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The packing density at the boundary between crystalline and crosslinked polymers and the solid phase
1502 3. 4. 5. 6. 7. 8. 9. 10.
11. 12. 13.
14. 15. 16.
17. 18.
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M. K. ORLOFF and D. D. FITTS, Biochim et biophys. Acta 47: 5996, 1961 Y. MATSUNAGA, Helv. Phys. A c t a 36: 800, 1963 F. GUTMAN and H. KEYZER, J. Chem. Phys. 46: 1963, 1967 J. SATO, N. KINOSHITA, M. SANO and H. AKAMATU, J. Chem. See. J a p a n 40: 2539, 1967 S. B. MAINTHIA, P. H. KRONICK and M. M. LABES, J. Chem. Phys. 41: 2206, 1964; H. HOEGL, J. Phys. Chem. 69: 755, 1965 G. G. SKVORTSOVA and G. N. KUROV, "Russian Authors' Cert. No. 241445, 1969; Byull. Izobret., No. 14, 1969 B. E. DAVYDOV, R. Z. ZAKHARYAN, G. P. KARPACHEVA, B. A. KRENTSEL, G. A. L A P r r S K I I and G. V. KHUTAREVA, Dokl. Akad. N a u k SSSR 160: 650, 1965 A. V. TOPCHIEV, Yu. V. KORSHAK, B. E. DAVYDOV and B. A. KRENTSEL, Dokl. Akad. N a u k SSSR 147: 645, 1962 A. A. DULOV and A. A. SLINKIN, Organicheskie poluprovodniki (Organic Semiconductors). 78, Izd. " N a u k a " , 1970 G. P. KARPACHEVA, Izv. Akad. N a u k SSSR, seriya khim., 190, 1965 L. A. BLYUMENFEL'D, V. V. VOYEVODSKII and A. G. SEMENOV, Elektronnyi paramagnitnyi rezonans v khimii (Electron Spin Resonance in Chemistry). Izd. Sibir. Otdel. Akad. N a u k SSSR, 1962 N. I. SHERGINA, G. G. SKVORTSOVA, G. N. KUROV and D. D. TARYASHINOVA, Zhur. prikl. Spektroskopii 13: 845, 1970 R. E L ' D E R F I L ' D , Gcterotsiklicheskic soyedineniya, t. 6 (Heterocyclic Compounds, vol. 6). 576, Izd. inostr. Lit., 1960 A. R. KATRITSKII, Fizicheskie m e t o d y v khimii geterotsiklicheskikh soyedincnii (The Use of Physical Method in Heterocyclic Compounds Chemistry). 551, ~zd. "Khim i y a " , 1966 N. N. MATSCH and J. DELER, Canad.' 5. Chem. 47: 17, 31, 73, 1969 B. WITKOP and J. B. PATRICK, J. Am. Chem. Soc. 75: 4474, 1953; B. WITKOP and T. W. BEILER, J. Am. Chem. Soc. 76: 5589, 5597, 1954
THE PACKING DENSITY AT THE BOUNDARY BETWEEN CRYSTALLINE AND CROSSLINKED POLYMERS AND THE SOLID PHASE* Y~.. G. MOlSYA, G. M. SEMENOVICH and Yu. S. LIPATOV High Polymer Chemistry Institute,Ukr. S.S.R. Academy of Sciences \ (Received 18 August 1971)
THE d e n s i t y c h a n g e s i n t h e s u r f a c e l a y e r s o f p o l y m e r s s i t u a t e d a t t h e b o u n d a r y w i t h t h e s o l i d p h a s e a r e t h e s u b j e c t o f s e v e r a l s t u d i e s [1-5]. T h e b e h a v i o u r of the surface layers of crystalline and crosslinked polymers at such a boundary * Vysokomol. soyed. A15: No. 6, 1337-1342, 1973.
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i n d i c a t e s t h a t t h e p r o p e r t i e s also c h a n g e t h e r e w h e n c o m p a r e d w i t h t h o s e of t h e s a m e p o l y m e r i n a free s t a t e [6, 7]. T h e a i m o f t h i s i n v e s t i g a t i o n w a s t o s t u d y t h e d e n s i t y c h a n g e s i n t h e s u r f a c e l a y e r s o f c r y s t a l l i n e or s t r o n g l y c r o s s l i n k e d polymers:
EXPERIMENTAL The density changes were examined by means of the luminescence spectra produced by anthracene molecules used as "pIobes". The densities of the surroundings and their changes as a result of various activities were evaluated on the basis of the established method [8--10] of luminescence spectral shifts of the anthracene probe molecules added to the system. I n this study the following were used: low pressure polyethylene (PE) and the polyepoxide ED-5 containing different plasticizers, i.e. dioctyl sebaceate (DOS), the aliplmtie oligo-epoxide DEG-1, or the oligo-ether acrylate MGF-9. A glass fibre weave was used as t h(~ support in the case of ED-5, quartz or teflon in the case of PE. These supports were transparent to ultraviolet (UV) light and differed by having different surface energies. The polyepoxide was hardend at room temperature with polyethylene polyamine (10%). Differing methods of addition of"anthracene to the polymers were used: 1) xylene was used as solvent addition to the soft ED-5 or DEG-1, combined with heating to 50°C and mixing, after which the xylcne was vacuum-evaporated, the polymers hardened and heat treated. 2) a xylene solution of anthracene was added to the hardened polyepoxido before beat treatment during a 30 rain or longer swelling (up to several days); some of these samples ~crc then heat trcated. 3) the hardened and heat-treated samples were soaked (allowed to swell) for 30 rain in a xylene solution of anthracene. The first, method enabled us to assess the average density of the polymer (as the probe molecules were evenly distributed throughout the samples), the second, the effect of the solvent on the polymer with and without filler, and also the effect of the heat treatment, and the third method, a n y heterogeneity appearing in the sample as a result of heat t r e a t m e n t (the anthracene moleenlcs entered the loosest regions of the sample during the 30 rain swelling in the xylene solution). The average densities and those of the least dense regions (]ooscst structures) of the polymers given subsequently in the text are those obtained b y the anthracene tracer addition methods refcrred to above. The anthracene concentration in the poisoners was 10 -3 mole/l. I t entered the P E from the xylenc, after which the P E fihns were melted in an oven a n d then transferred to another oven for crystallization at difS~rcnt tempcr~turcs during a 2 bx heating period. Three melting temperatures were used, i.(,. 130, 150 and 175°C, a n d two crystallization temperature, 80 and 40°C, of which the first gives the faster development of spherulites, tb_e second the faster development of crystalliz~ltion centres [11, 12]. The snpermolecular structures were studied by means of polarization nfieroscope MIM-8; the thin sectior~s were produced from the films by the usual method. The luminescence, spectra of the anthracene tracer molecules werc recorded at 77°K on a DFS-12 spectrometer. Th(~ experimentation method had been reported earlier [8--10]. RESULTS
Polyethylene. T h e a n t h r a c e n e t r a c e r s p e c t r a c o n s i s t e d i n all cases o f t h e s u m o f t w o s p e c t r a : A: s p e c t r a o f t h e a n t h r a c e n e i n t h e a m o r p h o u s z o n e s o f :PE, K : i n t h e c r y s t a l l i n e z o n e s [8-10]. T h e e x c i t a t i o n o f t h e a n t h r a c e n e m o l e c u l e s was p r o d u c e d d i r e c t l y o n t h e s u p p o r t s , w h i l e i n s o m e cases t h e P E films w e r e also m e l t e d o n t h e m a n d c r y s t a l l i z e d , i.e. t h e c o n t a c t b e t w e e n t h e film a n d t h e solid surface was n o t d i s t u r b e d d u r i n g m e a s u r e m e n t s .
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Our optical polarization studies showed that the melting and crystallization conditions of PE, i.e. 175/80, 175/40, 150/80 and 150/40 (°C) gave rise to a transcrystalline surface layer on the quartz and the teflon supports; this had also been shown before [11, 12]. The morphological characteristics found under these conditions showed no surface energy differences on the supports; the only important fact is that a supermolecular structure formed on the interface with the solid support. However, the A-spectrum showed a distinct dependence on the melting time of the films on the support, i.e. an increase of the melting time produced a steady shift of this spectrum towards the long-wave range. Melting time, rain v~oA-1405cm -1 line position
20 40 80 100 120 24,870 24,860 24,840 24,820 24,800 '
The largest shift, 80-90 cm -1 for the 120 min period, was equivalent to an average density increase of 5% in the amorphous zones of P E according to our assessment. The results seem to be evidence for a polymer structure forming from a more homogenous melt which results in a more orderly packing of the molecular chains under these conditions. More complex and specific results were got with the conditions 130/80°C (Fig. 1). The fluorescence spectra then showed the largest A-spectral shifts equivalent to an about 15% density increase in the amorphous zones (40 min melting time), which approached that of the crystalline zones produced b y a 120 min melting time. The parts of the fluorescence spectral line v00A-1.400 cm -1 outside the reabsorption range are shown in Fig. 1. The lines of dashes are the peaks of curves 1-3 of the A-spectrum. Figure 1 shows that the A-spectrum steadily approaches the K-spectrum until it practically coincides with the latter. I t must be emphasized that the substantial structural changes detected in P E were caused particularly on the high-energy support (quartz); this was the only surface producing considerable adhesion and a substantial shift of the Aspectrum (Fig. 1). Nevertheless, the optical microscopic study of such samples showed the trans-crystallinity of the surface layer of P E to be less distinct in this case than in the preceding melting conditions. Our results show that no substantial density changes took place in the amorphous zones, even at higher melting temperatures (150, 175°C). The densities of the amorphous zones of the polymer can thus remain the same during the formation of a distinctly trans-crystalline layer on the solid surface as during the development of spherulites in the bulk of the polymer. I t was quite natural to assume that the treatment condition 130/80°C would cause a specific combination of .two factors, namely the incomplete destruction of the supermoleeular structures already existing in P E films and a strong reaction with the solid surface (quartz), in which stressed structures of P E participate. Evidence of a structural rearrangement of P E is the passage through the
Packing density at boundary between crosslinked polymers and solid phase
1505
amorphous stage (curve 6 in Fig. 1) when the film is detached from the quartz surface. The use of the anthracene molecules as probe thus led to the detection of density differences existing in the amorphous zones of P E and trans-crystalline surface layers, which have practically the same morphology regardless of the preparation conditions of the films. A rapid density increase in the amorphous zones at the interface does not have a unilateral link with the tra~s-crystallinity of the surface layer; it was also found that certain preparation conditions of the films can have a smoothing effect on their structure so that the energy characteristics of the solid surface will hardly become apparent. The fact that this solid surface exists is the only one of importance. Furthermore, the examination of the processes taking place in the boundary layers of polymers must bear in mind the possibility that several factors combine to affect the formation of the structure. For example, the melting resulting in an incomplete decomposition of the original structures on high-energy supports can cause the formation of stressed structures at the sttrface and a considerable density increase in the amorphous zones of these. The separation of such a polymer film from the support can produce a stress relaxation of these structures which, in some cases, progresses through an amorphization stage of the sample. Polyepoxides (assisted b y N. G. Popov). Some structural densification or loosening can take place in the studied compositions based on polyepoxide and plasticizers under the influence of different heat treatments. For example, the average densities of filled system ranged from 0.5 to 2~o, dependent on the t y p e of plasticizer used. The ED-5/DEG-1 and ED-5/DOS compositions showed different behaviour, i.e. the density increased in the first case but decreased in the second. This is explained b y the structural characteristics of the plasticizers. The epoxy groups of DEG-1 can enter the composition of the structural chain unit of the polymer, for example [1311 while DOS belongs to the passive plasticizers not miscible with ED-5 [14]. The average densities of the hardened polymer remained either unchanged, or changed only b y 0-5~o when the filler was added to the same compositions. Only that of the ED-5/DEG-1 composition changed b y 2.5-3% in the presence of the filler. The electron-spectral study of the probe molecules introduced into the above heat-treated samples from the xylene solution showed looser zones to be present, in which the density was 5-6% less than in the original sample. The average densities thus became irregular as a result of the filler addition. Additional tempering of such samples at 80°C made the structure more uniform. The average densities remained practically the same, while those of the looser zones increased b y 4-5~o and approached those of the original filled compositions. Still severer heat treatment conditions after that, e.g. at 160°C, will cause the heterogeneity to increase again, the average densities to decrease, and zones to appear with much lower densities. The effect of tempering at 80°C was the same as that of swelling the sample
YE. G. MoIsYA etal.
1506
of these systems in xylene, i.e. the densities of the looser zones increased and approached those of the unfilled original samples. The presence of the solvent caused the stressed regions, forming as a result of filler addition, to relax. A subsequent heat treatment at 80 or 160°C of these "relaxed" structures did not cause any noticeable density changes. K
A'
h
I
240
2// 5
250
~x I0"~ Om" I
FIo. 1
..A
Z# O
2# 5
250
YslO -z cm-i FIG. 2
FIG. 1. The shifts of the anthracene fluorescence spectra in P E due to structural changes in the polymer matrix by melting on a quartz surface: / - - o r i g i n a l sample; 2-5--samples after, 20, 40, 80 a n d 120 rain melting respectively; 6--sample separated from its quartz support. FIG. 2. The shifts of the anthracene luminescence spectra in: 1-3--unfilled; 4-6--filled polymer systems of ED-5 with DEG-1 duo to structural changes in the polymer matrix produced by heat treatment: 1,4--original samples without heat treatment, 2,g--samples heat-treated at 80°C, 3,6--as 2 , 5 - - b u t with a subsequent heat t r e a t m e n t at 160°C.
The comparisons of the structural changes of the heat-treated samples at 80 and 160°C with those swelled in xylene showed the heat treatment n o t to achieve the highest possible structural conversion; the latter continued on subsequent treatment at the higher temperature (160°C), or to the same extent during swelling in xylene. Our findings show that the filler addition, i.e. the appearance of a boundary layer between the polymer and the solid surface of the filler, produces considerable
Packing density at boundary between crosslinked polymers and solid phase
1507
structural changes. The samples will contain looser stressed zones having a 5-6 °/o lower density t h a n the original, unfilled compositions (curves 1 and 4 in Fig. 2) (This diagram contains only fragments of the luminescence spectra r0o-[-1.405 cm -1, i.e. those outside the reabsorption range [8-10]). The inhibiting influence of the filler on the polymer structure can be reduced, and even completely eliminated, by the appropriate heat t r e a t m e n t (curves 2 and 5, 3 and 6 in Fig. 2), or by the presence of a solvent swelling the polymer. Figure 2 shows the densities of unfilled and filled composition to be practically the same after heat treatment at 160°C (a vertical line has been drawn in the diagram). Our findings make it clear t h a t the degree of non-uniformity can vary, although all the filled systems are less equilibrated t h a n the unfilled because of the presence of the boundary layer [1]. The achievement of a state of equilibrium in each case would mean t h a t there should not, in principle, be any structural difference between unfilled and filled polymers. CONCLUSIONS
(1) The surface layers of crystalline polymers at the boundary with a solid particle is shown as causing additional heterogeneity and can cause the density to remain the same or to increase substantially as a result of the density increase in the amorphous zones. These structural changes in the b o u n d a r y layers of crystalline polymers are not unilaterally connected with the morphological characteristics of the surface layers (the trans-crystalline structure). (2) Looser stressed regions can form in crosslinked, filled polymer systems while their average density remains the same, or changes but slightly. These looser, stressed regions have a 5-6% lower than average density. (3) The influence of the boundary surface with the solid particle on the structure of the polymer produces a non-equilibrial system which can be made more equilibrial by the appropriate heat treatment of the sample.
Translated by K. A. ALLEN REFERENCES
l. Yu. S. LIPATOV, Fiziko-khimiya napolnennykh polimerov (The Physical Chemistry of Filled Polymers). Izd. "Naukova Dumka", 1967 2. Yu. S. LIPATOV, Vysokomol. soyed. 7: 1430, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 8, 1584, 1965) 3. Yu. S. LIPATOV and F. G. FABULYAK, Vysokomol. soyed. A10: 1695, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 7, 1858, 1968) 4. Yu. S. LIPATOV and L. M. SERGEYEVA, Kolloid. Zhur. 27: 43, 1965 5. Yu. S. LIPATOV and L. M. SERGEYEVA, Vysokomol. soyed. 8: 1895, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 11, 2093, 1966) 4i. Yu. S. LIPATOV and T. E. (~ELI,EI{, Vysokomol. soyed. A9: 222, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 1, 244, 1967) 7. Yu. S. LIPATOV, Vestnik Akad. Nauk Ukr. SSR, No. 9, 3, 1970 8. Ye. G. MOISYA and Yu. L. EGOROV, Zhur. prikl. Spoktroskopii 1: 363, 1964
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F. RANOGAYETS et al.
9. Ye. G. MOISYA and Yu. L. EGOROV, Zhur. teor. i eksper. K h i m 3: 131, 1967 10. Yu. L. EGOROV, Ye. G. MOISYA and I. A. AR'EV, Zhur. teor. i eksper, khim. 3: 772, 1967 11. H. SCHOUHORN, J. Polymer Sci. 5: 1913, 1967 12. H. SCHOUHORN, Macromolecules 1: 145, 1966 13. K. THINIUS, Plastifikatory (Plastlcizers). Izd. " K h i m i y a " , 1964 14. A. M. CHISTYAKOV, L. A. SUKHAREVA, L. M. KOVAL'CHUK and M. G. KISELEV, Plast. Massy, No. 5, 53, 1967
SOME OF THE PRINCIPLES OF POLYMERIZATION BY THE ZWITTER-IONIC MECHANISM* F . I~ANOGAYETS*, Y E . V. KOCHETOV, M. A . MARKEVIC~ a n d N . S. YENIKOLOPYAN ?"Rudzher Boshkovich" I n s t i t u t e Zagreb, Yugoslavia Chemical Physics Institute, U.S.S.R. Acad6my of Sciences
(Received 19 August 1971) THE work reported here is the continuation of polymerization studies b y the zwitter-ionie mechanism. This concerns the anionic polymerization of acrylonitrile (AN) [1], methacrylonitrile (MAN) [2], formaldehyde [3], fl-propiolactone [4] in the presence of tertiary phosphines and amines. The macromolecule developing d u r i n g a zwitter-ionic polymerization is a polymeric zwitter ion in which the opposing charges are situated at the ends of the same polymer molecules. The distances between the chain ends of a zwitterion polymer present in a solution are determined b y the conformation statistics of the polymer chain and b y the electrostatic reactions of the charges. An earlier study had shown [5] that the reactive centres are present as ion pairs or as free ions, depending on the correlations of the above factors. The monomolecular transition factor from one form to the other depends on the polymerization efficiency. The longer the zwitter-ion polymer, the more probable will be that the reactive centre is present as a free ion. As the rate constant of propagation is larger on the free ion than on the ionic pair, that of the polymer chain will increase with its length. The growing free ion can form an ionic pair also with the cation of another developing zwitter ion polymer, or with that of a decaying polymer molecule, as the latter retains the cation. Other work has shown, however, that one can neglect the reactions between ions of different chains during a slow initiation, or where the stationary concentration of the reactive centres is small, or the * Vysokomol. soyed. AIS: NO. 6, 1343-1349, 1973.
11. 12. 13.
14. 15. 16.
17. 18.
YE. G. MOISYA et al.
M. K. ORLOFF and D. D. FITTS, Biochim et biophys. Acta 47: 5996, 1961 Y. MATSUNAGA, Helv. Phys. A c t a 36: 800, 1963 F. GUTMAN and H. KEYZER, J. Chem. Phys. 46: 1963, 1967 J. SATO, N. KINOSHITA, M. SANO and H. AKAMATU, J. Chem. See. J a p a n 40: 2539, 1967 S. B. MAINTHIA, P. H. KRONICK and M. M. LABES, J. Chem. Phys. 41: 2206, 1964; H. HOEGL, J. Phys. Chem. 69: 755, 1965 G. G. SKVORTSOVA and G. N. KUROV, "Russian Authors' Cert. No. 241445, 1969; Byull. Izobret., No. 14, 1969 B. E. DAVYDOV, R. Z. ZAKHARYAN, G. P. KARPACHEVA, B. A. KRENTSEL, G. A. L A P r r S K I I and G. V. KHUTAREVA, Dokl. Akad. N a u k SSSR 160: 650, 1965 A. V. TOPCHIEV, Yu. V. KORSHAK, B. E. DAVYDOV and B. A. KRENTSEL, Dokl. Akad. N a u k SSSR 147: 645, 1962 A. A. DULOV and A. A. SLINKIN, Organicheskie poluprovodniki (Organic Semiconductors). 78, Izd. " N a u k a " , 1970 G. P. KARPACHEVA, Izv. Akad. N a u k SSSR, seriya khim., 190, 1965 L. A. BLYUMENFEL'D, V. V. VOYEVODSKII and A. G. SEMENOV, Elektronnyi paramagnitnyi rezonans v khimii (Electron Spin Resonance in Chemistry). Izd. Sibir. Otdel. Akad. N a u k SSSR, 1962 N. I. SHERGINA, G. G. SKVORTSOVA, G. N. KUROV and D. D. TARYASHINOVA, Zhur. prikl. Spektroskopii 13: 845, 1970 R. E L ' D E R F I L ' D , Gcterotsiklicheskic soyedineniya, t. 6 (Heterocyclic Compounds, vol. 6). 576, Izd. inostr. Lit., 1960 A. R. KATRITSKII, Fizicheskie m e t o d y v khimii geterotsiklicheskikh soyedincnii (The Use of Physical Method in Heterocyclic Compounds Chemistry). 551, ~zd. "Khim i y a " , 1966 N. N. MATSCH and J. DELER, Canad.' 5. Chem. 47: 17, 31, 73, 1969 B. WITKOP and J. B. PATRICK, J. Am. Chem. Soc. 75: 4474, 1953; B. WITKOP and T. W. BEILER, J. Am. Chem. Soc. 76: 5589, 5597, 1954
THE PACKING DENSITY AT THE BOUNDARY BETWEEN CRYSTALLINE AND CROSSLINKED POLYMERS AND THE SOLID PHASE* Y~.. G. MOlSYA, G. M. SEMENOVICH and Yu. S. LIPATOV High Polymer Chemistry Institute,Ukr. S.S.R. Academy of Sciences \ (Received 18 August 1971)
THE d e n s i t y c h a n g e s i n t h e s u r f a c e l a y e r s o f p o l y m e r s s i t u a t e d a t t h e b o u n d a r y w i t h t h e s o l i d p h a s e a r e t h e s u b j e c t o f s e v e r a l s t u d i e s [1-5]. T h e b e h a v i o u r of the surface layers of crystalline and crosslinked polymers at such a boundary * Vysokomol. soyed. A15: No. 6, 1337-1342, 1973.
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1503
i n d i c a t e s t h a t t h e p r o p e r t i e s also c h a n g e t h e r e w h e n c o m p a r e d w i t h t h o s e of t h e s a m e p o l y m e r i n a free s t a t e [6, 7]. T h e a i m o f t h i s i n v e s t i g a t i o n w a s t o s t u d y t h e d e n s i t y c h a n g e s i n t h e s u r f a c e l a y e r s o f c r y s t a l l i n e or s t r o n g l y c r o s s l i n k e d polymers:
EXPERIMENTAL The density changes were examined by means of the luminescence spectra produced by anthracene molecules used as "pIobes". The densities of the surroundings and their changes as a result of various activities were evaluated on the basis of the established method [8--10] of luminescence spectral shifts of the anthracene probe molecules added to the system. I n this study the following were used: low pressure polyethylene (PE) and the polyepoxide ED-5 containing different plasticizers, i.e. dioctyl sebaceate (DOS), the aliplmtie oligo-epoxide DEG-1, or the oligo-ether acrylate MGF-9. A glass fibre weave was used as t h(~ support in the case of ED-5, quartz or teflon in the case of PE. These supports were transparent to ultraviolet (UV) light and differed by having different surface energies. The polyepoxide was hardend at room temperature with polyethylene polyamine (10%). Differing methods of addition of"anthracene to the polymers were used: 1) xylene was used as solvent addition to the soft ED-5 or DEG-1, combined with heating to 50°C and mixing, after which the xylcne was vacuum-evaporated, the polymers hardened and heat treated. 2) a xylene solution of anthracene was added to the hardened polyepoxido before beat treatment during a 30 rain or longer swelling (up to several days); some of these samples ~crc then heat trcated. 3) the hardened and heat-treated samples were soaked (allowed to swell) for 30 rain in a xylene solution of anthracene. The first, method enabled us to assess the average density of the polymer (as the probe molecules were evenly distributed throughout the samples), the second, the effect of the solvent on the polymer with and without filler, and also the effect of the heat treatment, and the third method, a n y heterogeneity appearing in the sample as a result of heat t r e a t m e n t (the anthracene moleenlcs entered the loosest regions of the sample during the 30 rain swelling in the xylene solution). The average densities and those of the least dense regions (]ooscst structures) of the polymers given subsequently in the text are those obtained b y the anthracene tracer addition methods refcrred to above. The anthracene concentration in the poisoners was 10 -3 mole/l. I t entered the P E from the xylenc, after which the P E fihns were melted in an oven a n d then transferred to another oven for crystallization at difS~rcnt tempcr~turcs during a 2 bx heating period. Three melting temperatures were used, i.(,. 130, 150 and 175°C, a n d two crystallization temperature, 80 and 40°C, of which the first gives the faster development of spherulites, tb_e second the faster development of crystalliz~ltion centres [11, 12]. The snpermolecular structures were studied by means of polarization nfieroscope MIM-8; the thin sectior~s were produced from the films by the usual method. The luminescence, spectra of the anthracene tracer molecules werc recorded at 77°K on a DFS-12 spectrometer. Th(~ experimentation method had been reported earlier [8--10]. RESULTS
Polyethylene. T h e a n t h r a c e n e t r a c e r s p e c t r a c o n s i s t e d i n all cases o f t h e s u m o f t w o s p e c t r a : A: s p e c t r a o f t h e a n t h r a c e n e i n t h e a m o r p h o u s z o n e s o f :PE, K : i n t h e c r y s t a l l i n e z o n e s [8-10]. T h e e x c i t a t i o n o f t h e a n t h r a c e n e m o l e c u l e s was p r o d u c e d d i r e c t l y o n t h e s u p p o r t s , w h i l e i n s o m e cases t h e P E films w e r e also m e l t e d o n t h e m a n d c r y s t a l l i z e d , i.e. t h e c o n t a c t b e t w e e n t h e film a n d t h e solid surface was n o t d i s t u r b e d d u r i n g m e a s u r e m e n t s .
YE. G. MOISYA et al.
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Our optical polarization studies showed that the melting and crystallization conditions of PE, i.e. 175/80, 175/40, 150/80 and 150/40 (°C) gave rise to a transcrystalline surface layer on the quartz and the teflon supports; this had also been shown before [11, 12]. The morphological characteristics found under these conditions showed no surface energy differences on the supports; the only important fact is that a supermolecular structure formed on the interface with the solid support. However, the A-spectrum showed a distinct dependence on the melting time of the films on the support, i.e. an increase of the melting time produced a steady shift of this spectrum towards the long-wave range. Melting time, rain v~oA-1405cm -1 line position
20 40 80 100 120 24,870 24,860 24,840 24,820 24,800 '
The largest shift, 80-90 cm -1 for the 120 min period, was equivalent to an average density increase of 5% in the amorphous zones of P E according to our assessment. The results seem to be evidence for a polymer structure forming from a more homogenous melt which results in a more orderly packing of the molecular chains under these conditions. More complex and specific results were got with the conditions 130/80°C (Fig. 1). The fluorescence spectra then showed the largest A-spectral shifts equivalent to an about 15% density increase in the amorphous zones (40 min melting time), which approached that of the crystalline zones produced b y a 120 min melting time. The parts of the fluorescence spectral line v00A-1.400 cm -1 outside the reabsorption range are shown in Fig. 1. The lines of dashes are the peaks of curves 1-3 of the A-spectrum. Figure 1 shows that the A-spectrum steadily approaches the K-spectrum until it practically coincides with the latter. I t must be emphasized that the substantial structural changes detected in P E were caused particularly on the high-energy support (quartz); this was the only surface producing considerable adhesion and a substantial shift of the Aspectrum (Fig. 1). Nevertheless, the optical microscopic study of such samples showed the trans-crystallinity of the surface layer of P E to be less distinct in this case than in the preceding melting conditions. Our results show that no substantial density changes took place in the amorphous zones, even at higher melting temperatures (150, 175°C). The densities of the amorphous zones of the polymer can thus remain the same during the formation of a distinctly trans-crystalline layer on the solid surface as during the development of spherulites in the bulk of the polymer. I t was quite natural to assume that the treatment condition 130/80°C would cause a specific combination of .two factors, namely the incomplete destruction of the supermoleeular structures already existing in P E films and a strong reaction with the solid surface (quartz), in which stressed structures of P E participate. Evidence of a structural rearrangement of P E is the passage through the
Packing density at boundary between crosslinked polymers and solid phase
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amorphous stage (curve 6 in Fig. 1) when the film is detached from the quartz surface. The use of the anthracene molecules as probe thus led to the detection of density differences existing in the amorphous zones of P E and trans-crystalline surface layers, which have practically the same morphology regardless of the preparation conditions of the films. A rapid density increase in the amorphous zones at the interface does not have a unilateral link with the tra~s-crystallinity of the surface layer; it was also found that certain preparation conditions of the films can have a smoothing effect on their structure so that the energy characteristics of the solid surface will hardly become apparent. The fact that this solid surface exists is the only one of importance. Furthermore, the examination of the processes taking place in the boundary layers of polymers must bear in mind the possibility that several factors combine to affect the formation of the structure. For example, the melting resulting in an incomplete decomposition of the original structures on high-energy supports can cause the formation of stressed structures at the sttrface and a considerable density increase in the amorphous zones of these. The separation of such a polymer film from the support can produce a stress relaxation of these structures which, in some cases, progresses through an amorphization stage of the sample. Polyepoxides (assisted b y N. G. Popov). Some structural densification or loosening can take place in the studied compositions based on polyepoxide and plasticizers under the influence of different heat treatments. For example, the average densities of filled system ranged from 0.5 to 2~o, dependent on the t y p e of plasticizer used. The ED-5/DEG-1 and ED-5/DOS compositions showed different behaviour, i.e. the density increased in the first case but decreased in the second. This is explained b y the structural characteristics of the plasticizers. The epoxy groups of DEG-1 can enter the composition of the structural chain unit of the polymer, for example [1311 while DOS belongs to the passive plasticizers not miscible with ED-5 [14]. The average densities of the hardened polymer remained either unchanged, or changed only b y 0-5~o when the filler was added to the same compositions. Only that of the ED-5/DEG-1 composition changed b y 2.5-3% in the presence of the filler. The electron-spectral study of the probe molecules introduced into the above heat-treated samples from the xylene solution showed looser zones to be present, in which the density was 5-6% less than in the original sample. The average densities thus became irregular as a result of the filler addition. Additional tempering of such samples at 80°C made the structure more uniform. The average densities remained practically the same, while those of the looser zones increased b y 4-5~o and approached those of the original filled compositions. Still severer heat treatment conditions after that, e.g. at 160°C, will cause the heterogeneity to increase again, the average densities to decrease, and zones to appear with much lower densities. The effect of tempering at 80°C was the same as that of swelling the sample
YE. G. MoIsYA etal.
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of these systems in xylene, i.e. the densities of the looser zones increased and approached those of the unfilled original samples. The presence of the solvent caused the stressed regions, forming as a result of filler addition, to relax. A subsequent heat treatment at 80 or 160°C of these "relaxed" structures did not cause any noticeable density changes. K
A'
h
I
240
2// 5
250
~x I0"~ Om" I
FIo. 1
..A
Z# O
2# 5
250
YslO -z cm-i FIG. 2
FIG. 1. The shifts of the anthracene fluorescence spectra in P E due to structural changes in the polymer matrix by melting on a quartz surface: / - - o r i g i n a l sample; 2-5--samples after, 20, 40, 80 a n d 120 rain melting respectively; 6--sample separated from its quartz support. FIG. 2. The shifts of the anthracene luminescence spectra in: 1-3--unfilled; 4-6--filled polymer systems of ED-5 with DEG-1 duo to structural changes in the polymer matrix produced by heat treatment: 1,4--original samples without heat treatment, 2,g--samples heat-treated at 80°C, 3,6--as 2 , 5 - - b u t with a subsequent heat t r e a t m e n t at 160°C.
The comparisons of the structural changes of the heat-treated samples at 80 and 160°C with those swelled in xylene showed the heat treatment n o t to achieve the highest possible structural conversion; the latter continued on subsequent treatment at the higher temperature (160°C), or to the same extent during swelling in xylene. Our findings show that the filler addition, i.e. the appearance of a boundary layer between the polymer and the solid surface of the filler, produces considerable
Packing density at boundary between crosslinked polymers and solid phase
1507
structural changes. The samples will contain looser stressed zones having a 5-6 °/o lower density t h a n the original, unfilled compositions (curves 1 and 4 in Fig. 2) (This diagram contains only fragments of the luminescence spectra r0o-[-1.405 cm -1, i.e. those outside the reabsorption range [8-10]). The inhibiting influence of the filler on the polymer structure can be reduced, and even completely eliminated, by the appropriate heat t r e a t m e n t (curves 2 and 5, 3 and 6 in Fig. 2), or by the presence of a solvent swelling the polymer. Figure 2 shows the densities of unfilled and filled composition to be practically the same after heat treatment at 160°C (a vertical line has been drawn in the diagram). Our findings make it clear t h a t the degree of non-uniformity can vary, although all the filled systems are less equilibrated t h a n the unfilled because of the presence of the boundary layer [1]. The achievement of a state of equilibrium in each case would mean t h a t there should not, in principle, be any structural difference between unfilled and filled polymers. CONCLUSIONS
(1) The surface layers of crystalline polymers at the boundary with a solid particle is shown as causing additional heterogeneity and can cause the density to remain the same or to increase substantially as a result of the density increase in the amorphous zones. These structural changes in the b o u n d a r y layers of crystalline polymers are not unilaterally connected with the morphological characteristics of the surface layers (the trans-crystalline structure). (2) Looser stressed regions can form in crosslinked, filled polymer systems while their average density remains the same, or changes but slightly. These looser, stressed regions have a 5-6% lower than average density. (3) The influence of the boundary surface with the solid particle on the structure of the polymer produces a non-equilibrial system which can be made more equilibrial by the appropriate heat treatment of the sample.
Translated by K. A. ALLEN REFERENCES
l. Yu. S. LIPATOV, Fiziko-khimiya napolnennykh polimerov (The Physical Chemistry of Filled Polymers). Izd. "Naukova Dumka", 1967 2. Yu. S. LIPATOV, Vysokomol. soyed. 7: 1430, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 8, 1584, 1965) 3. Yu. S. LIPATOV and F. G. FABULYAK, Vysokomol. soyed. A10: 1695, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 7, 1858, 1968) 4. Yu. S. LIPATOV and L. M. SERGEYEVA, Kolloid. Zhur. 27: 43, 1965 5. Yu. S. LIPATOV and L. M. SERGEYEVA, Vysokomol. soyed. 8: 1895, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 11, 2093, 1966) 4i. Yu. S. LIPATOV and T. E. (~ELI,EI{, Vysokomol. soyed. A9: 222, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 1, 244, 1967) 7. Yu. S. LIPATOV, Vestnik Akad. Nauk Ukr. SSR, No. 9, 3, 1970 8. Ye. G. MOISYA and Yu. L. EGOROV, Zhur. prikl. Spoktroskopii 1: 363, 1964
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F. RANOGAYETS et al.
9. Ye. G. MOISYA and Yu. L. EGOROV, Zhur. teor. i eksper. K h i m 3: 131, 1967 10. Yu. L. EGOROV, Ye. G. MOISYA and I. A. AR'EV, Zhur. teor. i eksper, khim. 3: 772, 1967 11. H. SCHOUHORN, J. Polymer Sci. 5: 1913, 1967 12. H. SCHOUHORN, Macromolecules 1: 145, 1966 13. K. THINIUS, Plastifikatory (Plastlcizers). Izd. " K h i m i y a " , 1964 14. A. M. CHISTYAKOV, L. A. SUKHAREVA, L. M. KOVAL'CHUK and M. G. KISELEV, Plast. Massy, No. 5, 53, 1967
SOME OF THE PRINCIPLES OF POLYMERIZATION BY THE ZWITTER-IONIC MECHANISM* F . I~ANOGAYETS*, Y E . V. KOCHETOV, M. A . MARKEVIC~ a n d N . S. YENIKOLOPYAN ?"Rudzher Boshkovich" I n s t i t u t e Zagreb, Yugoslavia Chemical Physics Institute, U.S.S.R. Acad6my of Sciences
(Received 19 August 1971) THE work reported here is the continuation of polymerization studies b y the zwitter-ionie mechanism. This concerns the anionic polymerization of acrylonitrile (AN) [1], methacrylonitrile (MAN) [2], formaldehyde [3], fl-propiolactone [4] in the presence of tertiary phosphines and amines. The macromolecule developing d u r i n g a zwitter-ionic polymerization is a polymeric zwitter ion in which the opposing charges are situated at the ends of the same polymer molecules. The distances between the chain ends of a zwitterion polymer present in a solution are determined b y the conformation statistics of the polymer chain and b y the electrostatic reactions of the charges. An earlier study had shown [5] that the reactive centres are present as ion pairs or as free ions, depending on the correlations of the above factors. The monomolecular transition factor from one form to the other depends on the polymerization efficiency. The longer the zwitter-ion polymer, the more probable will be that the reactive centre is present as a free ion. As the rate constant of propagation is larger on the free ion than on the ionic pair, that of the polymer chain will increase with its length. The growing free ion can form an ionic pair also with the cation of another developing zwitter ion polymer, or with that of a decaying polymer molecule, as the latter retains the cation. Other work has shown, however, that one can neglect the reactions between ions of different chains during a slow initiation, or where the stationary concentration of the reactive centres is small, or the * Vysokomol. soyed. AIS: NO. 6, 1343-1349, 1973.