Nuclear magnetic resonance studies of polymers—IV. Stereospecific methylacrylate and butylacrylate polymers

Stereospecific methylacrylate polymers

79

14. W. L. HAWKINS, V. L. LANZA, B. B. LOEFFER, W. MATREYEK and F. H. WINSLOW, Rubber Chemistry and Technology 32: 1171, 1959 15. M.B. NEIMAN, A. S. KUZ'MINSKII and L. G. ANGERT, Vestnik Akad. Nauk SSSR 30: 38, 1960 16. A. A. BERLIN, Z. V. POPOVA and D. M. YANOVSKII, Dokl. Akad. Nauk SSSR 131: 593, 1960 17. N. M. EMANUEL and Yu. N. LYASKOVSKAYA, Tormozheniye protsessov okisleniya zhirov. (Retarding F a t Oxidation Processes.) Pishchepromizdat, 1961 18. P. I. LEVIN, A. F. LUKOVNIKOV, M. B. NEIMAN and M. S. KHLOPLYANKINA, Vysokomol. soyed. 2: 1243, 1961 19. V. P. CALKINS and H. A. MATTILL, J. Amer. Chem. Soc. 66: 239, 1944 20. C. GOLUMBIC and H. A. MATTILL, J. Amer. Chem. Soc. 63: 79, 1941 21. W. L. HAWKINS and M. A. WORTHINGTON, Chem. and Ind. 32, 1023, London, 1960 22. G. I. LIKHTENSHTEIN, Papers Presented at the All Union Conference on the Aging and Stabilization of Polymers, Moscow, 1961 23. B. T. LEHMANN and B. M. WATTS, J. Amer. Oil Chem. Soe. 28: 475, 1951 24. G. W. KENNERLY and W. L. PATTERSON, Ind. Eng. Chem. 48: 1917, 1956 25. A. A. BERLIN and M. I. CHERKASHIN, Vysokomol. soyed. 1: 1817, 1959 26. Yu. A. SHLYAPNIKOV, V. B. MILLER, M. B. NEIMAN, Ye. S. TORSUYEVA and B. A. GROMOV, Vysokomol. soyed. 2: 1409, 1960

NUCLEAR MAGNETIC RESONANCE STUDIES OF POLYMERS--IV. STEREOSPECIFIC METHYLACRYLATE AND BUTYLACRYLATE POLYMERS * N . M . BAZHENOV, M . V . V O L ' K E N S H T E I N a n d A . S. K H A C H A T U R O V Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences

(Received 28 December 1961) TO INCREASE ouc knowledge of stereospecific macromolecular compounds re-

liable methods of assessing the nature of and degree of regularity of the macromolecules are required. Besides X-ray diffraction methods and infrared spectral analysis, which can provide certain information on microtactic polymers, that of nuclear magnetic resonance (NMR) can also be used. In some cases high resolution NMR spectra not only provide information on the prevalent form of stereoregularity of the polymers, but they also permit quantitative assessment of the relation of the different sequences in polymer chains without drawing on information provided by other methods. The problem of the connection between the shape of high resolution NMR spectra and the degree and nature of the stereoregulaxity of polymers, particularly * Vysokomol. soyed. 5: No. 7, 1025-1028, 1963.

80

N. M. BAZHENOVet

al.

p o l y m e t h y l m e t h a c r y l a t e (PMMA), has been studied by a num ber of authors [1-5]. The stereospecific nature of PMMA has been given a particularly detailed study in the work by B ove y and Tiers [3]. Using free radical and anionic initiation, different solvents and temperature conditions, t hey synthesized PMMA specimens which showed mainly isotactic and syndiotactic structures. The study of the proton NMR spectra of these specimens led the authors to the following principal conclusions: 1) the absorption bands of the m e t h o x y group undergo no particular changes with change in the structural regularity of the polymer, 2) as was to be expected from general considerations, the methylene group gives a single absorption band in the syndiotactic structure, and this splits up into a q u ar tet in isotactic form, 3) an absorption band corresponding to the meth y l group directly joined to the principal chain consists of three bands. The high intensity of these bands is determined by the ratios between the syndio-, iso- and hetero-sequencies in the PMMA macromolecule. I f the specimen has block copolymer structure the size of the blocks can be found on the relative intensities of the heterosequence bands. Accepting this interpretation of the NMR spectra, the authors assert t h a t the free radical PMMA is mainly obtained in the syndiotactic form, while PMMA specimens obtained with anionic initiators are principally isotactic, which is quite consistent with other data. We have also unde r t aken the study of variations in high resolution NMR spectra with variation in the quantitative ratio of syndio- and iso-sequencies in a PMMA solution. The aim of the work was, on one hand, to obtain more on the proton resonance spectrum of stereo regular PMMA and, on the other, to solve the purely analytic problem of determining the form of stereoregularity in PMMA specimens obtained by different methods in the K o r o t k o v laboratory of our I n s t i t u t e [6]. Besides PMMA we studied p o l y b u t y l m e t h a c r y l a t e (PBMA), also obtained b y different methods in the K o r o t k o v laboratory of our Institute [7]. EXPERIMENTAL All the studies were conducted on a high resolution (10-8) radio spectrometer JNM-3 with a frequency of 40 me/s at 20 °. High resolution NMR spectra were recorded from a number of PMMA specimens synthesized under different conditions. Chloroform was used as the solvent and the concentration of the solution was around 10%. Bearing in mind Bovey's remarks [3], two PMMA specimens were chosen. One with maximum content of isotactic configurations and one with maximum syndiotactie. The first specimen was prepared by polymerization in toluene with butyl lithium at --60 °. We will call this isotactic. The second, prepared in ammonium medium at --50 ° also with butyl lithium, will be regarded at syndiotactic. The NMR spectra of the specimens are shown in Fig. 1. From these two "pure" specimens artificial binary mixtures were made containing 10 and 90%, 25 and 75%, 50 and 50%, 75 and 25% and 90 and 10% isotactie and syndiotactic PMMA respectively. The NMR spectra of these mixtures dissolved in chloroform, and those of commercial PMMA produced by the radical polymerization method, are shown in Fig. 2. The NMR spectra of a number of PBMA specimens are shown in Fig. 3.

81

Stereospecific methylacrylate polymers 37

37

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F[(~. 1. High resolution NMR spectra for isotactic and syndiotactic PMMA: a--isotactic, b-- syndiotactic. DISCUSSION

The PMMA and MR spectra (Fig. 1 and 2) have certain features which were not noted in the work by Bovey and Tiers. The spectrum of the pure syndiotactic PMMA does not have such a sharp and intense peak in the CHa triplet as t h a t of the "pure" isotactic one. This cannot be attributed to lack of resolution on the part of the spectrometer, or to the fact t h a t the PMMA specimej~ which we have formally described as purely syndiotactic, actually contains a marked quantity of configuration impurities of another kind. The broadening of the CH a peak to be seen where the polymer structure is predominately syndiotactic could be due to the presence of a considerable amount of hetero co]~figuration. For them to form, however, a considerable amount of isotactic configurations would have to be present. But, as can be seen from a comparison of the spectras from PMMA mixtures (Fig. 2) the increase in the percentage concentration of the isotactic polymer has a marked effect. Most probable exp]a,nation of the difference in the width of the methyl group peak between the iso- and syndiotactic

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54

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FIG. 2. High resolution NMR spectra for binary mixtures for iso- and syndiotactic PMMA: a--purely isotactic, b - 90~o iso- plus 10 syndio-; c--75~o iso- plus 25~o syndio-; d--50~o iso- plus 50~o syndio-; e--25~o iso- plus 75% syndio-; f--10~o iso- plus 90°Jo syndio-; g--purely syndiotactic; h--commercial.

60

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83

Stereospecificmethyiacrylate polymers

configurations seems to lie in a change in the mobility of CH 8 group due to a change both in the relative disposition of the carbonyl groups, and also in the configuration of the main chain of the polymer. It can be seen from a direct comparison of the spectra from different PMMA nfixtures t h a t even if there is a relatively small amount (10%) of isotactic configurations, there is a clearly defined peak at 6 = 6 1 . * At the same time, the appearance of a marked peak at = 64, for the syndiotactic form, requires an even higher concentration of syndio configurations (about 50 %).

a

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Fro. 3. High resolution NMR spectra of PBMA: a--isotactic; b--syndiotactic. It must be remembered that the results of the study of artificial binary mixtures are not quite as full as they should be for the study of specimens of polymers with variable microtactic configurations in the chain. In the first case a summary is made of the effects created by whole macromolecules of different stereo configuration, and in the second, there should be a large number of hetero transitions which m a y appear in the NMR spectra. However, if there is any substantials surplus of one of the configurations then corrections for hereto configuration would have to be used. Commercial PMMA prepared by radical polymerization is regarded as atactic. This follows from chemical considerations because certain of the physical properties of the specimen are intermediate between those ofiso- and syndiotactic PMMA. This relates, for example, to the embrittlement temperature and the temperature course of the second moment [2]. The high solution NMR spectrum of this "atactic" polymer (Fig. 2) is virtually identical with t h a t of "pure" syndiotactic PMMA. The so-called "atactic" polymer thus has in fact a predominantly syndiotaetic structure. In essence this might have been expected on the basis of simple theoretical considerations regarding the high thermo* Here 6 is the chemical shift round benzene. The numerical magnitude of the shift is determined from the equation 6~((H--Ho)/H )" 10v) where H and H 0 are the resonance field for the measured and standard peaks.

84

N . M . BAZH]~NOVet al.

dynamic probability of syndiotactic combination of units in radical polymerization. The syndiotactic nature of PMMA seems to lead to the conclusion that the embrittlement temperature and the mobility of the macromolecules do not vary symbiotieally with increase in a certain form of regula.rity. It may be thought, however, that the difference in the mobility of the macromolecules in atactic and syndiotactic PMMA, which was established in [1, 2], is due to the presence of low-molecular impurities in the specimens, to which the chemical characteristics are particularly sensitive. The NMR spectra of stereoisomeric forms of PMMA are distinguished mainly by the multiplet structure of the methylene group peak. The same is to be expected for PBMA, but here the problem is considerably complicated due to the presence of methylene groups in the weight increment. The absorption bands of these groups overlap the methylene group spectra of the main chain and thus considerably mask its structure which, of course, should also have a multiplet nature for an isotactic polymer. It is therefore considerably more difficult to use the NMR method to assess the shape and degree of the stereoisomer content for PBMA, however, the general regularities observed in the PBMA NMR spectra are similar to those described in PMMA, and they can be used to provide a qualitative assessment of the prevailing type of stereoconfiguration. On passing from syndiotactic PBMA structure to the isotactic there is a gradual dissappearance of the division of the principal peak into two components. PBMA whose spectrum shows the clearest division of the peaks at J = 6 0 (Fig. 3), is in the most syndiotactic state of all those studied by us. This polymer was produced in ammonium medium in the presence of metallic lithium and a polymerization time of 60 min. The PBMA corresponding to the spectrum with the least division of these peaks (Fig. 3) was prepared in hexane with butyl lithium at --50 ° with a polymerization of 60 min, and it appears to be the most isotactic. CONCLUSIONS

High resolution proton magnetic resonance spectra have been obtained from different PMMA and PBMA specimens. The considerable differences in the spectra of iso- and syndiotactic PMMA have been used, by means of artificial mixtures, to establish the influence of the relative concentration of the stereoisomers on the spectrum. It has been demonstrated that commercial PMMA has mainly syndiotactic structure. The differences in the spectra of isomeric PBMA are similar to those observed for PMMA. Translated by V. ALFORD

REFERENCES 1. N. M. BAZHENOV, M. V. VOL'KENSHTEIN, A. I. KOL'TSOV and A. S. KHACHATUROV, Vysokomol. soyed. 1: 1048, 1959 2. N. M. BAZHENOV, M. V. VOL'KENSHTEIN, A. I. KOL'TSOV and A. S. KHACHATUROV, Vysokomol. soyed. 3: 290, 1961

Ziegler polymerization of vinylchloride

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3. F. A. BOVEY and G. V. D. TIERS, J. Polymer Sei. 44: 173, 1960 4. U. JOHNSEN and K. TESSMAR, Kolloid-Z. 2: 160, 1960 5. A. NISHIOKA H. WATANABE J. IAMAGUCHI and H. SHIMIZU, J. Polymer Sci. 45: 232, 1960 6. A. A. KOROTKOV, S. P. MITSENGENDLER, V. N. KRASULINA ,and L. A. VOLKOVA, Vysokomol. soyed. 1: 1319, 1959 7. Z. A. AZIMOV, S. P. MITSENGENDLER and A. A. KOROTKOV, Vysokomol. ,~oye(1. 4: 835, 1962

POLYMERIZATION

OF VINYLCHLORIDE IN T H E P R E S E N C E OF Z I E G L E R TYPE CATALYSTS*

G. A. RAZUVAYEV, K. S. MINSKER, A. I. GRAYEVSKII, Z. S. SMOLYAN, G . T. FEDOSEYEVA and D. N. BORT (Received 28 Dece,mber 1961)

ZIEGLER-NATTA catalysts are widely used to prepare crystalline polymers from non-polar unsaturated compounds. Polar monomers of the vinylchloride, methylmethacrylate, acrylic nitrfle type and so on, are reduced in the presence of these catalysts. For instance, due to the influence of Ziegler-Natta catalysts in a supersaturated hydrocarbon medium vinyl chloride will separate HC1 [1]. Methylmethacrylate is also reduced during polymerization in the presence of a]uminium alkyls. Nevertheless it has been demonstrated [2] that an ordinary Ziegler catalyst consisting of a mixture of organoaluminium compounds with titanium tetrachloride can be used to polymerize vinyl chloride with formation of a crystalline polymer. The electron diffraction pattern of this product was in the shape of 10 clearly defined reflexions in tLe interp]anar range d=5.27 to 1.69 A. Under these conditions, however, polymerization will only proceed with satisfactory yields where there are certain complex-forming additions of the nucleophilic type which lower the total reducing capacity of the system and also, probably, may lead to a change in the polarity of the C--X bond in the monomer (X is the hetero atom), which makes the reduction of the functional groups of an unsaturated compound difficult. A description has been published of the polymerization of vinyl chloride and methylmethacrylate on a heterogeneous catalytic system consisting of a mixture of tri-isobutyl aluminium and vanadium trichloride at 30 ° in a medium of tetrahydrofuran or in the presence of triethyl alum inium, an ester and vanadium compound [3]. * Vysokomol. soyed. 5: No. 7, 1030-1033, 1963,