registrate the part of radicals because of high constant of the rate of their
destruction [166].
According to the data, given in Figure 2.1., decrease of light intensity by 20 times leads
to decrease of the rate of observed radicals formation by 80 times.
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