STABILIZATION AND MODIFICATION OF CELLULOSE DIACETATE - Photochemical Reactions in Heterochain Polymers - page 63

CDA. Proceeding from these two factors one may come to a conclusion that HAC does not
act as an inhibitor.

Table 13A. Dependence of stabilizer efficiency on its structure
(concentration of stabilizer is 5% of polymer mass)

Stabilizer А=W 0 / W st ·i φ Stabilizer А=W 0 / W st ·i φ

HAC-1 0,111 HAC-6 0,072

HAC-2 0,150 HAC-7 0,070

P-3 0,230 HAC-8 0,084

HAC-4 0,260 P-9 0,111

HAC-5 0,111

If the additive does not act as inhibitor, but only as ultraviolet shield and photosensitizer,
then dependence of quantum yield of photooxidation ФO 2 on light intensity I 0 at full
absorption of incident light should be described by well-known equation (5)
Фо 2 = W/I 0 + αФ i + K n [RH]/√K г ·√Ф·10 -3 ·1/√IεC (5)

where: W - the rate of O 2 absorption in terms of 1cm 2 of the sample surface, mole/cm 2 ·s;
Ф 1 - quantum yield of photoinitiation, caused by photosensitization of the dye; α - quantity
of O 2 molecules absorbed in non-chain process of oxidation per one formed radical; ε -
extinction coefficient; C - concentration of the additive.
Large photosensitizing activity of HAC - LI is successfully explained by the fact that
compound (LI) may have two tautomeric resonance states, in one of which it contains free
aminogroups, owing to which it displays photosensitizing properties, that quite well agrees
with [10].

Light stabilizing action of HAC - XLIX and HAC - L is proved by the data on decrease
of reduced viscosity of CDA acetone solution after ultraviolet irradiation of films, containing
HAC - XLIX and HAC - L (Table 14).
Investigation of CDA photooxidation was carried out in order to get additional
information about light-stabilizing action of HAC. Figure 2.7 shows dependence of
concentration of absorbed oxygen (∆O2) on the time of irradiation at photooxidation of three
CDA samples, that is of unstabilized film (curve 1) and stabilized HAC - XLIX (curve 2) and
2,2,6,6 - tetramethyl - 4 - hydrooxipiperidine - 4 - hydroxyl - 1 - oxyl - (mitroxylic radical)
(curve 3). As it is seen from Figure2.7 HAC decreases the rate of CDA photooxidation.