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Phototransformations in polymers of phenols subjected to steric hindrance
Phototr~nsformations in polymers of phenols
237
'~. V. A. MARIKHIN, I Vsesoyuznyi simpozium po kriogennym m e t o d a m v elektronnoi mlkroskopii (I All-Union Symposium on Cryogenic Methods in Electron Microscopy}. Pushehino, 1975 3. T. M. BIRSHTEIN, V sb. Sostoyaniye i rol' v o d y v biologichcskikh o b " y e k t a k h (Symp, The State a n d Role of W a t e r in Biological Substances) Izd. " N a u k a " , 1967 4. M. A. ASAUBEKOV, Izv. AN KazSSR, set. khim. 1: 81, 1976 ~. S. I. SEN'KOVICH, Ye. M. BELAVTSEVA, E. V. KAMENSKAYA and Yu. A. K L Y A CH]KO, I I Vsesoyuznyi simpozium po kriogennym m e t o d a m preparirovaniya ( I I AllUnion S y m p c s m m on Cryogenic Methods of Preparatmn). Pushchino, 1977 ~}. S. N. RUSCHER, J. Polymer Sci. C16: 2923, 1967 7. BACHMANN and W. W. SCHMITT, Naturwissenschaften 58: 217, 1971 8. A. GROBE, R. MARON and H. J. PURZ, Faserforsch. und Textiltechn. 17: 458, 1966 9. Ye. M. BELAVTSEVA and Ye. F. TITOVA, Vysokomol. soyed. 14: 1659, 1972 (Translated in P o l y m e r Sci. U.S.S.R. 14: 7, 1861, 1972) 10. T. NEI, Principles and Techn, ques of SEM (edited b y M. A. Bayat) v. 1., New York, 1974 11. M. ~EN and V. MARINKOVIC, St/irke 4: 125, 1963 12. Ye. M. BELAVTSEVA a n d Ye. F. TITOVA, I I Vsesoyuznyi simpozium po kriogennym m e t o d a m preparirovaniya (II All-Umon Symposium on Cryogenic Methods of Prepaparation). Pushchino, 1977 13. Ye. F. TIT0VA, Ye. M. BELAVTSEVA, Ye. Ye. BRAUDE and V. B. TOLSTOGUSOV, Colloid and Polymer Sci., 252, 1974
0032-3950/80/0101-0237507.5010
• ~olymer Science U.S.S.R. Vol. 22, pp. 237-247. .4~ Pergamon Press Ltd. 1980. Printed in Poland
PHOTOTRANSFORMATIONS IN POLYMERS OF PHENOLS SUBJECTED TO STERIC HINDRANCE* ~L. V. SAMSOlq'OVA, V. YA. SHLYAPINTOKH
and V. V. YERSHOV
Instituteof Chemical Physics, U.S.S.R. Academy of Sciences (Received 22 November 1978) Phototransformation of 4-phenyl-2,6-di-tert.butylphenol in PMMA, PP, cell u l o s e t r i a c e t a t e and a b u t y l m e t h a c r y l a t e - m e t h a c r y l i c acid copolymer takes place ~rith a q u a n t u m yield of N 0.02 and shows little dependence on the t y p e of polymer. 'The q u a n t u m yield measured according to initial rates of consumption of 4-phenyl~2,6-di-tert. butylphenol in PMMA and cellulose triacetate, is independent of phenol cone e n t r a t i o n even with a hundred fold variation of this value. A t the same time kinetics o f phototransformation of phenol are described b y a second order kinetic law. This discrepancy is, apparently, caused b y the kinetic non-equivalence of phenol molecules 4arranged in various positions of the "rigid" polymer. I n the absence of oxygen the rate ~ f phototransformation of 4-phenyl-2,6-eh-tert.butylphenol a n d 4-methyl-2,6-di-tert. * Vysokomol. soyed. A22: No. 1,209-217, 1980.
2.38
L. V. SAMSO~OVAeL a/.
butylphcnol and 2,4,6-tri-tert.butylphenol decreases by one or two orders of magnitude. An acceleration of the photoreaction with oxygen is due to the chemical interaction of O3 with the triplet state of phenols. Oxygen also markedly acceleratea the phototransformation of phenoxyl radicals. WHEI~ using phenols and phenol derivatives subjected to steric hindrance for the~ stabilization of various polymeric materials the part of similar compounds i n photochemical processes taking place in polymers is not considered usually~ Light m a y cause direct photolysis of phenol stabilizers. The existence in the polymer composition of impurities and a number of additives of aromatic compounds a n d various dyes m a y induce, under conditions of radiation, the formation o f singlet oxygen which readily reacts with phenols [1-4]. Intermediate producta formed in the photochemical reactions m a y accelerate or inhibit the ageing process of the polymer material. Studies carried out up to the present time, normally, only gave an evaluation of the gross effect of the photochemical activity of some a n t i o x i d a n t s - - t h e i r effect on the variation of colour and physical and mechanical properties of polymers during photodegradation. I t was only recently t h a t papers were published [5-10] concerning the effect~ of phenols on the photodegradation of polymers on a quantitative level. I t w aa shown in our earlier studies [11-13] t h a t various phenols initiate the degradation o f PMMA and quantum yields of phototransformation were determined in the~ l~resence of thiobisphenol and bisphenol 22-46. Initiating l~roperties of phenola (methylox) were also noted for P P [8, 9]. I t was established [6] that, according t o ]phenol concentration, photodegradation of triacetylcellulose (TAC) m a y either be accelerated, or inhibited. However, kinetics and the mechanism of photochemical transformations of phenols subjected to sterie hindrance in polymers have~ been very little investigated. This s t u d y is concerned with the mechanism of phototransformation anc~ obtaining quantitative data concerning phototransformation of phenols subjected~ t o steric hindrance in various polymer matrices. Phototransformation of 4-phenyl-2,6-di-tert.butylphenol (PDTBP), 4-methyl-2,6-di* ~rt.butylphenol (ionol) and 2,4,6-tm-tert.butylphenol (TTBP) was mainly examined ir~ various polymers. A significant proportion of experiments was carried out with PMMA~ Photoreaction of phenols was studied in a number of experiments in TAC, PP, a butyl* methacryl-methacrylic acid copolymer (5%) (BMK-5) and in PA-548 aliphatic polyamide. Phenols were purified by crystallization from ethanol, followed by chromatbgraphic~ separation on silica gel. PMMA of the Chemical Combine "Orgsteklo" of M ~ 175,000 conraining ~ 1% monomer, TAC of the Kaunas Works producing synthetic fibre, PP grade"Moplen" of M ~ 80,000 and a degree of crystallinity of 50 %, BMK°5 of the Yarloslav Chemical Combine, PA-548--an industmal polymer prepared by polycondensation of adipat@ and hexamethylene diamine, salts of sebacic acid and hexamethylene diamine and a-caprolactam were used for the study. PMMA, TAC and BMK-5 films were prepared by applying a polymer solution in methylQne chloride on ~ polished glass surface [14]. Films on quartz substrates prepared by elon-
Phototransformations in polymers of phenols
23~,
gating the latter at a constant rate ( ~ 2 mm]min) from a 10% polymer solution containing am additive (PMMA and TAC) in methylene chloride or acetone (BMK-5) were used in some, experiments. Polyamide films were prepared by a method previously described [15]. Polypropylene films were compressed in vacuum under a pressure of 0.02 kg/em s at~ 220° and then rapidly cooled m hquld nitrogen. Antioxldant additives were introduced im transparent polymer films (~ 100 /lm in thmkness), kept m sealed ampoules in saturated vapour of an antioxldant used m considerable excess at 60° for about 20 hr. If the concentration of the antioxidant in the film had to be reduced, its surplus was removed by evacuation at 100° and a pressure of ~ 10-3 torr. Film thickness was measured with an error o f =[=0.2 ~m using an IKV vertical optmal caliper. The light of a BUV-30P lamp was used, 80% of radiatmn being on the line of 253.7 nm (light intensity was 2 × 101~ quantum" cm -2 sec-~), the remaining 20% being mainly onu the line of 438 nm and not absorbed by the polymers and phenols examined. I t may therefore be assumed that the samples were exposed to monochromatic hght of wave length 253.2 rim. The full or filtered light of a DRSh-1000 lamp was also used. The concentration variation of phenol durmg the reactmn was recorded spectrophotometrically (using SF-4A or Specord UV-VIS spectrophotometers) according to the optical~ density vamation in the maximum of absorption band (265 nm), the variation of fluorescence intensity being measured by an L K I P AMN, U.S.S.R. spectrofluorometer and by the formation of phenoxyl radicals which is measured by au EPR-2 (Institute of Chemica~ Physics, U.S.S.R. Academy of Scmnces) or EPR-V radmspectrometer. All these methods, gave corresponding results.
Effect of oxygen on phototransformation. W e f o u n d [12, 16] t h a t p h o t o t r a n s f o r m a t i o n of phenols subjected to steric h i n d r a n c e ( P D T B P , ionol, TTBP) in p o l y mers (PMMA, P P , TAC, BMK-5, PA-548) w i t h o u t o x y g e n takes place a t a r a t e w h i c h is lower b y 1-2 orders of m a g n i t u d e t h a n the r a t e in air. R e p l a c e m e n t o f v a c u u m b y a n i n e r t a t m o s p h e r e (carbon dioxide, argon, helium) has no effect. o n process rate. I t is o n l y o x y g e n which has a n accelerating effect. As a n example~ Figs. 1 a n d 2 show its effect on kinetics o f p h o t o t r a n s f o r m a t i o n o f P D T B P int P M M A a n d PP. The accelerating effect o f o x y g e n was later also observed in_ p h o t o t r a n s f o r m a t i o n o f m e t h y l o x in P P [9]. E x p e r i m e n t s carried o u t in this s t u d y indicate t h a t the r e a c t i o n is also accelerated in the presence of o x y g e n w h e r t exposing ionol a n d T T B P to r a d i a t i o n in TAC, B M K - 5 a n d PA-48. R e s u l t a suggest t h a t t h e effect is also tsTical of o t h e r phenols subjected to steric hindrance~ a n d dissolved in polymers. I n order t o establish the m e c h a n i s m of a c t i o n of o x y g e n we e x a m i n e the~ general kinetic s y s t e m of p h o t o t r a n s f o r m a t i o n of p h e n o l PhOH*
-*PhO'q-H"
(1~
PhOH*-FRH(X) -*products
(2~
PhOH*q-30,
-*PhO" q-HO,"
(3~
Ph0H+X*
-*products
(4~
Ph0H+lOl
-*PhO'+H0s"
(5~
PhOH~-ROs"
-*PhO'-}-R00H
(6~
Ph0H-]- R '
-,PhO'-}- R ' H
(7~
'~40
L. V. S ~ s o z c o v A e~ a/.
H e r e P h O H , P h O H * a n d X , X * are phenol a n d a n i m p u r i t y in the basic a n d activa t e d states respectively; P h O ' , t h e p h e n o x y l radical; R H , the polymer; R , t h e radical f o r m e d during t h e p h o t o d e c o m p o s i t i o n of quinolide peroxide, which is f o r m e d b y t h e reaction of the p h e n o x y l radical w i t h o x y g e n O"
0 II
I
0 II
0
II
_.,+
+, l~
R'/~O0"
R~OOH
(R') a'/~O •
Reactions (2) a n d (4) m a y be exchtded based on t h e f a c t t h a t q u a n t u m yields • o f p h o t o t r a n s f o r m a t i o n of phenol in PMMA, TAC a n d B M K - 5 (Table) are similax.* Otherwise, it could be assumed t h a t all these polymers h a v e the same r e a c t i v i t y in relation to PhOH" or contain the same i m p u r i t y in the same con-oentration.
I ' 0 ~
a
. os r'el.un. IRIs. l'lt
0"8
0
~ I
I0
3
30 50 Time, rain FIG. 1
~
50 I00 b
0
3
20 ~0 Time, rain Fro. 2
~1~o. 1. Kinetic curves of phenoxyl radical formation on exposing PMMA films containing "3-55 X 10-I mole/kg PDTBP to light of 253.7 nm in air (1, 3) and in vacuum (2). Arrow shows the moment of air intake. FIG. 2. Kinetic curves of optical density variation of PDTBP in a PP fihn by the action •+of light of 253.7 nm (a) and phenoxyl radical formation by the action of light of > 290 nm ~(b) in vacuum (1), carbon dioxide (2) and aw (3). Arrows indicate the moment of changing the atmosphere of wradiation. R e a c t i o n (6) m a y be excluded f r o m consideration since the light resistance o f the polymers studied varies m a r k e d l y . F o r example, q u a n t u m yields of p h o t o •~ e c o m p o s i t i o n of c h r o m o p h o r e ester groups are 0.01 for TAC [6] a n d a b o u t 1 * A similar quantum ymld (0.027) was obtained for the phototransformation of another ~phenol subjected to sterie hindrance--methylox, in PP [9].
Phototransformations in polymers of phenols
241
for PMMA [5], it m a y therefore be assumed t h a t the rates of radical f o r m a t i o n
are different in TAC and PMMA. This, however, has no influence on q u a n t u m yields of phenol consumption. A further argument against the share of reaction (6) is the agreement of rates of phenol consumption in PMMA and TAC (Fig. 3) not only b y the action of light of 253-7 nm absorbed both b y polymers and phenol, b u t also b y the action of light of 2 > 2 9 0 nm only absorbed b y phenol. As shown b y Fig. 2, the oxygen effect is also observed in the latter ~ s e . c/co
a
I'0~
• I
"
0"48
e
1.0
0"8~ , I , ~
l
4 Time, rnin
8
0"~0~ | I ' ' ' 1 I0
Fro. 3
| 30 Time, rain
O--
I i 5O
Fro. 4
Fzo. 3. Kinetic curves of PDTBP consumption (3-55× 10-8 mole/kg) in PMMA (1) and TAC (2) films by the action of light of 253.7 nm (a) and >290 nm (b). Fxo. 4. Optical density variation of PDTBP in a PMMA film by the action of light of >320 (a, c, e), >290 (b) and 253.7 nm (d). According to results in the literature [17, 18] it m a y be assumed that 10 s taking part in reaction (5) m a y be formed b y the interaction of phenol in the triplet state (PhOH T) with oxygen in the basic state of sO 2 PhOHT+ sOa-~[PhOH •xOs] , where the cell, in which the tO 2 molecule appears in the first moment of t h e reaction, is shown in brackets. 10 2 m a y subsequently react inside the cell with the same phenol molecule, or outside it, with another. The probability of reaction taking place outside the cell depends on the ratio of reaction rate (5) azld the rate of deactivation of 10 z. Therefore, in the range of low phenol concentrations, when the distance between molecules is considerable, reaction (5) only takes 101ace in the cell and is of first order for phenol, while in the range of high concentrations, is of second order. According to tabulated results, in PMMA the quantum yield of phototransformation of phenol is independent of concentration on changing this value from 3.5× 10 -4 to 1.4× 10 -I mole/kg. In this matrix (PMMA) for the photo-oxidation of anthracene with 10 3 it was found that t h e reaction takes place b y second order in the range of anthracene concentrations
L. V. SAMSOZ~OVA e~ a/.
exceeding 1 X 10-s mole/1. [17, 18]. The rate constant of reaction (5)for the phenol examined is higher by one order of magnitude than for anthracene, therefore, for the participation of xO~ quantum yield of phototransformation of phenol increases with [PhOH]0>l × 10-3 mole/l. Since this does not take place even with concentrations higher by one order of magnitude, reaction (5) may be exeluded from consideration. ke~
n.zo:I-~ io oZZio
a o
°
°
s l
o I
T
i
I
200
t
=
500
I
800
o)A/ ZU ~
I ~'Ul
-2 -I Fro. 5
o
t
I
I
2 Io9
I
28
p
i
BO
I
i
18g
i
I
/40
T/me ~ rn[n FZG. 6
F r o . 5. D e p e n d e n c e on o x y g e n pressure (dependence b is given in logarithmic coordmatos} o f t h e r a t e c o n s t a n t ,of p h o t o t r a n s f o r m a t l o n of P D T B P m a P P film (a) a n d t h e r a t e o f c o n s u m p t i o n of P D T B P m P P (b) b y t h e action of h g h t of 253.7 nm. FIG. 6. K i n e t i c curves of f o r m a t i o n and c o n s m n p t i o n of p h e n o x y l radicals on exposing a P M M A film containing 1.4 × 10 -I mole/kg P D T B P to light of different w a v e length: 1 -- ~> 290 n m (absorbed b y phenol) m alr, 2 - - ~ 320 n m (absorbed b y p h e n o x y l radicals only) u n d e r c o n d i t i o n s of 02 shortage (after e v a c u a t i o n v ~ t h o u t heating), 3 - - ~ 2 9 0 n m u n d e r conditions of O2 shortage, 4 - - > 320 nin w l t h O8 shortage after p h o t o c h e m i c a l f o r m a t i o n of phen o x y l radicals u n d e r these conditions f r o m phenol, 5 - - ~ 320 n m m air.
In order to evaluate the part of reaction (7) in phototransformation of phenol, a study was made of the effect of the spectroscopic composition of light on t h e rate of this reaction. We proceeded from earlier studies [9, 10], where it was shown for methylox in P P that previous exposure to short wave light of 2 = 2~3.7 nm results in the consumption of methylox by the action of long wave light (2>300 nm) not absorbed by it. This was explained [10] by reaction (7). In our experiments, as sho~m by l~ig. 4, long wave light (2>320 nm) has no effect on the consumption of PDTBP in PMMA either before, or after exposure to short wave light (2----253.7 nm and 2>290 nm), absorbed by phenol. T h i s means t h a t under conditions of our experiments reaction (7) is of no marked significance. There are two further reactions which need to be examined: photo-dissociation of phenol (1) and interaction between the electronically activated molecule o£ phenol and the oxygen molecule in the basic state (3), the rate of the second reaction being much higher, as shown by experiments concerning the effect of oxygen. The quantum yield of reaction (1) in liquid phase is considerably higher.
2,tg
P h o t o t r a n s f o r m a t i o n s in polymers of phenols
i t is possible that in reaction (1) further activation energy* is formed in the polymer matrix, 4-6 kJ/mole being sufficient for a rate reduction by one order of magnitude. Another explanation is the reversibility of photo-dissociation taking place by a homolytie mechanism P h O H ~ [PhO" ... H ' ] - , P h O ' - ] - H"
(la)
or a heterolytic mechanism P h O H ~ [ P h O H "+ ... e-] - , [ P h O " . . . H ' ] -~PhO" + H "
(It)
J- - - ÷ P h O H + - ] - 6 -
(lc)
We do not have any results available at the present time that would enable ns to give preference to one explanation
over the other. It may only be noted
1.0
ol
[R],
0.2
pek.n.
+2 ×,3,
I 1"2
04 i
I
60
i
r
I
I
180 .Time ~ rain Fzo. 7
I
I I i i I
8
I
Y
,,,,I
....
I,,,,I
5
r
/5 T/me ,m/n
Fro. 8
FIG. 7. K i n e t i c curves of p h e n o x y l radical f o r m a t i o n on exposing P M M A films containing3-55x l0 -~ mole/kg P D T B P to light of > 2 9 0 n m u n d e r conditions of o x y g e n shortage (1) a n d in air (2). F r o . 8. K m e t m curves of P D T B P c o n s u m p t m n in PMMA b y the action of light of 253.7 n m m air (a) a n d semi-logarithmic t r a n s f o r m a t i o n s (b); 1, 2 - - 3 . 5 5 × 10 -3 (two different experiments), 3 - - 3 . 5 5 × 10 -4 mole/kg; 1, 3--luminescence, 2 - - s p e c t r o p h o t o m e t r i c m e t h o d .
that reaction (la) can hardly ensure an almost complete reversibility of the process, since for this it would be necessary that the H atom be only exposed to diffusion in the direction of the phenoxyl radical. In order to establish the type of activated state of phenol in reaction (7), fluoroseenee measurements were carried out, which showed that oxygen has no * This hypothesis was p u t forward b y V. M. A n i s i m o v w h e n discussing the s t u d y ,
~44
L.V. SAMSO~OVAe~ a/.
effect on intensity. This enabled the interaction between the singlet activated
state of phenol and oxygen to be excluded. In polymers the rate constant of oxygen diffusion is lower by at least 2-3 orders of magnitude than in solutions. Oxygen at atmospheric pressure cannot therefore, generally, suppress fluoresce nce. The diffusion rate constant in P P is ~ l0 s 1./mole.see. The life time of the triplet state of phenol is equal in order of magnitude to 1 sec [19]. According to these results, to halve the concentration of the triplet state of phenol an oxygen pressure of the order of 10 -2 tort is required. This estimate is in agreement with experimental results shown in Fig. 5, from which it follows that the effective rate constant of phototransformation of phenol increases with an increase in oxygen pressure in the range of 0.01-1 tort and is independent of Po~ on further increasing pressure. It may hence be concluded that reaction (7) takes place with the participation of the triplet state of phenol. The accelerating effect of oxygen was also observed in phototransformation of phenoxyl radicals. Figure 6 indicates that without oxygen exposure of the PMMA film containing phenol and PhO" to light with 2~320 nm, which is only absorbed by PhO', does not change the concentration of phenoxyl radicals. A reduction in the concentration of radicals only starts after air has entered the ampoules. Figure 7 indicates that after evacuation without heating in the course of the next exposure to light with 2~290 nm absorbed both by phenol and PhO" (curve 1), PhO" radicals are formed and their concentration then remains practically unchanged. This may be explained by the fact that PhO" radicals are formed by the action of remaining oxygen. Their formation practically ceases after using up O2. At the same time, the concentration of PhO" radicals remains approximately the same. Consequently, without 02 PhO" radie= cals are stable. When irradiation is carried out in air (curve 2) radicals are not only formed, but they undergo phototransformation. The existence of an extrem u m on the kinetic curve is related to this fact. Kinetic features. As indicated, in solid polymers phototransformation of phenols subjected to steric hindrance is due to the reaction of PhOHT-t-O~. Oxygen is continuously supplied to the film from the atmosphere. Therefore, in the kinetic region, when diffusion does not limit reaction rate d [PhOH] dt
:Plabs
(I)
where Iabs is the amount of light absorbed by phenol in unit time
Iabs=Io (1-- 10- ~[PhOH]l-~ 2"3 I0 e~ l [PhOH]
(II)
where I o is the intensity of incident light; e~ and l, the molar coefficient of absorption and film thickness, respectively. The approximate formula derived is valid when 8~ [PhOH] l<
Phototransformations in polymers of phenols k i n e t i c curves o f t h e v a r i a t i o n o f relative p h e n o l c o n c e n t r a t i o n (in u n i t s of [ P h 0 H ] / /[PhOH]0 ) agree for t h e t w o initial c o n c e n t r a t i o n s o f [ P h 0 H ] 0 , w h i c h show a 10-fold difference. These curves, however, are n o t rectified in a semi-logarithmic
1/
co/c
-log c/co
-io~ c/co
°I
i
I
,
I
I
I
q 8 I2 Time, m[n
50
150 Time, rain
FIG. 9
~0
80
FIG. 10
FIG. 9. Transformation of kinetic curves showing the consumption of PDTBP in PMMA films (1) and TAC films (2) by the action of light of 253.7 nm. FIG. 10. Somi-logarithrnic transformations of kinetic curves showing PDTBP consumption m PP (a) and BMK-5 films (b) by the action of light of 253.7 nm m air.
c o o r d i n a t e s (Fig. 8b); a t t h e initial stage r a t e decreases more r a p i d l y t h a n b y a first order equation. F i g u r e 9 indicates t h a t kinetics satisfy a second order rule. A t t h e same time, if o n l y t h e initial r a t e s are considered, e q u a t i o n (I) holds g o o d QUA_N-£oM Y I E L D S OF PHOTOTRANSFORMATION ( P ) OF
PDTBP
I N POLYMER8
MEASURED ACCORDING TO CONSUMPTION BY T I l E ACTION OF L I G H T OF
253-7 NMIN Am
Medium PMMA
[PhOH]o, mole/l. 1-42 × 7.10× 3.55 × 1.78 × 3.55 ×
10-1 10-t 10-z 10-s 10-*
wo X lOs, mole/1..seo
labs X 10',
einst 1..sec
7.1 5.4 2'4 3.7 1.6
3-0 2.7 1.3 2.4 1.0
1-9 3.0
1.2 1.5
1.78 × 10 - s
TAC BMK-5
3.55 × 10-4 3.55 × 10-s 1.0 × 10 -*
P X 10= 2.4 2.0 1-9 1-6 1.6 1.6 1.6 1.6 2.0
a n d t h e P value is i n d e p e n d e n t of the initial c o n c e n t r a t i o n of p h e n o l on c h a n g i n g i t w i t h i n wide limits (Table). These relations are t y p i c a l of p h o t o t r a n s f o r m a t i o n o f p h e n o l carried o u t in P M M A a n d TAC.
246
L. V. S~so~ovA et al.
An increase was observed in recent years in the reaction order in the polymer (compared with the liquid phase) for photo-oxidation of a number of aromatic hydrocarbons in PS [17, 18], trans-cis-photoisomerization of some azo-compounds in PS, PMMA and polycarbonate [20, 21] and phototransformation of FeC1a in PMMA [22]. To explain irregular kinetics it is assumed [17, 21, 22] t h a t reagent particles arranged in various points of the polymer m a y have different reactivity values. The most reactive particles react first of all. With low mobility of the polymer matrix the initial distribution of particles according to reactivity is "fl'ozen" and cannot be restored during the reaction. In polymers with fairly high mobility, particles are redistributed according to reactivity at a high rate a n d reaction kinetics correspond to liquid phase reaction kinetics. In order to explain whether there is agreement between the "rigidity" of the polymer and the kinetic law of phototransformation, kinetics of phototransform a t i o n of P D T B P in "softer" polymers (BMK-5 and PP) having much lower glass temperatures (~-40 and --40 °, respectively) were measured. As shown b y Fig. 10, the photoreaction of P D T B P takes place by a first order rule in t h e s e polymers. According to results of previous studies [17, 18, 20-22], deviations from a first order kinetic rule m a y be explained by the kinetic non-equivalence of phenol molecules in PMMA and TAC. Translated by R. S~.~I~ERE REFERENCES
1. T. MATSUURA, N. YOSLIMURA, A. NISHINAGA and I. SAITO, Tetrahedron Letterl, No. 21, 1669, 1969 2. K. PFOERTNER and B. B~SE, Helv. China. Aeta 53: 1553, 1970 3. A. P. SNY~,KIN, L. V. SAMSONOVA, V. Ya. SHLYAPINTOKH and V. V. YERSHOV, Izv. AN SSSR, ser. khim., 55, 1978 4. L. V. SAMSONOVA, L. TAIMR and J. POSPISIL, Angew. Makromolek. Chemic 65: 197, 1977 5. V. Ya. SLYAPINTOKH and V. I. GOLDEN-BERG, Europ. Polymer J. 10: 679, 1974 6. V. I. GOL'DENBERG, Ire. V. BYSTRITSKAYA, V. I. YUSTL, O. A. IN, V. Ira. SHLYAPINTOKH and I. Ya. KALONTAROV,Vysokomol. soyed. A17: 2779, 1975 (Translated
in Polymer Scl. U.S.S.R. 17: 12, 3192, 1975) 7. B. J. FOSTER, P. H. WHITLING, J. M. MELLER and D. PHILLIPS, J. Appl. Polymer Sin. 22: 1129, 1978 8. Ye. M. SLOBODETSKAYA,O. N. KARPUKHIN and V. V. AMERIK, Vysokomol. soyed. B18: 184, 1976 (Not translated in Polymer Sei. U.S.S.R.) 9. Ye. M. SLOBODETSKAYA, M. G. VOROB'YEV and O. N. KARPUKHIN, Vysokomol. soyed. A17: 2533, 1975 (Translated m Polymer Sel. U.S.S.R. 17: 11, 2916, 1975) 10. O. N. KARPUKHIN and Ye. M. SLOBODETSKAYA,Vysokomol. soyed. B19: 488, 1977 (Not translated in Polymer Sci. U.S.S.R.) 11. Ye. M. BYSTRITSKAYA, V. I. GOL'DENBERG, G. B. PARIISKII, L. V. SAMSONOVA and V. Ya. SHLYAPINTOKH, Vysokomol. soyed. A14: 1727, 1972 (Translated in Po]ymer Sei. U.S.S.R. 14: 8, 1931, 1972) 12. L. V. SAMSONOVA, V. I. GOL'DENBERG, Ye. M. BYSTRITSKAYA, G. A. NIKIFOROV and V. Ira. SHLYAPINTOKH, Mitt. Chem. Forchungs, Witt. Osters 26: 5242, 1972
Non-stoichiometrie polyelectrolyte complexes
247
13. I. N. M O R O Z O V A , L. V. S A M S O N O V A , V. I. G O L ' D E N B E R G a n d V. Ya. S H I Y A P I N T O K H , Vysokomol. soyed. A16: 1820, 1974 (Translated m Polymer Sci. U.S.S.R. 16:
8, 2106, 1974) 14. V. I. GOL'DENBERG, K a n d l d a t s k a y a dissertatsiya (Post-Graduate Thesis), Moscow, I K h F , U.S.S.R. Academy of Sciences, 1972 15. A. L. MARGOLIN, I. A. KABANOVA, L. M. POSTNIKOV and V. Ya. SHLYAPINTOKH, Vysokomol. soyed. A18: 1094, 1976 (Translated m Polymer Sci. U.S.S.R. 18: 5, 1258, 1976) 16. L. V. SAMSONOVA, V. Ya. SHLYAPINTOKH, G. A. NIKIFOROV and V. V. YERSHOV, Mitt. Chem. Forehungs. Wltt. esters 28: 75, 1974 17. V. M. ANISIMOV and O. N. KARPUKHIN, Izv. AN SSSR, ser. khim., 1914, 1973 18. V. M. ANISIMOV, O. N. KARPUKHIN and A. M. MATTUCCI, Dokl. AN SSSR 214: 828, 1974 19. S. PARKER, Fotolyummestsentsiya rastvorov (Photoluminescvnee of Solutions) Izd. "Mir", 1972 20. Yc. M. BYSTRITSKAYA, T. S. KARPOVICH and (). N. KARPUKHIN, Dokl. AN SSSR 228: 632, 1976 21. O. N. KARPUKHIN, Doktorskaya dissertatsiya (Doctor's Thesm). Moscow, I K h F , A_NI SSSR, 1974 22. T. V. POKHOLOK, N. L ZAITSEVA, G. B. PARIISKII and D. Ya. TOPTYGIN, Vysokomol. soyed. A19, 2049, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 9, 2351, 1977)
aPolymer Science U.S.S.R. Vol. 22, pp. 247-254.
003fi-3950/80/0101-0247507.50~
PergamonPress Ltd. 1980.Printedin Poland
ASSOCIATION AND DISSOCIATION PROCESSES IN SOLUTIONS OF NON-STOICHIOMETRIC POLYELECTROLYTE COMPLEXES* O . A. KHAREN~O, V. A. ~[ZU1KRUDOV, A. V. KHAREI~KO, V. A. KASAIKIN,
A. B. ZEZI~ and V. A. KABA~OV M. V. Lomonosov State University, Moscow
(Received 23 November 1978) A study was made of association and dissociation processes in solutions of n o n . ~toichiometric water soluble poly-complexes. I t was shown that the formation of ~ssociated particles m solutions of these poly-complexes is a general feature of these macromolecular compounds, which is independent of the type of polyelectrolyte contained in the poly-complex m excess. Association of particles of non-stoichlometric ])ely-complexes is due to intermolecular segregation of hydrophobic umts consisting ,of double sequences of pairs of polyelectrolyte umts forlmng salt bonds. The degree of ~ssoclation of non-stmchiometrm poly-complexes is first of all determined b y the ratio of hydrophobic and hydrophllic sequences of iomzed polyelectrolyte groups cont a m e d m excess in the poly-complex, which do not form salt bonds (units) and secondly; b y the state of hydrophilic units determined b y interaction of ionized groups cont a i n e d in excess in the poly-complex with low molecular weight counterious. * Vysokomol. soyed. A22: No. 1, 218-224, 1980.
237
'~. V. A. MARIKHIN, I Vsesoyuznyi simpozium po kriogennym m e t o d a m v elektronnoi mlkroskopii (I All-Union Symposium on Cryogenic Methods in Electron Microscopy}. Pushehino, 1975 3. T. M. BIRSHTEIN, V sb. Sostoyaniye i rol' v o d y v biologichcskikh o b " y e k t a k h (Symp, The State a n d Role of W a t e r in Biological Substances) Izd. " N a u k a " , 1967 4. M. A. ASAUBEKOV, Izv. AN KazSSR, set. khim. 1: 81, 1976 ~. S. I. SEN'KOVICH, Ye. M. BELAVTSEVA, E. V. KAMENSKAYA and Yu. A. K L Y A CH]KO, I I Vsesoyuznyi simpozium po kriogennym m e t o d a m preparirovaniya ( I I AllUnion S y m p c s m m on Cryogenic Methods of Preparatmn). Pushchino, 1977 ~}. S. N. RUSCHER, J. Polymer Sci. C16: 2923, 1967 7. BACHMANN and W. W. SCHMITT, Naturwissenschaften 58: 217, 1971 8. A. GROBE, R. MARON and H. J. PURZ, Faserforsch. und Textiltechn. 17: 458, 1966 9. Ye. M. BELAVTSEVA and Ye. F. TITOVA, Vysokomol. soyed. 14: 1659, 1972 (Translated in P o l y m e r Sci. U.S.S.R. 14: 7, 1861, 1972) 10. T. NEI, Principles and Techn, ques of SEM (edited b y M. A. Bayat) v. 1., New York, 1974 11. M. ~EN and V. MARINKOVIC, St/irke 4: 125, 1963 12. Ye. M. BELAVTSEVA a n d Ye. F. TITOVA, I I Vsesoyuznyi simpozium po kriogennym m e t o d a m preparirovaniya (II All-Umon Symposium on Cryogenic Methods of Prepaparation). Pushchino, 1977 13. Ye. F. TIT0VA, Ye. M. BELAVTSEVA, Ye. Ye. BRAUDE and V. B. TOLSTOGUSOV, Colloid and Polymer Sci., 252, 1974
0032-3950/80/0101-0237507.5010
• ~olymer Science U.S.S.R. Vol. 22, pp. 237-247. .4~ Pergamon Press Ltd. 1980. Printed in Poland
PHOTOTRANSFORMATIONS IN POLYMERS OF PHENOLS SUBJECTED TO STERIC HINDRANCE* ~L. V. SAMSOlq'OVA, V. YA. SHLYAPINTOKH
and V. V. YERSHOV
Instituteof Chemical Physics, U.S.S.R. Academy of Sciences (Received 22 November 1978) Phototransformation of 4-phenyl-2,6-di-tert.butylphenol in PMMA, PP, cell u l o s e t r i a c e t a t e and a b u t y l m e t h a c r y l a t e - m e t h a c r y l i c acid copolymer takes place ~rith a q u a n t u m yield of N 0.02 and shows little dependence on the t y p e of polymer. 'The q u a n t u m yield measured according to initial rates of consumption of 4-phenyl~2,6-di-tert. butylphenol in PMMA and cellulose triacetate, is independent of phenol cone e n t r a t i o n even with a hundred fold variation of this value. A t the same time kinetics o f phototransformation of phenol are described b y a second order kinetic law. This discrepancy is, apparently, caused b y the kinetic non-equivalence of phenol molecules 4arranged in various positions of the "rigid" polymer. I n the absence of oxygen the rate ~ f phototransformation of 4-phenyl-2,6-eh-tert.butylphenol a n d 4-methyl-2,6-di-tert. * Vysokomol. soyed. A22: No. 1,209-217, 1980.
2.38
L. V. SAMSO~OVAeL a/.
butylphcnol and 2,4,6-tri-tert.butylphenol decreases by one or two orders of magnitude. An acceleration of the photoreaction with oxygen is due to the chemical interaction of O3 with the triplet state of phenols. Oxygen also markedly acceleratea the phototransformation of phenoxyl radicals. WHEI~ using phenols and phenol derivatives subjected to steric hindrance for the~ stabilization of various polymeric materials the part of similar compounds i n photochemical processes taking place in polymers is not considered usually~ Light m a y cause direct photolysis of phenol stabilizers. The existence in the polymer composition of impurities and a number of additives of aromatic compounds a n d various dyes m a y induce, under conditions of radiation, the formation o f singlet oxygen which readily reacts with phenols [1-4]. Intermediate producta formed in the photochemical reactions m a y accelerate or inhibit the ageing process of the polymer material. Studies carried out up to the present time, normally, only gave an evaluation of the gross effect of the photochemical activity of some a n t i o x i d a n t s - - t h e i r effect on the variation of colour and physical and mechanical properties of polymers during photodegradation. I t was only recently t h a t papers were published [5-10] concerning the effect~ of phenols on the photodegradation of polymers on a quantitative level. I t w aa shown in our earlier studies [11-13] t h a t various phenols initiate the degradation o f PMMA and quantum yields of phototransformation were determined in the~ l~resence of thiobisphenol and bisphenol 22-46. Initiating l~roperties of phenola (methylox) were also noted for P P [8, 9]. I t was established [6] that, according t o ]phenol concentration, photodegradation of triacetylcellulose (TAC) m a y either be accelerated, or inhibited. However, kinetics and the mechanism of photochemical transformations of phenols subjected to sterie hindrance in polymers have~ been very little investigated. This s t u d y is concerned with the mechanism of phototransformation anc~ obtaining quantitative data concerning phototransformation of phenols subjected~ t o steric hindrance in various polymer matrices. Phototransformation of 4-phenyl-2,6-di-tert.butylphenol (PDTBP), 4-methyl-2,6-di* ~rt.butylphenol (ionol) and 2,4,6-tm-tert.butylphenol (TTBP) was mainly examined ir~ various polymers. A significant proportion of experiments was carried out with PMMA~ Photoreaction of phenols was studied in a number of experiments in TAC, PP, a butyl* methacryl-methacrylic acid copolymer (5%) (BMK-5) and in PA-548 aliphatic polyamide. Phenols were purified by crystallization from ethanol, followed by chromatbgraphic~ separation on silica gel. PMMA of the Chemical Combine "Orgsteklo" of M ~ 175,000 conraining ~ 1% monomer, TAC of the Kaunas Works producing synthetic fibre, PP grade"Moplen" of M ~ 80,000 and a degree of crystallinity of 50 %, BMK°5 of the Yarloslav Chemical Combine, PA-548--an industmal polymer prepared by polycondensation of adipat@ and hexamethylene diamine, salts of sebacic acid and hexamethylene diamine and a-caprolactam were used for the study. PMMA, TAC and BMK-5 films were prepared by applying a polymer solution in methylQne chloride on ~ polished glass surface [14]. Films on quartz substrates prepared by elon-
Phototransformations in polymers of phenols
23~,
gating the latter at a constant rate ( ~ 2 mm]min) from a 10% polymer solution containing am additive (PMMA and TAC) in methylene chloride or acetone (BMK-5) were used in some, experiments. Polyamide films were prepared by a method previously described [15]. Polypropylene films were compressed in vacuum under a pressure of 0.02 kg/em s at~ 220° and then rapidly cooled m hquld nitrogen. Antioxldant additives were introduced im transparent polymer films (~ 100 /lm in thmkness), kept m sealed ampoules in saturated vapour of an antioxldant used m considerable excess at 60° for about 20 hr. If the concentration of the antioxidant in the film had to be reduced, its surplus was removed by evacuation at 100° and a pressure of ~ 10-3 torr. Film thickness was measured with an error o f =[=0.2 ~m using an IKV vertical optmal caliper. The light of a BUV-30P lamp was used, 80% of radiatmn being on the line of 253.7 nm (light intensity was 2 × 101~ quantum" cm -2 sec-~), the remaining 20% being mainly onu the line of 438 nm and not absorbed by the polymers and phenols examined. I t may therefore be assumed that the samples were exposed to monochromatic hght of wave length 253.2 rim. The full or filtered light of a DRSh-1000 lamp was also used. The concentration variation of phenol durmg the reactmn was recorded spectrophotometrically (using SF-4A or Specord UV-VIS spectrophotometers) according to the optical~ density vamation in the maximum of absorption band (265 nm), the variation of fluorescence intensity being measured by an L K I P AMN, U.S.S.R. spectrofluorometer and by the formation of phenoxyl radicals which is measured by au EPR-2 (Institute of Chemica~ Physics, U.S.S.R. Academy of Scmnces) or EPR-V radmspectrometer. All these methods, gave corresponding results.
Effect of oxygen on phototransformation. W e f o u n d [12, 16] t h a t p h o t o t r a n s f o r m a t i o n of phenols subjected to steric h i n d r a n c e ( P D T B P , ionol, TTBP) in p o l y mers (PMMA, P P , TAC, BMK-5, PA-548) w i t h o u t o x y g e n takes place a t a r a t e w h i c h is lower b y 1-2 orders of m a g n i t u d e t h a n the r a t e in air. R e p l a c e m e n t o f v a c u u m b y a n i n e r t a t m o s p h e r e (carbon dioxide, argon, helium) has no effect. o n process rate. I t is o n l y o x y g e n which has a n accelerating effect. As a n example~ Figs. 1 a n d 2 show its effect on kinetics o f p h o t o t r a n s f o r m a t i o n o f P D T B P int P M M A a n d PP. The accelerating effect o f o x y g e n was later also observed in_ p h o t o t r a n s f o r m a t i o n o f m e t h y l o x in P P [9]. E x p e r i m e n t s carried o u t in this s t u d y indicate t h a t the r e a c t i o n is also accelerated in the presence of o x y g e n w h e r t exposing ionol a n d T T B P to r a d i a t i o n in TAC, B M K - 5 a n d PA-48. R e s u l t a suggest t h a t t h e effect is also tsTical of o t h e r phenols subjected to steric hindrance~ a n d dissolved in polymers. I n order t o establish the m e c h a n i s m of a c t i o n of o x y g e n we e x a m i n e the~ general kinetic s y s t e m of p h o t o t r a n s f o r m a t i o n of p h e n o l PhOH*
-*PhO'q-H"
(1~
PhOH*-FRH(X) -*products
(2~
PhOH*q-30,
-*PhO" q-HO,"
(3~
Ph0H+X*
-*products
(4~
Ph0H+lOl
-*PhO'+H0s"
(5~
PhOH~-ROs"
-*PhO'-}-R00H
(6~
Ph0H-]- R '
-,PhO'-}- R ' H
(7~
'~40
L. V. S ~ s o z c o v A e~ a/.
H e r e P h O H , P h O H * a n d X , X * are phenol a n d a n i m p u r i t y in the basic a n d activa t e d states respectively; P h O ' , t h e p h e n o x y l radical; R H , the polymer; R , t h e radical f o r m e d during t h e p h o t o d e c o m p o s i t i o n of quinolide peroxide, which is f o r m e d b y t h e reaction of the p h e n o x y l radical w i t h o x y g e n O"
0 II
I
0 II
0
II
_.,+
+, l~
R'/~O0"
R~OOH
(R') a'/~O •
Reactions (2) a n d (4) m a y be exchtded based on t h e f a c t t h a t q u a n t u m yields • o f p h o t o t r a n s f o r m a t i o n of phenol in PMMA, TAC a n d B M K - 5 (Table) are similax.* Otherwise, it could be assumed t h a t all these polymers h a v e the same r e a c t i v i t y in relation to PhOH" or contain the same i m p u r i t y in the same con-oentration.
I ' 0 ~
a
. os r'el.un. IRIs. l'lt
0"8
0
~ I
I0
3
30 50 Time, rain FIG. 1
~
50 I00 b
0
3
20 ~0 Time, rain Fro. 2
~1~o. 1. Kinetic curves of phenoxyl radical formation on exposing PMMA films containing "3-55 X 10-I mole/kg PDTBP to light of 253.7 nm in air (1, 3) and in vacuum (2). Arrow shows the moment of air intake. FIG. 2. Kinetic curves of optical density variation of PDTBP in a PP fihn by the action •+of light of 253.7 nm (a) and phenoxyl radical formation by the action of light of > 290 nm ~(b) in vacuum (1), carbon dioxide (2) and aw (3). Arrows indicate the moment of changing the atmosphere of wradiation. R e a c t i o n (6) m a y be excluded f r o m consideration since the light resistance o f the polymers studied varies m a r k e d l y . F o r example, q u a n t u m yields of p h o t o •~ e c o m p o s i t i o n of c h r o m o p h o r e ester groups are 0.01 for TAC [6] a n d a b o u t 1 * A similar quantum ymld (0.027) was obtained for the phototransformation of another ~phenol subjected to sterie hindrance--methylox, in PP [9].
Phototransformations in polymers of phenols
241
for PMMA [5], it m a y therefore be assumed t h a t the rates of radical f o r m a t i o n
are different in TAC and PMMA. This, however, has no influence on q u a n t u m yields of phenol consumption. A further argument against the share of reaction (6) is the agreement of rates of phenol consumption in PMMA and TAC (Fig. 3) not only b y the action of light of 253-7 nm absorbed both b y polymers and phenol, b u t also b y the action of light of 2 > 2 9 0 nm only absorbed b y phenol. As shown b y Fig. 2, the oxygen effect is also observed in the latter ~ s e . c/co
a
I'0~
• I
"
0"48
e
1.0
0"8~ , I , ~
l
4 Time, rnin
8
0"~0~ | I ' ' ' 1 I0
Fro. 3
| 30 Time, rain
O--
I i 5O
Fro. 4
Fzo. 3. Kinetic curves of PDTBP consumption (3-55× 10-8 mole/kg) in PMMA (1) and TAC (2) films by the action of light of 253.7 nm (a) and >290 nm (b). Fxo. 4. Optical density variation of PDTBP in a PMMA film by the action of light of >320 (a, c, e), >290 (b) and 253.7 nm (d). According to results in the literature [17, 18] it m a y be assumed that 10 s taking part in reaction (5) m a y be formed b y the interaction of phenol in the triplet state (PhOH T) with oxygen in the basic state of sO 2 PhOHT+ sOa-~[PhOH •xOs] , where the cell, in which the tO 2 molecule appears in the first moment of t h e reaction, is shown in brackets. 10 2 m a y subsequently react inside the cell with the same phenol molecule, or outside it, with another. The probability of reaction taking place outside the cell depends on the ratio of reaction rate (5) azld the rate of deactivation of 10 z. Therefore, in the range of low phenol concentrations, when the distance between molecules is considerable, reaction (5) only takes 101ace in the cell and is of first order for phenol, while in the range of high concentrations, is of second order. According to tabulated results, in PMMA the quantum yield of phototransformation of phenol is independent of concentration on changing this value from 3.5× 10 -4 to 1.4× 10 -I mole/kg. In this matrix (PMMA) for the photo-oxidation of anthracene with 10 3 it was found that t h e reaction takes place b y second order in the range of anthracene concentrations
L. V. SAMSOZ~OVA e~ a/.
exceeding 1 X 10-s mole/1. [17, 18]. The rate constant of reaction (5)for the phenol examined is higher by one order of magnitude than for anthracene, therefore, for the participation of xO~ quantum yield of phototransformation of phenol increases with [PhOH]0>l × 10-3 mole/l. Since this does not take place even with concentrations higher by one order of magnitude, reaction (5) may be exeluded from consideration. ke~
n.zo:I-~ io oZZio
a o
°
°
s l
o I
T
i
I
200
t
=
500
I
800
o)A/ ZU ~
I ~'Ul
-2 -I Fro. 5
o
t
I
I
2 Io9
I
28
p
i
BO
I
i
18g
i
I
/40
T/me ~ rn[n FZG. 6
F r o . 5. D e p e n d e n c e on o x y g e n pressure (dependence b is given in logarithmic coordmatos} o f t h e r a t e c o n s t a n t ,of p h o t o t r a n s f o r m a t l o n of P D T B P m a P P film (a) a n d t h e r a t e o f c o n s u m p t i o n of P D T B P m P P (b) b y t h e action of h g h t of 253.7 nm. FIG. 6. K i n e t i c curves of f o r m a t i o n and c o n s m n p t i o n of p h e n o x y l radicals on exposing a P M M A film containing 1.4 × 10 -I mole/kg P D T B P to light of different w a v e length: 1 -- ~> 290 n m (absorbed b y phenol) m alr, 2 - - ~ 320 n m (absorbed b y p h e n o x y l radicals only) u n d e r c o n d i t i o n s of 02 shortage (after e v a c u a t i o n v ~ t h o u t heating), 3 - - ~ 2 9 0 n m u n d e r conditions of O2 shortage, 4 - - > 320 nin w l t h O8 shortage after p h o t o c h e m i c a l f o r m a t i o n of phen o x y l radicals u n d e r these conditions f r o m phenol, 5 - - ~ 320 n m m air.
In order to evaluate the part of reaction (7) in phototransformation of phenol, a study was made of the effect of the spectroscopic composition of light on t h e rate of this reaction. We proceeded from earlier studies [9, 10], where it was shown for methylox in P P that previous exposure to short wave light of 2 = 2~3.7 nm results in the consumption of methylox by the action of long wave light (2>300 nm) not absorbed by it. This was explained [10] by reaction (7). In our experiments, as sho~m by l~ig. 4, long wave light (2>320 nm) has no effect on the consumption of PDTBP in PMMA either before, or after exposure to short wave light (2----253.7 nm and 2>290 nm), absorbed by phenol. T h i s means t h a t under conditions of our experiments reaction (7) is of no marked significance. There are two further reactions which need to be examined: photo-dissociation of phenol (1) and interaction between the electronically activated molecule o£ phenol and the oxygen molecule in the basic state (3), the rate of the second reaction being much higher, as shown by experiments concerning the effect of oxygen. The quantum yield of reaction (1) in liquid phase is considerably higher.
2,tg
P h o t o t r a n s f o r m a t i o n s in polymers of phenols
i t is possible that in reaction (1) further activation energy* is formed in the polymer matrix, 4-6 kJ/mole being sufficient for a rate reduction by one order of magnitude. Another explanation is the reversibility of photo-dissociation taking place by a homolytie mechanism P h O H ~ [PhO" ... H ' ] - , P h O ' - ] - H"
(la)
or a heterolytic mechanism P h O H ~ [ P h O H "+ ... e-] - , [ P h O " . . . H ' ] -~PhO" + H "
(It)
J- - - ÷ P h O H + - ] - 6 -
(lc)
We do not have any results available at the present time that would enable ns to give preference to one explanation
over the other. It may only be noted
1.0
ol
[R],
0.2
pek.n.
+2 ×,3,
I 1"2
04 i
I
60
i
r
I
I
180 .Time ~ rain Fzo. 7
I
I I i i I
8
I
Y
,,,,I
....
I,,,,I
5
r
/5 T/me ,m/n
Fro. 8
FIG. 7. K i n e t i c curves of p h e n o x y l radical f o r m a t i o n on exposing P M M A films containing3-55x l0 -~ mole/kg P D T B P to light of > 2 9 0 n m u n d e r conditions of o x y g e n shortage (1) a n d in air (2). F r o . 8. K m e t m curves of P D T B P c o n s u m p t m n in PMMA b y the action of light of 253.7 n m m air (a) a n d semi-logarithmic t r a n s f o r m a t i o n s (b); 1, 2 - - 3 . 5 5 × 10 -3 (two different experiments), 3 - - 3 . 5 5 × 10 -4 mole/kg; 1, 3--luminescence, 2 - - s p e c t r o p h o t o m e t r i c m e t h o d .
that reaction (la) can hardly ensure an almost complete reversibility of the process, since for this it would be necessary that the H atom be only exposed to diffusion in the direction of the phenoxyl radical. In order to establish the type of activated state of phenol in reaction (7), fluoroseenee measurements were carried out, which showed that oxygen has no * This hypothesis was p u t forward b y V. M. A n i s i m o v w h e n discussing the s t u d y ,
~44
L.V. SAMSO~OVAe~ a/.
effect on intensity. This enabled the interaction between the singlet activated
state of phenol and oxygen to be excluded. In polymers the rate constant of oxygen diffusion is lower by at least 2-3 orders of magnitude than in solutions. Oxygen at atmospheric pressure cannot therefore, generally, suppress fluoresce nce. The diffusion rate constant in P P is ~ l0 s 1./mole.see. The life time of the triplet state of phenol is equal in order of magnitude to 1 sec [19]. According to these results, to halve the concentration of the triplet state of phenol an oxygen pressure of the order of 10 -2 tort is required. This estimate is in agreement with experimental results shown in Fig. 5, from which it follows that the effective rate constant of phototransformation of phenol increases with an increase in oxygen pressure in the range of 0.01-1 tort and is independent of Po~ on further increasing pressure. It may hence be concluded that reaction (7) takes place with the participation of the triplet state of phenol. The accelerating effect of oxygen was also observed in phototransformation of phenoxyl radicals. Figure 6 indicates that without oxygen exposure of the PMMA film containing phenol and PhO" to light with 2~320 nm, which is only absorbed by PhO', does not change the concentration of phenoxyl radicals. A reduction in the concentration of radicals only starts after air has entered the ampoules. Figure 7 indicates that after evacuation without heating in the course of the next exposure to light with 2~290 nm absorbed both by phenol and PhO" (curve 1), PhO" radicals are formed and their concentration then remains practically unchanged. This may be explained by the fact that PhO" radicals are formed by the action of remaining oxygen. Their formation practically ceases after using up O2. At the same time, the concentration of PhO" radicals remains approximately the same. Consequently, without 02 PhO" radie= cals are stable. When irradiation is carried out in air (curve 2) radicals are not only formed, but they undergo phototransformation. The existence of an extrem u m on the kinetic curve is related to this fact. Kinetic features. As indicated, in solid polymers phototransformation of phenols subjected to steric hindrance is due to the reaction of PhOHT-t-O~. Oxygen is continuously supplied to the film from the atmosphere. Therefore, in the kinetic region, when diffusion does not limit reaction rate d [PhOH] dt
:Plabs
(I)
where Iabs is the amount of light absorbed by phenol in unit time
Iabs=Io (1-- 10- ~[PhOH]l-~ 2"3 I0 e~ l [PhOH]
(II)
where I o is the intensity of incident light; e~ and l, the molar coefficient of absorption and film thickness, respectively. The approximate formula derived is valid when 8~ [PhOH] l<
Phototransformations in polymers of phenols k i n e t i c curves o f t h e v a r i a t i o n o f relative p h e n o l c o n c e n t r a t i o n (in u n i t s of [ P h 0 H ] / /[PhOH]0 ) agree for t h e t w o initial c o n c e n t r a t i o n s o f [ P h 0 H ] 0 , w h i c h show a 10-fold difference. These curves, however, are n o t rectified in a semi-logarithmic
1/
co/c
-log c/co
-io~ c/co
°I
i
I
,
I
I
I
q 8 I2 Time, m[n
50
150 Time, rain
FIG. 9
~0
80
FIG. 10
FIG. 9. Transformation of kinetic curves showing the consumption of PDTBP in PMMA films (1) and TAC films (2) by the action of light of 253.7 nm. FIG. 10. Somi-logarithrnic transformations of kinetic curves showing PDTBP consumption m PP (a) and BMK-5 films (b) by the action of light of 253.7 nm m air.
c o o r d i n a t e s (Fig. 8b); a t t h e initial stage r a t e decreases more r a p i d l y t h a n b y a first order equation. F i g u r e 9 indicates t h a t kinetics satisfy a second order rule. A t t h e same time, if o n l y t h e initial r a t e s are considered, e q u a t i o n (I) holds g o o d QUA_N-£oM Y I E L D S OF PHOTOTRANSFORMATION ( P ) OF
PDTBP
I N POLYMER8
MEASURED ACCORDING TO CONSUMPTION BY T I l E ACTION OF L I G H T OF
253-7 NMIN Am
Medium PMMA
[PhOH]o, mole/l. 1-42 × 7.10× 3.55 × 1.78 × 3.55 ×
10-1 10-t 10-z 10-s 10-*
wo X lOs, mole/1..seo
labs X 10',
einst 1..sec
7.1 5.4 2'4 3.7 1.6
3-0 2.7 1.3 2.4 1.0
1-9 3.0
1.2 1.5
1.78 × 10 - s
TAC BMK-5
3.55 × 10-4 3.55 × 10-s 1.0 × 10 -*
P X 10= 2.4 2.0 1-9 1-6 1.6 1.6 1.6 1.6 2.0
a n d t h e P value is i n d e p e n d e n t of the initial c o n c e n t r a t i o n of p h e n o l on c h a n g i n g i t w i t h i n wide limits (Table). These relations are t y p i c a l of p h o t o t r a n s f o r m a t i o n o f p h e n o l carried o u t in P M M A a n d TAC.
246
L. V. S~so~ovA et al.
An increase was observed in recent years in the reaction order in the polymer (compared with the liquid phase) for photo-oxidation of a number of aromatic hydrocarbons in PS [17, 18], trans-cis-photoisomerization of some azo-compounds in PS, PMMA and polycarbonate [20, 21] and phototransformation of FeC1a in PMMA [22]. To explain irregular kinetics it is assumed [17, 21, 22] t h a t reagent particles arranged in various points of the polymer m a y have different reactivity values. The most reactive particles react first of all. With low mobility of the polymer matrix the initial distribution of particles according to reactivity is "fl'ozen" and cannot be restored during the reaction. In polymers with fairly high mobility, particles are redistributed according to reactivity at a high rate a n d reaction kinetics correspond to liquid phase reaction kinetics. In order to explain whether there is agreement between the "rigidity" of the polymer and the kinetic law of phototransformation, kinetics of phototransform a t i o n of P D T B P in "softer" polymers (BMK-5 and PP) having much lower glass temperatures (~-40 and --40 °, respectively) were measured. As shown b y Fig. 10, the photoreaction of P D T B P takes place by a first order rule in t h e s e polymers. According to results of previous studies [17, 18, 20-22], deviations from a first order kinetic rule m a y be explained by the kinetic non-equivalence of phenol molecules in PMMA and TAC. Translated by R. S~.~I~ERE REFERENCES
1. T. MATSUURA, N. YOSLIMURA, A. NISHINAGA and I. SAITO, Tetrahedron Letterl, No. 21, 1669, 1969 2. K. PFOERTNER and B. B~SE, Helv. China. Aeta 53: 1553, 1970 3. A. P. SNY~,KIN, L. V. SAMSONOVA, V. Ya. SHLYAPINTOKH and V. V. YERSHOV, Izv. AN SSSR, ser. khim., 55, 1978 4. L. V. SAMSONOVA, L. TAIMR and J. POSPISIL, Angew. Makromolek. Chemic 65: 197, 1977 5. V. Ya. SLYAPINTOKH and V. I. GOLDEN-BERG, Europ. Polymer J. 10: 679, 1974 6. V. I. GOL'DENBERG, Ire. V. BYSTRITSKAYA, V. I. YUSTL, O. A. IN, V. Ira. SHLYAPINTOKH and I. Ya. KALONTAROV,Vysokomol. soyed. A17: 2779, 1975 (Translated
in Polymer Scl. U.S.S.R. 17: 12, 3192, 1975) 7. B. J. FOSTER, P. H. WHITLING, J. M. MELLER and D. PHILLIPS, J. Appl. Polymer Sin. 22: 1129, 1978 8. Ye. M. SLOBODETSKAYA,O. N. KARPUKHIN and V. V. AMERIK, Vysokomol. soyed. B18: 184, 1976 (Not translated in Polymer Sei. U.S.S.R.) 9. Ye. M. SLOBODETSKAYA, M. G. VOROB'YEV and O. N. KARPUKHIN, Vysokomol. soyed. A17: 2533, 1975 (Translated m Polymer Sel. U.S.S.R. 17: 11, 2916, 1975) 10. O. N. KARPUKHIN and Ye. M. SLOBODETSKAYA,Vysokomol. soyed. B19: 488, 1977 (Not translated in Polymer Sci. U.S.S.R.) 11. Ye. M. BYSTRITSKAYA, V. I. GOL'DENBERG, G. B. PARIISKII, L. V. SAMSONOVA and V. Ya. SHLYAPINTOKH, Vysokomol. soyed. A14: 1727, 1972 (Translated in Po]ymer Sei. U.S.S.R. 14: 8, 1931, 1972) 12. L. V. SAMSONOVA, V. I. GOL'DENBERG, Ye. M. BYSTRITSKAYA, G. A. NIKIFOROV and V. Ira. SHLYAPINTOKH, Mitt. Chem. Forchungs, Witt. Osters 26: 5242, 1972
Non-stoichiometrie polyelectrolyte complexes
247
13. I. N. M O R O Z O V A , L. V. S A M S O N O V A , V. I. G O L ' D E N B E R G a n d V. Ya. S H I Y A P I N T O K H , Vysokomol. soyed. A16: 1820, 1974 (Translated m Polymer Sci. U.S.S.R. 16:
8, 2106, 1974) 14. V. I. GOL'DENBERG, K a n d l d a t s k a y a dissertatsiya (Post-Graduate Thesis), Moscow, I K h F , U.S.S.R. Academy of Sciences, 1972 15. A. L. MARGOLIN, I. A. KABANOVA, L. M. POSTNIKOV and V. Ya. SHLYAPINTOKH, Vysokomol. soyed. A18: 1094, 1976 (Translated m Polymer Sci. U.S.S.R. 18: 5, 1258, 1976) 16. L. V. SAMSONOVA, V. Ya. SHLYAPINTOKH, G. A. NIKIFOROV and V. V. YERSHOV, Mitt. Chem. Forehungs. Wltt. esters 28: 75, 1974 17. V. M. ANISIMOV and O. N. KARPUKHIN, Izv. AN SSSR, ser. khim., 1914, 1973 18. V. M. ANISIMOV, O. N. KARPUKHIN and A. M. MATTUCCI, Dokl. AN SSSR 214: 828, 1974 19. S. PARKER, Fotolyummestsentsiya rastvorov (Photoluminescvnee of Solutions) Izd. "Mir", 1972 20. Yc. M. BYSTRITSKAYA, T. S. KARPOVICH and (). N. KARPUKHIN, Dokl. AN SSSR 228: 632, 1976 21. O. N. KARPUKHIN, Doktorskaya dissertatsiya (Doctor's Thesm). Moscow, I K h F , A_NI SSSR, 1974 22. T. V. POKHOLOK, N. L ZAITSEVA, G. B. PARIISKII and D. Ya. TOPTYGIN, Vysokomol. soyed. A19, 2049, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 9, 2351, 1977)
aPolymer Science U.S.S.R. Vol. 22, pp. 247-254.
003fi-3950/80/0101-0247507.50~
PergamonPress Ltd. 1980.Printedin Poland
ASSOCIATION AND DISSOCIATION PROCESSES IN SOLUTIONS OF NON-STOICHIOMETRIC POLYELECTROLYTE COMPLEXES* O . A. KHAREN~O, V. A. ~[ZU1KRUDOV, A. V. KHAREI~KO, V. A. KASAIKIN,
A. B. ZEZI~ and V. A. KABA~OV M. V. Lomonosov State University, Moscow
(Received 23 November 1978) A study was made of association and dissociation processes in solutions of n o n . ~toichiometric water soluble poly-complexes. I t was shown that the formation of ~ssociated particles m solutions of these poly-complexes is a general feature of these macromolecular compounds, which is independent of the type of polyelectrolyte contained in the poly-complex m excess. Association of particles of non-stoichlometric ])ely-complexes is due to intermolecular segregation of hydrophobic umts consisting ,of double sequences of pairs of polyelectrolyte umts forlmng salt bonds. The degree of ~ssoclation of non-stmchiometrm poly-complexes is first of all determined b y the ratio of hydrophobic and hydrophllic sequences of iomzed polyelectrolyte groups cont a m e d m excess in the poly-complex, which do not form salt bonds (units) and secondly; b y the state of hydrophilic units determined b y interaction of ionized groups cont a i n e d in excess in the poly-complex with low molecular weight counterious. * Vysokomol. soyed. A22: No. 1, 218-224, 1980.