STABILIZATION AND MODIFICATION OF POLYCAPROAMIDE - Photochemical Reactions in Heterochain Polymers - page 7

lengths of oligoenimic chain in the process of thermooxidation correlate well with
experimental kinetic data on thermooxidation of PA-6 and PA-66 at 160-180 0 C.
Data on thermogravimetric analysis of PA-6 destruction in the air are given in the work
[38]. PA loses 25% of mass at warming up in the interval 25-325 0 C, and main
transformation (92% of mass) finishes at 470 0 C. The authors of the work [39] have studied
composition of gas phase, formed at thermal destruction of PCA using infrared spectroscopy.
Comparison of obtained spectra with spectra of model compounds allowed to identify water
steams, CO 2 , and also MeOH and EtOH in the gas phase.
With the aim to study PA transformations Makarov [40] used method of free radicals
initiation by thermal and photochemical decomposition of peroxides. The author succeeded in
finding high efficiency of PA macromolecules breakages under the action of free radicals at
the temperature 20-98 0 C (within the limits of operational temperatures). He also succeeded
in determination of reactions sequence and revealing the phase directly responsible for the
acts of polymer chains destruction. It is shown that in the conditions of thermal initiation
transformations of peroxides are caused by macroradicals and photochemical - by own
radicals of peroxides.
Postnikov and Makarov [41] investigated thermal decomposition of benzoyl in PA at
temperature 65-100 0 C in atmosphere of O 2 and in inert atmosphere. They offered the formal
scheme of the process allowing to explain all obtained experimental kinetic regularities
according to which there takes place initiation without breakage of macromolecule at
homolytical decay of (C 6 H 5 ) 2 O 2 with further breaking of hydrogen atom from polymer with
the formation of benzoic acid and macroradical P 1 *(CH 2 CONHC*HCH 2 ). These works were
probably the only where there was made an attempt to describe quantitatively the process of
thermal PA destruction.
Thus, analysis of literary data shows that up to now there is not clear and full idea about
the mechanism of PA thermooxidative destruction. And, as a result, there is much indefinite
in the question of its stabilization and modification, the more at introducing additives directly
into polymer melt [41]. Besides, it should be taken into consideration that majority of these
additives possess low thermal stability, and this eliminates their use at the synthesis and
production of fibers.
1.1.4. Photostabilization of Polyamides
Need for PA material stabilization arises at the stage of polymer processing, as in this
case the polymer, as a rule, should be transferred into flowing state. Stabilization of polymer
materials plays a very important role, first of all, to the action of light and heat, oxygen and
air.
Interest to this problem is proved by a great number of scientific publications in our
country and abroad [1, 2, 8, 10, 42]. However, it is impossible to make systematic analysis of
stabilizers efficiency, mechanism of their action, to form scientific approach to the synthesis
and use of additives in different and specific cases according to literature surveys [44, 45] and
patent information [46, 47], where many classes of compounds are presented as light
stabilizers. Interaction of stabilizing efficiency of the additive with its structure is not