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C O M M U N I C A T I O N S TO THE EDITOR
Broadening of Carbonyl Stretching Vibration Bands Appearing for Acrylate Copolymers
Sir: Environmental effects upon infrared and nmr spectra have been discussed for the purpose of investigating the sequence distribution in copolymer However, reports available to date concerning this subject in infrared spectroscopy have been confined mainly to the shift of characteristic bands and the change in absorbing i n t e n s i t i e ~ . ' ~The ~~~ present communication deals with a preliminary result that the 1730-cm-l band characteristic of the stretching vibration of C=O groups in methyl acrylate (MA)styrene (ST) copolymers exhibited broadening with increase in the MA content. The half band width measurement in this study was made tentatively using the apparent band profile obtained directly on recording paper. The samples were prepared by copolymerizing MA and ST monomers in benzene with azobisisobutyronitrile as the initiator at 75". The whole polymers thus obtained were used for the infrared measurement. The infrared spectra were taken with a Perkin-Elmer Model 521 spectrometer with grating. The spectrometer was calibrated against the 1609.7- and 1603.0-cm-l bands of indene and polystyrene, respectively. The spectra were recorded using films prepared from benzene solutions. The film thickness foS each measurement was adjusted in such a way that the absorbance a t 1730 cm-l for each sample fell in a range of 0.7-0.8. The slit width of the spectrometer was set a t 125 p (80 cm-l), and this affected the band height only by 1% according to the Ramsay estimation,S*6 so that possible distortions of the true band shape in question should have been minimized. The spectra in the proximity of the 1730-cm-l band for copolymer samples and an MA homopolymer are shown in Figure 1, from which the peak position and the half band width (measured in cm-l) were read. The reproducible accuracy of these readings was within *0.5 ern-'. The result is given in Table I. It can be seen from Table 1 that although no shift of peak position is observed practically with changes in the composition, the half band width, Ai%, decreases regularly with decreasing the MA content. Thus an attempt was made to interpret this trend in terms of the sequence length in copolymer chain, and values of Aijh were plotted against P2 and P B , which are the probabilities for finding the connections MA-MA and MA-MA-MA in a chain, respectively. These proba-
bilities were evaluated from the reactivity ratios for ST(1) and MA(2); r1 = 0.75 and r2 = 0.20 at 70°.' Figure 2 shows that Aiih is linearly proportional Table I: Changes in Peak Position and Half Band Width of Carbonyl Absorption Band with Acrylate Content MA
Peak
Polymer code
content, mole % '
position, cm-'
PMA 1
100 74.2 57.5 47.3 34.2 22.4
1733 1733 1733 1734 1733 1733
S M 25 SM 40 SM 50 SM 65 SM 76-1
Band width, om-1
36.1 31.2 22.4 19.2 19.2 17.5
L 173
1734
1733
WAVE NUMBER (e")
Figure 1. Absorption band profiles for carbonyl groups in the proximity of 1730 cm-1. Curves A, B, and C are for PMA 1, S M 50 and SM 76-1, respectively.
to Ps,the triad sequence probability. This fact implies, at least, that the principal factor producing broadening of the 1730-cm-l band is undoubtedly perturbation by neighboring carbonyl groups in an (1) G. M. Kline, "Analytical Chemistry of Polymers," Part 11, John Wiley and Sons, Inc., New York, N. Y., 1962. (2) G. Schnell, Ber. Bunsenges. Physik. Chem., 70, 297 (1966). (3) U.Johnsen, ibid., 70, 320 (1966). (4) Y. Yamashita, Kagaku (Kyoto), 27, 59 (1966). (5) K. S. Seshadri and R. N. Jones, Spectrochim. Acta, 19, 1013 (1963). (6) D. A. Ramsay, J . A m . Chem. Soc., 74, 72 (1952). (7) T. Alfrey, Jr., E. Mers, and H. Mark, J . Polymer Sci., 1, 37 (1946).
Volume 7 1 , Number 1.2 November 1967
COMMUNICATIONS TO THE EDITOR
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intramolecular sense. I n addition, it is of interest to note that the plot passes, when extrapolated to Pa = 0, through an intercept which corresponds to the Aijh value obtained for MA homopolymer in benzene solution (17.7 cm-l). Another finding is that the band width tends to increase with elevating temperature.
Proton Ejection Accompanying Light-Induced Electron Transfer in the Chlorophyll-Quinone System
Sir: Linschitz and Rennert' have shown that chlorophyll undergoes a reversible photobleaching in the presence of benzoquinone. Tollin and his co-workers2,8 demonstrated by esr measurements that the benzosemiquinone ion radical is formed in these light-activated single electron transfer reactions. The present paper presents evidence to show that these reactions are accompanied by the ejection of a proton. Studies performed in the aprotic solvent, dimethylformamide, demonstrate that chlorophyll is the proton source. The apparatus used to measure the proton ejection has recently been de~cribed.~A Corning 52-61 filter, which is opaque to all wavelengths below 600 mp, was used. Chlorophylls a and b were prepared by the method of Zscheile and C ~ m a r . p-Benzoquinone ~ was purified by sublimation, p-chloranil was recrystallized from acetone, dimethylformamide was distilled under vacuum from calcium hydride, and the methanol used was the spectrophotometric grade (Fisher). Benzoquinone in alcohol slowly forms a species which absorbs at 355 mp. Since this species is not formed in Figure 2. Plots of half band width against dyad and triad either dimethylformamide or with chloranil, it is assequence probability, Pz and Pa,respectively. sumed to have little or no effect on the final results For details, see text. presented. Figure 1 shows the apparent proton ejection from both the chlorophyll a- and b-quinone systems in I n connection with the above observations, it should methanol. Solutions were deaerated by flushing with be noted that the half band width of the C=O band nitrogen pretreated with a chromous chloride solution. found for dimethyl fumarate is clearly smaller than The dashed line illustrates results obtained after the that for dimethyl maleate when they are determined air-free solutions were exposed to air for at least 0.5 hr. in benzene solution. The difference in the steric conThese are typical results obtained in a series of light figuration of carbonyl groups appears to be reflected and dark intervals. Irradiation of the chlorophylls in the band width. Further detailed observations alone in methanol in the presence of air gives irreversible and a pertinent interpretation of this phenomenon alkaline reactions which are probably due to the basicity will be given in due course. of the products from the photooxidation of the chlorophylls. Air-free systems of chlorophyll b give no pH Acknowledgments. The authors thank Professor response but a slight alkaline reaction is obtained with Toru Takenaka, Institute for Chemical Research, and chlorophyll a. This may be due to residual oxygen Professor Hirotsugd Matsuda, Research Institute for present in the system. Studies of the chlorophyll bFundamental Physics, Kyoto University, for their p-chloranil system in methanol showed that more prohelpful discussions during the course of this work. tons are ejected than observed with benzoquinone. The RESEARCH LABORATORY FUMIO KAMIYAMA apparent proton ejection activity is in the range of SEKISUICHEMICAL COMPANY MISHIMA-GUN, OSAKA-FU, JAPAN
HISAYUKI MATSUDA
(1) H. Linschits and J. Rennert, Nature, 169, 193 (1952). (2) G. Tollin and G. Green, Bwchim. Bwphys. Acta, 60, 524 (1962). INSTITUTE FOR CHEMICAL RESEARCH HIROSHIINAGAKI (3) G. Tollin, K. K. Chatterjee, and G. Green, Photochem. Photobwl., KYOTO UNIVERSITY 4, 592 (1965). TAKATSUKI, OSAKA-FU, JAPAN (4) K. P. Quinlan and E. Fujimori, ibid., 6 , 665 (1967). (5) F. P. Zscheile and C. L. Comar, Botan. Guz., 102, 463 (1941). RECEIVED AUGUST 3, 1967
The Journal of Phyeical Chemietry
