STABILIZATION AND MODIFICATION OF POLYCAPROAMIDE - Photochemical Reactions in Heterochain Polymers - page 26

changes. Its surface is completely covered by the particles of irregular shape: hollows, holes,
cracks (products of decay) which show the destruction of surface layer in the process of
photooxidation.
Stabilized sample does not practically undergo great changes after irradiation. Its surface
is smooth without visible traces of products of decay. It is seen here that presence of
stabilizing compounds in polymer macromolecule inhibits the process of photodestruction.
It should be also noted that modified unirradiated fibre displays more distinct tendency to
crystallization. There were found plate-like and even spherulitic formations. In our opinion
this is connected with the fact that derivatives of bis-aroilenbenzimidazole play the role of
peculiar centres of crystallization and this causes change of molecular orientaton in the fibre
at the moment of forming when supermolecular structure begins to organize. Besides, new
more regulated structure, typical for ordered state, is formed which agrees well with
conclusions of the works [129, 130]. The authors consider that dyes influence the rate of
formation of nucleation centres at the expence of decreasing surface energy of crystallites
leading to greater degree of order of the structure and decrease of crystallites critical sizes.
Structural changes in dyed fibres improve stability of PCA fibre to photooxidative
destruction. Data of electron microscopy are proved by X-ray study of initial and stabilized
fibres before and after irradiation.
X - ray studies of initial and dyed by bis - (1', 8' - naphthoilene - 1, 2 - benzimidazole)
oxide (XLY) PCA studies have been carried out with the purpose of investigating possible
changes in amorphous - crystalline structure of PCA fibre at the time of introducing such
volumetric dyes as bis-aroilenbenzimidazoles and their distribution in the fibre.
Data, obtained during the analysis of large-angle ionization X-rayograms, characterizing
the structure of both dyed and undyed PCA-fibres are given in Table 7.
Identity of the angles of diffraction maximums and equality of their hemispheres show
that introduction of XLY does not change interplane distances of polymer crystallites and
their sizes.
The degree of polymer crystallinity, which characterizes the share of regularly packed
molecules is estimated by the intensity of dispersion in maximum 1 m. Some differences
connected with introduction of a dye are observed, namely intensity of dispersion is a bit
lower both along the equator and meridian. This speaks about the fact that introduction of the
additive leads to the decrease of a number of reflective planes (decrease of reflection centres),
which, in its turn, is connected either with deterioration of polymer crystalline structure or
with rotation of reflective planes.
Results of small-angle meridional measurements (Figure1.5.) show the absence of small-
angle diffraction maximum and this shows the absence of large-period structure, that is in this
case there is no regular alternation of crystalline and amorphous sections along the axis of the
fibre.
Presence of small-angle diffusion dispersion speaks about the presence of submicrovoids
(SMV) in the fibre. Rearranging SADD according to the data of Figure1.5 in coordinates 1g I
from φ 2 (Figure 1.6.) by the procedure described in the work [131] there may be defined the

Δ I lg

size of H n (H n =1,29 ) and concentration of SMV - (N tr )(Assuming the form of

Δ ϕ

SMV as spherical).