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Activity of acrylo-, methacrylo- and crotononitriles in the reactions of radical homo- and copolymerization
758
R. Yo. MAKUSKA et al.
9. N. V. KARYAKIN, I. B. RABINOVICH and L. B. SOKOLOV, Vysokomol. soyed. B20: 622, 1978 (Not translated in Polymer Sei. U.S.S.R.) 10. D. STOLL, E. W E S T R A M and G. ZINKER, Khimicheskaya termodinamika organicheskikh soyedinenii (Chemical Thermodynamics of Organic Compounds). Moscow, 1971 11. N. V. KARYAKIN, I. B. RABINOVICH and A. L. RUSANOV, Usp. khimii 54: 1009, 1985 12. N. V. KARYAKIN and I. B. RABINOVICH, Dokl. Akad. Nauk SSSR 271: 1429, 1983 13. N. V. KARYAKIN, I. B. RABINOVICH, V. V. KORSHAK, A. L. RUSANOV, D. S. T U G U S H I , A. N. M O C H A L O V and V. N. SAPOZHNIKOV, Vysokomol. soyed. A16: 691, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 4, 795, 1974) 14. N. V. KARYAKIN, V. N. SAPOZHNIKOV, G. P. KAMELOVA, V. V. KORSHAK, G. L. BERESTNEVA and D. R. TUR, Ibid. A21: 18, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 1, 20, 1979) 15. N. V. KARYAKIN, K. G. SHVETSOVA, G. P. KAMELOVA, A. L. RUSANOV, L. Kh. PLIYEVA and V. V. KORSHAK, Ibid A26: 36, 1984 (Translated in Polymer Sci. U.S.S.R. 26: 1, 40, 1984) 16. N. V. KARYAKIN, V. N. SAPOZHNIKOV, A. L. RUSANOV, Ts. G. IREMASHVILI, I. B. RABINOVICH and V. V. KORSHAK, Trudy po khimii i khim. tekhnologii (Work on Chemistry and Chemical Technology). No. 1 (32), p. 62, Gorkii, 1973
Polymer Science U.S.S.R. Vol. 29, No. 4, pp. 758-766, 1987 Printed in Poland
0032-3950/87 $10.00+ .00 © 1988 Pergamon Press plc
ACTIVITY OF ACRYLO-, METHACRYLO- AND CROTONONITRILES IN THE REACTIONS OF RADICAL HOMO- AND COPOLYMERIZATION* R. Y u . MAKUSKA, G. J. BAJORAS, S. M . BUDRIENE a n d M. Z. BALYAVICHYUS Kapsukas Vilnius State University (Received 9 August 1985)
A comparative analysis has been made of the polymerization activity of acrylo-, methacrylo- and crotononitriles from the data of their copolymerization with methacrylic acid in D M S O solutions. The CINDO/2 and ] N D O methods were used to calculate the electron structure and some quantum chemical characteristics of the molecules and radicals of the unsaturated nitriles. It is shown that the relatively low rate of polymerization of the methacrylonitrile is due to the low activity of the radicals and the absence of homopolymerization and low activity in copolymerization for crotononitrile is predetermined, in the main, by the spatial shielding of the monomer molecules. * Vysokomol. soyed. A29: No. 4, 685-691, 1987.
Activity of acrylo-, methacrylo- and crotononitriles
759
Trm problems o f synthesis of acrylonitrile (AN) (co) polymers are considered in [1~ 2]. The (co)polymerization o f the ~ and fl methyl derivatives o f A N - m e t h a c r y l o n i t r i l e ( M A N ) and crotononitrile (CN) have been far less studied. The aim o f the present w o r k is to c o m p a r e the polymerization activity o f A N , M A N and C N in identical conditions and from calculations of the electron structure of the m o n o m e r s and radicals seek to explain the differences in their reactivities. AN was washed free of stabilizer with 10% solution of alkali and distilled water to a neutral reaction, dried over CaCI2 and distilled in a rectification column. The fraction with BP 349.6-350.2 K, 20 n , 1.3935 was taken. MAN and CN were synthesized in the VNIIOlefine (Baku) directed by Mekhtiyev. MAN was purified by the technique in [3]. CN was isolated by rectification on a column taking the fractions cis-CN (BP 378-379 K, n~° 1.4180) and trans-CN (BP 393-395 K. n 2° 1'4228). Methacrylic acid (MAA) and the solvents were purified by the technique in [4]. Copolymerization was carried out in DMSO in sealed ampoules (atmosphere N2) at 343_+0.1 K, total concentration of monomers (apart from the cases indicated in the text) 3.75, initiator AIBN 1"6 × 10 -2 mole/1. The copolymers were precipitated and reprecipitated from acetone with acidified water (5 ~ HC1) or a mixture of it with diethyl ether, repeatedly washed with distilled water (or with a mixture of the precipitants-for the copolymers enriched with acid) and dried in vacuo. The conversion of the monomers was evaluated gravimetrically, the composition of the copolymers was determined from the nitrogen content, the relative activities were calculated by an analytical method [5] (for the pairs AN-MAA and MAN-MAA) and the modified Fineman-Ross method [6] for CN-MAA). The kinetics of polymerization of MAN in DMSO and acetonitrile (ACN) was investigated dilatometrically by the technique in [3]. The parameters of the electron structure of the molecules of AN, MAN and CN and their radicals were calculated by the CINDO/2 and INDO methods [7]. The lengths of the bonds in the molecules and their radicals and also the angles between bonds corresponded to the published data [8, 9]. It is k n o w n [6, 10] that C N like other mono-olefines with internal double b o n d is not h o m o p o l y m e r i z e d by the radical m o d e but enters into copolymerization with a n u m b e r o f monomers. F o r the comparative analysis o f the activities o f the nitriles we studied the copolymerization o f A N , M A N and C N with MA.A. Earlier experimental investigations on the eopolymerization o f t r a n s and c i s - C N had showed [11, 12] that the activity o f the isomers practically does not differ. F o r this w o r k we used the c i s - C N fraction. Figure l a, gives the dependences o f the initial rate o f eopolymerization o f the unsaturated nitriles and MAA. on the composition o f the initial m o n o m e r mixture. In all cases on addition to MAA. o f a second m o n o m e r vl diminished. In the region o f large amounts of nitrile on copolymerization o f A N and MA.A. its fall is completely described by the scheme of Abkin [13] if one takes the relative activities of the c o m o n o m e r s calculated by us (Table 1). The rate o f copolymerization of M A N - M A . A in nearly all the interval o f compositions of the m o n o m e r mixtures is considerably lower than for C N - M A A . This is not surprising since the copolymer contains exceptionally little C N (Fig. lb), in limiting cases not more than 10 mole % (similar f n d i n g s have also been obtained on copolymerization o f C N with methylmethacrylate [14]). On the other hand, the relative activity o f M A N in copolymerization with M A A is high, even higher than for A N (Fig. lb, Table 1). In reference [15] it is shown that the other vinyl too-
760
R. Yu. MAKUSKAet aL
nomers having the e-CHa group are also distinguished by raised activity in copolymerization as compared with the corresponding e-nonsubstituted monomers. We shall discuss this phenomenon in greater detail after analysing the electron structure of the molecules and radicals of the unsaturated nitriles. T h u s , analysis of Fig. 1 shows major differences in the reactivity of the nitriles. The rate of polymerization of M A N is lower by an order than for AN and CN is not polymerized at all by the radical mechanism; nor is it possible on copolymerization with other monomers to obtain copolymers with a practically significant amount of the nitrile. ;ui , I0'~ m o l e . t - 1.see'i
ml , mole %
8
75 q i
b
1 25
25
75 M1,mole%
25
75 i'll,mole%
FI6. 1. Initial rate of copolymerization (a) and the composition of the copolymer (b) as a function of the composition of the initial monomer mixture in DMSO: 1-AN-MAA; 2-CN-MAA; 3 - MAN-MAA (Ma - nitrile). The different behaviour of the unsaturated nitriles on copolymerization is also shown by the concentration dependences of the kinetic curves (Fig. 2). On copolymerization of MAN and MAA. and also CN and MA.A in DMSO .solutions of different concentrations it was established that with rise in the total concentration of the monomers their conversion per unit time drops. On the other hand, copolymerization of A N and MAA. proceeds more rapidly in more concentrated solutions. The order of the reaction by the sum of monomers [M~ +Mz]" for the first two systems i.e. M A N M A A and CN-MAA, is less than unity and depends on the concentration of the solution and the composition of the monomer mixture: n assumes the smallest value on copolymerization of systems enriched with nitrile, especially with CN. Study of the concentration dependence of polymerization of M A N in DMSO showed (Fig. 3) that in dilute solution ( l - 4 mole/l.) the reaction order for the monomer does not exceed 0-75 and at high monomer concentrations (9-10 moles/C) assumes even negative values. These anomalies are evidently due to solvation effects and chain transfer to the monomer. It is known [16, 17] that on worsening of the thermodynamic quality o f the reaction medium (with maintenance of the homophasic character of the system) because of change in the conformational state of the growing macroradicals the poly-
Activity of acrylo-, methacrylo- and crotononitriles
761
TABLE 1. RELATIW AC'nVtT~ES OF THE COMONOMERS ON COPOLYMER~ZATtON rN DMSO Comonomers M1-M2
rl
l I
r2
rlr2
Comonomers MrM2
AN-MAA 10.25+0.02 0.75+0-03! 0 " 1 9 CN-MAA MAN-MAA [0~'(2_+0.0610.50_~0.04! 0.36 ! MAN-AN
r~
r2
r~r2
0 I 31+3 [ 0 3.50+0.2510.47+0.03 i 1.65
merization rate decreases. Polymerization of M A N in bulk comes about close to 0-conditions. The reaction mixture during synthesis is visually homophasic although on reaching critical conversion (6-8 ~). cooling the solution leads to its clouding. Gradual increase in the amount of D M S O in the solution enhances its solvating capacity, the compactness of the coils of the macroradicals diminishes and the reaction rate rises. Such an interpretation is also confirmed by the fact that rise in the concentration of M A N in a solution of A C N does not lead to anomalous dependence in the coordinates log vj-log [M] (Fig. 3). The M A N and A C N molecules in their nature and electron donor properties are similar and, therefore, change in the amount of A.CN in the reaction mixture, in principle, does not change its thermodynamic quality and thereby also the conformation of the M A N macroradicals. The reaction order for the m o n o m e r in this case is now 0.90. q,%
a t lo9 vi --6
1
~
~
1"6
I
""---.o--
2O
t.o
8 6 [MI + 1"12], molo/l. Fro. 2
1
I
025
o.75
logfMl
FIG. 3
FIG. 2, Conversion of monomers as a function of the concentration of solution on copolymerization in DMSO of mixtures of equimolar composition: 1-AN-MAA; 2 - CN-MAA; 3-MAN-MAA. Time of polymerization I hr. F~G. 3. Dependence of log vi on log [M] on polymerization of MAN in DMSO (1) and ACN (2). H o m o - and copolymerization of AN, M A N and CN greatly differ in chain transfer to the monomer. F o r A N the transfer constant to the monomer CM =2"7 × 10 -5 while for C N CM =1"8 x 10 -3 [18]. CM on polymerization of M A N in 3.75 mole/l. D M S O solution is (8.6_+ 1.2)× 10 -4 [15] (the other published findings on chain transfer to the M A N m o n o m e r are contradictory: reference [19] gives a CM value close to that calculated by us while in [20] chain tlansfer to M A N was virtually not found). It may be expected that the solvent used will also make its own contribution correlating chain
762
R. YU. MAKU~)KA
et al.
transfer to the monomer. Thus, if the dipole-dipole interactions - C = N
and ) S = O f
differ in their magnitude from those between - C = N and - C - - N then evidently tbis will be reflected in the electron structure of the monomer and the density of electrons at the carbon atom of the c(-methyl groups of the associated M A N will change. Then both chain transfer to M A N and CN on (co)polymerization in bulk (or in ACN) and in D M S O must differ particularly since the differences in CM as a function of the solvents are known for a number of monomers [21]. With such a condition chain transfer to the monomer may make its own contribution determining the reaction order for the monomer.
ct
O.OI8
b o of7
o.oz~
o.o~.~.Ole
o~'° C
0.019
t9
_o.o,.yc 4
o~J
W" 0"03G~2 O'O24 0.~861~ N
FIo. 4. Spatial structure and charges on the ato ms of the molecules of AN (a) MAN (b) and CN (c).
.o8,,
~-~-©ql o.~08
o.o ,
/[ ~
0 010 oo3z
°oz1~o,,
'~
07]-~'007 A
ool
~o87~ c ~
~"[/ . . . .
C
~ o o ~ 8
~o,2 o.oi0 0-01, -01711N2
O°06r.~_~
Oosz~Cs
o.ooz ~" \ c 7 o
J..--~o.o33
0.035 .
-ooo~ o.oio,,-/°~o o.006- 1/
0.o81~.3 -o.156uN1
\
'o.olo _o.l,6~oNv
0.010
FIo. 5. Spatial structure and charges on the atoms of the radicals of AN (a), MAN (b) and CN (c).
Activity of acrylo-, methacrylo- and crotononitriles
763
The differences in the activity of the unsaturated nitriles are due to the electron structure and steric effects of the monomers and their radicals. We attempted to estimate the contribution of these factors on the basis of the results of quantochemical calculations. The spatial structure and charges on the atoms of the monomers and radicals studied are presented in Figs. 4 and 5. The spin density p of the unpaired electron was calculated in the growing radical, i.e. after attachment of the second monomer unit to the hypothetical primary radical (Fig. 5). The activity of the AN, M A N and CN molecules was evaluated from the bond order P and the Wiberg index W for the double bond (Table 2) characterizing to a certain degree its strength [22]. The smaller P and W t h e more readily does the bound undergo attack by the radical. Taking only the electron structure of the monomers (Table 2) it may be stated that the greatest activity must be displayed by the CN molecule and the least by the A N molecule. It should be noted that calculations by different methods (CINDO/2 and iNDO) gave well reproducible results. It is natural to assume that the activity of the radical depends on the probability of finding an electxon with unpaired spin in a certain region of space and, therefore, correlates with the value of spin density Pl on the atomic 2p~ orbital o f the C2 atom (Fig. 5). The activity of the radical must rise with increase in spin density. According to Table 3 pl is the smallest (and consequently also the activity) in the growing M A N radical while the pa values for the A N and CN radicals are close. After attachment of the radical to the molecule hybridization sp 2 of the C1 (Fig. 4) and C2 (Fig. 5) atoms passes into the hybridization sp 3. It is natural to assume that the activity of the molecules and radicals depends on the energy of such a transition AE reflecting the steric factors. Therefore, an attempt was made to evaluate ,dE by calculating the difference in the total energy of the two conformations; fiat (hybridization sp 2) and pyramidal (hybridization sp 3) dispositions of the atoms of the "tail" of the M A N and CN molecules AETAIL and the corresponding radicals with similar disposition of the atoms of the "head" A E , EAO. The energy of the transition of the "tails" of the monomers to the configuration AETAIL necessary for the reaction for M A N and CN TABLE 2. QUANTUM CHEMICAL CHARACTERISTICS OF THE MOLECULES OF (ACCORDING TO FIG. 4)
Configuration of the Method of "tail" of the molecule calculation Flat INDO P c l -c2 CINDO/2 Tetragonal Flat INDO ~FrCI --C2 CINDO/2 Tetragonal ~9 Total energy Flat IND 0/2 of molecule E, kJ/mole Tetragonal CINDO/2 ,dETAIL,kJ/mole Parameter
UNSATURATED
NITRILES
Values of the parameter AN MAN CN 0.960 0"940 0"934 0.961 0.940 0'934 0.827 0.842 1.952 1"898 1"887 1'951 1.896 1.885 1.752 1.791 91,542 114,383 114,395 114,107 114,076 276 319
764
R. Yu. MAKUSKA et al.
TABLE 3. QUANTUMCHEMICALCHARACTERISTICSOF THE RADICALSOF UNSATURATEDNITRILES
Configuration of the "head" of the radical Flat
Parameter Spind-ensity-0n the C2 atom pl (Fig. 5)
Tetragonal Spin density on C1 atom P2 (Fig. 6) Spin density on C3 atom p3 (Fig. 6) Total energy of the priFlat mary radical E, kJ/mole Tetragonal AEHEAV,kJ/mole
Method of calculation INDO CINDO/2
Values of the parameter AN MAN CN 0.778 0"726 0.788 0'772 0.719 0.783 0'420 0.460 0.645 0.586 -
CINDO/2
-
-
-
- -
CINDO/2
- -
0'645
0.570
116,506 115,758 748
116,448 116,346 102
are close (Table 2) i.e. the fl-methyl group has almost no influence on the transition of the "tail" of the m o n o m e r to the tetragonal arrangement. On the other hand, the electron density on the double bond changes differently. Judging from the P and W values (Table 2) for the tetragonal configuration of the "tail" the polymerization activity of the C N molecule is already less than for the M A N molecule. AEHEAD for M A N is considerably greater than for C N (Table 3), i.e. the e-methyl group greatly hampers the transition of the flat M A N radical to the pyramidal conformation. The spin density of the unpaired electron in the transformed M A N and C N radicals remains in the previous sequence.
O.
0"025 -
.u~C,Ikc 1
b
0.025 ,_ro.oqT)cY ~
3 oo,, ~ c~o,o
"
0.026
0.034
- o ~ c , ~ O-022
0'~20
-0149 - N
0-034~ C4 -o.~l
ON
Fro. 6. Spatial structure and charges on the atoms of the radicals formed after chain transfer to MAN (a) and CN (b). It is natural to expect that it is easier to detach the hydrogen atom from the methyl groups of the M A N and C N molecules than from the vinyl group of the A N molecule: the radicals formed after chain transfer to the m o n o m e r (Fig. 6) are resonantly stabilized. In fact, the spin density P2 and P3 (Table 3) in such radicals is reduced especially in the case of CN and they can hardly initiate the chain reaction. Growth of the chain on polymerization of C N may come about evidently only when the nitrile group of the radical and the//-methyl group of the m o n o m e r are in a certain spatial configuration. The number of such "favourable" collisions is statistically very
Activity of acrylo-, rnethacrylo- and crotononitriles
765
small and, therefore, the role of chain transfer increases. These two factors also predetermine the absence in C N of radical polymerization. Of course, because of the spatial screening of the molecules CN is also little active in copolymerization. On the other hand, the relatively low rate of polymerization of M A N is due to the low activity of the radicals depending both on its electron structure and spatial configuration. From the quantum chemical characteristics of the A N and M A N molecules and radicals (Tables 2 and 3) it is not hard to explain the influence of the e-methyl group of the vinyl monomers on their relative activities during copolymerization. As an example let us look at copolymerization of M A N and A N (Table 1). The methyl group in the radical Mt lessens its activity because of the fall in the spin density although it raises the activity of the corresponding molecule of the monomer by reducing the order of the double bond. This accounts for the relative fall in the value of the growth rate constant of the chain k~2 (as compared with kH) and increase in kzt (as compared with k22). Thus, the ratio r~ =kit/k12 increases but the ratio rz =k22/k21 falls.
Translated by A. CROZY REFERENCES
1. A. F. NIKOLAYEV, Sinteticheskiye polimery i plasticheskiye massy na ikh osnove (Synthetic Polymers and Plastics Based on them), p. 355, Khimiya, Moscow-Leningrad, 1964 2. G. HENRICI-OLIVI~ and S. OLIVE, Adv. Polymer Sci. 32: 123, 1979 3. G. I. BAJORAS, G. V. GUSAKOVA, R. Yu. MAKUSKA, Z. A. ROGANOVA and A. L. SMOLYANSKII, Vysokomol. soyed. A25: 1496, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 7, 1730, 1983) 4. R. Yu. MAKUSKA, G. I. BAJORAS, Yu. K. SHULSKUS, A. B. BOLOTIN, Z. A. ROGANOVA and A. L. SMOLYANSKII, Ibid. A27: 567, 1985 (Translated in Polymer Sci. U.S.S.R. 27: 3, 634, 1985) 5. A. I. YEZRIYELEV, E. L. BROKHINA and Ye. S. ROSKIN, Ibid. All: 1670, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 8, 1894, 1969) 6. Y. MINOURA, T. TADAKORO and Y. SUZUKI, J. Polymer Sci. A-15: 2641, 1967 7. Kvantovokhimicheskiye metody rascheta molekul (Quantumchemical Methods for Calculating Molecules) (Ed. Yu. A. Ustynyuk). 256 pp., Khimiya, Moscow, 1980 8. A. I. KITAIGORODSKII, P. M. ZORKII and V. P. BEL'SKII, Stroyeniye organicheskogo veshchestva (Structure of Organic Matter). 648 pp., Nauka, Moscow, 1980 9. L. PAULING and P. PAULING, Khimiya (Chemistry). 688 pp., Mir, Moscow, 1978 10. D. JAMES and T. OGAWA, J. Polymer Sci. 2: 991, 1964 1I. S. M. BUDRIENE, Aktual'nye problemy razvitiya nauchnykh issledovanii molodykh uchenykh Vil'nyus Univ. im V. Kapsukasa (Current Problems in the Development of Scientific Research by Young Scientists of the Vilnius Kapsukas University). p. 81, VGU, Vilnius, 1980 12. G. I. BAJORAS and S. M. BUDRIENE, Tez. dokl. respubl, konf. po voprosam, khimii i tekhnologii organicheskikh materialov (Summaries of Reports to the Republic Conference on Problems of the Chemistry and Technology of Organic Materials). p. 100, KPI, Kaunas, 1981 13. A. D. ABKIN, Voprosy khimicheskoi kinetiki, kataliza i reaktsionnoi sposobnosti (Problems of Chemical Kinetics, Catalysis and Reactivity). p. 338, Akad. Nauk SSSR, Moscow, 1955 14. G. L BAJORAS, S. M. BUDRIENE and G. I. MIKSHITE, Polimernye materialy i ikh issledovaniye (Polymer Materials and Study of Them). 16, p. 70, Vilnius, 1981 15. R. Yu. MAKUSKA, Dissert. Cand. Chem. Sci. 163 pp., VGU, Vilnius, 1983
766
L . L . RAZUMOVAet al.
16. G. VIDOTTO, A. CROSATO-ARNALDI and G. TALAMINI, Makromolek. Chem. 122: 91, 1969 17. M. RYSKA, M. KOLINSKY and D. LIM, J. Polymer Sci. Symp. 16, 621, 1967 18. J. ULBRICHT and B. SANDNER, Faserforsch. und Textiltechn. 17: 208, 1966 19. N. GRASSIE and E. VANCE, Trans. Faraday Soc. 52: 727, 1956 20. G. AYREY, B. C. HEAD and J. D. WONG, Europ. Polymer J. 10: 85, 1974 21. Spravochnik po khimii polimerov (Polymer Chemistry Reference Book) (Ed. Yu. S. Lipatov). p. 104, Nauk. dumka, Kiev, 1971 22. R. ZAGRADNIK and R. POLAK, Osnovy kvantovoi khimii (Bases of Quantum Chemistry). 504 pp., Mir~ Moscow, 1979
Polymer Science U.S.S.R. Vol. 29, No. 4, pp. 766-772, 1987 Printed in Poland
0032-3950/87 $10.00+ .00 © 1988 Pergamon Press plc
RESORPTION OF Ca ALGINATE FIBRES WITH HAEMOSTATIC PROPERTIES IN AN AQUEOUS MEDIUM* L. L. RAZUMOVA, A. A. VERETENNIKOVA, G. YE. ZAIKOV, S. L. DAVYDOVA, L. D. NARKEVICH, T. N. KALININA, YE. L. ILLARIONOVAand L. A. VOL'E Institute of Chemical Physics, U.S.S.R. Academy of Sciences Topchiyev Institute of Petrochemical Synthesis Kirov Institute of the Textile and Light Industry (Received 9 Auqust 1985)
The behaviour of various Ca alginate fibres in solutions modelling the medium of the body has been investigated by atomic-absorption spectroscopy, X-ray diffraction and from the weight loss. Brisk release into solution of Ca and alginate mass in the first ~ 10 sec of incubation of the fibres was found. It is shown that the resorption of the fibres depends on their content of chemically bound Ca and is inhibited by the presence in the solutions of amounts of Ca close to physiological and by the low tensions of the fibres. MEDICAL practice requires effective haemostatic materials. Substances used as haemostatics with a local action include gauze and t a m p o n s based on cellulose, catgut, casein, PVC, fibrin, etc. and also materials with grafted t h r o m b u s - f o r m i n g substances [1-4]. Haemostatics based on alginic acids and alginates are attracting attention (polysaccharides o f marine a l g a e - b r o w n algae). T h e y rapidly arrest blood flow, do not irritate the surrounding tissues, do not stick, take up moisture well, do n o t disturb enzymatic process in the b o d y and do not compete with medicinals but, on the contrary, m a y be * Vysokomol. soyed. A29: No. 4, 692-697, 1987.
R. Yo. MAKUSKA et al.
9. N. V. KARYAKIN, I. B. RABINOVICH and L. B. SOKOLOV, Vysokomol. soyed. B20: 622, 1978 (Not translated in Polymer Sei. U.S.S.R.) 10. D. STOLL, E. W E S T R A M and G. ZINKER, Khimicheskaya termodinamika organicheskikh soyedinenii (Chemical Thermodynamics of Organic Compounds). Moscow, 1971 11. N. V. KARYAKIN, I. B. RABINOVICH and A. L. RUSANOV, Usp. khimii 54: 1009, 1985 12. N. V. KARYAKIN and I. B. RABINOVICH, Dokl. Akad. Nauk SSSR 271: 1429, 1983 13. N. V. KARYAKIN, I. B. RABINOVICH, V. V. KORSHAK, A. L. RUSANOV, D. S. T U G U S H I , A. N. M O C H A L O V and V. N. SAPOZHNIKOV, Vysokomol. soyed. A16: 691, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 4, 795, 1974) 14. N. V. KARYAKIN, V. N. SAPOZHNIKOV, G. P. KAMELOVA, V. V. KORSHAK, G. L. BERESTNEVA and D. R. TUR, Ibid. A21: 18, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 1, 20, 1979) 15. N. V. KARYAKIN, K. G. SHVETSOVA, G. P. KAMELOVA, A. L. RUSANOV, L. Kh. PLIYEVA and V. V. KORSHAK, Ibid A26: 36, 1984 (Translated in Polymer Sci. U.S.S.R. 26: 1, 40, 1984) 16. N. V. KARYAKIN, V. N. SAPOZHNIKOV, A. L. RUSANOV, Ts. G. IREMASHVILI, I. B. RABINOVICH and V. V. KORSHAK, Trudy po khimii i khim. tekhnologii (Work on Chemistry and Chemical Technology). No. 1 (32), p. 62, Gorkii, 1973
Polymer Science U.S.S.R. Vol. 29, No. 4, pp. 758-766, 1987 Printed in Poland
0032-3950/87 $10.00+ .00 © 1988 Pergamon Press plc
ACTIVITY OF ACRYLO-, METHACRYLO- AND CROTONONITRILES IN THE REACTIONS OF RADICAL HOMO- AND COPOLYMERIZATION* R. Y u . MAKUSKA, G. J. BAJORAS, S. M . BUDRIENE a n d M. Z. BALYAVICHYUS Kapsukas Vilnius State University (Received 9 August 1985)
A comparative analysis has been made of the polymerization activity of acrylo-, methacrylo- and crotononitriles from the data of their copolymerization with methacrylic acid in D M S O solutions. The CINDO/2 and ] N D O methods were used to calculate the electron structure and some quantum chemical characteristics of the molecules and radicals of the unsaturated nitriles. It is shown that the relatively low rate of polymerization of the methacrylonitrile is due to the low activity of the radicals and the absence of homopolymerization and low activity in copolymerization for crotononitrile is predetermined, in the main, by the spatial shielding of the monomer molecules. * Vysokomol. soyed. A29: No. 4, 685-691, 1987.
Activity of acrylo-, methacrylo- and crotononitriles
759
Trm problems o f synthesis of acrylonitrile (AN) (co) polymers are considered in [1~ 2]. The (co)polymerization o f the ~ and fl methyl derivatives o f A N - m e t h a c r y l o n i t r i l e ( M A N ) and crotononitrile (CN) have been far less studied. The aim o f the present w o r k is to c o m p a r e the polymerization activity o f A N , M A N and C N in identical conditions and from calculations of the electron structure of the m o n o m e r s and radicals seek to explain the differences in their reactivities. AN was washed free of stabilizer with 10% solution of alkali and distilled water to a neutral reaction, dried over CaCI2 and distilled in a rectification column. The fraction with BP 349.6-350.2 K, 20 n , 1.3935 was taken. MAN and CN were synthesized in the VNIIOlefine (Baku) directed by Mekhtiyev. MAN was purified by the technique in [3]. CN was isolated by rectification on a column taking the fractions cis-CN (BP 378-379 K, n~° 1.4180) and trans-CN (BP 393-395 K. n 2° 1'4228). Methacrylic acid (MAA) and the solvents were purified by the technique in [4]. Copolymerization was carried out in DMSO in sealed ampoules (atmosphere N2) at 343_+0.1 K, total concentration of monomers (apart from the cases indicated in the text) 3.75, initiator AIBN 1"6 × 10 -2 mole/1. The copolymers were precipitated and reprecipitated from acetone with acidified water (5 ~ HC1) or a mixture of it with diethyl ether, repeatedly washed with distilled water (or with a mixture of the precipitants-for the copolymers enriched with acid) and dried in vacuo. The conversion of the monomers was evaluated gravimetrically, the composition of the copolymers was determined from the nitrogen content, the relative activities were calculated by an analytical method [5] (for the pairs AN-MAA and MAN-MAA) and the modified Fineman-Ross method [6] for CN-MAA). The kinetics of polymerization of MAN in DMSO and acetonitrile (ACN) was investigated dilatometrically by the technique in [3]. The parameters of the electron structure of the molecules of AN, MAN and CN and their radicals were calculated by the CINDO/2 and INDO methods [7]. The lengths of the bonds in the molecules and their radicals and also the angles between bonds corresponded to the published data [8, 9]. It is k n o w n [6, 10] that C N like other mono-olefines with internal double b o n d is not h o m o p o l y m e r i z e d by the radical m o d e but enters into copolymerization with a n u m b e r o f monomers. F o r the comparative analysis o f the activities o f the nitriles we studied the copolymerization o f A N , M A N and C N with MA.A. Earlier experimental investigations on the eopolymerization o f t r a n s and c i s - C N had showed [11, 12] that the activity o f the isomers practically does not differ. F o r this w o r k we used the c i s - C N fraction. Figure l a, gives the dependences o f the initial rate o f eopolymerization o f the unsaturated nitriles and MAA. on the composition o f the initial m o n o m e r mixture. In all cases on addition to MAA. o f a second m o n o m e r vl diminished. In the region o f large amounts of nitrile on copolymerization o f A N and MA.A. its fall is completely described by the scheme of Abkin [13] if one takes the relative activities of the c o m o n o m e r s calculated by us (Table 1). The rate o f copolymerization of M A N - M A . A in nearly all the interval o f compositions of the m o n o m e r mixtures is considerably lower than for C N - M A A . This is not surprising since the copolymer contains exceptionally little C N (Fig. lb), in limiting cases not more than 10 mole % (similar f n d i n g s have also been obtained on copolymerization o f C N with methylmethacrylate [14]). On the other hand, the relative activity o f M A N in copolymerization with M A A is high, even higher than for A N (Fig. lb, Table 1). In reference [15] it is shown that the other vinyl too-
760
R. Yu. MAKUSKAet aL
nomers having the e-CHa group are also distinguished by raised activity in copolymerization as compared with the corresponding e-nonsubstituted monomers. We shall discuss this phenomenon in greater detail after analysing the electron structure of the molecules and radicals of the unsaturated nitriles. T h u s , analysis of Fig. 1 shows major differences in the reactivity of the nitriles. The rate of polymerization of M A N is lower by an order than for AN and CN is not polymerized at all by the radical mechanism; nor is it possible on copolymerization with other monomers to obtain copolymers with a practically significant amount of the nitrile. ;ui , I0'~ m o l e . t - 1.see'i
ml , mole %
8
75 q i
b
1 25
25
75 M1,mole%
25
75 i'll,mole%
FI6. 1. Initial rate of copolymerization (a) and the composition of the copolymer (b) as a function of the composition of the initial monomer mixture in DMSO: 1-AN-MAA; 2-CN-MAA; 3 - MAN-MAA (Ma - nitrile). The different behaviour of the unsaturated nitriles on copolymerization is also shown by the concentration dependences of the kinetic curves (Fig. 2). On copolymerization of MAN and MAA. and also CN and MA.A in DMSO .solutions of different concentrations it was established that with rise in the total concentration of the monomers their conversion per unit time drops. On the other hand, copolymerization of A N and MAA. proceeds more rapidly in more concentrated solutions. The order of the reaction by the sum of monomers [M~ +Mz]" for the first two systems i.e. M A N M A A and CN-MAA, is less than unity and depends on the concentration of the solution and the composition of the monomer mixture: n assumes the smallest value on copolymerization of systems enriched with nitrile, especially with CN. Study of the concentration dependence of polymerization of M A N in DMSO showed (Fig. 3) that in dilute solution ( l - 4 mole/l.) the reaction order for the monomer does not exceed 0-75 and at high monomer concentrations (9-10 moles/C) assumes even negative values. These anomalies are evidently due to solvation effects and chain transfer to the monomer. It is known [16, 17] that on worsening of the thermodynamic quality o f the reaction medium (with maintenance of the homophasic character of the system) because of change in the conformational state of the growing macroradicals the poly-
Activity of acrylo-, methacrylo- and crotononitriles
761
TABLE 1. RELATIW AC'nVtT~ES OF THE COMONOMERS ON COPOLYMER~ZATtON rN DMSO Comonomers M1-M2
rl
l I
r2
rlr2
Comonomers MrM2
AN-MAA 10.25+0.02 0.75+0-03! 0 " 1 9 CN-MAA MAN-MAA [0~'(2_+0.0610.50_~0.04! 0.36 ! MAN-AN
r~
r2
r~r2
0 I 31+3 [ 0 3.50+0.2510.47+0.03 i 1.65
merization rate decreases. Polymerization of M A N in bulk comes about close to 0-conditions. The reaction mixture during synthesis is visually homophasic although on reaching critical conversion (6-8 ~). cooling the solution leads to its clouding. Gradual increase in the amount of D M S O in the solution enhances its solvating capacity, the compactness of the coils of the macroradicals diminishes and the reaction rate rises. Such an interpretation is also confirmed by the fact that rise in the concentration of M A N in a solution of A C N does not lead to anomalous dependence in the coordinates log vj-log [M] (Fig. 3). The M A N and A C N molecules in their nature and electron donor properties are similar and, therefore, change in the amount of A.CN in the reaction mixture, in principle, does not change its thermodynamic quality and thereby also the conformation of the M A N macroradicals. The reaction order for the m o n o m e r in this case is now 0.90. q,%
a t lo9 vi --6
1
~
~
1"6
I
""---.o--
2O
t.o
8 6 [MI + 1"12], molo/l. Fro. 2
1
I
025
o.75
logfMl
FIG. 3
FIG. 2, Conversion of monomers as a function of the concentration of solution on copolymerization in DMSO of mixtures of equimolar composition: 1-AN-MAA; 2 - CN-MAA; 3-MAN-MAA. Time of polymerization I hr. F~G. 3. Dependence of log vi on log [M] on polymerization of MAN in DMSO (1) and ACN (2). H o m o - and copolymerization of AN, M A N and CN greatly differ in chain transfer to the monomer. F o r A N the transfer constant to the monomer CM =2"7 × 10 -5 while for C N CM =1"8 x 10 -3 [18]. CM on polymerization of M A N in 3.75 mole/l. D M S O solution is (8.6_+ 1.2)× 10 -4 [15] (the other published findings on chain transfer to the M A N m o n o m e r are contradictory: reference [19] gives a CM value close to that calculated by us while in [20] chain tlansfer to M A N was virtually not found). It may be expected that the solvent used will also make its own contribution correlating chain
762
R. YU. MAKU~)KA
et al.
transfer to the monomer. Thus, if the dipole-dipole interactions - C = N
and ) S = O f
differ in their magnitude from those between - C = N and - C - - N then evidently tbis will be reflected in the electron structure of the monomer and the density of electrons at the carbon atom of the c(-methyl groups of the associated M A N will change. Then both chain transfer to M A N and CN on (co)polymerization in bulk (or in ACN) and in D M S O must differ particularly since the differences in CM as a function of the solvents are known for a number of monomers [21]. With such a condition chain transfer to the monomer may make its own contribution determining the reaction order for the monomer.
ct
O.OI8
b o of7
o.oz~
o.o~.~.Ole
o~'° C
0.019
t9
_o.o,.yc 4
o~J
W" 0"03G~2 O'O24 0.~861~ N
FIo. 4. Spatial structure and charges on the ato ms of the molecules of AN (a) MAN (b) and CN (c).
.o8,,
~-~-©ql o.~08
o.o ,
/[ ~
0 010 oo3z
°oz1~o,,
'~
07]-~'007 A
ool
~o87~ c ~
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C
~ o o ~ 8
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Oosz~Cs
o.ooz ~" \ c 7 o
J..--~o.o33
0.035 .
-ooo~ o.oio,,-/°~o o.006- 1/
0.o81~.3 -o.156uN1
\
'o.olo _o.l,6~oNv
0.010
FIo. 5. Spatial structure and charges on the atoms of the radicals of AN (a), MAN (b) and CN (c).
Activity of acrylo-, methacrylo- and crotononitriles
763
The differences in the activity of the unsaturated nitriles are due to the electron structure and steric effects of the monomers and their radicals. We attempted to estimate the contribution of these factors on the basis of the results of quantochemical calculations. The spatial structure and charges on the atoms of the monomers and radicals studied are presented in Figs. 4 and 5. The spin density p of the unpaired electron was calculated in the growing radical, i.e. after attachment of the second monomer unit to the hypothetical primary radical (Fig. 5). The activity of the AN, M A N and CN molecules was evaluated from the bond order P and the Wiberg index W for the double bond (Table 2) characterizing to a certain degree its strength [22]. The smaller P and W t h e more readily does the bound undergo attack by the radical. Taking only the electron structure of the monomers (Table 2) it may be stated that the greatest activity must be displayed by the CN molecule and the least by the A N molecule. It should be noted that calculations by different methods (CINDO/2 and iNDO) gave well reproducible results. It is natural to assume that the activity of the radical depends on the probability of finding an electxon with unpaired spin in a certain region of space and, therefore, correlates with the value of spin density Pl on the atomic 2p~ orbital o f the C2 atom (Fig. 5). The activity of the radical must rise with increase in spin density. According to Table 3 pl is the smallest (and consequently also the activity) in the growing M A N radical while the pa values for the A N and CN radicals are close. After attachment of the radical to the molecule hybridization sp 2 of the C1 (Fig. 4) and C2 (Fig. 5) atoms passes into the hybridization sp 3. It is natural to assume that the activity of the molecules and radicals depends on the energy of such a transition AE reflecting the steric factors. Therefore, an attempt was made to evaluate ,dE by calculating the difference in the total energy of the two conformations; fiat (hybridization sp 2) and pyramidal (hybridization sp 3) dispositions of the atoms of the "tail" of the M A N and CN molecules AETAIL and the corresponding radicals with similar disposition of the atoms of the "head" A E , EAO. The energy of the transition of the "tails" of the monomers to the configuration AETAIL necessary for the reaction for M A N and CN TABLE 2. QUANTUM CHEMICAL CHARACTERISTICS OF THE MOLECULES OF (ACCORDING TO FIG. 4)
Configuration of the Method of "tail" of the molecule calculation Flat INDO P c l -c2 CINDO/2 Tetragonal Flat INDO ~FrCI --C2 CINDO/2 Tetragonal ~9 Total energy Flat IND 0/2 of molecule E, kJ/mole Tetragonal CINDO/2 ,dETAIL,kJ/mole Parameter
UNSATURATED
NITRILES
Values of the parameter AN MAN CN 0.960 0"940 0"934 0.961 0.940 0'934 0.827 0.842 1.952 1"898 1"887 1'951 1.896 1.885 1.752 1.791 91,542 114,383 114,395 114,107 114,076 276 319
764
R. Yu. MAKUSKA et al.
TABLE 3. QUANTUMCHEMICALCHARACTERISTICSOF THE RADICALSOF UNSATURATEDNITRILES
Configuration of the "head" of the radical Flat
Parameter Spind-ensity-0n the C2 atom pl (Fig. 5)
Tetragonal Spin density on C1 atom P2 (Fig. 6) Spin density on C3 atom p3 (Fig. 6) Total energy of the priFlat mary radical E, kJ/mole Tetragonal AEHEAV,kJ/mole
Method of calculation INDO CINDO/2
Values of the parameter AN MAN CN 0.778 0"726 0.788 0'772 0.719 0.783 0'420 0.460 0.645 0.586 -
CINDO/2
-
-
-
- -
CINDO/2
- -
0'645
0.570
116,506 115,758 748
116,448 116,346 102
are close (Table 2) i.e. the fl-methyl group has almost no influence on the transition of the "tail" of the m o n o m e r to the tetragonal arrangement. On the other hand, the electron density on the double bond changes differently. Judging from the P and W values (Table 2) for the tetragonal configuration of the "tail" the polymerization activity of the C N molecule is already less than for the M A N molecule. AEHEAD for M A N is considerably greater than for C N (Table 3), i.e. the e-methyl group greatly hampers the transition of the flat M A N radical to the pyramidal conformation. The spin density of the unpaired electron in the transformed M A N and C N radicals remains in the previous sequence.
O.
0"025 -
.u~C,Ikc 1
b
0.025 ,_ro.oqT)cY ~
3 oo,, ~ c~o,o
"
0.026
0.034
- o ~ c , ~ O-022
0'~20
-0149 - N
0-034~ C4 -o.~l
ON
Fro. 6. Spatial structure and charges on the atoms of the radicals formed after chain transfer to MAN (a) and CN (b). It is natural to expect that it is easier to detach the hydrogen atom from the methyl groups of the M A N and C N molecules than from the vinyl group of the A N molecule: the radicals formed after chain transfer to the m o n o m e r (Fig. 6) are resonantly stabilized. In fact, the spin density P2 and P3 (Table 3) in such radicals is reduced especially in the case of CN and they can hardly initiate the chain reaction. Growth of the chain on polymerization of C N may come about evidently only when the nitrile group of the radical and the//-methyl group of the m o n o m e r are in a certain spatial configuration. The number of such "favourable" collisions is statistically very
Activity of acrylo-, rnethacrylo- and crotononitriles
765
small and, therefore, the role of chain transfer increases. These two factors also predetermine the absence in C N of radical polymerization. Of course, because of the spatial screening of the molecules CN is also little active in copolymerization. On the other hand, the relatively low rate of polymerization of M A N is due to the low activity of the radicals depending both on its electron structure and spatial configuration. From the quantum chemical characteristics of the A N and M A N molecules and radicals (Tables 2 and 3) it is not hard to explain the influence of the e-methyl group of the vinyl monomers on their relative activities during copolymerization. As an example let us look at copolymerization of M A N and A N (Table 1). The methyl group in the radical Mt lessens its activity because of the fall in the spin density although it raises the activity of the corresponding molecule of the monomer by reducing the order of the double bond. This accounts for the relative fall in the value of the growth rate constant of the chain k~2 (as compared with kH) and increase in kzt (as compared with k22). Thus, the ratio r~ =kit/k12 increases but the ratio rz =k22/k21 falls.
Translated by A. CROZY REFERENCES
1. A. F. NIKOLAYEV, Sinteticheskiye polimery i plasticheskiye massy na ikh osnove (Synthetic Polymers and Plastics Based on them), p. 355, Khimiya, Moscow-Leningrad, 1964 2. G. HENRICI-OLIVI~ and S. OLIVE, Adv. Polymer Sci. 32: 123, 1979 3. G. I. BAJORAS, G. V. GUSAKOVA, R. Yu. MAKUSKA, Z. A. ROGANOVA and A. L. SMOLYANSKII, Vysokomol. soyed. A25: 1496, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 7, 1730, 1983) 4. R. Yu. MAKUSKA, G. I. BAJORAS, Yu. K. SHULSKUS, A. B. BOLOTIN, Z. A. ROGANOVA and A. L. SMOLYANSKII, Ibid. A27: 567, 1985 (Translated in Polymer Sci. U.S.S.R. 27: 3, 634, 1985) 5. A. I. YEZRIYELEV, E. L. BROKHINA and Ye. S. ROSKIN, Ibid. All: 1670, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 8, 1894, 1969) 6. Y. MINOURA, T. TADAKORO and Y. SUZUKI, J. Polymer Sci. A-15: 2641, 1967 7. Kvantovokhimicheskiye metody rascheta molekul (Quantumchemical Methods for Calculating Molecules) (Ed. Yu. A. Ustynyuk). 256 pp., Khimiya, Moscow, 1980 8. A. I. KITAIGORODSKII, P. M. ZORKII and V. P. BEL'SKII, Stroyeniye organicheskogo veshchestva (Structure of Organic Matter). 648 pp., Nauka, Moscow, 1980 9. L. PAULING and P. PAULING, Khimiya (Chemistry). 688 pp., Mir, Moscow, 1978 10. D. JAMES and T. OGAWA, J. Polymer Sci. 2: 991, 1964 1I. S. M. BUDRIENE, Aktual'nye problemy razvitiya nauchnykh issledovanii molodykh uchenykh Vil'nyus Univ. im V. Kapsukasa (Current Problems in the Development of Scientific Research by Young Scientists of the Vilnius Kapsukas University). p. 81, VGU, Vilnius, 1980 12. G. I. BAJORAS and S. M. BUDRIENE, Tez. dokl. respubl, konf. po voprosam, khimii i tekhnologii organicheskikh materialov (Summaries of Reports to the Republic Conference on Problems of the Chemistry and Technology of Organic Materials). p. 100, KPI, Kaunas, 1981 13. A. D. ABKIN, Voprosy khimicheskoi kinetiki, kataliza i reaktsionnoi sposobnosti (Problems of Chemical Kinetics, Catalysis and Reactivity). p. 338, Akad. Nauk SSSR, Moscow, 1955 14. G. L BAJORAS, S. M. BUDRIENE and G. I. MIKSHITE, Polimernye materialy i ikh issledovaniye (Polymer Materials and Study of Them). 16, p. 70, Vilnius, 1981 15. R. Yu. MAKUSKA, Dissert. Cand. Chem. Sci. 163 pp., VGU, Vilnius, 1983
766
L . L . RAZUMOVAet al.
16. G. VIDOTTO, A. CROSATO-ARNALDI and G. TALAMINI, Makromolek. Chem. 122: 91, 1969 17. M. RYSKA, M. KOLINSKY and D. LIM, J. Polymer Sci. Symp. 16, 621, 1967 18. J. ULBRICHT and B. SANDNER, Faserforsch. und Textiltechn. 17: 208, 1966 19. N. GRASSIE and E. VANCE, Trans. Faraday Soc. 52: 727, 1956 20. G. AYREY, B. C. HEAD and J. D. WONG, Europ. Polymer J. 10: 85, 1974 21. Spravochnik po khimii polimerov (Polymer Chemistry Reference Book) (Ed. Yu. S. Lipatov). p. 104, Nauk. dumka, Kiev, 1971 22. R. ZAGRADNIK and R. POLAK, Osnovy kvantovoi khimii (Bases of Quantum Chemistry). 504 pp., Mir~ Moscow, 1979
Polymer Science U.S.S.R. Vol. 29, No. 4, pp. 766-772, 1987 Printed in Poland
0032-3950/87 $10.00+ .00 © 1988 Pergamon Press plc
RESORPTION OF Ca ALGINATE FIBRES WITH HAEMOSTATIC PROPERTIES IN AN AQUEOUS MEDIUM* L. L. RAZUMOVA, A. A. VERETENNIKOVA, G. YE. ZAIKOV, S. L. DAVYDOVA, L. D. NARKEVICH, T. N. KALININA, YE. L. ILLARIONOVAand L. A. VOL'E Institute of Chemical Physics, U.S.S.R. Academy of Sciences Topchiyev Institute of Petrochemical Synthesis Kirov Institute of the Textile and Light Industry (Received 9 Auqust 1985)
The behaviour of various Ca alginate fibres in solutions modelling the medium of the body has been investigated by atomic-absorption spectroscopy, X-ray diffraction and from the weight loss. Brisk release into solution of Ca and alginate mass in the first ~ 10 sec of incubation of the fibres was found. It is shown that the resorption of the fibres depends on their content of chemically bound Ca and is inhibited by the presence in the solutions of amounts of Ca close to physiological and by the low tensions of the fibres. MEDICAL practice requires effective haemostatic materials. Substances used as haemostatics with a local action include gauze and t a m p o n s based on cellulose, catgut, casein, PVC, fibrin, etc. and also materials with grafted t h r o m b u s - f o r m i n g substances [1-4]. Haemostatics based on alginic acids and alginates are attracting attention (polysaccharides o f marine a l g a e - b r o w n algae). T h e y rapidly arrest blood flow, do not irritate the surrounding tissues, do not stick, take up moisture well, do n o t disturb enzymatic process in the b o d y and do not compete with medicinals but, on the contrary, m a y be * Vysokomol. soyed. A29: No. 4, 692-697, 1987.