- Email: [email protected]
Photo- and radiation-chemical charge-transfer chain reactions in Poly-N-Vinylcarbazol films
2106
O . V . KOLNINOV et al.
6. L. M. YARYSHEVA, N. B. GAL'PERINA, O. V. ARZHAKOVA, A.L. VOLYNSKII and N.F. BAKEYEV, Vysokomol. soyed. B31: 3,211, 1989 (not translated in Polymer Sci. U.S.S.R.). 7. E . J . KRAMER, Advances in Polymer Sci. 52/53: 2, 1983. 8. C. B. BUCKNELL, Udarprochnyye plastiki (Impact-Resistant Plastics). Leningrad, pp. 327 (Russian translation), 1981. 9. V. V. BONDAREV, Dissertation presented for the degree of candidate of Chemical Sciences. Moscow, MGU, 1983. 10. A. L. VOLYNSKII, Ye. M. UKOLOVA, L. M. YARYSHEVA, P.V. KOZLOV and N. F. BAKEYEV, Vysokomol. soyed. B30: 11,859, 1988 (not translated in Polymer Sci. U.S.S.R.). 11. O. V. ARZHAKOVA, L. M. YARYSHEVA, N. B. GAL'PERINA, A. L. VOLYNSKII and N. F. BAKEYEV, Vysokomoi. soyed. B31: 12,887, 1989 (not translated in Polymer Sci. U.S.S.R.). 12. It. R. BROWN and N. G. NJOKI, J. Polymer Sci. Polymer Phys. Ed. 24: 1, 11, 1986. 13. Ye. A. SHMATOK, O. V. KOZLOVA, L. M. YARYSHEVA, A. L. VOLYNSKII and N. F. BAKEYEV, Dokl. AN SSSR. 302: 6, 1428, 1989. 14. A. L. VOLYNSKII, Ye. M. UKOLOVA, Ye. A. SHMATOK, O. V. ARZHAKOVA, L. M. YARYSItEVA, G. M. LUKOVKIN and N. F. BAKEYEV, Dokl. AN SSSR, 310: 2, 380, 1990.
PolymerScience U.S.S.R. Vol. 32, No. 10, pp. 2106-2112, 1990
Printed in GreatBritain.
0032-3950/90$10.00+ .00 © 1991PergamonPressplc
PHOTO- AND RADIATION-CHEMICAL CHARGE-TRANSFER CHAIN REACTIONS IN POLY-N-VINYLCARBAZOL FILMS* O . V. KOLNINOV, V. V. KOLESNIKOVA, T. A . KRASAVINA a n d V. K. MILINCHUK Branch of L. Ya. Karpov Physico-ChemicaiResearch Institute (Received 29 September 1989)
The kinetics and mechanism of the photo- and radiation-initiated redox reaction in N-vinylcarbazol films during chemical development of iodine in solution were studied by EPR and spectrophotometric methods. The reaction is of chain type, and it proceeds by two-electron oxidation with the participation of carbazol radicals. The kinetic chain length of the reaction in the system with CHI3 and photoinitiation is ~103, with radiation-initiation it is ~ 10 2, while in poly-N-vinylcarbazolewithout additive and with radiation-initiation it is 430. WE HAVE developed a photographic process based on carbazole-containing polymers and iodoform, with chemical d e v e l o p m e n t of iodine in solution, producing images with gradation of optical density and relief depth [1, 2]. In reference [3], the photochemical oxidation of poly-N-vinylcarbazole (PVK) was studied in films containing CHI3 and CBr4 as electron-accepting additives. The aim of the present work was a study of the kinetics and mechanism of the redox reaction in P V K films, initiated by light or 3,-irradiation, during chemical development. P V K films 5 - 4 0 / z m thick, including the CHI3 additive, were prepared by evaporating a solution in dichloroethane or toluene on a lavsan support. P V K "Lyuvikan M-170", of M, 7 = 5 x 105, was *Vysokomol. soyed. A32: No. 10, 2192-2197, 1990.
Photo- and radiation-chemical charge-transfer chain reactions
2107
used. The films were irradiated with light from the source DKsEI-1000, through the monochromator MDR-3, with an intensity of 1015-1016 quant/cm 2 s, and also with y-radiation from a 6°Co source by doses of (0.4-3) × 105 Gr, at absorbed dose intensity of 4 Gr/s. Irradiation was carried out in vacuum and in air, at 77 and 300 K. After irradiation the samples were developed in a CC14 solution of 12, with a concentration of 0.3 mol/l, for 10 s at 330 K. Absorption spectra were measured with the spectrophotometer SP-700. The effect of the concentration of the reacting products--of initial PVK, 12 in solution and of the intermediate carbazole PVK macroradicai, on the course of the reaction was investigated. The rate of the developing reaction was expressed as the concentration increment of the oxidized form of the polymer, PVK22+, in unit time, as determined from the optical density at 15000cm -1. The concentration of PVK in the films was varied by including in the sample a copolymer composed of 35% acrylonitrile and 65% styrene (SAN) (M,~ = 2 x 105). EPR spectra were recorded at 77 K with the radiospectrometer type RE-1306. The concentration of paramagnetic centres was determined by the conventional method with the standard CuCI2 x 2H20. Previously [3] it was shown that PVK forms with halogenomethanes, particularly with CHi3, weak charge-transfer complexes (CTC) which act as photosensitivity centres. Under the action of light, the CTC undergo photodissociation leading to the formation of carbazol macroradicals PVK ° , with a quantum yield q~-3 x 10 -4, and of 12 with ~o-0.1. By interacting with 12, the PVK macroradicals initiate a chain reaction of polymer crosslinking, by way of cation-radical dimerization through the 3,6-positions of the carbazol groups, generating in the crosslink positions the highly conjugated dication PVK22+, absorbing at 15 000 cm -~. In solid films, however, this reaction is limited by the diffusion of molecules and halogen atoms. Therefore it proceeds slowly, in the course of several hours, with a small chain length of - 3 0 . The kinetic curves of the concentration changes of the dication PVK22+ (curves 1,3) and of the macroradicals PVK ° (curves 2, 4) in the PVK film with CHI3 after illumination with light in the absorption range of the CTC, and after y-irradiation at 300 K are shown in Fig. 1. Curve 1 shows that the rapid initial concentration growth of PVK22+ is followed by a longer period of slower growth. Curve 2 represents the corresponding decay of the concentration of PVK" macroradicals. The kinetic curves of the loss of PVK" macroradicals at 300 K practically coincide for illuminated and y-irradiated samples (Fig. 1, curves 2 and 4). In both cases the final reaction product is the PVK22+ dication; its accumulation curves are also very similar (curves 1 and 3). For the y-irradiated PVK films without CHI3, the EPR spectrum at 300 K is also mainly determined by carbazolyl macroradicals. However, the kinetics of their concentration change is different, with a slower rate of radical decay (curve 5). Moreover, in absence of CHI3, in y-irradiated samples the oxidized form PVK22+ is not formed, while optical adsorption appears in the range, 28,000-20,000cm-~; according to the data of reference [4], this corresponds to the products of PVK oxidation with molecular oxygen (Fig. 2, curve 2). Thus it appears that the carbazolyl macroradicals, stabilized by delocalization of the unpaired electron, interact more readily with I2--the product of photo- or radiation-chemical decomposition of CHI3, than with 02. The quantum yield of PVK oxidation in the presence of CHI3 is equal to 0.01. During development of the photoirradiated PVK film containing CHI3 in a solution of I2, the original optical density at 15,000 cm-l increases 100 fold, and accordingly the overall yield of the redox reaction increases to unity. It is assumed that in the development process, the unreacted long-lasting carbazolyl macroradicals in photoirradiated samples initiate a chain reaction, interacting with iodine which diffuses from the solution into the swelling polymer layer. The kinetics of the dark amplifying reaction was studied in dependence on the concentration of the reacting PVK, 12 and PVK ° components. The change in the reaction rate in dependence on PVK concentration in
2108
O . V . KOLNINOVet al. [R]/tR o] B
LO~Z 5
c~
O,q
0
a,z 2 I
20
I ~ 25
I
I
ao Time, roin FIG. 1
"t-,
2O
I x 15 1~. /if-3
CM-f
FIG. 2
Fro. 1. Kinetic curves of concentration change of PVK2 2+ (1,3) and of the relative concentration of PVK" (2,4) at 300 K in PVK film with CHI3 (1 kmol/m 3) after irradiation with light through the filter C3C21 for 15 min at 300 K (1,2), and after y-irradiation with a dose of 7 x 104 Gr at 300 K (3,4), and also of PVK ° in PVK film without additive, y-irradiated with a dose of 7 x 104 Gr at 300 K (5). Fio. 2.
Absorption spectra of PVK film without additive (1), after y-irradiation with a dose of 2 x 105 Gr at 300 K (2) and development in a solution of 12 in CC!4 (3).
films with the same content of CHI3 is shown in Fig. 3. The reaction kinetics corresponds to first order with respect to PVK. The dependence of the reaction rate on the concentration (I2] 0.5 in the developing solution is shown in Fig. 4 for two exposures. The obtained straight lines indicate a fractional order of the reaction with respect to 12, equal to 0.5. The same reaction order is also observed with respect to the carbazolyl macroradicals (Fig. 5). The curve representing the dependence of the reaction rate on the concentration of macroradicals becomes straight in the coordinates [PVK22÷ ] and JR] °5. Reaction orders of 0.5 with respect to the reacting components are characteristic for unbranched chain reactions with quadratic chain termination [5]. Therefore the following scheme can be proposed for the chain oxidation of photoirradiated PVK with iodine in the developing solution: Chain initiation ko
PVK" + I2
PVKI + I.
)
(1)
Chain propagation kl
PVK+I
) PVK'+I k2
PVK" +I- + PVK PVK2"+I- + 12
k3
) PVK2" +I-
> PVK22+2I - + I.
(2) (3) (4)
Chain termination I+ I
>
I2.
(5)
The scheme presumes a two-electron oxidation of PVK and dimerization of carbazole groups through 3,6-positions, resulting in polymer linking by reaction (3). This path of PVK oxidation appears as typical of N-substituted carbazole derivatives [6, 7]. The proposed scheme of a chain reaction in quasistationary approximation yields the kinetic equation
P h o t o - a n d r a d i a t i o n - c h e m i c a l c h a r g e - t r a n s f e r chain r e a c t i o n s
2109
[PVK][PVK'][I2] °'5,
d[PVK22+] = kl
dt w h e r e [PVKa 2+ ] is the c o n c e n t r a t i o n of P V K o x i d a t i o n products.
A [PVK2Z+]x 102 krnol/m3 8
/
*
A [PVK 2+Ix 102 kmol/m3 8
6
-
4# z/
Z
I
2
I
~t
#
8,!
Jill',",
[PVK], kmol/m3
n ol/I
FIG. 4
FIG. 3
A [PVI~ ,2+Ix 102, kmollm 3 8
°~
--
°
,-./'/ I
I
I
[Rio,, × 7d- . o-' FzG. 5
FnG. 3. Dependence of the change in the concentration of PVK22÷ on concentration of PVK for a film containing SAN, PVK and CHI3 (0.6 kmol/m3), after irradiation with light of A = 400 nm for 6 min at 300 K, and treatment in the developing solution for 10 s. FIG. 4. Dependence of the change in the concentration of PVK22+ on the concentration of I2 in the developing solution for a PVK film with CHI3 (0.6 kmoi/m3), irradiated with a light of A = 400 nm for 6 (1) and 3 min (2) at 300 K after development for 10 s. Fic. 5. Dependence of the change in the concentration of PVK22+ on the concentration of the radical PVk" for a PVK film with CHI3 (0.6 kmol/m3) after irradiation with light of a = 400 nm at 240 K and treatment in the developing solution for 10 s.
This simplified e q u a t i o n for a r e a c t i o n of o r d e r s 1 a n d 0.5 with respect to the original a n d i n i t i a t i n g c o m p o n e n t s is in good a g r e e m e n t with e x p e r i m e n t a l d a t a , i n d i c a t i n g correctness of the p r o p o s e d s c h e m e , a n d s h o w i n g also that the r e a c t i o n p r e d o m i n a n t l y p r o c e e d s in the kinetic r a n g e ,
2110
O . V . KOLNINOVet al.
at the expense of film swelling in the developing solution. The basic charge transfer reaction (2) in the chain propagation stage appears to be the limiting one. The chain length of --103 was determined from the ratio of the quantum yields of the reaction product PVK22+ and of the macroradicals PVK" in the irradiated sample. The dark redox reduction was observed in 3,-irradiated samples of PVK with CHI3, but in smaller yield. It was found that this reaction can also proceed in 3,-irradiated PVK films without halogen-containing additives, but in such case it only becomes possible in the process of postradiation development in 12 solution. In this case, PVK22+ is formed with a radiation yield of 5 x 10 -2 (Fig. 2, curve 3). Prior to development in 12 solution, the products of PVK radiolysis are oxides (Fig. 2, curve 2). In order to elucidate the mechanism of these radiation-chemical transformations, we have studied the nature of the radical products of PVK radiolysis. The EPR spectrum of poly-N-vinylcarbazole 3,-irradiated at 77 K in air, has the form of a triplet with a splitting of 5 mT, and each component further split into two lines with a separation of 0.9 mT. The splitting of the central triplet component is masked by overlap with a narrow signal, probably caused by radicals formed during separation of H atoms (Fig. 6a). The obtained EPR spectrum is characteristic of many 3,-irradiated aromatic hydrocarbons [8]. The splitting and intensity ratio of the lines of the hyperfine structure indicates assignment to cyclohexadienyl macroradicais, formed by addition of H atoms in position 3 or 6 of the carbazol ring, resulting in substantial change in its ~r-electron structure. By heating of the samples in the temperature range of 100-140 K, the cyclohexadienyl macroradicals are transformed into peroxidic macroradicals, with a characteristic asymmetrical line in their EPR spectrum (Fig. 6b). On further increasing the temperature to 273 K, the peroxidic macroradicals disappear, and only the thermally more stable carbazolyl PVK" radicals remain in the polymer. This type of radicals becomes predominant and determines the structure of the spectrum in the temperature range 273-300 K (Fig. 6c,d). A spectrum with the same structure was observed for the radical PVK" in references [9, 10], with the constants aH~l = 3.8mT, all/32 = 0.9 mT, art~3 = 4.1 mT and art~4 = 1.3 mT. The EPR spectrum of poly-N-vinylcarbazole 3'-irradiated at 77 K is the same as that irradiated in air (Fig. 6a). Differences become apparent during heating of the irradiated sample. In vacuum the cyclohexadienyl macroradicals decay considerably less rapidly than in air with the participation of oxygen. Therefore in the evacuated sample heated to 300 K both carbazolyl, and cyclohexadienyl macroradicals are present (Fig. 6e). The EPR spectrum of poly-N-vinylcarbazol 3,-irradiated at 300 K in air is shown in Fig. 6f. On the basis of its structure, this spectrum can be assigned to carbazolyl macroradicals. From the analysis of EPR spectra it therefore follows that the intermediates of PVK radiolysis are carbazolyl (I) and cyclohexadienyl (II) macroradicals, of the following structure H
OcO
N 1 ~H~C--C'--CH~
I
OsO<
N I ~H2C--C--CH~ f H II
The short-lived cyclohexadienyl radicals are oxidized by oxygen and form oxides. The carbazolyl radicals, as the most stable ones, take part in the initiation of the chain reaction of PVK oxidation in iodine solution according to the above proposed scheme. The length of this reaction chain in 3,-irradiated films was determined to be ~30 for PVK, and ~100 for PVK with CHI 3. The
Photo- and radiation-chemical charge-transfer chain reactions
j 9
2111
(c)
rr-
/
f 5mT
J
S
FI~. 6. EPR spectrum of poly-N-vinylcarbazole3,-irradiated with a dose of 7 x 104 Gr at 77 K in air or in vacuum (a), after heating in air to 140 (b), 273 (c) and 300 K (d), after heating in vacuum to 300 K (e), and of PVK y-irradiated with a dose of 7 x 104 Gr at 300 K in air (f).
shortening of the chain of the radiation-initiated chain reaction in comparison to the photoinitiated one can be explained by the appearance of a new effective termination path due to the formation of the oxidation products of cyclohexadienyl radicals. Radiation induced perturbations of the electronic structure of the heterocycles in these products should prevent the two-electron oxidation of P V K by reactions (3) and (4). Therefore the damaged heterocycles should be regarded as the loci of chain termination. Thus at irradiation with a dose of 10 Mrad, the concentration of such defects amounts to 2 x 1 0 1 8 g -1. The length of the chain can be determined as a quantity inversely proportional to the probability of chain termination [5]. In this case it reaches the limiting value of --500, in a g r e e m e n t with experimental data. Thus the photo- and radiation-chemical reactions of P V K oxidation with iodine proceed by a chain mechanism with the participation of carbazolyl macroradicals and with the transfer of two electrons. The effectiveness of these reactions depends on the type of radiation. With 3,-radiolysis, the chain reaction involves relatively short chains and the formation of cyclohexadienyl macroradicals. By illumination with light in the range of C T C absorption, the cyclohexadienyl radicals are not formed; consequently the rate of chain termination is smaller and the reaction chain length increases to 103 .
Translated by D. DOSKO(:ILOVA REFERENCES 1. O. V. KOLNINOV, V. K. MILINCHUK, V. V. KOLESNIKOVA and N.I. OSIPOVA, A.c.729544 U.S.S.R.; B.I. No. 15, 1980. 2. O . V . KOLNINOV, V. V. KOLESNIKOVA, V. K. MILINCHUK, N. D. SIZOVA and N. S. BORODKINA, Zhurn. nauch, i prikl, foto- i kinematografii No. 5, p. 345, 1986. 3. O. V. KOLNINOV, V. V. KOLESNIKOVA and V. K. MILINCHUK, Vysokomol. soyed. A32: 3,473, 1990 (translated in Polymer Sci. U.S.S.R. 32: 3,413, 1990). 4. A. ITAYA, K. OKAMOTO and S. KUSABAYASHI, Bull. Chem. Soc. Japan 52: 2218, 1979.
2112
O . A . SHMELEVA and V. P. MILESHKEVICH
5. N. M. EMANUEL' and D. G. KNORRE, Kurs khimicheskoi kinetiki (Textbook of chemical kinetics). Moscow, p. 369, 1984. 6. J. E. AMBROSE, L. L. CARPENTER and R. F. NELSON, J. Electrochem. Soc. 122: 876, 1975. 7. J. E. AMBROSE and R. F. NELSON, J. Electrochem. Soc. 115: 1159, 1968. 8. S. Ya. PSHEZHETSKII, A. G. KOTOV, V. K. MILINCHUK, V. A. ROGINSKII and V. I. TUPIKOV, EPR svobodnykh radikaiov v radiotsionnoi khimii (EPR of free radicals in radiation chemistry). Moscow, p. 184, 1972. 9. J. TINO, F. SZOCZ and Z. HLOUSKOVA, Polymer 23: 1443, 1982. 10. Z. HLOUSKOVA and F. SZOCZ, Makromolek. Chem. B187: 157, 1968.
PolymerScience U.S.S.R. Vol.32, No. 10, pp. 2112-2117, 1990
Printed in GreatBritain.
0032-3950/90$10.00+ .00 © 1991PergamonPressplc
STUDY OF THE EQUILIBRIUM COPOLYMERIZATION OF DIMETHYL- AND METHYL(3,3,3-TRIFLUOROPROPYL)CYCLOSILOXANES* O . A . SHMELEVA a n d V. P. MILESHKEVICH S. V. Lebedev All-Union Research Institute of Synthetic Rubber (Received 29 September 1989)
By the methods of PMR spectroscopy and GLC, the changes in the composition and microstructure of the copolymers, as well as the composition and yield of cyclosiloxanes were studied in the course of the equilibrium anionic copolymerization of 1,3,5-trimethyl-l,3,5-tris-(3,3,3-trifluoropropyl)cyclotrisiloxane (F3) with dimethylcyclosiloxanes.It was shown that even after the equilibrium yield of the copolymer has been reached, its microstructure and composition of rings continue to change. As the polymerization of F3 in the given medium is considerably more rapid than the homopolymerization, the assumption is presented that the dimethylcyclosiloxanesplay a promoting role. ONE OF THE methods of preparing copolymeric polymethyl(3,3,3-trifluoropropyl)dimethylsiloxanes is the equilibrium copolymerization of cyclosiloxanes F3 with dimethylcyclosiloxanes (Dn). In references [1, 2], the cyclosiloxanes formed in the process of rearrangement were studied, their n u m b e r attaining 18. A t equal molar content of F and D units in the copolymer, its equilibrium yield amounts to about 80%, while the equilibrium yield of the h o m o p o l y m e r s D , and Fn amounts to 85 and 10%, respectively; the h o m o p o l y m e r Fn is formed in quantitative yield by non-equilibrium polymerization of F3 which, similarly as other cyclotrisiloxanes, is a strained ring. The kinetics of the equilibrium F-D-copolymerization process has not been previously investigated. We have studied the copolymerization of F3 with a mixture of dimethylcyclosiloxanes in the composition D4:Ds:D 6 = 90:20:2 (by mass) in the presence of 0.01 w t % of potassium polymethyl-tris-(3,3,3trifluoropropyl)siloxandiolate (PSDK) at 140°C in bulk. *Vysokomol. soyed. A32: No. 10, 2198-2202, 1990.
O . V . KOLNINOV et al.
6. L. M. YARYSHEVA, N. B. GAL'PERINA, O. V. ARZHAKOVA, A.L. VOLYNSKII and N.F. BAKEYEV, Vysokomol. soyed. B31: 3,211, 1989 (not translated in Polymer Sci. U.S.S.R.). 7. E . J . KRAMER, Advances in Polymer Sci. 52/53: 2, 1983. 8. C. B. BUCKNELL, Udarprochnyye plastiki (Impact-Resistant Plastics). Leningrad, pp. 327 (Russian translation), 1981. 9. V. V. BONDAREV, Dissertation presented for the degree of candidate of Chemical Sciences. Moscow, MGU, 1983. 10. A. L. VOLYNSKII, Ye. M. UKOLOVA, L. M. YARYSHEVA, P.V. KOZLOV and N. F. BAKEYEV, Vysokomol. soyed. B30: 11,859, 1988 (not translated in Polymer Sci. U.S.S.R.). 11. O. V. ARZHAKOVA, L. M. YARYSHEVA, N. B. GAL'PERINA, A. L. VOLYNSKII and N. F. BAKEYEV, Vysokomoi. soyed. B31: 12,887, 1989 (not translated in Polymer Sci. U.S.S.R.). 12. It. R. BROWN and N. G. NJOKI, J. Polymer Sci. Polymer Phys. Ed. 24: 1, 11, 1986. 13. Ye. A. SHMATOK, O. V. KOZLOVA, L. M. YARYSHEVA, A. L. VOLYNSKII and N. F. BAKEYEV, Dokl. AN SSSR. 302: 6, 1428, 1989. 14. A. L. VOLYNSKII, Ye. M. UKOLOVA, Ye. A. SHMATOK, O. V. ARZHAKOVA, L. M. YARYSItEVA, G. M. LUKOVKIN and N. F. BAKEYEV, Dokl. AN SSSR, 310: 2, 380, 1990.
PolymerScience U.S.S.R. Vol. 32, No. 10, pp. 2106-2112, 1990
Printed in GreatBritain.
0032-3950/90$10.00+ .00 © 1991PergamonPressplc
PHOTO- AND RADIATION-CHEMICAL CHARGE-TRANSFER CHAIN REACTIONS IN POLY-N-VINYLCARBAZOL FILMS* O . V. KOLNINOV, V. V. KOLESNIKOVA, T. A . KRASAVINA a n d V. K. MILINCHUK Branch of L. Ya. Karpov Physico-ChemicaiResearch Institute (Received 29 September 1989)
The kinetics and mechanism of the photo- and radiation-initiated redox reaction in N-vinylcarbazol films during chemical development of iodine in solution were studied by EPR and spectrophotometric methods. The reaction is of chain type, and it proceeds by two-electron oxidation with the participation of carbazol radicals. The kinetic chain length of the reaction in the system with CHI3 and photoinitiation is ~103, with radiation-initiation it is ~ 10 2, while in poly-N-vinylcarbazolewithout additive and with radiation-initiation it is 430. WE HAVE developed a photographic process based on carbazole-containing polymers and iodoform, with chemical d e v e l o p m e n t of iodine in solution, producing images with gradation of optical density and relief depth [1, 2]. In reference [3], the photochemical oxidation of poly-N-vinylcarbazole (PVK) was studied in films containing CHI3 and CBr4 as electron-accepting additives. The aim of the present work was a study of the kinetics and mechanism of the redox reaction in P V K films, initiated by light or 3,-irradiation, during chemical development. P V K films 5 - 4 0 / z m thick, including the CHI3 additive, were prepared by evaporating a solution in dichloroethane or toluene on a lavsan support. P V K "Lyuvikan M-170", of M, 7 = 5 x 105, was *Vysokomol. soyed. A32: No. 10, 2192-2197, 1990.
Photo- and radiation-chemical charge-transfer chain reactions
2107
used. The films were irradiated with light from the source DKsEI-1000, through the monochromator MDR-3, with an intensity of 1015-1016 quant/cm 2 s, and also with y-radiation from a 6°Co source by doses of (0.4-3) × 105 Gr, at absorbed dose intensity of 4 Gr/s. Irradiation was carried out in vacuum and in air, at 77 and 300 K. After irradiation the samples were developed in a CC14 solution of 12, with a concentration of 0.3 mol/l, for 10 s at 330 K. Absorption spectra were measured with the spectrophotometer SP-700. The effect of the concentration of the reacting products--of initial PVK, 12 in solution and of the intermediate carbazole PVK macroradicai, on the course of the reaction was investigated. The rate of the developing reaction was expressed as the concentration increment of the oxidized form of the polymer, PVK22+, in unit time, as determined from the optical density at 15000cm -1. The concentration of PVK in the films was varied by including in the sample a copolymer composed of 35% acrylonitrile and 65% styrene (SAN) (M,~ = 2 x 105). EPR spectra were recorded at 77 K with the radiospectrometer type RE-1306. The concentration of paramagnetic centres was determined by the conventional method with the standard CuCI2 x 2H20. Previously [3] it was shown that PVK forms with halogenomethanes, particularly with CHi3, weak charge-transfer complexes (CTC) which act as photosensitivity centres. Under the action of light, the CTC undergo photodissociation leading to the formation of carbazol macroradicals PVK ° , with a quantum yield q~-3 x 10 -4, and of 12 with ~o-0.1. By interacting with 12, the PVK macroradicals initiate a chain reaction of polymer crosslinking, by way of cation-radical dimerization through the 3,6-positions of the carbazol groups, generating in the crosslink positions the highly conjugated dication PVK22+, absorbing at 15 000 cm -~. In solid films, however, this reaction is limited by the diffusion of molecules and halogen atoms. Therefore it proceeds slowly, in the course of several hours, with a small chain length of - 3 0 . The kinetic curves of the concentration changes of the dication PVK22+ (curves 1,3) and of the macroradicals PVK ° (curves 2, 4) in the PVK film with CHI3 after illumination with light in the absorption range of the CTC, and after y-irradiation at 300 K are shown in Fig. 1. Curve 1 shows that the rapid initial concentration growth of PVK22+ is followed by a longer period of slower growth. Curve 2 represents the corresponding decay of the concentration of PVK" macroradicals. The kinetic curves of the loss of PVK" macroradicals at 300 K practically coincide for illuminated and y-irradiated samples (Fig. 1, curves 2 and 4). In both cases the final reaction product is the PVK22+ dication; its accumulation curves are also very similar (curves 1 and 3). For the y-irradiated PVK films without CHI3, the EPR spectrum at 300 K is also mainly determined by carbazolyl macroradicals. However, the kinetics of their concentration change is different, with a slower rate of radical decay (curve 5). Moreover, in absence of CHI3, in y-irradiated samples the oxidized form PVK22+ is not formed, while optical adsorption appears in the range, 28,000-20,000cm-~; according to the data of reference [4], this corresponds to the products of PVK oxidation with molecular oxygen (Fig. 2, curve 2). Thus it appears that the carbazolyl macroradicals, stabilized by delocalization of the unpaired electron, interact more readily with I2--the product of photo- or radiation-chemical decomposition of CHI3, than with 02. The quantum yield of PVK oxidation in the presence of CHI3 is equal to 0.01. During development of the photoirradiated PVK film containing CHI3 in a solution of I2, the original optical density at 15,000 cm-l increases 100 fold, and accordingly the overall yield of the redox reaction increases to unity. It is assumed that in the development process, the unreacted long-lasting carbazolyl macroradicals in photoirradiated samples initiate a chain reaction, interacting with iodine which diffuses from the solution into the swelling polymer layer. The kinetics of the dark amplifying reaction was studied in dependence on the concentration of the reacting PVK, 12 and PVK ° components. The change in the reaction rate in dependence on PVK concentration in
2108
O . V . KOLNINOVet al. [R]/tR o] B
LO~Z 5
c~
O,q
0
a,z 2 I
20
I ~ 25
I
I
ao Time, roin FIG. 1
"t-,
2O
I x 15 1~. /if-3
CM-f
FIG. 2
Fro. 1. Kinetic curves of concentration change of PVK2 2+ (1,3) and of the relative concentration of PVK" (2,4) at 300 K in PVK film with CHI3 (1 kmol/m 3) after irradiation with light through the filter C3C21 for 15 min at 300 K (1,2), and after y-irradiation with a dose of 7 x 104 Gr at 300 K (3,4), and also of PVK ° in PVK film without additive, y-irradiated with a dose of 7 x 104 Gr at 300 K (5). Fio. 2.
Absorption spectra of PVK film without additive (1), after y-irradiation with a dose of 2 x 105 Gr at 300 K (2) and development in a solution of 12 in CC!4 (3).
films with the same content of CHI3 is shown in Fig. 3. The reaction kinetics corresponds to first order with respect to PVK. The dependence of the reaction rate on the concentration (I2] 0.5 in the developing solution is shown in Fig. 4 for two exposures. The obtained straight lines indicate a fractional order of the reaction with respect to 12, equal to 0.5. The same reaction order is also observed with respect to the carbazolyl macroradicals (Fig. 5). The curve representing the dependence of the reaction rate on the concentration of macroradicals becomes straight in the coordinates [PVK22÷ ] and JR] °5. Reaction orders of 0.5 with respect to the reacting components are characteristic for unbranched chain reactions with quadratic chain termination [5]. Therefore the following scheme can be proposed for the chain oxidation of photoirradiated PVK with iodine in the developing solution: Chain initiation ko
PVK" + I2
PVKI + I.
)
(1)
Chain propagation kl
PVK+I
) PVK'+I k2
PVK" +I- + PVK PVK2"+I- + 12
k3
) PVK2" +I-
> PVK22+2I - + I.
(2) (3) (4)
Chain termination I+ I
>
I2.
(5)
The scheme presumes a two-electron oxidation of PVK and dimerization of carbazole groups through 3,6-positions, resulting in polymer linking by reaction (3). This path of PVK oxidation appears as typical of N-substituted carbazole derivatives [6, 7]. The proposed scheme of a chain reaction in quasistationary approximation yields the kinetic equation
P h o t o - a n d r a d i a t i o n - c h e m i c a l c h a r g e - t r a n s f e r chain r e a c t i o n s
2109
[PVK][PVK'][I2] °'5,
d[PVK22+] = kl
dt w h e r e [PVKa 2+ ] is the c o n c e n t r a t i o n of P V K o x i d a t i o n products.
A [PVK2Z+]x 102 krnol/m3 8
/
*
A [PVK 2+Ix 102 kmol/m3 8
6
-
4# z/
Z
I
2
I
~t
#
8,!
Jill',",
[PVK], kmol/m3
n ol/I
FIG. 4
FIG. 3
A [PVI~ ,2+Ix 102, kmollm 3 8
°~
--
°
,-./'/ I
I
I
[Rio,, × 7d- . o-' FzG. 5
FnG. 3. Dependence of the change in the concentration of PVK22÷ on concentration of PVK for a film containing SAN, PVK and CHI3 (0.6 kmol/m3), after irradiation with light of A = 400 nm for 6 min at 300 K, and treatment in the developing solution for 10 s. FIG. 4. Dependence of the change in the concentration of PVK22+ on the concentration of I2 in the developing solution for a PVK film with CHI3 (0.6 kmoi/m3), irradiated with a light of A = 400 nm for 6 (1) and 3 min (2) at 300 K after development for 10 s. Fic. 5. Dependence of the change in the concentration of PVK22+ on the concentration of the radical PVk" for a PVK film with CHI3 (0.6 kmol/m3) after irradiation with light of a = 400 nm at 240 K and treatment in the developing solution for 10 s.
This simplified e q u a t i o n for a r e a c t i o n of o r d e r s 1 a n d 0.5 with respect to the original a n d i n i t i a t i n g c o m p o n e n t s is in good a g r e e m e n t with e x p e r i m e n t a l d a t a , i n d i c a t i n g correctness of the p r o p o s e d s c h e m e , a n d s h o w i n g also that the r e a c t i o n p r e d o m i n a n t l y p r o c e e d s in the kinetic r a n g e ,
2110
O . V . KOLNINOVet al.
at the expense of film swelling in the developing solution. The basic charge transfer reaction (2) in the chain propagation stage appears to be the limiting one. The chain length of --103 was determined from the ratio of the quantum yields of the reaction product PVK22+ and of the macroradicals PVK" in the irradiated sample. The dark redox reduction was observed in 3,-irradiated samples of PVK with CHI3, but in smaller yield. It was found that this reaction can also proceed in 3,-irradiated PVK films without halogen-containing additives, but in such case it only becomes possible in the process of postradiation development in 12 solution. In this case, PVK22+ is formed with a radiation yield of 5 x 10 -2 (Fig. 2, curve 3). Prior to development in 12 solution, the products of PVK radiolysis are oxides (Fig. 2, curve 2). In order to elucidate the mechanism of these radiation-chemical transformations, we have studied the nature of the radical products of PVK radiolysis. The EPR spectrum of poly-N-vinylcarbazole 3,-irradiated at 77 K in air, has the form of a triplet with a splitting of 5 mT, and each component further split into two lines with a separation of 0.9 mT. The splitting of the central triplet component is masked by overlap with a narrow signal, probably caused by radicals formed during separation of H atoms (Fig. 6a). The obtained EPR spectrum is characteristic of many 3,-irradiated aromatic hydrocarbons [8]. The splitting and intensity ratio of the lines of the hyperfine structure indicates assignment to cyclohexadienyl macroradicais, formed by addition of H atoms in position 3 or 6 of the carbazol ring, resulting in substantial change in its ~r-electron structure. By heating of the samples in the temperature range of 100-140 K, the cyclohexadienyl macroradicals are transformed into peroxidic macroradicals, with a characteristic asymmetrical line in their EPR spectrum (Fig. 6b). On further increasing the temperature to 273 K, the peroxidic macroradicals disappear, and only the thermally more stable carbazolyl PVK" radicals remain in the polymer. This type of radicals becomes predominant and determines the structure of the spectrum in the temperature range 273-300 K (Fig. 6c,d). A spectrum with the same structure was observed for the radical PVK" in references [9, 10], with the constants aH~l = 3.8mT, all/32 = 0.9 mT, art~3 = 4.1 mT and art~4 = 1.3 mT. The EPR spectrum of poly-N-vinylcarbazole 3'-irradiated at 77 K is the same as that irradiated in air (Fig. 6a). Differences become apparent during heating of the irradiated sample. In vacuum the cyclohexadienyl macroradicals decay considerably less rapidly than in air with the participation of oxygen. Therefore in the evacuated sample heated to 300 K both carbazolyl, and cyclohexadienyl macroradicals are present (Fig. 6e). The EPR spectrum of poly-N-vinylcarbazol 3,-irradiated at 300 K in air is shown in Fig. 6f. On the basis of its structure, this spectrum can be assigned to carbazolyl macroradicals. From the analysis of EPR spectra it therefore follows that the intermediates of PVK radiolysis are carbazolyl (I) and cyclohexadienyl (II) macroradicals, of the following structure H
OcO
N 1 ~H~C--C'--CH~
I
OsO<
N I ~H2C--C--CH~ f H II
The short-lived cyclohexadienyl radicals are oxidized by oxygen and form oxides. The carbazolyl radicals, as the most stable ones, take part in the initiation of the chain reaction of PVK oxidation in iodine solution according to the above proposed scheme. The length of this reaction chain in 3,-irradiated films was determined to be ~30 for PVK, and ~100 for PVK with CHI 3. The
Photo- and radiation-chemical charge-transfer chain reactions
j 9
2111
(c)
rr-
/
f 5mT
J
S
FI~. 6. EPR spectrum of poly-N-vinylcarbazole3,-irradiated with a dose of 7 x 104 Gr at 77 K in air or in vacuum (a), after heating in air to 140 (b), 273 (c) and 300 K (d), after heating in vacuum to 300 K (e), and of PVK y-irradiated with a dose of 7 x 104 Gr at 300 K in air (f).
shortening of the chain of the radiation-initiated chain reaction in comparison to the photoinitiated one can be explained by the appearance of a new effective termination path due to the formation of the oxidation products of cyclohexadienyl radicals. Radiation induced perturbations of the electronic structure of the heterocycles in these products should prevent the two-electron oxidation of P V K by reactions (3) and (4). Therefore the damaged heterocycles should be regarded as the loci of chain termination. Thus at irradiation with a dose of 10 Mrad, the concentration of such defects amounts to 2 x 1 0 1 8 g -1. The length of the chain can be determined as a quantity inversely proportional to the probability of chain termination [5]. In this case it reaches the limiting value of --500, in a g r e e m e n t with experimental data. Thus the photo- and radiation-chemical reactions of P V K oxidation with iodine proceed by a chain mechanism with the participation of carbazolyl macroradicals and with the transfer of two electrons. The effectiveness of these reactions depends on the type of radiation. With 3,-radiolysis, the chain reaction involves relatively short chains and the formation of cyclohexadienyl macroradicals. By illumination with light in the range of C T C absorption, the cyclohexadienyl radicals are not formed; consequently the rate of chain termination is smaller and the reaction chain length increases to 103 .
Translated by D. DOSKO(:ILOVA REFERENCES 1. O. V. KOLNINOV, V. K. MILINCHUK, V. V. KOLESNIKOVA and N.I. OSIPOVA, A.c.729544 U.S.S.R.; B.I. No. 15, 1980. 2. O . V . KOLNINOV, V. V. KOLESNIKOVA, V. K. MILINCHUK, N. D. SIZOVA and N. S. BORODKINA, Zhurn. nauch, i prikl, foto- i kinematografii No. 5, p. 345, 1986. 3. O. V. KOLNINOV, V. V. KOLESNIKOVA and V. K. MILINCHUK, Vysokomol. soyed. A32: 3,473, 1990 (translated in Polymer Sci. U.S.S.R. 32: 3,413, 1990). 4. A. ITAYA, K. OKAMOTO and S. KUSABAYASHI, Bull. Chem. Soc. Japan 52: 2218, 1979.
2112
O . A . SHMELEVA and V. P. MILESHKEVICH
5. N. M. EMANUEL' and D. G. KNORRE, Kurs khimicheskoi kinetiki (Textbook of chemical kinetics). Moscow, p. 369, 1984. 6. J. E. AMBROSE, L. L. CARPENTER and R. F. NELSON, J. Electrochem. Soc. 122: 876, 1975. 7. J. E. AMBROSE and R. F. NELSON, J. Electrochem. Soc. 115: 1159, 1968. 8. S. Ya. PSHEZHETSKII, A. G. KOTOV, V. K. MILINCHUK, V. A. ROGINSKII and V. I. TUPIKOV, EPR svobodnykh radikaiov v radiotsionnoi khimii (EPR of free radicals in radiation chemistry). Moscow, p. 184, 1972. 9. J. TINO, F. SZOCZ and Z. HLOUSKOVA, Polymer 23: 1443, 1982. 10. Z. HLOUSKOVA and F. SZOCZ, Makromolek. Chem. B187: 157, 1968.
PolymerScience U.S.S.R. Vol.32, No. 10, pp. 2112-2117, 1990
Printed in GreatBritain.
0032-3950/90$10.00+ .00 © 1991PergamonPressplc
STUDY OF THE EQUILIBRIUM COPOLYMERIZATION OF DIMETHYL- AND METHYL(3,3,3-TRIFLUOROPROPYL)CYCLOSILOXANES* O . A . SHMELEVA a n d V. P. MILESHKEVICH S. V. Lebedev All-Union Research Institute of Synthetic Rubber (Received 29 September 1989)
By the methods of PMR spectroscopy and GLC, the changes in the composition and microstructure of the copolymers, as well as the composition and yield of cyclosiloxanes were studied in the course of the equilibrium anionic copolymerization of 1,3,5-trimethyl-l,3,5-tris-(3,3,3-trifluoropropyl)cyclotrisiloxane (F3) with dimethylcyclosiloxanes.It was shown that even after the equilibrium yield of the copolymer has been reached, its microstructure and composition of rings continue to change. As the polymerization of F3 in the given medium is considerably more rapid than the homopolymerization, the assumption is presented that the dimethylcyclosiloxanesplay a promoting role. ONE OF THE methods of preparing copolymeric polymethyl(3,3,3-trifluoropropyl)dimethylsiloxanes is the equilibrium copolymerization of cyclosiloxanes F3 with dimethylcyclosiloxanes (Dn). In references [1, 2], the cyclosiloxanes formed in the process of rearrangement were studied, their n u m b e r attaining 18. A t equal molar content of F and D units in the copolymer, its equilibrium yield amounts to about 80%, while the equilibrium yield of the h o m o p o l y m e r s D , and Fn amounts to 85 and 10%, respectively; the h o m o p o l y m e r Fn is formed in quantitative yield by non-equilibrium polymerization of F3 which, similarly as other cyclotrisiloxanes, is a strained ring. The kinetics of the equilibrium F-D-copolymerization process has not been previously investigated. We have studied the copolymerization of F3 with a mixture of dimethylcyclosiloxanes in the composition D4:Ds:D 6 = 90:20:2 (by mass) in the presence of 0.01 w t % of potassium polymethyl-tris-(3,3,3trifluoropropyl)siloxandiolate (PSDK) at 140°C in bulk. *Vysokomol. soyed. A32: No. 10, 2198-2202, 1990.