10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

G . P . L a r o f f , R. W. F e s s e n d e n , and R. H. Schuler~ J . Am. Chem. Soc., 94, 9062 (1972). S. Steenken and G. Olbrich, Photochem. Photobiol., 18, 43 (1973). R . D . McAlpine, M. C o c i v e r a , and H. Chen, Can. J. Chem., 51, 1682 (1973). Y. K i r i n o and T. Kwan, Chem. P h a r m . Bull., 19, 718, 831 (1971). E . V . S h t a m m and Yu. I. Skurlatov, Zh. Fiz. Khim., 4__88,1454 (1974). B . H . Bielski, D. A. C o m s t o c k , and R. A. Boven, J. A m . Chem. Soc., 93, 5624 (1971). M. Sch~neshSfer, Z. N a t u r f o r s c h . , 27, 649 (1972). E . V . S h t a m m , A. P. P u r m a l ' , and Yu. I. Skurlatov, Zh. Fiz. Khim., 4_88, 2233 (1974). B . R . J a m e s and R. J . P. W i l l i a m s , J . Chem. Soc., 2007 (1961). Yu. I. Skurlatov and A. P. P u r m a l ' , Zh. Fiz. Khim., 43, 1580 (1969).

RADICAL

REACTIONS

IN THE

BENZOYL

PEROXIDE

IN SOLID

O. A. Ledneva, Yu. and D. Ya. Toptygin

A.

PHOTODECOMPOSITION

OF

POLYCARBONATE

Mlkheev,

UDC 541.515:541.14:547.582.3

Study has shown that the t h e r m a l breakdown of benzoyl p e r o x i d e (BP) in solid p o l y c a r b o n a t e (PC) at 80100~ is a c c o m p a n i e d by a chain d e c o m p o s i t i o n p r o c e s s leading to the f o r m a t i o n of benzoate r a d i c a l s which t h e m s e l v e s a t t a c k the PC m a c r o m o l e c u l e s [1, 2]. The kinetics of the BP and PC r e a c t i o n s under UV i r r a d i a t i o n have b e e n studied in the p r e s e n t work, the a i m being to e x p l o r e the p o s s i b i l i t y that benzoate r a d i c a l s p a r t i c i p a t e in the chain d e c o m p o s i t i o n of BP as well as PC. The p o s s i b i l i t y , f i r s t s u g g e s t e d in [3], that p o l y m e r i c m a c r o r a d i c a l s r e a c t with PC m a c r o m o l e c u l e s has a l s o been tested h e r e . EXPERIMENTAL This w o r k w a s c a r r i e d out with Dillon MV-32000 p o l y c a r b o n a t e . Sheets of p o l y m e r , 20-30 # m thick and containing B P at c o n c e n t r a t i o n s ranging f r o m 0.06 to 0.40 mole kg, w e r e p r e p a r e d by s i m u l t a n e o u s dissolution of p o l y m e r and p e r o x i d e in CH2C12. The r e s i d u a l CH2C12 was d r i v e n off f r o m t h e s e s h e e t s by v a c u u m drying f o r 24 h. Using a DRSh-500 m e r c u r y l a m p and a BS-4 filter (X >290 nm), the sheets w e r e i r r a d i a t e d in a t h e r m o s t a t e d cell, workh~g in v a c u u m and in a i r . The intensity of the r a d i a t i o n a b s o r b e d by the p e r o x i d e was m e a s u r e d with a f e r r i o x a l a t e a c t i n o m e t e r , using BS-4 and BS-6 f i l t e r s to s e p a r a t e out the ~ 303-313 nm region of the s p e c t r u m . The p e r o x i d e consumption was d e t e r m i n e d by i o d o m e t r i c t i t r a t i o n with s p e c t r o m e t r i c r e c o r d i n g of the p r o d u c t iodine [4]. A Specord UV-VIS s p e c t r o p h o t o m e t e r was used to obtain the UV s p e c t r a of the PC s a m p l e s during PB p h o t o l y s i s . The n u m b e r C of m a c r o m o l e c u l e s f r a c t u r e d w a s calculated f r o m the equation C = t.9t

--

9t0s mole/kg

Mv0 and Mvt being the m e a n - v i s c o s i t y m o l e c u l a r weights b e f o r e and a f t e r i r r a d i a t i o n . The calculation of C p r o c e e d e d exactly as in [2], the p o l y m e r u s e d h e r e being such that Mw/Mn = 2, where M w and M n being the r e s p e c t i v e w e i g h t - m e a n and n u m b e r - m e a n m o l e c u l a r weights. The amount of insoluble g e l - f r a c t i o n in the i r r a d i a t e d s a m p l e was det'ermined g r a v i m e t r i e a l l y , f i r s t r e m o v i n g the CH2C1 r. soluble gel fraction, and then vacuu m d r y i n g the r e s i d u e to c o n s t a n t weight. DISCUSSION

OF

RESULTS

The k i n e t i c s of BP consumption, in c a r b o - c h a i n p o l y m e r s [5] and in PC during t h e r m a l breakdown, a r e d e s c r i b e d by the equation d[ BP ] dt

= ko

[;sp l +kcta[ sp l~

(I)

Institute of C h e m i c a l P h y s i c s , A c a d e m y of Sciences of the USSR, Moscow. T r a n s l a t e d f r o m I z v e s t i y a Akademii Nauk SSSR, S e r i y a K h i m i c h e s k a y a , No. 1, pp. 66-74, J a n u a r y , 1977. Original a r t i c l e submitted D e c e m b e r 11, 1975. o f this publication m a y be reproduced, stored in a retrieval system, or transmitted, in any form" or by any means, electronic, mechanical, photocopying, nicrofilming, recording or otherwise, w i t h o u t written permission o f the publisher. A c o p y o f this article is available from the publisher for $ 7.50.

54

i

b

3

2 3 !

2

gs

!

o.~

J

Fig. 1. Linear a n a m o r p h i s m s of the kinetic BP consumption c u r v e s , a: Time, 3 min; T, ~ 1) 20; 2) 40; 3) 50. b: Time, 3 min; intensity of incident radiation, I . 1017 kW/cm2: 1) 1.8; 2) 3.2; 3) 6.5.

or by the integrated f o r m

[ Be Jo ----e ~ + (ek# _ l).kch[ sP lo [SP b

(II)

k 0 and kch being the r e s p e c t i v e rate constants for m o n o m o I e c u l a r and chain PB decomposition. Data on the photochemical decomposition of BP, obtained at various values of [BP]0, t e m p e r a t u r e , and irradiation intensity I0, a r e given in Table 1. These w e r e used to c o n s t r u c t kinetic BP consumption c u r v e s and the latter used, in turn, to develop c u r v e s showing [BP]0/[BP]t as a function of [BP]0 for a fixed time of 3 min {Fig. 1). These last were straight lines satisfying Eq. (II). According t 0 t h i s equation, the point of i n t e r s e c t i o n of such a l i n e with the axis of ordinates should give the value of ek0 t. The c u r v e s of Fig. la, each c o r r e s p o n d i n g to BI? decomposition at a different t e m p e r a t u r e , all cut the axis of ordinates at the s a m e point, the indication being that the value of k 0 was temperature--independent. F r o m this it could be concluded that radical initiation resulted f r o m BP photodissociation. The slopes of the lines of Fig. 1 were used to calculate values of kch and Ech, the effective activation e n e r g y for chain BP decomposition, then obtained as 4.5 k c a l / m o l e f r o m the t e m p e r a t u r e variation of these constants. Values of k 0 and kch a r e given in Table 2. The fact that the photodecomposition of BP followed Eqs. (I) and (II) was an indication that the d e c o m p o s i tion was induced by BP r a d i c a l s and not by m a c r o r a d i c a l s , the situation being s i m i l a r to that met with the c a r b o - c h a i n p o l y m e r s . F r o m this it followed that the radical reaction m e c h a n i s m must include radical chain BP processes. On this basis it was concluded that the radical reaction s c h e m e for t h e r m a l BP breakdo~m developed e a r l i e r [1, 2] should be applicable here as well with ~fo

BP --~ 2R" kl

R" 4- BP --~ tl'--t-CO~~- PhCOOPh R" -4- PH --> RH-4- P'" ks

ka

R ~+ PH -* RPH ~ P: + Destruction products R" + P:P'" } . ~ P" d" P" Fracture products

(1) (2) (3,4) (5)

where PH is the p o l y m e r m a c r o m o l e c u l e ; P ' , P-', and R P ' H a r e m a c r o r a d i c a l s ; and R is PhCOO" This s c h e m e suggests that kch is only an effective rate constant, being itself a combination of e l e m e n t a r y - s t e p rate constants

55

TABLE 2. Rate Constants for the P h o t o c h e m i c a l Decomposition of Benzoyl P e r o x i d e in Solid P o l y c a r bonate and T h e i r Variation with the T e m p e r a t u r e and the Intensity of the Incident Radiation (Eeh = 4.5 kcal/mole) 101v, kW/cm~ sec , 3,2

i,8

Constant I 20~

40~

I 50"

ko 9 10 a,

1,01

1,01

1,01

1~h. I o3, (kg/mole.

0,6

0,95 1 1,3

~C'I

I

6,5

1,8

3,5

0,9

1,6

l

sea)

kch =

k0. kl (kz ~t. ks) [PHi

HI

The value of E c h m e a s u r e d under BP photolysis, viz., 4.5 k c a l / m o l e , was consistent with the proposed r a d i c a l r e a c t i o n m e c h a n i s m . Application of Eq. (II) to PB photodecomposition with E 0 ~ 0 showed that Ech is d e t e r m i n e d solely by the t e m p e r a t u r e variation o f the t e r m kx (k~-t- ks) [PH]" The t e m p e r a t u r e variation of this t e r m is the s a m e as for t h e r m a l B P breakdown, a p r o c e s s e s d e s c r i b e d by the above s c h e m e with Ech = 34, E 0 = 30 k c a l / m o l e [1, 2]. F r o m this it could be concluded that the s a m e r e a c h o n m e c h a n i s m applies to both t h e r m a l and photolytic BP decomposition. Study of the changes o c c u r r i n g in the UV a b s o r p t i o n s p e c t r u m of PC during BP photolysis (Fig. 2) indicated that this p r o c e s s led to the formation of a product with a s t r o n g a b s o r p t i o n band at ~ 336 nm. This same a b s o r p t i o n band a p p e a r s during photolysis of liquid peroxide solutions, and during peroxide photodecomposition in solid cellulose t r i a c e t a t e (CTA) and p o l y m e t h y l m e t h a c r y l a t e (PMMA) as well [6], a r i s i n g f r o m the formation of o-oxybenzophenone (OBPh) through photoregrouping of phenylbenzoate, a BP decomposition product [reaction (1)]. OH \

C6I-I6C00C6tt6---.-, C6t-I~O--'-Detection of OBPh during the photolysis of BP in PC gave indirect support for the inclusion of reaction (1) in the p r o p o s e d r e a c t i o n s c h e m e . F i g u r e 3 shows the effect of a t m o s p h e r i c oxygen on the kinetics of BP photodecomposition to have been the s a m e as in the t h e r m a l decomposition [71. This s i m i l a r i t y suggested that benzoate r a d i c a l s always r e a c t in the s a m e way in solid PC, r e g a r d l e s s of whether it is a m a t t e r of t h e r m a l decomposition or photochemical breakdown. It is seen f r o m Fig. 2 that photochemical coloring of the PC was due not only to the appearance of the absorption band at X 336 nm but also to an i n c r e a s e of u n s t r u c t u r e d absorption in that region of the s p e c t r u m over which t h e r e is a d e c r e a s e in absorption intensity with i n c r e a s i n g wavelength. P r o d u c t buildup was rapid in the initial s t a g e s of B P photolysis where the OBPh band at X 336 nm had not yet put in its appearance (cf. Fig. 2, s p e c t r a 2 and 3). The fact that there was a slow buildup of OBPh and, a c c o r d i n g to Fig. 3c, a d i r e c t p r o p o r tionality between the WD, the initml rate m e a s u r e d by the change in intensity at X 336 nm, and the initial BP c o n c e n t r a t i o n was taken as indication that a s t e a d y - s t a t e phenylbenzoate concentration was established in the photodeeomposition of BP in p c , the situation here being s i m i l a r to that o b s e r v e d in the photolysis of BP in PMNA and CTA [6]. At this s t e a d y - s t a t e phenylbenzoate concentration, one should find that WOBPh = kch[PB]2. The existence of a d i r e c t proportionality between the rate of buildup of products with u n s t r u c t u r e d a b s o r p tion s p e c t r u m and the initml B P concentration suggested by m e a s u r e m e n t s at X 336 nm in the e a r l y stages of reaction, was itself indication that these products were p o l y m e r s r a t h e r than products resulting f r o m reactions between B P and the benzoate r a d i c a l s . E a r l i e r it was a s s u m e d [3] that the products with u n s t r u c t u r e d absorption

56

O,ti ),t5

3,i9 9,12

3,16

0,048 0,037

0,125 0,098

0,15

0,20

40-

i'8"t017 *

I0, in k W / c m 2 9 s e c .

3,04 0,02

~ I n t e n s i t y of i r r a d i a t i o n ,

0,05

),i2

O,l

3,3

m

),05

~),055

0,t4

3,13

0,i2

i0

0,06

0,20

0,22

0,i8

),i8

5

m

0,25

0,28

0,24

3

I

O,i

0,35

!

~,o"

0,025

0,07

0,08

0,1

iO

[

3,048

0,t2

0,t8

0,28

,i

),085

3,098

3,i3

0,042 ),033

0,1t

0,15

0,t8

so"

O,iO

0,025

0,07

0,08

I

0,o~

0,i5

0,20

i

and I n t e n s i t y o f I r r a d i a t i o n

time, min

1. V a r i a t i o n of [BP]t ( m o l e / k g ) w i t h t h e T e m p e r a t u r e

0,4

:BP]0, ~ole/kg [

tABLE

0,087

07

5

0,04

0,026

0,06 i 0,042

0,t2

0,t85

3

so"

3'2"t01;*

0,02

0,025

0,75

0,t25

i0

0,043

0,028

0,08i

0,ti8

~o"

I 6'$'~0u*

1/

a

b 6

"

'

5

o,~

o.

1 3aO

280

#18

ZS0

$33

~lS;t, nm

Fig. 2. UV s p e c t r a of PC containing 5% BP (a), and of p u r e PC (b), u n d e r v a c u u m i r r a d i a t i o n with UV light with X > 295 nm, I 0 = 3.2. 1017 k W / c m 2. s e c . a : T i m e of i r r a d i a t i o n , min: 1) 0; 2) 1; 3) 2; 4) 5; 5) 10; 6) 20. b: T i m e of i r r a d i a t i o n , min: 1) 0; 2) 20; 4) s p e c t r u m of PC containing 5% BP, under i r r a d i a t i o n in a i r ; 5) in v a c u u m ; 3) d i f f e r e n c e between s p e c t r u m 4 and s p e c t r u m 5. C, mole/kg ~4

b

\ 0,2 ~

_

o.o5

1 r~36

t 10

J 20

10

c/,#'3 //

~/~

i ,v.'-;

10

ms

"

o,l I/.z:<.---< "

20

d

, 20

I

2

0,4 W

P

20"'

, 40

, 60 min

Fig. 3. Kinetic c u r v e s for the consumption of BP and the buildup of c o l o r e d p r o d u c t s , in v a c u u m (full-line curve) and i n a i r (dashed-line c u r v e ) , a, b) BP consumption; c) buildupof colored p r o d u c t s with a b s o r p t i o n at ~ 336 nm, for the following values of [BP]0, m o l e / k g : 1) 0.1; 2) 0.2; 3) 0.4. d) Buildup of colored p r o d ucts at 20(1), 38(2), and 50~ s p e c t r a (cf. Fig. 2b) r e s u l t f r o m r e a c t i o n s between m a c r o r a d i c a l s with PC m a c r o m o l e c u l e s under UV i r r a d i a tion, and a r e t h e r e f o r e polyconjugated. F i g u r e 2b shows a b s o r p t i o n s p e c t r a for an i r r a d i a t e d s a m p l e of PC which contained no BP. Although t h e r e was a g r a d u a l c o l o r a t i o n of the PC, even in the a b s e n c e of BP, the r a t e of c o l o r a t i o n could be c o n s i d e r a b l y i n c r e a s e d by r a d i c a l initiation through BP photolysis. Even though this was an indication that the c o l o r e d p r o d u c t s r e s u l t e d f r o m r a d i c a l r e a c t i o n s , the p r e s e n c e of these p r o d u c t s could not

58

C'IO z mole/kg

10

20

#0 r a i n

30

Fig. 4. Change in PC rnacromolecule fraction concentration during vacuum BP p h o t o d e c o m p o s i t i o n : l ) 2; 2) 20; 3) 60~

/

CBP

]

/

/

-

2~3

eel. % 7O

/

60

50

/

D

0,2 /

o,8

~0

/

/ ff

40

// w" .,' ___.~

Z0

.

0,4

10 !

I

I

I

~

80

60

120

180

2bO

min

Fig. 5. Kinetic c u r v e s for BF consumption (1), buildup of the colored products with absorption at ~. 336 nm (2}, and of the gel fraction (3), during irradiation of a PC film containing 5% BP, I 0 = 1.8 9 10 t7 k W / c m 2- see. be explained in t e r m s of the s c h e m e of (1)-(5) for the BP photolysis since they appeared even in the absence of thin compound. Another point is that the c h r o m o p h o r e groups of the products of reactions (1)-(5) a r e not polyconjugated. F o r this r e a s o n the coloration produced in that portion of the PC s p e c t r u m lying at X > 300 nm is w e a k e r in t h e r m a l decomposition [8] than in photochemical decomposition. Figure 4 shows the change in the number of m a c r o m o l e c u l e f r a c t u r e s at 2, 20, and 60~ It is seen that the n u m b e r of f r a c t u r e s ceased to i n c r e a s e once the peroxide was completely consumed, falling off, in fact, in the c o u r s e of f r u t h e r irradiation. Under extended i r r a d i a t i o n in vacuum, PC b e c o m e s insoluble in CH2C12. This effect was not o b s e r v e d in t h e r m a l decomposition where reaction ceased when the BP was completely consumed. F i g u r e 5 gives a c o m p a r i s o n of kinetic c u r v e s for B P consumption, i n c r e a s e in colored product absorption at ), 336 nm, and buildup of the insoluble gel fraction under vacuum irradiation. It is evident the PC coloration" continued a f t e r BP decomposition was completed, extending o v e r into the region of gel formation. The degree of coloration and the amount of the gel fraction were much higher here than in the irradiation of pure PC s a m ples, but the p r e s e n c e of air markedly reduced the r a t e s of coloration and of gel fraction buildup. In light of these facts it could be concluded that the s c h e m e of (1)-(5) is inadequate for d e s c r i b i n g the photodecomposition p r o c e s s e s . It has, however, been pointed out above that the kinetics of r a d i c a l - chain BP reactions under UV i r r a d i a t i o n a r e identical with the kinetics of thermal breakdown. In both c a s e s t h e r e is the s a m e type of PC molecule d e s t r u c t i o n under the action of the benzoate r a d i c a l s . In p a r t i c u l a r , the value of Ep, the activation e n e r g y for m a c r o m o l e c u l e f r a c t u r e calculated f r o m the initial s e g m e n t s of the kinetic curves of Fig. 5, was 6 • k c a l / m o l e . The fact that this r e s u l t is identmal with the E p - E 0 = 37-30 k c a l / m o l e calculated f o r t h e r m a l breakdown of BP in PC [2] is p r o o f of s i m i l a r i t y of the m e c h a n i s m s for chain BP r e a c t i o n and PC molecule f r a c t u r e in the two c a s e s . 59

Gel,

b

2,0-

80! a ~2

I

o,'

1

2

3

~

I

~

,,,

4 b

Fig. 6. Kinetic c u r v e s for the g e l - f r a c t i o n buildup. a) PC film containing 5% BP: 1) 22; 2) 37; 3) 54 ~ b) L i n e a r a n a m o r p h i s m in the c o o r d i n a t e s of the C h a r l s b y equation [10]. Thus it could be concluded that the s c h e m e for the p h o t o p r o c e s s e s involved in i r r a d i a t i o n of BP in PC must include r e a c t i o n s (1)-(4) of the e a r l i e r s c h e m e , together with other r e a c t i o n s accounting for the intense PC coloration under the r a d i c a l a c t i o n , the f o r m a t i o n of a gel fraction in the l a t e r stages of the p r o c e s s , and the continuous buildup of c o l o r e d products. Account must also be taken of the fact that the initial coloration rate and the r a t e of d e s t r u c t i o n w e r e both p r o p o r t i o n a l to the BP concentration, while EII, the activation e n e r g y for c o l o r e d product buildul~ had the value 6 k c a l / m o l e (calculation being f r o m the initial segments of the c u r v e s of Fig. 3d) and was thus a l m o s t identmal with value of Ep for m a c r o m o l e c u l e destruction as obtained f r o m the length of the initial p e r i o d for the photoreaction. These details of the p h o t o p r o c e s s can be r a t h e r fully accounted f o r in t e r m s of PC m a c r o r a d i c a l i n t e r a c t i o n with m a c r o m o l e c u l e s [3]. Study of r a d i c a l PC d e s t r u c t i o n p r o c e s s e s [9] has disclosed the existence of P" m a c r o r a d i c a l s resulting f r o m r e a c t i o n (4). It is c l e a r that these r a d i c a l s must r e a c t with the PC m a c r o m o l e c u l e s in photolysis just as do the benzoate r a d i c a l s , the only difference being that colored products a r e f o r m e d h e r e : ka'

k4

P" 4- PH ~ P15H -* P" 4- P*H (colored products) The r e a c t i o n s leading to free valence d e s t r u c t i o n a r e now d e s c r i b e d by the s c h e m e k 5"

t{% P" 4- P*H-----> RP"H, P "PH

(5'}

k~

R ' + RP"H --~ R - - P H - - R (sol-fraction)

(6)

k 6,

P? -4- PPH----~ P

P H - - P (gel-f~action)

(6')

Once the BP r e a c t i o n has gotten under way, radical destruction becomes p r i m a r i l y a m a t t e r of interaction with benzoate r a d i c a l s , and g e l - f r a c t i o n accumulation in the s y s t e m c e a s e s . The c h e m i c a l l y modified PC functions as the r a d i c a l initiator a f t e r the BP has been consumed, the free valences being then destroyed by reaction with the P" r a d i c a l s and f o r m a t i o n of the gel fraction. So considered, the difference between photochemical and thermal decomposition is that the f o r m e r involves a chain r e a c t i o n between the PC and P" r a d i c a l s which have bec o m e activated under i r r a d i a t i o n . The fact that these radicals a r e f o r m e d after the BP has been consumed is due to initiation by the c h e m i c a l l y modified PC itself, the reaction hv

PH* --+ 2P: -- CO, CO~ a s s u r i n g continuous extension of the chain p r o c e s s . The e x p e r i m e n t a l r e s u l t s can be explained by a modified photoreaction s c h e m e in which provision is made for a change in initiator, the development of a new chain of r e a c t i o n involving the m a c r o r a d i c a l s , and d e s t r u c tion of the f r e e valences on the c o l o r e d m a c r o m o l e c u l a r products. Study was also made of the kinetics of the buildup of the insoluble-in-CH2C12 gel fraction in vacuum at 22, 37, and 54~ (Fig. 6a, b). The data on gel buildup have been plotted in Charlsby coordinates in Fig. 6b. Although an i n c r e a s e in the t e m p e r a t u r e i n c r e a s e d the rate of gel formation, it can be seen that the formation

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r e a c t i o n began only at the end of a t i m e period during which PC d e s t r u c t i o n had been the p r e d o m i n a t i n g p r o c e s s . The amount of the gel f r a c t i o n and the r a t e of f o r m a t i o n of the colored p r o d u c t w e r e both reduced by c a r r y i n g out the e x p e r i m e n t s in the p r e s e n c e of a i r (cf. Fig. 3c). On the other hand, the r a t e of OBPh buildup was unaffected by the p r e s e n c e o f a i r [6]. F r o m this it could be concluded that gel f o r m a t i o n was u n r e l a t e d to the OBPh r e a c t i o n . Calculated f r o m the data of Fig. 6a, b, the effective activation e n e r g y for gel buildup p r o v e d to be 6 +3 k c a l / m o l e ; this value was e s s e n t i a l l y identical with the E for d e s t r u c t i o n in the gel f o r m a t i o n stage and r e mained constant throughout the e n t i r e p h o t o p r o c e s s , despite the change in initiator. T h e s e o b s e r v a t i o n s w e r e in a g r e e m e n t with p r e d i c t i o n s b a s e d on the p r o p o s e d photoreaction s c h e m e . CONCLUSIONS The d e c o m p o s i t i o n of benzoyl p e r o x i d e in solid p o l y c a r b o n a t e under UV i r r a d i a t i o n is a m o n o m o l e c u l a r chain p r o c e s s . This p r o c e s s is a c c o m p a n i e d by the intensive f o r m a t i o n of colored p r o d u c t s . A f t e r c o m p l e t e d e c o m p o s i tion of the benzoyt peroxide, this p r o c e s s p a s s e s o v e r to a new initiator stage for continued photoreaction of the p o l y c a r b o n a t e . A r e a c t i o n s c h e m e is p r o p o s e d which involves chain r a d i c a l r e a c t i o n s , s o m e with p a r t i c i p a tion of p o l y c a r b o n a t e m a c r o r a d i c a l s . LITERATURE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

CITED

Yu. A. Mikheev, O. A. Ledneva, and D. Ya. Toptygin, Vysokomol. Soedin., A18, 931 (1971). O . A . Ledneva, D. Ya. Toptygin, and Yu. A. Mikheev, Vysokomol in., Soed., A15, 2335 (1973}. V . P . Pustoshnyi, Yu. A. Mikheev, and D. Ya. Toptygin, Dokl. Akad. Nauk SSSR, 219, 389 (1974). V . A . Balandina and D. B. Gurvich, Analysis of P o l y m e r i z e d P l a s t i c s [in Russian], Khimiya, Leningrad (1967). R. Rado, Chem. Listy, 6, 785 (1967). L . N . Guseva, Yu. A. Mikheev, and D. Ya. Toptygin, Dokl. Akad. Nauk SSSR, 213, 871 (1973). R. Rado and M. L a z a r , Vysokomol. Soedin., A.3 , 310 (1961). Yu. A. Mikheev, O. A. Ledneva, and D. Ya. Toptygin, Izv. Akad. Nauk SSSR, Ser. Khim., 1313 (1972). E. Ya. Davydov, O. A. Ledneva, Yu. A. Mikheev, G. B. P a r i i s k i , and D. Ya. Toptygin, Dokl. Akad. Nauk SSSR, 195, 875 (1970). A. C h a r l s b y and S. H. Pinner, P r o c . Roy. Soc., A249, 367 (1959).

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