Crystallization of stereoregular polydimethylmethacrylate

CRYSTALLIZATION OF STEREOREGULAR POLYDIMETHYLMETHACRYLATE* V . N . : N I K I T I N , :N. V . I~¢[IKI-IAILOVA a n d L . A . V O L K O V A I n s t i t u t e of Macromolecular Compounds, U.S.S.R. Academy of Sciences

(Received 12 August 1964)

AS ESTABLISHED in [1-4], under certain conditions of methylmethacrylate polymerization, macromolecules are formed with different stereoregular structures. These are isotactic and syndiotactic polymethylmethacrylate (PMMA) and the block copolymer. These polymers have the capacity to crystallize and have different diffraction patterns, glass points, erystallite melting points and density. Their I R spectra are also different. In [5], for instance, it was found that syndioPMMA in the amorphous state has absorption bands 1482, 1060, 910 and 822 cm-1; in iso-PMMA these are seen as a very faint absorption. The unit cell of iso-PMMA was established by X-ray diffraction analysis of oriented specimens [6], and this form was found to crystallize as a 5~ coil with an identity period of 10.55A along the axis. The X-ray diffraction analysis results for syndio-PMMA are not so reliable, but it is assumed to have the coil 104. In [7] we studied the I R spectra of amorphous and crystalline iso-PMMA and found t h a t the crystal state had the absorption bands 1560 and 1580 cm-*. The present investigation dealt with the crystalline forms of iso- and syndioPMMA. Three methods were used: II~ spectroscopy, X-ray diffraction analysis and polarization microscopy. PROCEDURE The iso- a n d syndio-PMMA were prepared in the same way as in [4]~. Two fractions were studied, soluble and insoluble in acetone. The films were prepared from a solution in chloroform b y forming them on K B r plates or glass. The starting films, made of soluble and insoluble fractions, were amorphous. Crystallization was effected b y swelling the films in 4-heptanone for 16 hr at room temperature, and drying them afterwards. 2 hr heating at 100-120 ° increases their crystallinity. The crystallization polymer was established b y X-ray diffraction analysis a n d I R spectra. The crystallized iso-PMMA films were oriented b y drawing them to ten times at 70 °. The spectra were t a k e n on a UR-10 spectrometer. The polarizers were selenium films, which were p u t into the two channels of the spectrometer. * Vysokomol. soyed. 7: No. 7, 1235-1240, 1965. We would like to t h a n k A. A. Korotkov, S. P. MitzengencUer a n d V. N. Krasulina for presenting the stereoregular PMMA specimens. 1368

Stereoregular polydimethylmethacrylate

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RESULTS A N D DISCUSSION

The PMMA fraction insoluble in acetone was found to crystallize much b e t t e r t h a n t h e s o l u b l e one. I t c o u l d b e t h a t t h e s o l u b l e a n d i n s o l u b l e f r a c t i o n s i n iso- a n d s y n d i o - P M M A h a v e d i f f e r e n t d e g r e e s o f m i c r o t a c t i c i t y . B u t c o m p a r i s o n o f t h e i n t e n s i t i e s o f t h e 1482, 1060, 910 a n d 822 c m -1 b a n d s ]n t h e s p e c t r a o f t h e t w o f r a c t i o n s s u g g e s t s t h a t i t is p r a c t i c a l l y t h e s a m e . T h a t there was little difference in the m i c r o t a c t i c i t y of the two fractions w a s also e s t a b l i s h e d b y n u c l e a r m a g n e t i c r e s o n a n c e , w h i c h s h o w e d t h a t t h e i s o t a c t i c i t y o f t h e s o l u b l e a n d i n s o l u b l e f r a c t i o n w a s a p p r o x . 8 0 % for t h e i s o t a c t i c s p e c i m e n . T h e m e t h o d u s e d w a s t h a t d e s c r i b e d i n [8]*. T h e d i f f e r e n t c a p a c i t y I R SPECTRAOF ISO- AND SYI~DIO-PM~CIAIN THE AMORPHOUSA~D CRYSTALLIZEDSTATE Isotactic' amor phous, v, cm_ 1

Syndiotactic amor phous, v, cm_l

crystalline v, cm -1

polarization

1730 1580 1560

~ ~ a

1730 ~ 1590

1730 15801 1560]~

crystalline

1482" 1444 1435 1385 1367" 1262

1482" 1444 1435" 1385 1367" 1262

~ a

1482 1448 1438 1385 1367

1482 1448 1438" 1385 1367

Ja(a--CHs) ~(CHa) $,(CH3--O) 8,(~--CHs) ~,(~--CHs)

1242 1190 1150 1060t 990 950

1242 1190 1150 1060 t 990 950

1272 1242 1190 1150 1060 982 962 910 860

1722~ 1242J

va(C--C--O)-~v(C--O)

1730 ~ 1590

a"

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identification

r(c=0)

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--

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840

840

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807 756 555 515 483

807 756 555

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483 450

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840 822 807 748 555 515 483

1 1 9 0 1

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lattice valence % ~(CH) v , ( C - - O - - C ) + y(CHs--O) 7(~--CHs) intensity diminishes on crystallization

lattice valeneeW~(CHs)

crystalline

* Radious t Very week r a d i o u e * We would like to t h a n k A. I. Koltsov for carrying out the measurements.

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V.N. NIKITINet al.

of these fractions to crystallize is probably connected with their different stereo block structure, i.e., the molecular chains in the insoluble fraction consist of larger stereoregular fragments than in the soluble one. The subsequent s t u d y of the crystallization of iso- and syndio-PMMA was performed on fractions insoluble in acetone. Figure 1 shows the spectra of amorphous and crystalline films of iso- and syndio-PMMA prepared from insoluble fractions. The polarization frequencies and bands described are given in the Table. The bands were taken from [9]. f08

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FIG. 1. I R spectra: a--iso-, and b - - s y n c L i o - P ~ .

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Films approx. 20 # thick. Solid

curves for amorphous, dashed for crystalline specimens. As we can see from Figs, 1 and 2, on crystallization, intense 1580 and 1560 cm -z and the band 450 cm -1 appear in the I R spectrum of iso- and syndio-PMMA. I f the atactic specimen is treated with 4-heptanone, it' is interesting to note that these kinds of variations do not appear in the I R spectrum. This suggests that the appearance of the new bands is not associated with any. chemical transformations which occur when i s o - a n d syndio-PMMA is treated in this way. Besides this, there is a full conformity between the appearance of new bands in the spectrum and t h e X-ray diffraction pattern of the crystallized specimens.

Stereoregular polydimethylmethacrylate

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I n [9] stereoregular PMMA was crystallized, not in 4-heptanone, but by heating drawn films. No new absorption bands appeared in the I R spectra of these specimens, the only thing seen was the change in the intensity of certain bands. I n t h a t work it was found t h a t the X-ray diffraction pattern of the oriented iso-PMMA was exactly the same as t h a t derived in [2]. This confirmation is not convincing, since different diffraction patterns, of oriented and disoriented specimens, were prepared.

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c/~7-¢ 150o FIG. 2. Variation in absorption in the 1500-1700 em-1 band when stereoregular PMMA is treated in 4-heptanone and heated: 1--original amorphous film, 2--same film swollen in 4-heptanone for 16 hr, 3--swollen in 4-heptanone and dried at room temperature for several days, 4--heated for 2 hr a t 110% 5--crystallized film heated at 220° for 1 hr, 6--the same film heated at 220° for several hr more. We studied the intensities of the bands 1580, 1560 and 450 cm -1 as functions of the heating temperature of crystallized specimens. Beginning from 160 °, the intensity of these bands was found to fall a little. Big changes in intensity were observed at higher temperatures (220°): the 450 band disappeared and, instead of the 1560 and 1580 bands, only one wide band remained, at approx. 1590 cm -1 (see Fig. 2). The intensity variations depend not only on the tempera° ture, but also on the heating time. For instance, on heating at approx. 220 °, the 1580, 1560 and 450 cm -1 bands disappear after 2-3 hr for iso- and syndio-PMMA; in the isotactic polymer these bands disappear after approx. 20 hr at approx. 180-190 °, whil~ in the syndiotactic polymer .their intensity only diminishes. From X - r a y diffraction analyses of crystallized films of isotactic PMMA, it was

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V.N. NIKITINet al.

established that there is a marked reduction in crystallinity at approx. 180-200 °. This reduction increases with the heating time. There is a big drop in crystallinity at 200-220 ° after heating for about 3 hr. Studies in a polarization microscope showed that the crystallized films, which give an anisotropic picture (Fig. 3a) only become isotropic after heating

FIG. 3. Pattern observed in polarization microscope: a--crystalline iso-PMMA, b--the same swollen in chloroform.

at 220 ° for approx. 2 hr. 3 hr heating at approx. 180 ° hardly alters the anisotropic pattern at all for iso-PMMA. According to [1, 3], the melting point of iso-PMMA is 160 °, and for syndio-PMMA, 190 or ~ 2 0 0 °. Our studies showed that the melting point is substantially dependent on the heating time. The high melting point of stereoregular PMMA and its low melting rate are probably associated with the rigidity of the molecular chains which are in spiral conformation, where the bariers to inner rotation are high and dictated b y the large COOCH 8 groups in the chain.

Stereoregular polydimethylmethacrylate

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• Figure 4 shows spectra of oriented c~stallized films of isotactie PMMA in polarized light. The 1560 and 1580 bands have opposing dichroism, o a n d ~ respectively; the 450 c m , z b a n d has ~-dichroism. "Crystalline'? b a n d s are known to have strong dichroism; this is also the case for the bands above.

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Figure 5 shows the variation in the dichroism in the band 1580 cm -1 as a function of temperature. I t can be seen t h a t the crystalline orientation varies very little right up to approx. 200°; at 210 ° there is practically no dichroism. This curve reflects the melting of crystallites and their disorientation. The inflection found at 65 ° corresponds t o t h e glass point of the polymer, and the second one shows the melting of the crystallites. D,,/~

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Fig. 5. Dichroism of. band 1580 cm-I as a function of the temperature of the specimen. Specimen held for 2 hr at each temperature given. Thus, as recorded by X-ray diffraction analysis, the crystallization of iso- and syndio-PMMA is accompanied by the appearance of the 1580, 1560 and 450 cm -1 bands in the I R spectrum. Melting changes the intensity of these bands. All this

1374

V.N. NrKITZNe~a/,,

suggests t h a t these bands characterize the crystal state of stereoregular PMMA. The appearance of the same absorption bands on the crystallization of iso- and syndioPMMA is probably associated with the fact t h a t their crystallites have the same structure. I t is interesting to compare this with the fact that, according to X-ray structural data the principal valency chains in the iso- and syndio-PMMA crystal seem to h a v e the same spiral conformation [6]. I t could be that the 1580, 1560 and 450 bands disappear on dissolution of the crystallized specimens if this leads to breakdown of the crystsllites and spiral conformation of the chain. Our experiments have shown that these bands are retained on swelling and also when the specimens are dissolved in chloroform, benzene and CC14 (slight reduction in intensity if the solution is diluted), which m a y be due to the presence of crystalline formations in the solution. These formations cannot be established by X-ray diffraction analysis. The swelling of pre-crystallized PMMA film chloroform produced amorphous diffraction patterns, indicating the absence of any strictly three-dimensional order. Studies in a polarization microscope revealed (see Fig. 3b) isotropic formations in this kind of swollen film~. When the films were dried their crystsllinity was partly re-established. Films prepared from slightly concetrated solutions (1-2%) of crystallized specimens also gave crystalline diffraction patterns. We found t h a t ff a small a m o u n t of 4-heptanone was added to a solution (approx. 2%) of amorphous PMMA in chloroform, benzene or CC14, after abount 16 hr the 1580, 1560 and 450 cm -1 bands appeared in the spectrum of this solution, their intensity being less t h a n in the film. Films made of this solution gave crystalline diffraction patterns. • •• The X-ray diffraction method is thus not sensitivt~ e n o u g h to reveal the molecular formations in swollen specimens, but t h e y can be Seen ~n~a polarization microscope, and also in the I R spectrum (1580, 1560, 450 cm-Z~bands). I t is suggested t h a t these molecular formations are precrystalline structures, existing not only in swollen crystallized specimens but also in their solutions. The results suggest t h a t the 1580, 1560 and 450 cm -1 bands are not only typical of the crystalline, but also of the preerystalline state of the polymer with spiral macromolecular conformations. CONCLUSIONS

(1) By IR" spectroscopy, X-ray diffraction analysis and polarization microscope studies, the melting kinetics of crystallized stereoregular polymethylmethacrylate have been investigated. (2) I t has been found t h a t the crystallization of the polymer is characterized b y the 1580, 1'560 and 450 cm -I bands in the I R spectrum. t Birefringence, which can be used to stucty the molecular formations of PMMA in a polarization microscope, gives no proof of. the crystalline structure of these formations; it only indicates the existence of 'chain molecule orientation.

Critical opalescence in solutions of a polymer

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(3) Stable precrystalline formations exist in a solution of the crystallized polymer. Tran~lat~ by V. ALFORD REFERENCES 1. T. G. FOX, B. S. GARRETT, W. E. GOODE, S GRATCH, J. F. KINCAID, A. SPELL

and J. D. STROUPE, J. Amer. Chem. Soc. 80: 1768, 1958 2. T. G. FOX, W. E. GOODE, S. GKATCH, C. M. HUGGETT, J. F. KINCAID, A. SPELL

and J. D. STROUPE, J. Polymer Sci. 31: 173, 1958 3. R. G. MILLER, B. MILLS, P. A. SMALL, A. TURNER~ONES, D. G. M. WOOD, Chem-

istry and Industry 1323, 1958 4. A. A. KOROTKOV, 8. P. M]TSENGENDLER, V. N. KRA8ULINA and I~. A. VOLKOVA, Vysokomol. soyed. 1: 1319, 1959 5. U. BAUMANN, H. SCHEIBER and K. TESSMAR, Makromol. chem. 86: 81, 1959 6. J. D. STROUPE, R. E. HUGHES, J. Amer. chem. Soc. 80: 2341, 1958 7. V. N. NTIgITIN and N. V; MIKHAILOVA, Dokl. Akad. ~Tauk SSSR 148: 624, 1963 8. N. M. MAZHENOV, M. V. VOLKENSHTEIN and A. S. KH.ACHATUROV, Vysokomol. soyed. 5: 1025, 1963 9. H. NAGAI, J. Appl. Polymer Sci. 7: 1697, 1963

CRITICAL OPALESCENCE AND INTERMOLECULAR INTERACTION IN SOLUTIONS OF" POLY-p-YINYLNAPHTHALENE* V. YE. ESKIN a n d A. YE. NESTEROV Institute of High-Molecular Weight .Compounds, U.S.S.R. Academy of Sciences • (Received 12 A~ua~ 1964)

AFTER Debye had predicted the possibility of observing critical opalescence in polymer solutions [1], this effect was detected and studied in several papers [2-i0]. Similar investigations m a k e it possible t o determine the mean quadratic radius of gyration: of spheroidal'molecules (~)1/~ in solutions of moderate con: centration (2,10%) and compare it with t h e same value at " i n f i n i t e dilution" (R~) 1/2. The greatest interest is, however, attached to the possibility of finding certain parameters which characterize intermolecular, interaction in polymer solutions, particularly the mean effective radius of intermolecular forces I. According to the theory of effect [1], the latter value is averaged in respect of all the three types of intermolecular interaction in solution (polymer-polymer 2-2, polymer-solvent 1-2, solvent-solvent 1-1):

* Vysokomol. soyed. 7: No. 7, 1241-1247, 1965