- Email: [email protected]
Formation of porous systems from crystallizing polyolefines
~840
V.I.
SELIKHOVA el al.
14. 15. 16. 17.
W . J . KOROS, D. R. PAUL and A. A. ROCHA, J. Polymer Sci. Polymer Phys. Ed. 14: 687, I976 S. A. STERN and A. H. MERINGO, J. Polymer Sci. Polymer Phys. Ed. 16: 735, 1978 W. J. KOROS and D. R. PAUL, J. Polymer Sci. Polymer Phys. Ed. 16: 1947, 1978 Yu. P. YAMPOL'SKII, S. G. DURGAR'YAN and N. S. NAMETKIN, Vysokomol. soyed. A2,4: 536, 1982 (Translated in Polymer Sci. U.S.S.R. 24: 3, 592, 1982) 18. IL TOI, G. MOREL and D. R. PAUL, J. Appl. Polymer Sci. 27: 2997, 1982 59. K. ROGERS, Problemy fiziki i khimii tverdogo sostoyaniya organicheskikh soyedinenii (Problems of the Physics and Chemistry of the Solid State of Organic Compounds). p. 229, Mir, Mo#cow, 1968 20. R. F. BOYER, J. Appl. Phys. 20: 540, 1949
Polymer S c i ~
~
U.S.S.R. Vot. 26, No. 8, pp. 1840-1847, 1984
in Poland
0032-$950[84 $10.00+ .00
© 1985PergamonProwLtd.
F O R M A T I O N OF P O R O U S S Y S T E M S F R O M CRYSTALLIZING POLYOLEFINES* V. I. SELIKHOVA, S. L PAKHOMOV, M. G . FELIN, N . F. BAKEYEV,
Yu. A. Ztmov and G. P. Am3R[ANOVA Karpov Physicochemical Research Institute Moscow Light Industry Technological Institute
(Received 20 February 1983) The article describes the formation of porous systems based on linear PE a n d isotactic PP by treating the initial monolithic films with solvent at raised temperature without deformazion. It is shown that the non-oriented porous films obtained are characterized by a quite well developed inner surface. The results of investigations of their structural features are presented. POROUS materials with different structures and parameters of the porous structure are
being increasingly used in technology and the national economy and a large number of methods have been devised to obtain them [1, 2]. Nonetheless, the search for new methods of regulating porosity is continuing. Of great interest is the development of methods of forming porous systems which would make it possible to maintain the continuity of the processes of obtaining porous materials in a single technological cycle into monolithic sheets and films. Existing methods are in the main associated with the use, as a rule, of crystallizing polymers and are based on the stretching of the initial monolithic films [3, 4] sometimes with use of adsorption-active media or an agent causing the polymer to swell [5]. However the need to create high degrees of extension and to keep the film in the stretched state during fixation and stabilization * Vysokomol. soyed. A26: No. 8, 1647-1652, 1984.
Formation of porous systems from crystallizing polyolefines
1841
of the structure formed and also the removal of solvent by air drying seriously complicates the process and hampers its continuous organization primarily because of the heavy increase in the duration of the individual operations. The present work describes the results of investigation of the special aspects of the structure and properties of POROUSsystems based on linear PE and isotactic PP obtained by a new method of forming them [6] by treating the monolithic films with solvent at raised temperature without resorting to deformation agents. We used polymers distinguished by a sufficiently high degree of crystallinity, PE and PP samplea produced at home and abroad, and the characteristics of which are given in Table 1. The initial non-oriented films of the polymer were obtained by pressing fused granules or powders followed by sufficiently slow (at the rate of ~ 2 deg/min) cooling of the melt. In the case of PE, monolithic films were formed by hardening the melt in iced water. The crystalline structure of the initial and porous films was studied by X-ray structural analysis at small and wide angles with use of nickel-filtered CuK, radiation. The radiographic investigation at wide angles was by the photographic method in a planocasette camera and with the DRON-1 diffractometer. The mean size of the crystallitea along the direction of the molecular chains and in the direction perpendicular to the chains was determined in line with the technique in [7]. The small angle X-ray study of the samples was with the K R M - I apparatus with slit collimation of the primary X-ray beam and to lower the diffuse scatter the porous samples were impregnated with dibutylphthalate [8].
TABLE 1. CHARACTERISTICS OF INITIAL PE AND PP FILMS
Polymer PE-I PE-2 PE "Marlex 5005" (PE-3) PE "Hostalen GD-6250" (PE-4) PP-1 PP " M o p l e n " (PP-2) PP - i o r ' (pP-3)
/~f,x 10 -4 30 55 14 II 20 35 13
T~p 134 132 126 125 161 160 165
Degree of ~ystallinity, ~ 68 66 63 58 58 59 60
The surface inhomogeneity and microstructure of the films were studied by a direct method with the JSM-2 electron scanning microscope at magnifications from 300 to 10,000. A silver layer up to 1000 A thick was dusted on to the chips of the samples obtained in liquid nitrogen to impart electrical conductivity and for contrast. The dusting was with the VUP-1 vacuum sprayer. To characterize the porous structure of the films obtained we also used the methods of mercury porometry and low temperature sorption of nitrogen at constant pressure. With the first method "the porous sample was placed in mercury, the pressure raised and the volume of the mercury compressed into the pores measured, the curve of the dependence of this volume on the pressure applied plotted and from it the differential volume of the pores determined. Information on pore size was obtained by differentiating the integral porograms [9]. The specific surface was measured on chilling the ampoule containing the sample with liquid nitrogen. The free volume of the apparatus was measured with helium assuming that it is practically not adsorbed in these conditions. The area occupied by one cubic centimetre of nitrogen was taken as equal to 4.4 m 2. The thermophysical properties of films were studied with the DSM-2 differential scanning calorimeter with exclusion of the effect of recrystallization and reheating by using a set of heating rates
1842
V.I. SELIKHOVAet al.
from 0'4 to 50 degrees/rain [10]. The values of the experimental heat of fusion were used to determine the degree of crystallinity. The heat of fusion of the completely crystalline PE sample was taken as equal to 292'6 J/g [11] and for PP 146.3 J/g [12]. The value of 3S/vwas determined from the limiting viscosity number It/] at 135°C in decalin. The deformation-strength characteristics of the porous films were studied with an instrument of the "Polyani" type fitted with a strain gauge at a speed of movement of the lower clamp of 4 ram/ /rain and at room temperature. The method of producing a porous structure proposed consisted in bringing m o n o lithic non-oriented polymer films for a certain time at raised temperatures into contact with an organic liquid with a high boiling point and causing swelling of the polymer as which we used trans-decalin or o-xylene. Then the film swollen and becoming transparent was transferred to a medium with a non-solvent (acetone) at 20°C when the porous structure formed was fixed and the agent causing swelling removed. The film was exposed to no deformation forces. After fixing the film it was further treated in acetone vapours to remove the traces of solvent and dried in a current of air to constant weight. The investigation carried out on a large number of samples with wide variation in the thickness of the films and conditions of the process of pore formation allowed us to fix the conditions of treatment optimal for obtaining a uniform porous structure of the films which are presented below. Film Thickness of initial monolithic films, mm Solvent
trans-Decalin,
trans-Decalin
Non-solvent Temperature of treatment of films with solvent, °C Time of treatment of film with solvent, rain Time of holding film in non-solvent, min Temperature of drying, °C
o-xylene Acetone 125-155 2-25 5-15 20-80
Acetone 100--125 2-35 5-30 20-80
PP 0.5-2.0
PE 0.5-2.0
The time of swelling naturally depends both on the temperature of pore formation, the thickness of the initial monolithic film and the M of the polymer studied. Rise in temperature helps to shorten the time of stay of the film in solvent. It should be noted that ihcrease in the M of the samples, on the one hand, considerably lengthened the time of swelling and, on the other, reduced the weight losses of the films on pore formation. For example, while in the porous PP-3 samples the percentage weight loss (as compared with the initial weight) reaches 6-7 in the corresponding PP-2 samples it was 3-4. To determine what part of the polymer passes into solution we measured the M of the dissolved polymer. It was found that these fractions had practically the same M as the initial polymer. This indicated that swelling of the polymers is not accompanied by passage into solution of the lawer molecular weight products but preferential dissolution of the surface layers of polymer film.
Formation of porous systems from crystallizing polyolefines
1843
In connexion with the problem to be solved in the present work it was of particular interest to study the special nature of the structure of porous systems. The results of such a comprehensive investigation are given in Table 2. TABLE 2. CHARACTERIZATION OF POROUS P E AND PP FILMS
Polymer-solvent system
PP-2-decalin PP-2-xylene PP-3-decalin PP-3-xylene PP-l-decalin PE-3-decalin PE-l-decalin
Conditions of treating film with solvent time, °C min 145 7 140 8 144 6 140 3 147 9 130 3 125 19
Specific surface, m2/g
Specific volume of pores, cma/g
Degree of crystallinity,
6.4 2"4 6.0 4.7 6.2 10'0 9'7
0"96 0"62 0'89 0"69 0"77 1 "94
69 65 66 67 61 66 70
1"50
T~p
Rupture strength, MPa
163 165 167 166 162 127 131
1.89 2.86 2.40 1.82 2-67 1.89 1.94
%
X-ray study showed that the porous PE and PP films are isotropic and contain the same crystallographic modifications as the initial polymers. The size of the crystallites in the direction of the chain molecules is 120-150 A and in the direction perpendicular to the chains ,,~ 300 A. A significant fall is observed in the intensity of the a m o r phous halo as compared with the initial films both slowly chilled and hardened (Fig. 1). This apparently reflects a well known f a c t - o n crystallization from solution lamellae form with more regular folds containing a smaller number of through chains and irregular loops as compared with the bulk material. Therefore, the number of amorphous regions falls and hence also the intensity of the amorphous halo. The degree of crystallinity of the porous systems is higher than for the corresponding initial samples. The large period in porous samples is 150-180 A and does not depend on the values of the large period of the initial films (Fig. 2). This fact points to the formation iln porous systems of new crystallites with a large period determined by the conditions of crystallization. F r o m the small angle scatter curves one may also judge that the porous samples are well impregnated with liquids even such viscous ones as dibutylphthalate. The diffuse scatter of the porous films in this case is low while in the unimpregnated porous films the small angle maxima are "blurred" by the diffuse background. The results given by mercury porometry and low temperature sorption of nitrogen show that in the porous samples the differential curve of the distribution of the pore volume by size usually has two to three maxima (Fig. 3). This testifies to the presence of several predominant pore sizes (0-0.15; 0.015-0.035 and >1 /tin) and is probably connected with the existence of certain intervals between the different eleme~n~ts of structure: crystallites, lamellae and spherulites. The influence of the M of tile polymer on the character of the porous structure obtained is such that the use
V. I. SEtaKHOVAet al.
1844
•o f polymers with a large value of ~/o involves increase in the specific volume of pores with a smaller radius. The values of the specific surface of the porous samples a n d the specific pore volume (Table 2) quite well agreeing between themselves suggests the formation of a more developed porous structure in the PE samples as compared with PP. This is also indicated by the results of electron-microscopy (Fig. 4). In the ~ase of PE the spherulites consist of numerous individual petal-plates not tightly con-
I,pu ~e/aec
710 200
1ooi
5~
.v : 1
20
I
25
20"
FIo. 1. Diffractometric curves of X-ray scatter by porous (1) and initial (2, 3) films of PE-2. 2-Slowly chilled film; 3-hardened.
150I~
I, pulse/sec
FIG. 2. Curves of small angle X-ray scatter for monolithic (1, 2) and porous (3, 4) PE-3 films. /-Slowly chilled film; 2-hardened; 3-porous system obtained from slowly chilled film; 4 - from hardened.
Formation of porous systems from crystallizing polyolefmes
1845
liguous and sometimes passing from one spherulite to another. In the PP films the spherulites are more compact and their internal structure is not visible on the chips, They are usually joined by strands. Possibly as a result of this the rupture strength of the porous PP films in most cases exceeds the strength values for the PE samples (Table 2). dV 1.0
2-0
m
b O#
/-5 0.6
/'0
0"5
O'2 -
!i
Z
1
1
I
2
q
6
2
4
l~j~s
FIo. 3. Differential (1) and integral (2) curves of the distribution of pore volume by radii for samples of porous PE-3 (a) and PP-2 (b) obtained on treating monolithic films in dccalin.
Thus, the results of the structural investigations show that porous material is obtained by radical rearrangement of the structure of the initial monolithic films with change both in the size of the structural elements and the amorphous-crystalline structure of the material. The crystalline structures grow in the porous films evidently on transfer to the precipitant of highly concentrated solution which in essence is the swollen
FIG. 4. Electron-microscopic photographs of porous films obtained on treating monolithic films in decalin: a - P P - 3 (x 2250), b - PP-I (x 750), c - P E - 4 (x 2250).
1846
V. I. SELIKHOVA e t aL
film. This solution, however, does not have time to become homogeneous since it irt all likelihood contains physical nodes in the form of residues of undissolved crystaUites. On cooling they become seeds on which the new structure of the material develops at a high rate. A certain analogy may be drawn between this method of obtaining a porous film, and the formation of porous systems by the lyophilic drying method. Dissolution of the polymer in an organic solvent results in the formation of a monophasic homogeneous system as a consequence of which the macromolecules, on average, are uniformly distributed over the volume of the solution. This means that the volume between the macromolecules is occupied by the solvent and the system as a whole is highly dispersed (if, of course, one disregards the possible formation or preservation of associates of the macromolecules). On subsequent freezing and rapid removal o f the solvent this highly dispersed structure is fixed and a porous system forms with a highly developed surface. In our case this idealized picture is not realized owing (as stated) to kinetic factors since holding the polymer film in solvent lasts a comparatively short time insufficient for the formation of an homogeneous solution. However the system becomes highly dispersed. Sufficiently sharp replacement of the solvent by precipitant results in the fixation of the structure which has had time to form by this moment. The precipitant leading to partial coalescence sharply restricts the mobility of the macromolecules and the structural elements and so fixes the structure of the material. Consequently, treatment of the films of linear PE and isotactic PP with solvent at high temperature and rapid cooling in a medium of precipitant without deformation give porous materials with a highly developed inner surface. The approach developed to the formation of the porous structure of crystalline polyolefines may clearly also be extended to a number of hydrophilic polymer materials, for example, polyamides, which is particularly important for ensuring a complex of hygienic properties (production of artificial skins, development of carcass systems implanted into the body, etc.). Translated by A. CROZY REFERENCES
1. A. A. BERLIN and F. A. SHUTOV, Osnovy khimi i tekhnologii gazonapolnennykh polimerov (Bases of the Chemistry and Technology of Gas-Filled Polymers). Khimiya, Moscow, 1980 2. Khimiya i tekhnologiya polimernykh plenochnykh materialov i iskusstvennoi kozhi (Chemistry and Technology of Polymer Film Materials and Artificial Skin). (Ed. G. P. Andrianova) Legkaya i pishchevaya promyshlennost, Moscow, ]981 3. Pat. 3801692 (U.S.A.), 1974 4. Pat. 4138459 (U.S.A.), 1979 5. Pat. 3839516 (U.S.A.), 1974 6. V.I. SELIKHOVA, G. P. ANDRIANOVA, N. F. BAKEYEV, S. I. PAKHOMOV, M. G. FELIN and Yu. A. ZUBOV, Pat. 973559 (U.S.S.R.) Publ. in B. I. No. 42, 1982 7. Yu. A. ZUBOV, V. I. SELIKItOVA, V. S. SHIRETS and A. N. OZERIN, Vysokomol. soyed. B16: 1681, 1974 (Not translated in Polymer Sci. U.S.S.R.)
Opening of triple bonds under the action of donor-acceptor complexes
1847
8. V. I. SELIKHOVA, A. N. OZERIN and G. P. BELOV, Ibid. B16: 301, 1974 (Not translated in Polymer Sci. U.S.S.R.) 9. A. V. KISELEV and V. P. DREVING, Eksperimental'nye metody v adsorbtsii i molekulyarnoi khromatografii (Experimental Methods in Adsorption and Molecular Chromatography), Mosc. State Univ,, Moscow, 1973 10. V. I. SELIKHOVA, Yu. A. ZUBOV, N. F. BAKEYEV and G. P. BELOV, Vysokomol. soyed. AI9: 759, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 4, 879, 1977) 1I. E. W, FISCHER and G. HINRICHSEN, Kolloid-Z. und Z. fiJr Polymere 213: 93, 1966 12. G. L. SLONIMSKII and Yu. K. GODOVSKII, Vysokomol. soyed. 7: 621, 1965 (Translated in Polymer Sci. U. S. S. R. 7: 4, 685, 1965)
Polymer Science U.S.S.R, Vol. 26, ]No. 8,.pp. 1847-1855, 1984 Printed in Poland
0032-3950/84 $10.00+.00 © 1985PergamonPress Ltd.
AN INVESTIGATION OF THE OPENING OF TRIPLE BONDS UNDER THE ACTION OF DONOR-ACCEPTOR COMPLEXES* L. L. STOTSKAYA, V. S. SEREBRYANIKOV, G. P. KARPACHF.VA' a n d A. M. KRAPIVIN A. V. Topchiyev Institute for Petrochemical Synthesis, U.S.S.R. Academy of Sciences
(Received 23 February 1983) Donor-acceptor complexes, formed between the monomer and organic-(flectron acceptors, have been used for the first time for the opening of the carbon-carbon triple bond, using as an example the polymerization of propargylamines. Investigation of the complex-formation reaction by UV, PMR and EPR spectroscopy has enabled it to be established that complexes with both partial and also with complete charge transfer are present, the proportions of these complexes depending on the magnitude of the energy of affinity of the acceptor towards the electron and on the polarity of the solvent. The composition and strength of the complexes have been determined. The kinetics of polymerization of diethylpropargylamine in the presence of tetracyanoethylene and trinitrobenzene have been studied. A mechanism for the polymerization is proposed that involves the participation of donor-acceptor complexes in the initiation of the polymeric chain and the formation of "activated" monomer. IT is k n o w n that the p o l y m e r i z a t i o n of a n u m b e r of vinyl as well as heterocyclic m o n o mers m a y be carried out by use of a d o n o r - a c c e p t o r interaction [1-8]. I n the present work, similar complexes have been used to open the triple c a r b o n - c a r b o n b o n d with the aim of o b t a i n i n g polymers with a c o n j u g a t e d system in the m a i n c h a i n [9-12]. It has been f o u n d that p r o p a r g y l a m i n e s , when they interact with o r g a n i c * Vysokomol. soyed. A26: No. 8, 1653-1659, 1984.
V.I.
SELIKHOVA el al.
14. 15. 16. 17.
W . J . KOROS, D. R. PAUL and A. A. ROCHA, J. Polymer Sci. Polymer Phys. Ed. 14: 687, I976 S. A. STERN and A. H. MERINGO, J. Polymer Sci. Polymer Phys. Ed. 16: 735, 1978 W. J. KOROS and D. R. PAUL, J. Polymer Sci. Polymer Phys. Ed. 16: 1947, 1978 Yu. P. YAMPOL'SKII, S. G. DURGAR'YAN and N. S. NAMETKIN, Vysokomol. soyed. A2,4: 536, 1982 (Translated in Polymer Sci. U.S.S.R. 24: 3, 592, 1982) 18. IL TOI, G. MOREL and D. R. PAUL, J. Appl. Polymer Sci. 27: 2997, 1982 59. K. ROGERS, Problemy fiziki i khimii tverdogo sostoyaniya organicheskikh soyedinenii (Problems of the Physics and Chemistry of the Solid State of Organic Compounds). p. 229, Mir, Mo#cow, 1968 20. R. F. BOYER, J. Appl. Phys. 20: 540, 1949
Polymer S c i ~
~
U.S.S.R. Vot. 26, No. 8, pp. 1840-1847, 1984
in Poland
0032-$950[84 $10.00+ .00
© 1985PergamonProwLtd.
F O R M A T I O N OF P O R O U S S Y S T E M S F R O M CRYSTALLIZING POLYOLEFINES* V. I. SELIKHOVA, S. L PAKHOMOV, M. G . FELIN, N . F. BAKEYEV,
Yu. A. Ztmov and G. P. Am3R[ANOVA Karpov Physicochemical Research Institute Moscow Light Industry Technological Institute
(Received 20 February 1983) The article describes the formation of porous systems based on linear PE a n d isotactic PP by treating the initial monolithic films with solvent at raised temperature without deformazion. It is shown that the non-oriented porous films obtained are characterized by a quite well developed inner surface. The results of investigations of their structural features are presented. POROUS materials with different structures and parameters of the porous structure are
being increasingly used in technology and the national economy and a large number of methods have been devised to obtain them [1, 2]. Nonetheless, the search for new methods of regulating porosity is continuing. Of great interest is the development of methods of forming porous systems which would make it possible to maintain the continuity of the processes of obtaining porous materials in a single technological cycle into monolithic sheets and films. Existing methods are in the main associated with the use, as a rule, of crystallizing polymers and are based on the stretching of the initial monolithic films [3, 4] sometimes with use of adsorption-active media or an agent causing the polymer to swell [5]. However the need to create high degrees of extension and to keep the film in the stretched state during fixation and stabilization * Vysokomol. soyed. A26: No. 8, 1647-1652, 1984.
Formation of porous systems from crystallizing polyolefines
1841
of the structure formed and also the removal of solvent by air drying seriously complicates the process and hampers its continuous organization primarily because of the heavy increase in the duration of the individual operations. The present work describes the results of investigation of the special aspects of the structure and properties of POROUSsystems based on linear PE and isotactic PP obtained by a new method of forming them [6] by treating the monolithic films with solvent at raised temperature without resorting to deformation agents. We used polymers distinguished by a sufficiently high degree of crystallinity, PE and PP samplea produced at home and abroad, and the characteristics of which are given in Table 1. The initial non-oriented films of the polymer were obtained by pressing fused granules or powders followed by sufficiently slow (at the rate of ~ 2 deg/min) cooling of the melt. In the case of PE, monolithic films were formed by hardening the melt in iced water. The crystalline structure of the initial and porous films was studied by X-ray structural analysis at small and wide angles with use of nickel-filtered CuK, radiation. The radiographic investigation at wide angles was by the photographic method in a planocasette camera and with the DRON-1 diffractometer. The mean size of the crystallitea along the direction of the molecular chains and in the direction perpendicular to the chains was determined in line with the technique in [7]. The small angle X-ray study of the samples was with the K R M - I apparatus with slit collimation of the primary X-ray beam and to lower the diffuse scatter the porous samples were impregnated with dibutylphthalate [8].
TABLE 1. CHARACTERISTICS OF INITIAL PE AND PP FILMS
Polymer PE-I PE-2 PE "Marlex 5005" (PE-3) PE "Hostalen GD-6250" (PE-4) PP-1 PP " M o p l e n " (PP-2) PP - i o r ' (pP-3)
/~f,x 10 -4 30 55 14 II 20 35 13
T~p 134 132 126 125 161 160 165
Degree of ~ystallinity, ~ 68 66 63 58 58 59 60
The surface inhomogeneity and microstructure of the films were studied by a direct method with the JSM-2 electron scanning microscope at magnifications from 300 to 10,000. A silver layer up to 1000 A thick was dusted on to the chips of the samples obtained in liquid nitrogen to impart electrical conductivity and for contrast. The dusting was with the VUP-1 vacuum sprayer. To characterize the porous structure of the films obtained we also used the methods of mercury porometry and low temperature sorption of nitrogen at constant pressure. With the first method "the porous sample was placed in mercury, the pressure raised and the volume of the mercury compressed into the pores measured, the curve of the dependence of this volume on the pressure applied plotted and from it the differential volume of the pores determined. Information on pore size was obtained by differentiating the integral porograms [9]. The specific surface was measured on chilling the ampoule containing the sample with liquid nitrogen. The free volume of the apparatus was measured with helium assuming that it is practically not adsorbed in these conditions. The area occupied by one cubic centimetre of nitrogen was taken as equal to 4.4 m 2. The thermophysical properties of films were studied with the DSM-2 differential scanning calorimeter with exclusion of the effect of recrystallization and reheating by using a set of heating rates
1842
V.I. SELIKHOVAet al.
from 0'4 to 50 degrees/rain [10]. The values of the experimental heat of fusion were used to determine the degree of crystallinity. The heat of fusion of the completely crystalline PE sample was taken as equal to 292'6 J/g [11] and for PP 146.3 J/g [12]. The value of 3S/vwas determined from the limiting viscosity number It/] at 135°C in decalin. The deformation-strength characteristics of the porous films were studied with an instrument of the "Polyani" type fitted with a strain gauge at a speed of movement of the lower clamp of 4 ram/ /rain and at room temperature. The method of producing a porous structure proposed consisted in bringing m o n o lithic non-oriented polymer films for a certain time at raised temperatures into contact with an organic liquid with a high boiling point and causing swelling of the polymer as which we used trans-decalin or o-xylene. Then the film swollen and becoming transparent was transferred to a medium with a non-solvent (acetone) at 20°C when the porous structure formed was fixed and the agent causing swelling removed. The film was exposed to no deformation forces. After fixing the film it was further treated in acetone vapours to remove the traces of solvent and dried in a current of air to constant weight. The investigation carried out on a large number of samples with wide variation in the thickness of the films and conditions of the process of pore formation allowed us to fix the conditions of treatment optimal for obtaining a uniform porous structure of the films which are presented below. Film Thickness of initial monolithic films, mm Solvent
trans-Decalin,
trans-Decalin
Non-solvent Temperature of treatment of films with solvent, °C Time of treatment of film with solvent, rain Time of holding film in non-solvent, min Temperature of drying, °C
o-xylene Acetone 125-155 2-25 5-15 20-80
Acetone 100--125 2-35 5-30 20-80
PP 0.5-2.0
PE 0.5-2.0
The time of swelling naturally depends both on the temperature of pore formation, the thickness of the initial monolithic film and the M of the polymer studied. Rise in temperature helps to shorten the time of stay of the film in solvent. It should be noted that ihcrease in the M of the samples, on the one hand, considerably lengthened the time of swelling and, on the other, reduced the weight losses of the films on pore formation. For example, while in the porous PP-3 samples the percentage weight loss (as compared with the initial weight) reaches 6-7 in the corresponding PP-2 samples it was 3-4. To determine what part of the polymer passes into solution we measured the M of the dissolved polymer. It was found that these fractions had practically the same M as the initial polymer. This indicated that swelling of the polymers is not accompanied by passage into solution of the lawer molecular weight products but preferential dissolution of the surface layers of polymer film.
Formation of porous systems from crystallizing polyolefines
1843
In connexion with the problem to be solved in the present work it was of particular interest to study the special nature of the structure of porous systems. The results of such a comprehensive investigation are given in Table 2. TABLE 2. CHARACTERIZATION OF POROUS P E AND PP FILMS
Polymer-solvent system
PP-2-decalin PP-2-xylene PP-3-decalin PP-3-xylene PP-l-decalin PE-3-decalin PE-l-decalin
Conditions of treating film with solvent time, °C min 145 7 140 8 144 6 140 3 147 9 130 3 125 19
Specific surface, m2/g
Specific volume of pores, cma/g
Degree of crystallinity,
6.4 2"4 6.0 4.7 6.2 10'0 9'7
0"96 0"62 0'89 0"69 0"77 1 "94
69 65 66 67 61 66 70
1"50
T~p
Rupture strength, MPa
163 165 167 166 162 127 131
1.89 2.86 2.40 1.82 2-67 1.89 1.94
%
X-ray study showed that the porous PE and PP films are isotropic and contain the same crystallographic modifications as the initial polymers. The size of the crystallites in the direction of the chain molecules is 120-150 A and in the direction perpendicular to the chains ,,~ 300 A. A significant fall is observed in the intensity of the a m o r phous halo as compared with the initial films both slowly chilled and hardened (Fig. 1). This apparently reflects a well known f a c t - o n crystallization from solution lamellae form with more regular folds containing a smaller number of through chains and irregular loops as compared with the bulk material. Therefore, the number of amorphous regions falls and hence also the intensity of the amorphous halo. The degree of crystallinity of the porous systems is higher than for the corresponding initial samples. The large period in porous samples is 150-180 A and does not depend on the values of the large period of the initial films (Fig. 2). This fact points to the formation iln porous systems of new crystallites with a large period determined by the conditions of crystallization. F r o m the small angle scatter curves one may also judge that the porous samples are well impregnated with liquids even such viscous ones as dibutylphthalate. The diffuse scatter of the porous films in this case is low while in the unimpregnated porous films the small angle maxima are "blurred" by the diffuse background. The results given by mercury porometry and low temperature sorption of nitrogen show that in the porous samples the differential curve of the distribution of the pore volume by size usually has two to three maxima (Fig. 3). This testifies to the presence of several predominant pore sizes (0-0.15; 0.015-0.035 and >1 /tin) and is probably connected with the existence of certain intervals between the different eleme~n~ts of structure: crystallites, lamellae and spherulites. The influence of the M of tile polymer on the character of the porous structure obtained is such that the use
V. I. SEtaKHOVAet al.
1844
•o f polymers with a large value of ~/o involves increase in the specific volume of pores with a smaller radius. The values of the specific surface of the porous samples a n d the specific pore volume (Table 2) quite well agreeing between themselves suggests the formation of a more developed porous structure in the PE samples as compared with PP. This is also indicated by the results of electron-microscopy (Fig. 4). In the ~ase of PE the spherulites consist of numerous individual petal-plates not tightly con-
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FIo. 1. Diffractometric curves of X-ray scatter by porous (1) and initial (2, 3) films of PE-2. 2-Slowly chilled film; 3-hardened.
150I~
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FIG. 2. Curves of small angle X-ray scatter for monolithic (1, 2) and porous (3, 4) PE-3 films. /-Slowly chilled film; 2-hardened; 3-porous system obtained from slowly chilled film; 4 - from hardened.
Formation of porous systems from crystallizing polyolefmes
1845
liguous and sometimes passing from one spherulite to another. In the PP films the spherulites are more compact and their internal structure is not visible on the chips, They are usually joined by strands. Possibly as a result of this the rupture strength of the porous PP films in most cases exceeds the strength values for the PE samples (Table 2). dV 1.0
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FIo. 3. Differential (1) and integral (2) curves of the distribution of pore volume by radii for samples of porous PE-3 (a) and PP-2 (b) obtained on treating monolithic films in dccalin.
Thus, the results of the structural investigations show that porous material is obtained by radical rearrangement of the structure of the initial monolithic films with change both in the size of the structural elements and the amorphous-crystalline structure of the material. The crystalline structures grow in the porous films evidently on transfer to the precipitant of highly concentrated solution which in essence is the swollen
FIG. 4. Electron-microscopic photographs of porous films obtained on treating monolithic films in decalin: a - P P - 3 (x 2250), b - PP-I (x 750), c - P E - 4 (x 2250).
1846
V. I. SELIKHOVA e t aL
film. This solution, however, does not have time to become homogeneous since it irt all likelihood contains physical nodes in the form of residues of undissolved crystaUites. On cooling they become seeds on which the new structure of the material develops at a high rate. A certain analogy may be drawn between this method of obtaining a porous film, and the formation of porous systems by the lyophilic drying method. Dissolution of the polymer in an organic solvent results in the formation of a monophasic homogeneous system as a consequence of which the macromolecules, on average, are uniformly distributed over the volume of the solution. This means that the volume between the macromolecules is occupied by the solvent and the system as a whole is highly dispersed (if, of course, one disregards the possible formation or preservation of associates of the macromolecules). On subsequent freezing and rapid removal o f the solvent this highly dispersed structure is fixed and a porous system forms with a highly developed surface. In our case this idealized picture is not realized owing (as stated) to kinetic factors since holding the polymer film in solvent lasts a comparatively short time insufficient for the formation of an homogeneous solution. However the system becomes highly dispersed. Sufficiently sharp replacement of the solvent by precipitant results in the fixation of the structure which has had time to form by this moment. The precipitant leading to partial coalescence sharply restricts the mobility of the macromolecules and the structural elements and so fixes the structure of the material. Consequently, treatment of the films of linear PE and isotactic PP with solvent at high temperature and rapid cooling in a medium of precipitant without deformation give porous materials with a highly developed inner surface. The approach developed to the formation of the porous structure of crystalline polyolefines may clearly also be extended to a number of hydrophilic polymer materials, for example, polyamides, which is particularly important for ensuring a complex of hygienic properties (production of artificial skins, development of carcass systems implanted into the body, etc.). Translated by A. CROZY REFERENCES
1. A. A. BERLIN and F. A. SHUTOV, Osnovy khimi i tekhnologii gazonapolnennykh polimerov (Bases of the Chemistry and Technology of Gas-Filled Polymers). Khimiya, Moscow, 1980 2. Khimiya i tekhnologiya polimernykh plenochnykh materialov i iskusstvennoi kozhi (Chemistry and Technology of Polymer Film Materials and Artificial Skin). (Ed. G. P. Andrianova) Legkaya i pishchevaya promyshlennost, Moscow, ]981 3. Pat. 3801692 (U.S.A.), 1974 4. Pat. 4138459 (U.S.A.), 1979 5. Pat. 3839516 (U.S.A.), 1974 6. V.I. SELIKHOVA, G. P. ANDRIANOVA, N. F. BAKEYEV, S. I. PAKHOMOV, M. G. FELIN and Yu. A. ZUBOV, Pat. 973559 (U.S.S.R.) Publ. in B. I. No. 42, 1982 7. Yu. A. ZUBOV, V. I. SELIKItOVA, V. S. SHIRETS and A. N. OZERIN, Vysokomol. soyed. B16: 1681, 1974 (Not translated in Polymer Sci. U.S.S.R.)
Opening of triple bonds under the action of donor-acceptor complexes
1847
8. V. I. SELIKHOVA, A. N. OZERIN and G. P. BELOV, Ibid. B16: 301, 1974 (Not translated in Polymer Sci. U.S.S.R.) 9. A. V. KISELEV and V. P. DREVING, Eksperimental'nye metody v adsorbtsii i molekulyarnoi khromatografii (Experimental Methods in Adsorption and Molecular Chromatography), Mosc. State Univ,, Moscow, 1973 10. V. I. SELIKHOVA, Yu. A. ZUBOV, N. F. BAKEYEV and G. P. BELOV, Vysokomol. soyed. AI9: 759, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 4, 879, 1977) 1I. E. W, FISCHER and G. HINRICHSEN, Kolloid-Z. und Z. fiJr Polymere 213: 93, 1966 12. G. L. SLONIMSKII and Yu. K. GODOVSKII, Vysokomol. soyed. 7: 621, 1965 (Translated in Polymer Sci. U. S. S. R. 7: 4, 685, 1965)
Polymer Science U.S.S.R, Vol. 26, ]No. 8,.pp. 1847-1855, 1984 Printed in Poland
0032-3950/84 $10.00+.00 © 1985PergamonPress Ltd.
AN INVESTIGATION OF THE OPENING OF TRIPLE BONDS UNDER THE ACTION OF DONOR-ACCEPTOR COMPLEXES* L. L. STOTSKAYA, V. S. SEREBRYANIKOV, G. P. KARPACHF.VA' a n d A. M. KRAPIVIN A. V. Topchiyev Institute for Petrochemical Synthesis, U.S.S.R. Academy of Sciences
(Received 23 February 1983) Donor-acceptor complexes, formed between the monomer and organic-(flectron acceptors, have been used for the first time for the opening of the carbon-carbon triple bond, using as an example the polymerization of propargylamines. Investigation of the complex-formation reaction by UV, PMR and EPR spectroscopy has enabled it to be established that complexes with both partial and also with complete charge transfer are present, the proportions of these complexes depending on the magnitude of the energy of affinity of the acceptor towards the electron and on the polarity of the solvent. The composition and strength of the complexes have been determined. The kinetics of polymerization of diethylpropargylamine in the presence of tetracyanoethylene and trinitrobenzene have been studied. A mechanism for the polymerization is proposed that involves the participation of donor-acceptor complexes in the initiation of the polymeric chain and the formation of "activated" monomer. IT is k n o w n that the p o l y m e r i z a t i o n of a n u m b e r of vinyl as well as heterocyclic m o n o mers m a y be carried out by use of a d o n o r - a c c e p t o r interaction [1-8]. I n the present work, similar complexes have been used to open the triple c a r b o n - c a r b o n b o n d with the aim of o b t a i n i n g polymers with a c o n j u g a t e d system in the m a i n c h a i n [9-12]. It has been f o u n d that p r o p a r g y l a m i n e s , when they interact with o r g a n i c * Vysokomol. soyed. A26: No. 8, 1653-1659, 1984.