- Email: [email protected]
On photochromic transformations of polymers
Photochromic transformations of polymers
453
As may be seen from the data in Table 2, the transformation of a diene macromolecule to a vinyl macromolecule increases the rigidity of the molecular chains, and the relative "unperturbed dimensions" (or parameter a) increase from 1.7 to 2.5-3.0. Moreover, whereas the unperturbed dimensions of the CSKI molecules in the binary systems (polymer-solvent) remain practically identical, in the triple s y s t e m s ( p o l y m e r - b i n a r y m i x t u r e ) t h e u n p e r t u r b e d dimensions d e p e n d to a consid e r a b l e e x t e n t on t h e t y p e o f solvent, a n d this agrees well w i t h p r e s e n t - d a y ideas a b o u t t h e influence of 0-solvents on t h e c o n f o r m a t i o n a n d flexibility o f C S K I molecules in t h e u n p e r t u r b e d s t a t e [8, 9]. T h e M a r k - K u h n - H o u w i n k e q u a t i o n o b t a i n e d for a s t r o n g l y p o l a r m e d i u m ( D C E - m e t h a n o l ) shows t h a t t h e Gaussian s t r u c t u r e of t h e m o l e c u l a r coils is slightly d i s t o r t e d in t h e u n p e r t u r b e d state, i.e. [7] ¢ K0" IT/÷ Translated by R J. A. HENDRY REFERENCES
1. M. T~KEI~A, R. ENDO and Y. MATSUURA, J Polymer Sci. C23: 487, 1969 2. I. Ya. PODDYBNYI and A. V. PODALINSKII, Zavodsk. lab a3: 1398, 1967 3. V. CRES~KENZI and P. FLORY, J. Chem. Soe 86: 141, 1964 4. L. Kh. SIMONYAN, A. V. GEVORKYAN, K. A. TOROSYAN and A. Sh. SAFAROV, Arm. khLmich, zh. 25: No. 9, 1972 5. W. STOKMAYER and M. FIXMAN, J Polymer Sei. CI: 137, 1963 6 P. FLORY, Principles of Polymer Chemistry, N. Y., 1953 7 I. Ya. PODDYBNYI ~Ye. G, ERENBURG and M. A. YEREMINA, Vysokomol. soyed. AIO: 1381, 1968 (Translated in Polymer Scl. U S.S.R. 1O: 6, 1603, 1968) 8. A. DON]DOS and H. BENOIT, Makromolek. Chem 129: 35, 1969 9. A. V. GEVORKYAN, Uspekhl khimu 41: 401, 1972
ON PHOTOCHROMIC TRANSFORMATIONS OF POLYMERS* •.
S KARDASH, V A. KRONGAUZ, YE. L
ZAITSEVA a n d A
V. MOVSHOVICK
L. Ya. Karpov'Physlcal Chemistry Research Institute (Reeewed 19 June 1972)
Novel photochromm polymers were synthesized, namely eopolymers of methyl methacrylate and sp~ropyran monomers, and their phototransformatlons were investigated. The mare kmetm and spectral charactermtlcs of the photochronne systems were determined: the quantum yields of eolouratlon and decolouratlon, the constants of the dark reactions and the coefficients of extraction for the coloured form. I t was found that the chemmal addition of photoehromm groups to the polymer mole* Vysokomol. soyed. A16: No. 2. 390-397, 1974
454
N . S. K ~ D A S H et al.
cule m a solid m e d m m is accompamed b y a marked reduetmn m the q u a n t u m yields of colouratmn of the photochrome compared with the corresponding solutions m methyl methacrylate and m ethyl acetate. ] n ethyl acetate the photochemmal behawour of the copolymers and the corresponding monomers is ldentmal. The conclusmn is reached that m the copolymers the reduced q u a n t u m yields of colouratmn are due to inhibited t u r n i n g of parts of the splropyran molecule relative to one another. The inhibited morton is due both to the high structural vlscomty of the medmm, and to the attachment of one portmn of the photoehrome molecule to the polymer chain.
THE photochromic phenomenon is exhibited by certain types of substances, and involves the reversible appearance of colouration under the action of light. Much study has been made of spiropyrans, and among the groups of photochromic compounds spiropyrans are of the greatest practical importance. Photochromic changes in spiropyran molecules take place through the rupture of C--O bonds and the turning of portions of the molecule relative to one another [1]. The resuiting meroeyanine form of spiropyran has an intense absorption band in the visible region of the spectrum. Reversible ring closure takes place in the dark or under the action of visible light in the region corresponding to the absorption of the meroeyanine form R
R
N/Xo--x]_~/--n [ R R
R
RO-
R
\//-I R
"R
Papers published recently contain information relating to the incorporation of spiropyraus in the composition of polymer molecules. The resultant polymers similarly posses photochromic properties. When spiropyran groups are included in polymer molecules, one would expect changes in the photochromic behaviour of the polymer, and equally in some of their properties which, from a practical standpoint, must influence possible applications of the polymers. Smets and Vandevijer [1-4] investigated copolymers of indolylspiropyran and thiospiran monomers with methyl methacrylate (MMA), styrene and p-vinylnaphthalene. These authors dealt mainly with problems of the polarity of solvents influencing the position of the maximum of the coloured form of the eopo]ymers, and with the kinetics of the dark process of deeolouration. Data in regard to photochemical reactions of the polymers are either scanty of non-existent. The purpose of our investigation was to elucidate phototransformations of copolymers of MMA with indolylspiropyran monomers. The behaviour of polymers containing the chemically incorporated photochromic groups was compared with that of rigid solutions of the corresponding photochromic monomers in PMMA. A further aim was to discover how far the viscosity of the medium is capable of influencing the kinetics of phototrausformation of the eopolymers. To do so we investigated solutions of photochromic copolymers and of the cor-
Photochrormc transformations of polymers
455
responding photochromic monomers in ethyl acetate; the ethyl acetate molecule and the monomer unit of PMMA are structurally similar. In order to characterize the photochromic systems we determined kinetic parameters such as the quantum yields of the colouration and decolouration, the constants of the dark reactions of decolouration, and the coefficients of extinction for the coloured form EXPERIMENTAL
Photochromic polymers were prepared b y eopolymerlzatmn of the sprropyran monomers CHs CHs
CHs CH3
N\^__~-~--NO~
tCH3U~CH~--CH----CH~ I
CH~
CHs
t
1
CH~--OCO--C=CH2 II
with MMA. The copolymenzation process was conducted in ~ m glass ampoules a t 65 ° for 10 hr. Dmltrile of azoisobutyrlc acid (DAA) was used as the polymerization initiator. The resulting copolymers were separated b y five-fold reprecipitatmn from methylene chloride by methanol. Depending on the compomtmn of the rnbrturo used for the polymerizatmn, copolymers containing dLffcrent amounts of photochromic groups were obtained (see Table 1).
T ~ a I ~ 1.
POLYM~
COMPOSITION R E L A T I V E TO CONCENTRATION RATIO :~[MA
Cope lymer
Spmapyran content, mole %
I N ~r~L~ M O N O ~ ' R
8
17
0"22 0.52 0"76
SPIROPYRAN :
t Spiropyran content, ,M X 10 -~
m themltiM in the ralxture eopolymer 3
OF
~x!t'uJ~E
26"3 12-6 26 3
Col}o. lymer
II
.
mole ~oo M× 10-* in the Lmtml m the mixture copolymer 0.7 5 10
0.66
3.7 7
123 141 112.2
The molecular weights of the copolymers, determined viscommetrmally, are included m Table 1. The polymemzatlon was continued up to advanced degrees of conversion, a n d it would therefore be imprachcable m the light of our data to estn~ate the q u a n t i t a h v e rea c t l m t y of the monomers participating m the polymerizahon. However, it m a y be seen from Table 1 that photochromm monomer I enters rote the copolymer compomtion m a ratio much smaller t h a n the ratio of monomer I m the matial mLxture, whde monomer LI la present m the copolymer composition m the same ratio as in the mixture used for the polymerization. Thin means t h a t while the reactiwties of photochromic monomer I I a n d MMA are mmdar, the reactivity of monomer I m much lower than t h a t of MM~i.o
456
N.S. KA~DASHetal.
The hght source was a DRSh-500 lamp provided with glass filters ebmlnatmg the 303-313 nm regmn and 545 nm. The intensity of the incident hght m the UV region was measured by means of a ferryoxalate aetmometer, whde m the UV regmn the intensity of the incident hght was measured with Remmke's salt [5] The SP-700 spectrophotometer ("Unmam") was used for the kmctm and the spectral measurements. All the experiments were earrmd out at room temperature. The kmetms of photochromatm transformatmns were determined from changes m the optmal density at the absorptmn maximum for the coloured form of the sp~ropyran m the vlmble regmn of the spectrum. The kmetms of photochromm transformatmns m solutmn, where dark decolouratmn of the coloured form takes place very rapidly, were recorded directly at the time of the lrrad~atmn, using the "crossed filters" method [6]. Films made from the photochrormc polymers and from rigid solutmns of the splropyrans m PMMA were prepared by slow evaporatmn of the solvent from solutmns of the polymers m methylene chloride. The films had a thmkness of ~ 10/lm. DISCUSSION OF RESULTS
U V irradiation of films of the p h o t o c h r o m i c copolymers leads to t h e appearance of a new a n d intense absorption b a n d in t h e visible region o f t h e s p e c t r u m
(~max--590nm) (Fig. 1). As m a y be seen f r o m Fig. 2, curve 1, the optical d e n s i t y o f t h e coloured f o r m reaches a m a x i m u m a t a certain m o m e n t of t i m e t, and t h e n falls away. W h e n the irradiation is s t o p p e d the optical density of the film colouring remains practically constant, i. e. during the period of t i m e of the e x p e r i m e n t processes o f d a r k decolouration of the coloured form m a y be disregarded. U n d e r t h e action o f visible light the reverse transition to a eolourless f o r m takes place in t h e region o f the a b s o r p t i o n m a x i m u m for the eoloured form. T h e f a c t t h a t t h e optical d e n s i t y of the coloured form, given sufficiently long exposure to U V light, passes t h r o u g h a m a x i m u m , points to irreversible processes taking place and resulting in t h e f o r m a t i o n of side-products, a n d in the a p p e a r a n c e of " f a t i g u e " in the system. As m a y be seen f r o m Fig. 2, the m a x i m u m optmal density of t h e colourat l o n obtainable in the second p h o t o c h r o m i c cycle (colouration b y light w i t h 2 : 3 0 3 - 3 1 3 n m - - d e c o l o u r a t i o n b y light with 2 = 5 4 5 nm) is m u c h lower comp a r e d with the first cycle, while in the t h i r d cycle it is lower t h a n in the second, etc. This m a y be the result of fatigue affecting t h e s y s t e m b o t h during t h e colouration on exposure to U V light, a n d during decolouration b y visible light, a n d similarly as a result of d a r k processes of ageing. P r e l i m m a r y tests showed t h a t t h e r e are practically no d a r k side reactions, 1. e. t h e r e are t h r e e possibilities t h a t have to be t a k e n into account, a n d these are: decomposition of b o t h forms t h r o u g h exposure to U V light, a n d decomposition of the coloured f o r m t h r o u g h exposure to visible light. A general scheme for the p h o t o c h r o m i c t r a n s f o r m a t i o n s o f t h e c o p o l y m e r could therefore be represented as follows: hv
C ~A
~-~ B by'
,~hv'
~E,
F ~vhere A and B are t h e initial a n d coloured forms o f spiropyran; C, E, F, are
Photochromac transformatxons of polymers
457
products of side reactions. These processes may be described by means of the following differential equations: consumption of the initial A form d[A] dt
--I ,.~f (D') e~[B]--I ,Bf (D') e'A[A]--IecI (D') e~[A]
(1)
accumulation of the B form
a[B] dt =IqBf (D') 4[A] --I~0d (D') e~[B]--IqF~(D') e~[B]
(2)
accumulation of fatigue products
a[E]
dt -----I~.f(D') e~[B]
(3)
d~C]=I~cf (D') e~[A],
(4)
where D'=8'A1 [A]+e~I [B]+e~I [C]+e~I [E], l--sample thickness, [A], [B], [C], ' *B, ' e'o and e~--molar coefficients of [E]--coneentrations of the components, eA extinction in the region of irradiation, f (D')= (1--10-D')/D ', /--intensity of the exciting UV light (einstein/1.. sec), assuming complete absorption of light by the actinometer, ~B--quantum yield of the colouration, ,A--quantum yield of the decolouration, , c , ,~.--quantum yields of the fatigue. Initial conditions: when t=0, [A]=[Ao], B = 0 , [C]=0, [E]----0. The process of decolouration by visible light may be expressed by the equation
d [B] dt --11(,.~+ ~) (1-- 10-~"),
(5)
where I i is the intensity of the visible light, ~ , quantum yield of the decolouration under the action of visible light, ~0r, quantum yield of ageing. The set of differential equations (1)--(4) can be solved only in cases where D' is small, or remains constant, during the course of the experiment. In the case under consideration the irradiation was carried out in the 303-313 nm region where, as may be seen from Fig. 1, the spiropyran has an isobestic point, i. e. the optical density remained constant during the irradiation process and f (D')=const. We therefore have a set of linear differential equations containing constant coefficients, and by solving this set of equations expressions for the concentrations of all the components in the course of the reaction are obtained [6]. Given the possibility of determining these concentrations, there will be no difficulty in finding all the kinetic and spectral characteristics for a photochromic system. Actually, however, one can take just the changes in the optical density of the B form in the visible region of the spectrum, as the spectra of both forms of the spiropyran
4~8
No S. KARDASH e$ a~.
and of the products of ageing differ only slightly in the UV region. Bearing in mind t h a t [B]=DB/eB l, where eB is the coefficient of extinction for the coloured form in the visible region of the spectrum, and having recourse to the solution of an analogous set of equations appearing in [6], we obtain lnDB_ t
1 2
If(D') e~.(~x--[--~pB+~C+ ~pE)t-{-ln eBIqBf(D')D'
(6)
The slope of the In (DB/t) vs. t curve gives the sum of the quantum yields qXq-qBq- ~0cq-qE (Fig. 3a). I t is seen from eqn. (2) that where t-*0 d [B]/dt tends to the value of I~Bf (D') e~t [A] or, in optical densities, dDE/dt,_,o=IqBsBf" (D') D'. Thus from the slope of the tangent at the point t----0 to the initial D
1"2 ..,.tr"
0.8
/
/
\
D
!
\
0"4 I
320
I
t
r
#20
i
520
I
I
820 ~,nm
FIG. 1
T/me FIG. 2
FIe. 1. Absorption spectra of the initial form (solid line) and the coloured form (dotted line) of photochromic copolymors I and II. Fie. 2. Scheme of suecesmve photochromic cycles of the copolymers. portion of the curve for B form accumulation one obtains the product of ~BeB =dDB/dt/If (D') D', since the values of 1, f (D') and D' are known. Integrating eqn. (5) we obtain -- log (10-D R - 1)------11( ~t + ~0~)8Bt+ const The slope of the --log (10-DR-1) vs. time curve gives the product of 8B(~'A + ~F) (Fig. 3b). The 9c values m a y be determined from two consecutive photochromic cycles by using the formula DmaX -1 2 and the 9~. values are obtained from the curve of DB vs. irradiation time, after it has passed through a maximum, by using the equation. 0DR at = --I~E]' (D') ~£DB
(8)
Photoehromm transformatmns of polymers
459
Thus by investigating the kinetics of photochromic transformations of the copolymer one obtains the products of the quantum yields for the direct and the reverse reactions and the coefficient of extinction for the coloured form at the
0.6 -15
a.
o
0~
/)
-/'4 0.2 1
20
I0
30
I
I
15
5
I
25
T/me, sec FIG. 3. Plots of In (DB/t) (a) and log (10DB- 1) (b) vs. lrradlatmn time for the photoehromm copolymer a t ).=303-313 (a) and 545 n m (b).
a b s o r p t i o n m a x i m u m f o r t h e l a t t e r i n t h e v i s i b l e r e g i o n o f t h e s p e c t r u m (2max ----590 n m ) a n d t h e s u m o f t h e q u a n t u m y i e l d s o f a l l t h e p r o c e s s e s o c c u r r i n g u n d e r t h e a c t i o n o f U V l i g h t . I n c o n t r a s t t o t h e e a s e c o n s i d e r e d i n p a p e r [6] (qx=0), the coefficient of extinction for the eoloured form cannot be determined TABZaZ 2. KINETIC
PARAMETERS AND
Copelymer I
II
~I
OF PHOTOCHROMIC
AND THE
Conditions Solutmn of monomer m ethyl acetate Soluhon of eopolymer in ethyl acetate Sohd solution of monomer m PMMA Copolymer of splropyran monomer with MMA Solution of monomer m ethyl acetate Solutmn of copolymer m ethyl acetate Sohd solution of monom e r m PMMA Copolymer of splropyran monomer with MMA
TRANSFORMATIONS
OF COPOLYMERS
CORRESPONDING MONOMERS*
¢~
CA
¢c
¢~
04
0.8
0.4
0.8
O1
01
0.1
0 003
0-015
0 05
0.06
0-003
06
¢~ ~ ¢1"
m
~¢1
K × × l0 s
1-2
2
1.2
2
0-015
03
O1
0.015
0"125
O1
0-5
1.1
2
06
05
I1
2
0-2
02
O2
0 004
0.015
0.6
0.1
0.06
0-4
0.3
0.004
0.015
0.75
0-1
* The error of measurementfor ~ , ¢c, pE, ¢'h,+ #F and X~I was± 20%, and for ~A, ±40%.
460
N . S . KA~DASH e~ a~.
from kinetic measurements. Determination of 8B was done by direct measurem e n t of the optical density of photocoloured solutions of monomerie spiropyrans at --30 °, when there are no decolouration processes taking place, i. e. the irradiation leads to complete transformation of the spiropyran to the coloured form. In this way it was found t h a t for spiropyran I the extinction coefficient ~B=4"65× l0 t, and for spiropyran II, 5.6× 1011./mole.cm. We assume that the ~B values are identical for the spiropyrans in the copolymer, in the PMMA matrix, and in ethyl acetate. Knowing the extinction coefficient for the coloured form in the visible region of the spectrum, we m a y now determine the quantum yield of the eolouration ~B and the sum of the quantum yields of the decolouration and ageing ~a~+ ~aFunder the action of visible light with ~=545 n m (Table 2). Table 2 also gives the ~A, f0c and ~E values for the eopolymers of spiropyrans I and I I calculated on the basis of eqns (7) and (8). 1
D 06
0.4 O.f
I
I
I0
40
I~--~70 T/me,sec
I00
FIG. 4. Kmetms of the photochromm tra~sformatmns of the copolymer solution measured at m a x i m u m absorption b y the coloured form.
The same kinetic scheme was also used in the case of films of the rigid solutions of spiropyran monomers I and I I in PMMA (see Table 2). The results of the investigation of solutions of the spiropyran monomers and copolymers in ethyl acetate show that in contrast to the films, the irradiation of the solutions with UV light results in the optical density of the coloured form tending in the visible region to a constant value of ~ (Fig. 4, curve 1), and, when the light is switched off, a process of rapid dark deeolouration takes place (curve 2) I n solutions the rate of colouration is much higher than in the films, assuming t h a t the light is in either case of equal intensity The concentration of the coloured form reaches a limiting value, but does not pass through a maximum. This means that fatigue processes are negligible in the solutions during the period of the experiment. A scheme for the photochromatic transformations of the spiropyran monomers and copolymers I and II, in solution, m a y therefore be represented as follows: hv
A ~ B
hr. kT
The accumulation of the coloured form under the action of LIV light is de-
Photochromm transformations of polymers
461
scribed by the equation
d [B]
dt --Iq~Bf (D') e'A/[A]- IqAf (D') ~]31[B]--k ['B]
(9)
Since the kinetics of the photochromic transformations are determined from change m the optical density DB of the B form, this equation m a y be written
dDB= I ~Bf(D') D%B1-- DB[If (D') ~'A1 ( q~A~- ~0B)~-k], dt
(10)
as where k is the rate of dark decolouration, and the remainder of the notation is the same as for the films. Starting conditions" when t=O, [A]=[A0], [B]----0, D'----e'Al [A] The irradiation was conducted at the isobestic point, and so s~,= e~ and f(D')----const From the steady-state condition of dDB/dt=O we obtain
[k 4- Ie'xf (D' ) l ( {oA+ ~B)]----=I ~OBeBf(D') D'l
(hi)
or putting Iq~Bssf(D')D'l=a and Ie~f(D')(~pA-~-epB)/~-k----B we have
a=bDS~
(12)
Hence we obtain the sum of the quantum ymlds ~B+ ~aAand the product of the quantum yield of the eolouration and the coefficient of extinction of the B form for the visible region qBeB. Using eqn. (12), we obtain, from expression (10), dDB/dt=b (D*~-DB) Hence In l - VDB / =bt .
(13)
which makes it possible to find the value of b (Fig. 5a) To find the sum of t h e quantum yields ~aAA-~Bit is necessary to know k. I t was shown t h a t the dark deeolouration of monomers I and I I and of the corresponding copolymers is a first-order process in ethyl acetate. The slope of the --log DR vs. t plot (Fig. 5b) gives the value of k. The quantum yields of the process and the constants for the dark deeolouration of solutions of monomers I and I I and of the corresponding copolymers will be found in Table 2. On comparing the data on the quantum yields of the photoproeesses given m Table 2, it is seen that on passing from solutions of spiropyran in ethyl acetate to the solutions in polymer the quantum yields of the spiropyran eolouration are substantially reduced, apparently as a result of increased viscosity of the medium. The factor underlying reduction in ~B, in polymer, could quite conceivably be a diminution of the ability of individual parts of the spiropyran molecule to shift relative to one another during the chemical reaction. The rupture of C--O in the pyran ring probably proceeds as effectively as in liquid solutions, though the inhibition of subsequent turning of the spiropyran molecule in the polymeric matrix results in reversible closing of the ring. The quantum yields of the eolouration, particularly in the case of eopolymex I, are still further
462
1~. S. KA~DASKe$ a/.
reduced when photochromes are incorporated in the polymer molecule. The reduced probability of the molecule turning is apparently especially marked when the spiropyran molecule is attached to the polymer chain. The lower quantum yield of the colouration in the copolymer is therefore due not only to the high structural viscosity, but also to the attachment of one part of the photochrome molecule to the polymer chain. -loTne
0.1 (l
L 0
FIG.
IO
20
I
I
I
L
3O
5. Plots of--log ((1 D--~BBt(a) ) and --log DB (b) vs. t,me m cases of ,rradlatmn (a) and
dark decolouratlon of the photochronnc copolymer (b) solution. On the ordinate axm in Fig. b the bottom graduation line corresponds to a value of 0.2 for --log Dn, and the upper graduation hne corresponds to a value of 1.0. It is noteworthy that the reduction in ~s for the ~copolymer of spiropyran with MMA, is much more marked, for the solution, than in the case of the copolymer of spiropyran II In the light of the available data one could not decide whether this difference in the behaviour of the spiropyrans in the copolymers is due to the fact t h a t spiropyran I is attached to the polymer chain in the pyran of the molecule, while spiropyran II is attached in the indoline part. I t could well be t h a t this is the result of differences in the length of the chains attaching the photochromic group to the polymer chain. In ethyl acetate solutions the photochemical behaviour of the polymers and the corresponding monomeric photochromes is identical. This means t h a t attachment of the photochrome to the polymer molecule does not in itself influence t h e quantum yield of the photoreaction. The effect due to incorporation of t h e photochrome molecule in the polymer chain seems to appear only m a rigid matrix. As m a y be seen from Table 2, the quantum yields of the photodecomposition of b o t h spiropyrans are considerably higher in the case of the A form, compared with the B form, and moreover these quantum yields are approximately the same in the copolymer as in solutions of the spiropyrans in polymer. Incorporation of t h e spiropyran into the polymer molecule therefore leads to a reduction in the steady-state concentration of the coloured form, compared with solutions in
Blrefrmgence and wscoszty of solutions of copolymer of styrene and MA
463
polymer, as a result of a reduction in ~B, the values of ~A and ~c remaining practically constant. On increasing the content of spiropyran I I in ~he copolymet from 0.6 to ~ 5 mole ~ the quantum yields of the photoprocesses remain constant. T h e results of this investigation show t h a t for practical purposes o f s p i r o p y r a n p h o t o c h r o m y the p r e p a r a t i o n of p h o t o c h r o m a t i c eopolymers o f t h e t y p e discussed in this p a p e r is less e x p e d i e n t t h a n dissolution of t h e p h o t o c h r o m e in a p o l y m e r i c matrix. Translated by R. J. A. HENI)~Y REFERENCES 1. 2. 3. 4.
P. H. VANDEVIJER and G. SMETS, J. Polymer Sei. C22: 231, 1968 P. H. VANDEVIJER and G. SMETS, J. Polymer Sci. 8, A-I: 2361, 1970 A. POOT and G. DELZENNE, French Pat. 194715, 1970 Kh. ONO, O. TOKAI and T. NAGATA, Jap. Pat. 28893, 1970; Refi Zh. Khnn, C286P, 1971 5. E. WEGNER and A. W. ADAMSON, J. Amer. Chem. Soc. 88: 394, 1966 6. A. A. PARSHUTKIN, V. P. BAZOV and V. A. KRONGAUZ, Khimiya vysokikh energii 4: 131. 1970
DYNAMIC BIREFRINGENCE AND VISCOSITY OF SOLUTIONS OF A COPOLYMER OF STYRENE AND METHACRYLIC ACID AND OF IONOMERS BASED ON THE COPOLYMER* YU. V. REVIZSKII, YU. ]3. MOI~AKOV, V. P. BUDTOV a n d S. R. R~,~IKOV Chermstry Institute of the Bashklr Affihated Branch of the U S S.R Academy of Scmnces (Received 19 June 1972) A dynamm flow blrefrmgence investigation was carrmd out for the copolymer of styrene and methacryhc amd (8 : 2) and lonomers based on it, the lonomers differing as to degree of neutrahzatlon by sodmm lens. The investigations were conducted at 30° m dlmethylformamlde, dnnethylformanude with NaI additions, bromoform, and bromoform with dlmethylformamlde additions. It is shown that vamatlons m thermodynamm rl~ndlty are only mstgmficant on going from the copolymer to the lonomers, and that the thermodynamm rigidity is shghtly higher than the corresponding value for polystyrene THE properties of neutralized c o p o l y m e r s of a-olefms a n d v i n y l derivatives with
unsaturated acids (ionomers) are mainly determined by the interaction of ionized carboxyl groups and free metal cations [1]. * Vysokomol. soyed. A16: No. 2, 398-401, 1974.
453
As may be seen from the data in Table 2, the transformation of a diene macromolecule to a vinyl macromolecule increases the rigidity of the molecular chains, and the relative "unperturbed dimensions" (or parameter a) increase from 1.7 to 2.5-3.0. Moreover, whereas the unperturbed dimensions of the CSKI molecules in the binary systems (polymer-solvent) remain practically identical, in the triple s y s t e m s ( p o l y m e r - b i n a r y m i x t u r e ) t h e u n p e r t u r b e d dimensions d e p e n d to a consid e r a b l e e x t e n t on t h e t y p e o f solvent, a n d this agrees well w i t h p r e s e n t - d a y ideas a b o u t t h e influence of 0-solvents on t h e c o n f o r m a t i o n a n d flexibility o f C S K I molecules in t h e u n p e r t u r b e d s t a t e [8, 9]. T h e M a r k - K u h n - H o u w i n k e q u a t i o n o b t a i n e d for a s t r o n g l y p o l a r m e d i u m ( D C E - m e t h a n o l ) shows t h a t t h e Gaussian s t r u c t u r e of t h e m o l e c u l a r coils is slightly d i s t o r t e d in t h e u n p e r t u r b e d state, i.e. [7] ¢ K0" IT/÷ Translated by R J. A. HENDRY REFERENCES
1. M. T~KEI~A, R. ENDO and Y. MATSUURA, J Polymer Sci. C23: 487, 1969 2. I. Ya. PODDYBNYI and A. V. PODALINSKII, Zavodsk. lab a3: 1398, 1967 3. V. CRES~KENZI and P. FLORY, J. Chem. Soe 86: 141, 1964 4. L. Kh. SIMONYAN, A. V. GEVORKYAN, K. A. TOROSYAN and A. Sh. SAFAROV, Arm. khLmich, zh. 25: No. 9, 1972 5. W. STOKMAYER and M. FIXMAN, J Polymer Sei. CI: 137, 1963 6 P. FLORY, Principles of Polymer Chemistry, N. Y., 1953 7 I. Ya. PODDYBNYI ~Ye. G, ERENBURG and M. A. YEREMINA, Vysokomol. soyed. AIO: 1381, 1968 (Translated in Polymer Scl. U S.S.R. 1O: 6, 1603, 1968) 8. A. DON]DOS and H. BENOIT, Makromolek. Chem 129: 35, 1969 9. A. V. GEVORKYAN, Uspekhl khimu 41: 401, 1972
ON PHOTOCHROMIC TRANSFORMATIONS OF POLYMERS* •.
S KARDASH, V A. KRONGAUZ, YE. L
ZAITSEVA a n d A
V. MOVSHOVICK
L. Ya. Karpov'Physlcal Chemistry Research Institute (Reeewed 19 June 1972)
Novel photochromm polymers were synthesized, namely eopolymers of methyl methacrylate and sp~ropyran monomers, and their phototransformatlons were investigated. The mare kmetm and spectral charactermtlcs of the photochronne systems were determined: the quantum yields of eolouratlon and decolouratlon, the constants of the dark reactions and the coefficients of extraction for the coloured form. I t was found that the chemmal addition of photoehromm groups to the polymer mole* Vysokomol. soyed. A16: No. 2. 390-397, 1974
454
N . S. K ~ D A S H et al.
cule m a solid m e d m m is accompamed b y a marked reduetmn m the q u a n t u m yields of colouratmn of the photochrome compared with the corresponding solutions m methyl methacrylate and m ethyl acetate. ] n ethyl acetate the photochemmal behawour of the copolymers and the corresponding monomers is ldentmal. The conclusmn is reached that m the copolymers the reduced q u a n t u m yields of colouratmn are due to inhibited t u r n i n g of parts of the splropyran molecule relative to one another. The inhibited morton is due both to the high structural vlscomty of the medmm, and to the attachment of one portmn of the photoehrome molecule to the polymer chain.
THE photochromic phenomenon is exhibited by certain types of substances, and involves the reversible appearance of colouration under the action of light. Much study has been made of spiropyrans, and among the groups of photochromic compounds spiropyrans are of the greatest practical importance. Photochromic changes in spiropyran molecules take place through the rupture of C--O bonds and the turning of portions of the molecule relative to one another [1]. The resuiting meroeyanine form of spiropyran has an intense absorption band in the visible region of the spectrum. Reversible ring closure takes place in the dark or under the action of visible light in the region corresponding to the absorption of the meroeyanine form R
R
N/Xo--x]_~/--n [ R R
R
RO-
R
\//-I R
"R
Papers published recently contain information relating to the incorporation of spiropyraus in the composition of polymer molecules. The resultant polymers similarly posses photochromic properties. When spiropyran groups are included in polymer molecules, one would expect changes in the photochromic behaviour of the polymer, and equally in some of their properties which, from a practical standpoint, must influence possible applications of the polymers. Smets and Vandevijer [1-4] investigated copolymers of indolylspiropyran and thiospiran monomers with methyl methacrylate (MMA), styrene and p-vinylnaphthalene. These authors dealt mainly with problems of the polarity of solvents influencing the position of the maximum of the coloured form of the eopo]ymers, and with the kinetics of the dark process of deeolouration. Data in regard to photochemical reactions of the polymers are either scanty of non-existent. The purpose of our investigation was to elucidate phototransformations of copolymers of MMA with indolylspiropyran monomers. The behaviour of polymers containing the chemically incorporated photochromic groups was compared with that of rigid solutions of the corresponding photochromic monomers in PMMA. A further aim was to discover how far the viscosity of the medium is capable of influencing the kinetics of phototrausformation of the eopolymers. To do so we investigated solutions of photochromic copolymers and of the cor-
Photochrormc transformations of polymers
455
responding photochromic monomers in ethyl acetate; the ethyl acetate molecule and the monomer unit of PMMA are structurally similar. In order to characterize the photochromic systems we determined kinetic parameters such as the quantum yields of the colouration and decolouration, the constants of the dark reactions of decolouration, and the coefficients of extinction for the coloured form EXPERIMENTAL
Photochromic polymers were prepared b y eopolymerlzatmn of the sprropyran monomers CHs CHs
CHs CH3
N\^__~-~--NO~
tCH3U~CH~--CH----CH~ I
CH~
CHs
t
1
CH~--OCO--C=CH2 II
with MMA. The copolymenzation process was conducted in ~ m glass ampoules a t 65 ° for 10 hr. Dmltrile of azoisobutyrlc acid (DAA) was used as the polymerization initiator. The resulting copolymers were separated b y five-fold reprecipitatmn from methylene chloride by methanol. Depending on the compomtmn of the rnbrturo used for the polymerizatmn, copolymers containing dLffcrent amounts of photochromic groups were obtained (see Table 1).
T ~ a I ~ 1.
POLYM~
COMPOSITION R E L A T I V E TO CONCENTRATION RATIO :~[MA
Cope lymer
Spmapyran content, mole %
I N ~r~L~ M O N O ~ ' R
8
17
0"22 0.52 0"76
SPIROPYRAN :
t Spiropyran content, ,M X 10 -~
m themltiM in the ralxture eopolymer 3
OF
~x!t'uJ~E
26"3 12-6 26 3
Col}o. lymer
II
.
mole ~oo M× 10-* in the Lmtml m the mixture copolymer 0.7 5 10
0.66
3.7 7
123 141 112.2
The molecular weights of the copolymers, determined viscommetrmally, are included m Table 1. The polymemzatlon was continued up to advanced degrees of conversion, a n d it would therefore be imprachcable m the light of our data to estn~ate the q u a n t i t a h v e rea c t l m t y of the monomers participating m the polymerizahon. However, it m a y be seen from Table 1 that photochromm monomer I enters rote the copolymer compomtion m a ratio much smaller t h a n the ratio of monomer I m the matial mLxture, whde monomer LI la present m the copolymer composition m the same ratio as in the mixture used for the polymerization. Thin means t h a t while the reactiwties of photochromic monomer I I a n d MMA are mmdar, the reactivity of monomer I m much lower than t h a t of MM~i.o
456
N.S. KA~DASHetal.
The hght source was a DRSh-500 lamp provided with glass filters ebmlnatmg the 303-313 nm regmn and 545 nm. The intensity of the incident hght m the UV region was measured by means of a ferryoxalate aetmometer, whde m the UV regmn the intensity of the incident hght was measured with Remmke's salt [5] The SP-700 spectrophotometer ("Unmam") was used for the kmctm and the spectral measurements. All the experiments were earrmd out at room temperature. The kmetms of photochromatm transformatmns were determined from changes m the optmal density at the absorptmn maximum for the coloured form of the sp~ropyran m the vlmble regmn of the spectrum. The kmetms of photochromm transformatmns m solutmn, where dark decolouratmn of the coloured form takes place very rapidly, were recorded directly at the time of the lrrad~atmn, using the "crossed filters" method [6]. Films made from the photochrormc polymers and from rigid solutmns of the splropyrans m PMMA were prepared by slow evaporatmn of the solvent from solutmns of the polymers m methylene chloride. The films had a thmkness of ~ 10/lm. DISCUSSION OF RESULTS
U V irradiation of films of the p h o t o c h r o m i c copolymers leads to t h e appearance of a new a n d intense absorption b a n d in t h e visible region o f t h e s p e c t r u m
(~max--590nm) (Fig. 1). As m a y be seen f r o m Fig. 2, curve 1, the optical d e n s i t y o f t h e coloured f o r m reaches a m a x i m u m a t a certain m o m e n t of t i m e t, and t h e n falls away. W h e n the irradiation is s t o p p e d the optical density of the film colouring remains practically constant, i. e. during the period of t i m e of the e x p e r i m e n t processes o f d a r k decolouration of the coloured form m a y be disregarded. U n d e r t h e action o f visible light the reverse transition to a eolourless f o r m takes place in t h e region o f the a b s o r p t i o n m a x i m u m for the eoloured form. T h e f a c t t h a t t h e optical d e n s i t y of the coloured form, given sufficiently long exposure to U V light, passes t h r o u g h a m a x i m u m , points to irreversible processes taking place and resulting in t h e f o r m a t i o n of side-products, a n d in the a p p e a r a n c e of " f a t i g u e " in the system. As m a y be seen f r o m Fig. 2, the m a x i m u m optmal density of t h e colourat l o n obtainable in the second p h o t o c h r o m i c cycle (colouration b y light w i t h 2 : 3 0 3 - 3 1 3 n m - - d e c o l o u r a t i o n b y light with 2 = 5 4 5 nm) is m u c h lower comp a r e d with the first cycle, while in the t h i r d cycle it is lower t h a n in the second, etc. This m a y be the result of fatigue affecting t h e s y s t e m b o t h during t h e colouration on exposure to U V light, a n d during decolouration b y visible light, a n d similarly as a result of d a r k processes of ageing. P r e l i m m a r y tests showed t h a t t h e r e are practically no d a r k side reactions, 1. e. t h e r e are t h r e e possibilities t h a t have to be t a k e n into account, a n d these are: decomposition of b o t h forms t h r o u g h exposure to U V light, a n d decomposition of the coloured f o r m t h r o u g h exposure to visible light. A general scheme for the p h o t o c h r o m i c t r a n s f o r m a t i o n s o f t h e c o p o l y m e r could therefore be represented as follows: hv
C ~A
~-~ B by'
,~hv'
~E,
F ~vhere A and B are t h e initial a n d coloured forms o f spiropyran; C, E, F, are
Photochromac transformatxons of polymers
457
products of side reactions. These processes may be described by means of the following differential equations: consumption of the initial A form d[A] dt
--I ,.~f (D') e~[B]--I ,Bf (D') e'A[A]--IecI (D') e~[A]
(1)
accumulation of the B form
a[B] dt =IqBf (D') 4[A] --I~0d (D') e~[B]--IqF~(D') e~[B]
(2)
accumulation of fatigue products
a[E]
dt -----I~.f(D') e~[B]
(3)
d~C]=I~cf (D') e~[A],
(4)
where D'=8'A1 [A]+e~I [B]+e~I [C]+e~I [E], l--sample thickness, [A], [B], [C], ' *B, ' e'o and e~--molar coefficients of [E]--coneentrations of the components, eA extinction in the region of irradiation, f (D')= (1--10-D')/D ', /--intensity of the exciting UV light (einstein/1.. sec), assuming complete absorption of light by the actinometer, ~B--quantum yield of the colouration, ,A--quantum yield of the decolouration, , c , ,~.--quantum yields of the fatigue. Initial conditions: when t=0, [A]=[Ao], B = 0 , [C]=0, [E]----0. The process of decolouration by visible light may be expressed by the equation
d [B] dt --11(,.~+ ~) (1-- 10-~"),
(5)
where I i is the intensity of the visible light, ~ , quantum yield of the decolouration under the action of visible light, ~0r, quantum yield of ageing. The set of differential equations (1)--(4) can be solved only in cases where D' is small, or remains constant, during the course of the experiment. In the case under consideration the irradiation was carried out in the 303-313 nm region where, as may be seen from Fig. 1, the spiropyran has an isobestic point, i. e. the optical density remained constant during the irradiation process and f (D')=const. We therefore have a set of linear differential equations containing constant coefficients, and by solving this set of equations expressions for the concentrations of all the components in the course of the reaction are obtained [6]. Given the possibility of determining these concentrations, there will be no difficulty in finding all the kinetic and spectral characteristics for a photochromic system. Actually, however, one can take just the changes in the optical density of the B form in the visible region of the spectrum, as the spectra of both forms of the spiropyran
4~8
No S. KARDASH e$ a~.
and of the products of ageing differ only slightly in the UV region. Bearing in mind t h a t [B]=DB/eB l, where eB is the coefficient of extinction for the coloured form in the visible region of the spectrum, and having recourse to the solution of an analogous set of equations appearing in [6], we obtain lnDB_ t
1 2
If(D') e~.(~x--[--~pB+~C+ ~pE)t-{-ln eBIqBf(D')D'
(6)
The slope of the In (DB/t) vs. t curve gives the sum of the quantum yields qXq-qBq- ~0cq-qE (Fig. 3a). I t is seen from eqn. (2) that where t-*0 d [B]/dt tends to the value of I~Bf (D') e~t [A] or, in optical densities, dDE/dt,_,o=IqBsBf" (D') D'. Thus from the slope of the tangent at the point t----0 to the initial D
1"2 ..,.tr"
0.8
/
/
\
D
!
\
0"4 I
320
I
t
r
#20
i
520
I
I
820 ~,nm
FIG. 1
T/me FIG. 2
FIe. 1. Absorption spectra of the initial form (solid line) and the coloured form (dotted line) of photochromic copolymors I and II. Fie. 2. Scheme of suecesmve photochromic cycles of the copolymers. portion of the curve for B form accumulation one obtains the product of ~BeB =dDB/dt/If (D') D', since the values of 1, f (D') and D' are known. Integrating eqn. (5) we obtain -- log (10-D R - 1)------11( ~t + ~0~)8Bt+ const The slope of the --log (10-DR-1) vs. time curve gives the product of 8B(~'A + ~F) (Fig. 3b). The 9c values m a y be determined from two consecutive photochromic cycles by using the formula DmaX -1 2 and the 9~. values are obtained from the curve of DB vs. irradiation time, after it has passed through a maximum, by using the equation. 0DR at = --I~E]' (D') ~£DB
(8)
Photoehromm transformatmns of polymers
459
Thus by investigating the kinetics of photochromic transformations of the copolymer one obtains the products of the quantum yields for the direct and the reverse reactions and the coefficient of extinction for the coloured form at the
0.6 -15
a.
o
0~
/)
-/'4 0.2 1
20
I0
30
I
I
15
5
I
25
T/me, sec FIG. 3. Plots of In (DB/t) (a) and log (10DB- 1) (b) vs. lrradlatmn time for the photoehromm copolymer a t ).=303-313 (a) and 545 n m (b).
a b s o r p t i o n m a x i m u m f o r t h e l a t t e r i n t h e v i s i b l e r e g i o n o f t h e s p e c t r u m (2max ----590 n m ) a n d t h e s u m o f t h e q u a n t u m y i e l d s o f a l l t h e p r o c e s s e s o c c u r r i n g u n d e r t h e a c t i o n o f U V l i g h t . I n c o n t r a s t t o t h e e a s e c o n s i d e r e d i n p a p e r [6] (qx=0), the coefficient of extinction for the eoloured form cannot be determined TABZaZ 2. KINETIC
PARAMETERS AND
Copelymer I
II
~I
OF PHOTOCHROMIC
AND THE
Conditions Solutmn of monomer m ethyl acetate Soluhon of eopolymer in ethyl acetate Sohd solution of monomer m PMMA Copolymer of splropyran monomer with MMA Solution of monomer m ethyl acetate Solutmn of copolymer m ethyl acetate Sohd solution of monom e r m PMMA Copolymer of splropyran monomer with MMA
TRANSFORMATIONS
OF COPOLYMERS
CORRESPONDING MONOMERS*
¢~
CA
¢c
¢~
04
0.8
0.4
0.8
O1
01
0.1
0 003
0-015
0 05
0.06
0-003
06
¢~ ~ ¢1"
m
~¢1
K × × l0 s
1-2
2
1.2
2
0-015
03
O1
0.015
0"125
O1
0-5
1.1
2
06
05
I1
2
0-2
02
O2
0 004
0.015
0.6
0.1
0.06
0-4
0.3
0.004
0.015
0.75
0-1
* The error of measurementfor ~ , ¢c, pE, ¢'h,+ #F and X~I was± 20%, and for ~A, ±40%.
460
N . S . KA~DASH e~ a~.
from kinetic measurements. Determination of 8B was done by direct measurem e n t of the optical density of photocoloured solutions of monomerie spiropyrans at --30 °, when there are no decolouration processes taking place, i. e. the irradiation leads to complete transformation of the spiropyran to the coloured form. In this way it was found t h a t for spiropyran I the extinction coefficient ~B=4"65× l0 t, and for spiropyran II, 5.6× 1011./mole.cm. We assume that the ~B values are identical for the spiropyrans in the copolymer, in the PMMA matrix, and in ethyl acetate. Knowing the extinction coefficient for the coloured form in the visible region of the spectrum, we m a y now determine the quantum yield of the eolouration ~B and the sum of the quantum yields of the decolouration and ageing ~a~+ ~aFunder the action of visible light with ~=545 n m (Table 2). Table 2 also gives the ~A, f0c and ~E values for the eopolymers of spiropyrans I and I I calculated on the basis of eqns (7) and (8). 1
D 06
0.4 O.f
I
I
I0
40
I~--~70 T/me,sec
I00
FIG. 4. Kmetms of the photochromm tra~sformatmns of the copolymer solution measured at m a x i m u m absorption b y the coloured form.
The same kinetic scheme was also used in the case of films of the rigid solutions of spiropyran monomers I and I I in PMMA (see Table 2). The results of the investigation of solutions of the spiropyran monomers and copolymers in ethyl acetate show that in contrast to the films, the irradiation of the solutions with UV light results in the optical density of the coloured form tending in the visible region to a constant value of ~ (Fig. 4, curve 1), and, when the light is switched off, a process of rapid dark deeolouration takes place (curve 2) I n solutions the rate of colouration is much higher than in the films, assuming t h a t the light is in either case of equal intensity The concentration of the coloured form reaches a limiting value, but does not pass through a maximum. This means that fatigue processes are negligible in the solutions during the period of the experiment. A scheme for the photochromatic transformations of the spiropyran monomers and copolymers I and II, in solution, m a y therefore be represented as follows: hv
A ~ B
hr. kT
The accumulation of the coloured form under the action of LIV light is de-
Photochromm transformations of polymers
461
scribed by the equation
d [B]
dt --Iq~Bf (D') e'A/[A]- IqAf (D') ~]31[B]--k ['B]
(9)
Since the kinetics of the photochromic transformations are determined from change m the optical density DB of the B form, this equation m a y be written
dDB= I ~Bf(D') D%B1-- DB[If (D') ~'A1 ( q~A~- ~0B)~-k], dt
(10)
as where k is the rate of dark decolouration, and the remainder of the notation is the same as for the films. Starting conditions" when t=O, [A]=[A0], [B]----0, D'----e'Al [A] The irradiation was conducted at the isobestic point, and so s~,= e~ and f(D')----const From the steady-state condition of dDB/dt=O we obtain
[k 4- Ie'xf (D' ) l ( {oA+ ~B)]----=I ~OBeBf(D') D'l
(hi)
or putting Iq~Bssf(D')D'l=a and Ie~f(D')(~pA-~-epB)/~-k----B we have
a=bDS~
(12)
Hence we obtain the sum of the quantum ymlds ~B+ ~aAand the product of the quantum yield of the eolouration and the coefficient of extinction of the B form for the visible region qBeB. Using eqn. (12), we obtain, from expression (10), dDB/dt=b (D*~-DB) Hence In l - VDB / =bt .
(13)
which makes it possible to find the value of b (Fig. 5a) To find the sum of t h e quantum yields ~aAA-~Bit is necessary to know k. I t was shown t h a t the dark deeolouration of monomers I and I I and of the corresponding copolymers is a first-order process in ethyl acetate. The slope of the --log DR vs. t plot (Fig. 5b) gives the value of k. The quantum yields of the process and the constants for the dark deeolouration of solutions of monomers I and I I and of the corresponding copolymers will be found in Table 2. On comparing the data on the quantum yields of the photoproeesses given m Table 2, it is seen that on passing from solutions of spiropyran in ethyl acetate to the solutions in polymer the quantum yields of the spiropyran eolouration are substantially reduced, apparently as a result of increased viscosity of the medium. The factor underlying reduction in ~B, in polymer, could quite conceivably be a diminution of the ability of individual parts of the spiropyran molecule to shift relative to one another during the chemical reaction. The rupture of C--O in the pyran ring probably proceeds as effectively as in liquid solutions, though the inhibition of subsequent turning of the spiropyran molecule in the polymeric matrix results in reversible closing of the ring. The quantum yields of the eolouration, particularly in the case of eopolymex I, are still further
462
1~. S. KA~DASKe$ a/.
reduced when photochromes are incorporated in the polymer molecule. The reduced probability of the molecule turning is apparently especially marked when the spiropyran molecule is attached to the polymer chain. The lower quantum yield of the colouration in the copolymer is therefore due not only to the high structural viscosity, but also to the attachment of one part of the photochrome molecule to the polymer chain. -loTne
0.1 (l
L 0
FIG.
IO
20
I
I
I
L
3O
5. Plots of--log ((1 D--~BBt(a) ) and --log DB (b) vs. t,me m cases of ,rradlatmn (a) and
dark decolouratlon of the photochronnc copolymer (b) solution. On the ordinate axm in Fig. b the bottom graduation line corresponds to a value of 0.2 for --log Dn, and the upper graduation hne corresponds to a value of 1.0. It is noteworthy that the reduction in ~s for the ~copolymer of spiropyran with MMA, is much more marked, for the solution, than in the case of the copolymer of spiropyran II In the light of the available data one could not decide whether this difference in the behaviour of the spiropyrans in the copolymers is due to the fact t h a t spiropyran I is attached to the polymer chain in the pyran of the molecule, while spiropyran II is attached in the indoline part. I t could well be t h a t this is the result of differences in the length of the chains attaching the photochromic group to the polymer chain. In ethyl acetate solutions the photochemical behaviour of the polymers and the corresponding monomeric photochromes is identical. This means t h a t attachment of the photochrome to the polymer molecule does not in itself influence t h e quantum yield of the photoreaction. The effect due to incorporation of t h e photochrome molecule in the polymer chain seems to appear only m a rigid matrix. As m a y be seen from Table 2, the quantum yields of the photodecomposition of b o t h spiropyrans are considerably higher in the case of the A form, compared with the B form, and moreover these quantum yields are approximately the same in the copolymer as in solutions of the spiropyrans in polymer. Incorporation of t h e spiropyran into the polymer molecule therefore leads to a reduction in the steady-state concentration of the coloured form, compared with solutions in
Blrefrmgence and wscoszty of solutions of copolymer of styrene and MA
463
polymer, as a result of a reduction in ~B, the values of ~A and ~c remaining practically constant. On increasing the content of spiropyran I I in ~he copolymet from 0.6 to ~ 5 mole ~ the quantum yields of the photoprocesses remain constant. T h e results of this investigation show t h a t for practical purposes o f s p i r o p y r a n p h o t o c h r o m y the p r e p a r a t i o n of p h o t o c h r o m a t i c eopolymers o f t h e t y p e discussed in this p a p e r is less e x p e d i e n t t h a n dissolution of t h e p h o t o c h r o m e in a p o l y m e r i c matrix. Translated by R. J. A. HENI)~Y REFERENCES 1. 2. 3. 4.
P. H. VANDEVIJER and G. SMETS, J. Polymer Sei. C22: 231, 1968 P. H. VANDEVIJER and G. SMETS, J. Polymer Sci. 8, A-I: 2361, 1970 A. POOT and G. DELZENNE, French Pat. 194715, 1970 Kh. ONO, O. TOKAI and T. NAGATA, Jap. Pat. 28893, 1970; Refi Zh. Khnn, C286P, 1971 5. E. WEGNER and A. W. ADAMSON, J. Amer. Chem. Soc. 88: 394, 1966 6. A. A. PARSHUTKIN, V. P. BAZOV and V. A. KRONGAUZ, Khimiya vysokikh energii 4: 131. 1970
DYNAMIC BIREFRINGENCE AND VISCOSITY OF SOLUTIONS OF A COPOLYMER OF STYRENE AND METHACRYLIC ACID AND OF IONOMERS BASED ON THE COPOLYMER* YU. V. REVIZSKII, YU. ]3. MOI~AKOV, V. P. BUDTOV a n d S. R. R~,~IKOV Chermstry Institute of the Bashklr Affihated Branch of the U S S.R Academy of Scmnces (Received 19 June 1972) A dynamm flow blrefrmgence investigation was carrmd out for the copolymer of styrene and methacryhc amd (8 : 2) and lonomers based on it, the lonomers differing as to degree of neutrahzatlon by sodmm lens. The investigations were conducted at 30° m dlmethylformamlde, dnnethylformanude with NaI additions, bromoform, and bromoform with dlmethylformamlde additions. It is shown that vamatlons m thermodynamm rl~ndlty are only mstgmficant on going from the copolymer to the lonomers, and that the thermodynamm rigidity is shghtly higher than the corresponding value for polystyrene THE properties of neutralized c o p o l y m e r s of a-olefms a n d v i n y l derivatives with
unsaturated acids (ionomers) are mainly determined by the interaction of ionized carboxyl groups and free metal cations [1]. * Vysokomol. soyed. A16: No. 2, 398-401, 1974.