STABILIZATION AND MODIFICATION OF CELLULOSE DIACETATE - Photochemical Reactions in Heterochain Polymers - page 57

Figure 2.5. EPR spectra at 77°K of CDA-film, irradiated by light (λ=254 nm) in the atmosphere of
helium at 253°K for 11 minutes: just after irradiation the same sample after warming up for 3 minutes
at 296°K; spectrum, obtained by graphic subtraction of spectrum b) from spectrum a).

Experimental data on the formation of acetic acid and radicals at CA photolysis can be
explained by Scheme 3.

X + hν → R * 1 , W ин (0)

R * 1 + hν → R * , K 1 (1)

R * 2 + hν → R * 1 , K 2 (2)

R * 1 + hν R1H → AcOH + R * 1 , K 3,T + K 3,Ф ·I

(3)

R * 1 + hν → destruction , К 4 (4)

R * 1 + R * 2 → destruction , К 5 (5)

R * 1 + R 2 → destruction , К 6

(6)

Scheme 3.

Here: X - chromophore (CA or photoinitiator); R 1 * - acetoxyalkyl radical with high
reactivity; R 2 * - low-active polyenyl radical with free valency, conjugated with double bond;
AcOH - acetic acid; K 1 - K 6 - constants of the rate of corresponding reactions. K 3 = K 3,T +
K 3,Ф , where K 3,T and K 3,Ф - constants of the rate of the process in the darkness and under light
action.
Scheme 3 describes the same principle of radicals photolysis as Scheme 2, and differs
from Scheme 2 only by the fact that it includes concrete reactions for those radicals, which
are experimentally identified.
By the method of numerical integration of differential kinetic equations of the Scheme 3
it has been found that this scheme quantitatively describes experimental data on kinetics of
accumulation of acetic acid and radicals at CA photolysis (Figure 2.1. - 2.4) at the following
set of kinetic parameters:

W in = 2,5·10 -22 ·I mole/kg·sec; К 1 = 5,5·10 -17 ·I sec -1 ; К 2 = 3,3·10 -18 ·I sec -1 ;
К 3 = 0,015 + 5,5·10 -16 ·I sec -1 ; К 4 = 1000 kg/mole·sec; К 5 = 3,6 kg/mole·sec;
К 6 = 0,013 kg/mole. (where I - light intensity in quantum/сm 2 ).