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and imides in substituted PA is much higher than in initial one [11]. Maximum of their
concentration grows with the increase of substitution degree. According to some authors
perspective light-stabilizers of alkyl substituted PA may be additives of reduced character
regarding hydroperoxides.
Irradiation of thin PA films in oxygen at the temperature 77K allowed to accumulate
radicals P
1
* which completely transformed into radicals P
1
O
2
* during heating up to 213K,
and irradiation at 213K allowed to registrate immediately formation of P
1
O
2
* [12]. However,
in this case there appears additional factor, influencing photooxidation, - it is diffusion
restrictions for oxygen penetration into solid polymer. That is why light ageing mainly
depends on the oxygen dissolved in polymer film. So, emission of hydrogen is observed in
diffusion region, but hydrogen was not found in kinetic region of photooxidation and this may
be explained by the interaction of hydrogen forerunner (for example, P
1
*) with oxygen [13].
Thus, at nonsensibilized photooxidation of PA formation of hydroperoxides does not
influence greatly the process of photooxidation and hydroperoxides are not main products;
radical P
1
* plays the main role as all other radicals may be formed from it, including
peroxides. Hence, while stabilizing PA against action of ultra-violet radiation we may use
additives which interact not only with peroxides but with other radicals.
1.1.1. Sensibilized Photooxidation of Polyamides
From the practical point of view mechanism of sensibilized PA photooxidation is
interesting, as there is possibility to consider mechanism of PA product light ageing , initiated
by impurities, products of oxidation and different additives (dyes, pigments, fillers and so on).
And this may be done if the process of destruction under the action of long-wave light, which
is not absorbed by polymer chromophore groups, will be investigated.
Impurities of mechanical character may get into polymer in the process of its production
or processing and also during polymer use. Some authors think that inpurites not only
deteriorate the process of polymer processing, but during irradiation in the air the lead to the
accumulation of aldehyde groups [14, 15].
In other works [16, 17] influence of impurities of ferrum, aluminium, coper on the rate of
PA destruction at initiated photooxidation is not found. Sensibilizing action of ferrum traces
and other transition metals in PA photooxidation is found in works [18-20] where it is shown
that the destruction process, catalyzed by ferrum impurities, flows slowly when products from
PA are stored at room temperature.
Mechanism of photooxidation of aliphatic PA in the conditions when absorption of light
by amide group (λmax=360 nm) is excluded and there are no special additives is studied in
the work [21]. The authors show that the product, sensibilizing oxidation, is formed under the
light action and this product, unlike other polymers, is not hydroperoxide. It is found that the
rate of photooxidation is defined by stationary concentration of this product and does not
depend on light intensity. The scheme of photooxidation, including quadratic break of the
chain, photobranching in semiproduct of dark oxidation and product destruction are given
here.
There was undertaken an attempt [12] to show, by methods of luminescence,
luminescence centres in PA, intensity of which does not depend on the light intensity, causing
photooxidation of polymer. Corrected spectra of PCA fluorescence are characterized by
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