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Infrared spectroscopy method for the quantitative determination of the stereoregulatory of polystyrene
INFRARED SPECTROSCOPY METHOD FOR THE QUANTITATIVE DETERMINATION OF THE STEREOREGULARITY OF POLYSTYRENE* YE. I. POKROVSKII and YE. F. FEDOROVA Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences
(Received 16 April 1963) THERE is as yet no known method for the quantitative determination of the stereo-regularity of polymers, although some idea of their structure can be obtained in a number of eases b y means of X-ray diffraction, light scattering, nuclear magnetic resonance and other methods. The most usual w a y of identifying syndio- and isotactie polymers is b y deciphering the structure of the unit cells of crystalline fractions of these polymers b y means of X-ray diffraction analysis. B u t this method cannot be applied to the s t u d y of amorphous polymers or to those with only slight crystallization. Recently infrared spectra have been obtained for a number of syndio- and isotaetie polymers and there have been found to be differences between them which could be used for a qualitative assessment of the predominance of the one or other from [1, 2, 3]. In an article published b y one of the authors together with Volkenshtein [4] it was pointed out that differences are to be found in the infrared absorption spectra of iso- and atactic polystyrene, and that these differences are not only connected with the crystallinity of the isotactic specimen. Besides some slight differences in the 1070 em -1 range, as already noted b y Italian writers [3], we also found considerable differences in the spectrum in the 560 to 540 cm -1 range. These differences remained in the absorption spectra of solutions. Below we give the results of a quantitative s t u d y of these variations, taken on a N i p p o n - B u n k o DS 301 spectrophotometer with K B r prisms in imxylene at polystyrene concentrations from 0.5 to 1.0 mol/1., while the dish was 0.0252 and 0.050 em deep. The temperature was measured in the range from 20 to 135 ° for the solutions in p-xylene, and from 20 to 250 ° for the powder pellets compacted with the KBr. In the isotactic polystyrene solutions only the absorption bands at 557 em -1 could be seen (Fig. 1) with a slight projection at 540 cm -5. In the ataetie polystyrene solutions, on the other hand, there were adsorption bands at 540 cm -1 and one which appeared as a spike at 557 cm -1 (Fig. 1.). When the amount of isotactic fraction was varied (for instance, b y extracting the polystyrene prepared * Vysokomol. soyed. 6: No. 4, 647-651, 1964. 714
Stereoregularity of polystyrene
715
over stereospecifie catalyst, with different solvents) the intensity of the 557 cm -1 band increased with the increase in the isotaetic state of the polystyrene, while t h a t at 540 cm -1 diminished (Figs. 2 and 3a, b). We determined the integral intensities of all the polystyrene specimens at our disposal, there being about ten of them and all of different origins. Between 600 and 500 cm -1 the integral intensity was always 1800 1..mol-~.em -~, which means t h a t with variation in the isotacticity of the polystyrene there was redistribution of the intensity of the 557 and 540 cm -~ absorption bands. For quantitative determination of the stereoregularity of the polystyrene, we compared the integral absorption of the bands at 557 and 540 em -~ for each of the test specimens studied. This was done by determining k=ln(Io/I)/cd in the absorption spectra taken on the spectrophotometer (where Io/I is the reciprocal of the percentage transmission, c is the concentration in mole/1, and d is the depth of the dish in cm). K 50
K 40
30
20
,%,
10 ,t ~
~.
~------
600
550 cm-1
FIG. 1
500
600
l
550
I
cm-1
500
FIG. 2
FIG. 1. Absorption spectra of iso- (solid curve) and atactic (dotted curve) polystyrene in p-xylene.
FIG. 2. Absorption spectrum of polystyrene with slight isotacticity. Dotted curve shows the separation of the absorption band. After plotting the k versus v curve from 600 to 500 cm -1 (k being determined for every 1 cm-1), we found ]Cm~x at the m a x i m u m for one of the absorption bands and determined Avl/2 . its half width. I t is always best to begin the calculation with the more intense of the absorption bands, although the result does not depend on the band with which one begins. Taking in a zero approximation, the kmax
716
YE. I . POKI~OVSKII a n d YR. F . FEDOROVA
found experimentally according to the dispersion formula kV=al(r--ro)2+b (where kv is the coefficient at any frequency r, r0 is the kmax position; b=(12 Arl/2) 2 and a=kma x + b ) , we f o u n d t h e outlines of one of the absorption bands neglecting, in our zero approximation, the superposition of the absorption of the K 50
K 50
a
'
i
30
30
/i'
fO i
,I
#l 11
860
10
\\.k
',\ \ ~,~ "\,~, ~"'~,
550 cm-f
- J.,.Ji,., I/I/-"\i;x.t
._ 500
800
550
500
cm-I
FIG. 3. Separation of the absorption bands (dashed curve) of isotactic (a) and atactic (b) polystyrene.
second band. The theoretical outline was calculated from the actual absorption in the band 600 to 500 cm -1, b y which means it was possible to determine the absorption from the second band. After finding kmax in this w a y for the second band, and its half width, its outline was found b y once again using the dispersion formula and, after calculating it from the actual curve, we foundkma x and Avll 2 of the first band in the next approximation (Fig. 2 and 3a). After the first three approximations, k in the maxima of both the half-width absorption bands and consequently their integral intensities, are usually diminished. The total integral intensities corresponded to the actual integral intensities in this range, 600 to 500 cm -1. B y comparing the integral intensities of the absorption bands 557 and 540 cm -1 we also found the relative amounts of isotactic polystyrene fraction. In our specimens the isotactic fraction was 85 to 60%. In the atactic specimens the isotactic part of the polymer was 50%. Unfortunately we had no syndiotactic polystyrene specimens on which we could verify our previous prediction that the absorption bands at 540 cm -1 belonged to the syndiotactic part. It is probable that the absorption bands which we studied and which are connected with the deformation vibrations of the benzene r i n g
Stereoregularity of polystyrene
717
h(B~) [5], form one absorption band in this range of the spectrum, which t h e n breaks up into two as a result of the different structures of the polystyrene, and t h a t these depend on the position of the benzene ring as regards the carbon chain [6-8]. We note t h a t if the amount of isotactic fraction in the polymer increases the absorption band maximum at 540 em -~ shifts slightly to higher
i/zo I0O -
CZ
fO0
.f
8o
_,,,
%
600
8o
//
Go
II
V',,
20
b
//
Go
40
-"
\',, /I
\
I 550
40 I 500 cm -~
20 600
t 550
I 500 cm -I
FIG. 4. A t a c t i c (a) a n d i s o t a e t i c (b) p o l y s t y r e n e in p - x y l e n e . Solid c u r v e - - a t 20 °, d a s h e d - - a t 130 ° .
frequencies. There was never more than an error of ~-2%.in determining the amount of isotactic fraction in the same specimens with repeated analyses and different concentrations, c. The weak 588 cm -1 absorption band becomes more intense with increase in the isotaetic polystyrene but its km~x is one order of magnitude smaller than kmax at 557 and 540 cm -~, and this does not introduce a large error in determining the isotacticity. The artificial mixture of the a t a c t i c a n d more isotactic polystyrene contained 64~o isotactic fraction, The figure found by the above method was 64=E1%. When solutions of polystyrene in p-xylene are heated up to 130 ° there is hardly any change in the ratio of the absorption band areas at 557 and 540 cm -1 (Fig. 4a and b). A slight decrease in absorption in this range is due to expansion of the solution on heating. With the polystyrene heated in K B r pellets up to melting point no particular change was noted. On melting the 567 cm -1 absorption band due to long range disappeared from the spectrum of the crystalline isotactic polystyrene (Fig. 5a). The 557 cm -~ band shifts to 550. I n the molten atactic polystyrene (Fig 5b) the 5540 absorption bands shift. We note t h a t both these bands are asymmetric in the melt, but it was impossible to distinguish the two. I t hardly seems likely t h a t the appearance of the 557 and 540 cm -1 bands could be connected with short range order still preserved in the solution, as their intensity ratio does not depend on temperature.
718
YE. I. PoKl~ovsKII an4 YE. F. FEDOROVA
I n conclusion we would like to thank B. G. Belen'kii and M. V. Vol'kenshtein for discussing the results.
IO0 80
a 250,,~
60 40 20
600
I
I
570
540
b
I
510cm-t J250°
8° I _
~
~
104°
60 40 20
_~
20"
l,
1
600
500
I,, 400 c m -/
FIG. 5. Absorption spectra of isotactic (a) and atactic (b) polystyrene in KBr pellets at various temperatures. CONCLUSIONS
(1) A procedure has been developed for the quantitative determination of the stereoregularity of polystyrene, using infrared absorption spectra. The bands used for the analysis were 557 and 540 cm -1, which belong to the iso- and syndiotactic structure of polystyrene respectively. (2) The stereoregularity of a number of polystyrenes with 85 to 60% isotactic fraction has been determined. Atactic specimens contained 50% each of iso- and syndiotactic fractions. Translated by V. ALFORD
Chemical conversions of polymers
719
REFERENCES 1. D. MORERO, A. SANTAMROGIO,. L. PORRI and F. CIAMPELLI, Chemica e industria 58: 758, 1959 2. G. NATTA, L. PORRI, A. MAZZEI a n d D. MORERO, Chemica e industria 41: 398, 1959 3. D. MORERO, E. MAUTICA, F. CIAMPELLI and D. SIANESI: ])el nuovo cimento supplemento ol XV: X, 1, 122, 1960 4. E. I. POKROVSKII and M. V. VOLKENSHTEIN, Izd. Akad. N a u k SSSR 23: 1208, 1959 5. C. LIANG and S. KRIM, J. Polymer Sci. 27: 241, 1958 6. M. TAKEDA, A. JIMURA, A. YAMADA a n d Y. IMAMUDA, Bull. Chem. Soc. J a p a n 32: 1150, 1959 7. H. TADOKARO, S. NOZAKURA, G. K I T A Z A W A , V. CASUHARA and S. MIRATTASHI, Bull. Chem. Soc. J a p a n 32: 313, 1959 8. M. TAKEDA, K. JIMURA, A. YAMADA and Y. 1MAMUDA, Bull. Chem. Soc. Japan, 33 : 1219, 1960
CHEMICAL CONVERSIONS OF POLYMERS--XV. SPECIFIC FEATURES OF THE THERMAL DEGRADATION OF POLYENANTHAMIDE* S, R, R A F I K O V , G. N . C H E L N O K O V A , V. V. R O D E , I. V. Z t t U R A V L E V A and R. A. S O R O K I N A Institute of Elementary Organic Compounds, U.S.S.R. Academy of Sciences
(Received 20 April 1963)
A NUMBER of investigators have studied the thermal degradation of polyamides [1]. In [2] it was found that polycapramide and polyhexamethylene adipamide readily undergo thermal degradation at quite low temperatures (270 to 350°), and this leads to loss of end groups, hydrolytic splitting of the amide bonds and a reduction in molecular weight. Besides this branched and crosslinked structures form in polyhexamcthylene adipamide. The present work deals with the thermal degradation of polyenanthamide at 300-350 ° under various different conditions, the aim being to compare its thermal stability with that of the polyamides mentioned above. EXPERIMENTAL
Initial polyamides. Polyenanthamide of the " e n a n t " type was prepared in the form of crumbs on the pilot plant of the V N I I V ; [~1]~-0.98, viscosity molecular weight 19,000, carboxyl group equivalent 4000, amino groups above 100,000; water content of the air dried polymer was 0.8~o and after 70 hr v a c u u m drying at 80 °, 0.12~o. * Vysokomol. soyed 6: No. 4, 652-654, 1964.
(Received 16 April 1963) THERE is as yet no known method for the quantitative determination of the stereo-regularity of polymers, although some idea of their structure can be obtained in a number of eases b y means of X-ray diffraction, light scattering, nuclear magnetic resonance and other methods. The most usual w a y of identifying syndio- and isotactie polymers is b y deciphering the structure of the unit cells of crystalline fractions of these polymers b y means of X-ray diffraction analysis. B u t this method cannot be applied to the s t u d y of amorphous polymers or to those with only slight crystallization. Recently infrared spectra have been obtained for a number of syndio- and isotaetie polymers and there have been found to be differences between them which could be used for a qualitative assessment of the predominance of the one or other from [1, 2, 3]. In an article published b y one of the authors together with Volkenshtein [4] it was pointed out that differences are to be found in the infrared absorption spectra of iso- and atactic polystyrene, and that these differences are not only connected with the crystallinity of the isotactic specimen. Besides some slight differences in the 1070 em -1 range, as already noted b y Italian writers [3], we also found considerable differences in the spectrum in the 560 to 540 cm -1 range. These differences remained in the absorption spectra of solutions. Below we give the results of a quantitative s t u d y of these variations, taken on a N i p p o n - B u n k o DS 301 spectrophotometer with K B r prisms in imxylene at polystyrene concentrations from 0.5 to 1.0 mol/1., while the dish was 0.0252 and 0.050 em deep. The temperature was measured in the range from 20 to 135 ° for the solutions in p-xylene, and from 20 to 250 ° for the powder pellets compacted with the KBr. In the isotactic polystyrene solutions only the absorption bands at 557 em -1 could be seen (Fig. 1) with a slight projection at 540 cm -5. In the ataetie polystyrene solutions, on the other hand, there were adsorption bands at 540 cm -1 and one which appeared as a spike at 557 cm -1 (Fig. 1.). When the amount of isotactic fraction was varied (for instance, b y extracting the polystyrene prepared * Vysokomol. soyed. 6: No. 4, 647-651, 1964. 714
Stereoregularity of polystyrene
715
over stereospecifie catalyst, with different solvents) the intensity of the 557 cm -1 band increased with the increase in the isotaetic state of the polystyrene, while t h a t at 540 cm -1 diminished (Figs. 2 and 3a, b). We determined the integral intensities of all the polystyrene specimens at our disposal, there being about ten of them and all of different origins. Between 600 and 500 cm -1 the integral intensity was always 1800 1..mol-~.em -~, which means t h a t with variation in the isotacticity of the polystyrene there was redistribution of the intensity of the 557 and 540 cm -~ absorption bands. For quantitative determination of the stereoregularity of the polystyrene, we compared the integral absorption of the bands at 557 and 540 em -~ for each of the test specimens studied. This was done by determining k=ln(Io/I)/cd in the absorption spectra taken on the spectrophotometer (where Io/I is the reciprocal of the percentage transmission, c is the concentration in mole/1, and d is the depth of the dish in cm). K 50
K 40
30
20
,%,
10 ,t ~
~.
~------
600
550 cm-1
FIG. 1
500
600
l
550
I
cm-1
500
FIG. 2
FIG. 1. Absorption spectra of iso- (solid curve) and atactic (dotted curve) polystyrene in p-xylene.
FIG. 2. Absorption spectrum of polystyrene with slight isotacticity. Dotted curve shows the separation of the absorption band. After plotting the k versus v curve from 600 to 500 cm -1 (k being determined for every 1 cm-1), we found ]Cm~x at the m a x i m u m for one of the absorption bands and determined Avl/2 . its half width. I t is always best to begin the calculation with the more intense of the absorption bands, although the result does not depend on the band with which one begins. Taking in a zero approximation, the kmax
716
YE. I . POKI~OVSKII a n d YR. F . FEDOROVA
found experimentally according to the dispersion formula kV=al(r--ro)2+b (where kv is the coefficient at any frequency r, r0 is the kmax position; b=(12 Arl/2) 2 and a=kma x + b ) , we f o u n d t h e outlines of one of the absorption bands neglecting, in our zero approximation, the superposition of the absorption of the K 50
K 50
a
'
i
30
30
/i'
fO i
,I
#l 11
860
10
\\.k
',\ \ ~,~ "\,~, ~"'~,
550 cm-f
- J.,.Ji,., I/I/-"\i;x.t
._ 500
800
550
500
cm-I
FIG. 3. Separation of the absorption bands (dashed curve) of isotactic (a) and atactic (b) polystyrene.
second band. The theoretical outline was calculated from the actual absorption in the band 600 to 500 cm -1, b y which means it was possible to determine the absorption from the second band. After finding kmax in this w a y for the second band, and its half width, its outline was found b y once again using the dispersion formula and, after calculating it from the actual curve, we foundkma x and Avll 2 of the first band in the next approximation (Fig. 2 and 3a). After the first three approximations, k in the maxima of both the half-width absorption bands and consequently their integral intensities, are usually diminished. The total integral intensities corresponded to the actual integral intensities in this range, 600 to 500 cm -1. B y comparing the integral intensities of the absorption bands 557 and 540 cm -1 we also found the relative amounts of isotactic polystyrene fraction. In our specimens the isotactic fraction was 85 to 60%. In the atactic specimens the isotactic part of the polymer was 50%. Unfortunately we had no syndiotactic polystyrene specimens on which we could verify our previous prediction that the absorption bands at 540 cm -1 belonged to the syndiotactic part. It is probable that the absorption bands which we studied and which are connected with the deformation vibrations of the benzene r i n g
Stereoregularity of polystyrene
717
h(B~) [5], form one absorption band in this range of the spectrum, which t h e n breaks up into two as a result of the different structures of the polystyrene, and t h a t these depend on the position of the benzene ring as regards the carbon chain [6-8]. We note t h a t if the amount of isotactic fraction in the polymer increases the absorption band maximum at 540 em -~ shifts slightly to higher
i/zo I0O -
CZ
fO0
.f
8o
_,,,
%
600
8o
//
Go
II
V',,
20
b
//
Go
40
-"
\',, /I
\
I 550
40 I 500 cm -~
20 600
t 550
I 500 cm -I
FIG. 4. A t a c t i c (a) a n d i s o t a e t i c (b) p o l y s t y r e n e in p - x y l e n e . Solid c u r v e - - a t 20 °, d a s h e d - - a t 130 ° .
frequencies. There was never more than an error of ~-2%.in determining the amount of isotactic fraction in the same specimens with repeated analyses and different concentrations, c. The weak 588 cm -1 absorption band becomes more intense with increase in the isotaetic polystyrene but its km~x is one order of magnitude smaller than kmax at 557 and 540 cm -~, and this does not introduce a large error in determining the isotacticity. The artificial mixture of the a t a c t i c a n d more isotactic polystyrene contained 64~o isotactic fraction, The figure found by the above method was 64=E1%. When solutions of polystyrene in p-xylene are heated up to 130 ° there is hardly any change in the ratio of the absorption band areas at 557 and 540 cm -1 (Fig. 4a and b). A slight decrease in absorption in this range is due to expansion of the solution on heating. With the polystyrene heated in K B r pellets up to melting point no particular change was noted. On melting the 567 cm -1 absorption band due to long range disappeared from the spectrum of the crystalline isotactic polystyrene (Fig. 5a). The 557 cm -~ band shifts to 550. I n the molten atactic polystyrene (Fig 5b) the 5540 absorption bands shift. We note t h a t both these bands are asymmetric in the melt, but it was impossible to distinguish the two. I t hardly seems likely t h a t the appearance of the 557 and 540 cm -1 bands could be connected with short range order still preserved in the solution, as their intensity ratio does not depend on temperature.
718
YE. I. PoKl~ovsKII an4 YE. F. FEDOROVA
I n conclusion we would like to thank B. G. Belen'kii and M. V. Vol'kenshtein for discussing the results.
IO0 80
a 250,,~
60 40 20
600
I
I
570
540
b
I
510cm-t J250°
8° I _
~
~
104°
60 40 20
_~
20"
l,
1
600
500
I,, 400 c m -/
FIG. 5. Absorption spectra of isotactic (a) and atactic (b) polystyrene in KBr pellets at various temperatures. CONCLUSIONS
(1) A procedure has been developed for the quantitative determination of the stereoregularity of polystyrene, using infrared absorption spectra. The bands used for the analysis were 557 and 540 cm -1, which belong to the iso- and syndiotactic structure of polystyrene respectively. (2) The stereoregularity of a number of polystyrenes with 85 to 60% isotactic fraction has been determined. Atactic specimens contained 50% each of iso- and syndiotactic fractions. Translated by V. ALFORD
Chemical conversions of polymers
719
REFERENCES 1. D. MORERO, A. SANTAMROGIO,. L. PORRI and F. CIAMPELLI, Chemica e industria 58: 758, 1959 2. G. NATTA, L. PORRI, A. MAZZEI a n d D. MORERO, Chemica e industria 41: 398, 1959 3. D. MORERO, E. MAUTICA, F. CIAMPELLI and D. SIANESI: ])el nuovo cimento supplemento ol XV: X, 1, 122, 1960 4. E. I. POKROVSKII and M. V. VOLKENSHTEIN, Izd. Akad. N a u k SSSR 23: 1208, 1959 5. C. LIANG and S. KRIM, J. Polymer Sci. 27: 241, 1958 6. M. TAKEDA, A. JIMURA, A. YAMADA a n d Y. IMAMUDA, Bull. Chem. Soc. J a p a n 32: 1150, 1959 7. H. TADOKARO, S. NOZAKURA, G. K I T A Z A W A , V. CASUHARA and S. MIRATTASHI, Bull. Chem. Soc. J a p a n 32: 313, 1959 8. M. TAKEDA, K. JIMURA, A. YAMADA and Y. 1MAMUDA, Bull. Chem. Soc. Japan, 33 : 1219, 1960
CHEMICAL CONVERSIONS OF POLYMERS--XV. SPECIFIC FEATURES OF THE THERMAL DEGRADATION OF POLYENANTHAMIDE* S, R, R A F I K O V , G. N . C H E L N O K O V A , V. V. R O D E , I. V. Z t t U R A V L E V A and R. A. S O R O K I N A Institute of Elementary Organic Compounds, U.S.S.R. Academy of Sciences
(Received 20 April 1963)
A NUMBER of investigators have studied the thermal degradation of polyamides [1]. In [2] it was found that polycapramide and polyhexamethylene adipamide readily undergo thermal degradation at quite low temperatures (270 to 350°), and this leads to loss of end groups, hydrolytic splitting of the amide bonds and a reduction in molecular weight. Besides this branched and crosslinked structures form in polyhexamcthylene adipamide. The present work deals with the thermal degradation of polyenanthamide at 300-350 ° under various different conditions, the aim being to compare its thermal stability with that of the polyamides mentioned above. EXPERIMENTAL
Initial polyamides. Polyenanthamide of the " e n a n t " type was prepared in the form of crumbs on the pilot plant of the V N I I V ; [~1]~-0.98, viscosity molecular weight 19,000, carboxyl group equivalent 4000, amino groups above 100,000; water content of the air dried polymer was 0.8~o and after 70 hr v a c u u m drying at 80 °, 0.12~o. * Vysokomol. soyed 6: No. 4, 652-654, 1964.