STABILIZATION AND MODIFICATION OF CELLULOSE DIACETATE - Photochemical Reactions in Heterochain Polymers - page 79

Figure 2.23. Change of the rate of acetic acid accumulation in the process of irradiation by sunlight. 1 -
CA-film without additive, 2 - CA-film + 2% XXXV.
It is seen from the data in Figure 2.24 that intensity of absorption bands at 1040 and 1230
cm -1 decreases considerably during 10 hours irradiation. This indicated that at irradiation of
CDA-films by mercury-quartz lamp splitting of ester bonds of acetyl groups takes place. But
introduction of XXXIV and XXXV oligomer products, containing different number of
conjugated bonds and also end amino-groups, into CDA considerably reduces number of
splitting acetyl groups while low-molecular BA product, which does not contain amino-
group, slightly influences this process. May be the last condition is described by the fact that
shielding effect of PAC depends on the level of conjugation. That is why introduction of
oligomer products XXXIV and XXXV with a large number of conjugated bonds shields the
effect of ultra-violet light quantums on CDA ester groups, which is proved by the data on
optical densities of the bands 1040 and 1230 cm -1 .
However, there is possibility that the presence of end amino-groups and also the last
consumption of PAC at prolonged irradiation influence stabilizing properties of oligomers.
Kinetics of optical density change of stabilized CA-films at absorption of additives (Figure
2.25) may help to judge about consumption of BA. From this figure it follows that low-
molecular BA is consumed faster than oligomers XXXIV and XXXV and this also confirms
more powerful and longer PAC action.
Data on carbonyl and aldehyde groups accumulation in initial and stabilized CA-films
during the process of irradiation by mercury-quartz lamp are given in Figure 2.26. From this
figure it is seen that carbonyl group accumulation is characterized by linear dependence.
Intensive accumulation of carbonyl and aldehyde groups is observed in initial CA-film while
slopes of strait lines of stabilized azomethine films (Figure 2.26, curve 2-6) are much smaller
and this shows decrease of the rate of these groups accumulation. It is interesting to note that
in this case BA also facilitates the decrease of carbonyl and aldehyde groups accumulation,
though oligomer XXXVII displays the greatest activity in this respect.