Chemistry Reference
In-Depth Information
Hence, one may come to a conclusion that oligomeric azomethine additives are, as a
matter of fact, regulators of radical polymerization of styrene and may be also used and for
this purpose. PAC products contain undivided ρ - electrons of heteroatom of nitrogen in the
chain of conjugation. That is why energy of conjugation (delocalization of PAC electrons) is
defined by the presence of not only π - π conjugation, when efficiency of delocalization is
φ=ΔЕ/ΔN·π, that is, it is defined by the energy of π - electrons transition from the basic to
excited state and depends not only on the length of the conjugation chain, but on competing
effect of ρ- π conjugation [179]. Owing to this, disproportionation of electronic density takes
place, the value of effective conjugation decreases and, unlike polyenes, bathochronic shift
with the growth of the length of conjugation chain is not observed.
It may be noted that efficiency of oligomeric PAC is more than 10 times higher
comparing with low-molecular analogs (Figure 2.19). Hence it follows that the increase of
conjugation
efficiency
decreases
reactivity
of
oligomers
in
the
range
-
XXXVII>XXXV>XXXIII.
Inhibitive activity grows with the rise of temperature of radical reaction, that is
characteristic for polyconjugated systems.
It is known that reaction activity of inhibitors in radical reactions may extremely change
depending on the inhibitor concentration.
Carried out investigations have shown (Figure 2.18) that the rate of polymerization
depends on the structure of being introduced oligomeric inhibitors and increases with the
growth of its concentration from 0,0003 to 0,001 mole/l.
So, there has been drawn a conclusion, that oligomers with conjugated azomethine bonds
are more effective, as inhibitors of radical reactions, than low-molecular analogs. Their
reactivity depends on the length of conjugation chain, its efficiency and on the concentration
of oligomer being introduced.
On the basis of performed investigations one may come to a conclusion that mechanism
of PAC stabilizing action is not unique and is caused by totality of effects of shielding,
inhibition of radical processes and acting as antioxidant.
Change of specific and intrinsic viscosity of CA, destruction of ester groups,
accumulation of acetic acid and carbonyl groups are the result of photochemical
transformations taking place in CA under the light action.
Above-mentioned facts, caused by CA phototransformations during irradiation by
different light sources, have been investigated, using methods of chemical analysis,
viscosimetry and spectroscopy, since it is known that phototransformation during irradiation
by different light sources, may differ in quantitative and qualitative ratio. Benzalaniline (BA),
XXXIV, XXXV, XXXVI, XXXI, XXXII have been used as additives, BA being model
compound.
Lightfastness of CA with and without the additive is characterized by the change of
specific and intrinsic viscosity of CA before and after irradiation by mercury-quartz lamp
PRK - 2. Data on PAC additives effect (2% from polymer mass) are given in Table 17.
From these data it is seen that introduction of PAC into CA slightly changes indices of
polymer viscosity in comparison with initial CA before irradiation. Data of Table 6 show that
azomethines XXXIV, XXXV, XXXI, XXXVI, XXXVII content in CA decreases specific
viscosity fall.
It also follows from Table 6 that introduction of 2% of PAC from CA mass facilitates
considerable conservation of initial indices of CA at irradiation. So, intrinsic viscosity of CA
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