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Mechanism of graft copolymerization of vinyl monomers with silk fibroin
1322
L.I.
BUTI~A et al.
4. V. B. GOLUBEV, V. P. ZUBOV, G. S. NAUMOV, L. 1. VALUYEV, V. A. KABANOV and V. A. KARGIN, Vysokomol. soyed. Al1: 2689, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 12, 3058, 1969) 5. Ye. T. DENISOV, Konstanty skorosti gomoliticheskikh zhidkofaznykh reaktsii (Rate Constants of Hemolytic Liquid-Phase Reactions). Izd. "Nauka", 1971 6. M. G. FOX, J. B. KINSINGER, H. F. MASON and E. M. SHUELE, Polymer 3: 72, 1962 7. W. H. STOCKMAYER, L. D. MOORE, M. FIXMAN and B. M. EPSTEIN, J. Polymer Sci. 16: 517, 1955 8. R. A. THOMSON and J. R. WALTERS, Trans. Faraday Soc. 67: 3046, 1971 9. N. FHURMAN and R. B. MESROBIAN, J. Amer. Chem. Soc. 76: 3281, 1954 10. Kh. S. BAGDASAR'YAN, Teoriya radikal'noi polimerizatsii (Theory of Radical Polymerization). Izd. "l~auka", 1969 11. N. G. GAYLORD, J. Polymer Sci. B7: 145, 1969
MECHANISM OF GRAFT COPOLYMERIZATION OF VINYL MONOMERS WITH SILK FIBROIN* L. I. BUTIIVA, M. V. SHISHKn~A,S. 1~. SADOVAand M. V. KORCHAGnv Moscow Textile Institute A. V. Topchiev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences
(Recsived 18 February 1974) In order to examine the mechanism of graft copolymerization to silk fibroin, polymethyhnethacrylate (PMMA) was synthesized using model systems of amino acid-ferrous iron-hydrogen peroxide. I t was shown that the phenol OH group of tyrosine and the indole N ~ group of tryptophan are the most active in chain transfer. The presence of amino acid residues in graft P M ~ A was established by I R spectroscopy.
THP. ferrous iron-hydrogen peroxide redox system was used for graft copolymerization with silk fibroin, as well as vinyl monomers: acrylonitrfle (AN), methyl methacrylate (MMA), styrene, aerylamine (AA). Graft copolymers were obtained with a variable weight increase (10-50%), according to the concentration of components of the redox system, monomer concentration, temperature and grafting time. Although the use of the ferrous iron-hydrogen peroxide redox system has been known for a long time for the modification of albumens (keratin in particular) by graft copolymerization [1], the reaction mechanism has not so far been studied. It has been assumed [2] that ferrous iron is combined with the carboxyl group of the polymer with a salt bond. During interaction of ferrous iron with * Vysokomol. soyod. AI7: No. 5, 1150-1153, 1975.
Graft copolymerization of vinyl monomers with silk fibroin
1323
hydrogen peroxide the following reaction takes place: Fe2+-4-H~O2-~Fe3++OH+OH. A graft polymer is formed when chain transfer to the albumen macromolecule is complete. The problem of the most likely places of localizing free radicals has so far not been studied in practice. To explain the mechanism of graft copolymerization of vinyl monomers with silk fibroin, an attempt was therefore made to synthesize vinyl monomers using systems which contain model compounds: ~-amino acid, ferrous iron-hydrogen peroxide redox system and a monomer. Freshly distilled MMA was u s e d as monomer.
I
8
I
I
1
28
3~ v,/O-~cm -I
I R absorption spectra of: the initial PMMA (1), PMMA graft to tyrosino (2) and t r y p t o p h a n (3). Conditions of carrying out experiments using model amino acid were similar to conditions of graft copolymerization using silk fibroin. An amino acid sample was used in which the proportion of carboxyl groups was equivalent to ,the carboxyl group content in 1 g fibre. An equimolecular amount of ferrous iron was used. Carefully weighed amino acid and ferrous iron samples were dissolved in 50 ml distilled water and a calculated amoun~ o f hydrogen peroxide added (0-008~/o). The reaction was carried out at 60 ° and lasted 60 rain. After the reaction th e residue was filtered, dried to constant weight and weighed. A control experiment without amino acid was carried out in parallel. A rust coloured residu~ was formed in this case which was readily soluble in 6 N hydrochloric acid. I t was establisheel
1324
L . I . B~rrnvA et al.
as a result that the residue contained ferric hydroxide. Bearing in m i n d the possibility of forming ferric hydroxide even in model experiments, the residues obtained were freed from ferric hydroxide by t r e a t m e n t in 6 z¢ hydrochloric acid. Final products were PMMA (Figure). Polymerization using model systems was carried out with fifteen amino acids contained in silk fibroin and with dipeptide (glycyl-glycine) (Table 1). TABLE
1. E F F E C T
O F T H E l q A T U R E O F A ~ I n q o A C I D O1~" T H E P O L Y M ~ R I Z A T I O I q
wt. Amino acid
Glycine DL-alanin D L -valine DL-serine D L -aspartic L-arginine HCl DL-phenylalanine DL-tyrosine Proline DL-tryptophane Dipeptide (glycyl-glycine) DL-leicine DL-threonine L-glutamic DL-lysine HC1 L-histidine HC1
Mol.
75.07 89.09 117.15 105.09 133.00 174.00 165-00 181-00 115.00 204.00 132-00 131.17 119.12 147-14 146-19 155.00
Amino acid sample, g
l~Iohr's salt sample, g
PlVIMA, g
0.027 0.032 0-042 0.037 0.047 0.062 0.058 0.064 0.041 0.072 0.047 0.047 0.042 0.052 0.052 0.058
0.0704 0.0704 0.0702 0.0690 0.0690 0-0800 0.0630 0.0690 0-0700 0-0691 0-0700 0.0700 0.0690 0.0693 0.0699 0.0704
0.0300 0.0121 Traces 0.0483 0.0418 0.0057 0.0216 0-1892 Traces 0.2105 0.0296 0.0252 0.0279 Traces 0.0061 0.0127
OF 1 ~
Monomer conversion,
% 6"00 2-42 9.66 8"36 1-14
4.32 37.84 42.10 5.92
5.04 5-58 1.12
2.54
As shown by Table 1, polymerization of MMA takes place to a very shght extent with practically all amino acids and dipeptide, monomer conversion varying up to 6 %. The result obtained using a model system with serine is somewhat different, where monomer conversion is 9.66%. In the presence of tyrosine-ferrous iron-hydrogen peroxide and tryptophanferrous iron-hydrogen peroxide model systems P~IMA is formed in significant proportions: monomer conversion is about 40%. Monomer conversion is 51.6% on silk fibroin under the same conditions. To verify further the possibility of chain transfer as a result of --CI-I2-- and ---CO--NH--, graft copolymerization was carried out with the redox system indicated using polyamide fibre (Kapron). Under conditions of reaction for a silk fibre, no graft copolymer had formed. These results indicate that chain transfer is most effective with phenol OH groups of tyrosine and indole NH groups oftryptophane, the aliphatic OI-I group of serine being much less effective in chain transfer. Chain transfer from aliphatie NH2 and CH groups (e.g. aspartic acid) is also possible. Considering the varying contents of amino acids in fibroin it should be borne in mind that the overall effect of each functional group on graft copolymeriza-
Graft copolymerization of vinyl monomers with silk fibroin
1325
tion varies and is determined not only b y activity, b u t also b y its quantitative content in fibroin. Knowing that the quantitative content in fibroin of tyrosine, one of the most active amino acids, is about 12.0~/o it m a y be assumed that it is precisely this amino acid which has the greatest effect on graft copolymerization. The mechanism of graft copolymerization involving OH groups of tyrosine as active centres m a y be as follows: R I
()It
nCH2=CH
fibroi,1 --CH2---, fibrom -- C H ~ I
T
OH
I 0
• fibroin--CH-. I
I i I O--(CIt~--CtI--)eth--Cff
Since tryptophan content in silk fibroin is low (0.6-1-2%), in spite of the highest activity of indole N H groups, the number of graft chains formed using tryptophyl residues cannot be significant. TABLE 2. OPTICAL DENSITY RATIO OF NI-I M.AXIM.AOF GRAFT P ~ k
Amino Acid Glycine Aspartic Serine
D1
D2
D
D
0.300 0.210 0.230
0.350 0.220 0-260
Amino acid Dipeptide Tyrosine Tryptophan
D1
Di
D
D
0.230 0.150 0.220
0.250 0.120 0.200
To confirm that PMMA obtained using model systems is chemically combined with amino acid residues, I R spectra were obtained of graft PMMA synthesized using model amino acids (glycine, aspartie acid, serine, dipeptide, tyrosine, tryptophan) and a spectrum of PMMA separated from graft copolymer b y alkaline hydrolysis of the albumen constituent [3]. I R absorption spectra were recorded using a UR-20 spectrophotometer with slot programme 4. To record the spectrum, PMMA was pelletized with potassium bromide (0.001-0.002 g for 0.200 g KBr). Spectra were recorded in the 400-4000 cm -1 range. These spectra are similar and are determined b y absorption of PMMA, end groups of amino acids being represented in spectra only with a double band of N H bond stretching vibrations in NH2 groups in the region of 3400 and 3500 cm -1 (e.g. using model amino acid, tyrosine, Figure). These bands represent the symmetrical and asymmetric forms of vibrations of N H groups, respectively. To evaluate the extent to which various amino acids are contained in PMMA, the optical density ratios of each of the N H maxima were calculated (D1 and D2)
1326
S . S . GusEv et al.
to the maximum of the band at 3000 cm-1 of PMMA (D), which characterizes the bond stretching vibration of C--H in the C(CH3)CO0 fragment. These ratios axe shown in Table 2 and their practically coincident values point to the absence of foreign absorption in this region. Translated by E. SEM.ERE REFERENCES 1. M. LIPSON a n d J. B. SPEAKMAN, J. Soc. I)yers and Colourists 65: 390, 1949 2. S. F. SADOVA a n d A. A. KONKtN, ZhVKhO ira. I). I. Mendeleyeva 11: 596, 1967 3. S. F. SADOVA a n d A. A. KONKIN, Vysokomol. soyed. BI0: 592, 1968 (l~ot translated in Polymer Sci. U.S.S.R.)
SPECTROSCOPIC AND CHEMICAL STUDY OF ATMOSPHERIC THERMAL CONVERSION OF CELLULOSE AND MONOCARBOXYL CELLULOSE* S. S. Gvsv.v, F. N. KAPVTSmI, V. Y~. KAPUTSK~ and E. P. KAI,UTSKAYA V. I. Lenin Byelorussian State University I n s t i t u t e of Physics, U.S.S.R. Academy of Sciences
(Received 20 February 1974) A study was made by spectroscopic, chemical and thermal methods of atmospheric oxidation of cellulose and monocarboxyl cellulose (IVICC)with different carboxyl group contents at temperatures of 80 to 400 ° . Two stages of decomposition were dis¢inguished and described using the information obtained. An auto-catalytic heterogeneous process of solid phase thermal oxidation b y atmospheric oxygen of cellulose a n d monocarboxyl cellulose is p u t forward as a hypothesis.
T~v. study deals with thermal conversions of cellulose and a polymeric acid, monocarboxylcellulose (MCC) obtained therefrom. The addition of ionogen groups to the polymer raised a further problem of studying variations of exchange adsorption properties under strict thermal conditions. Systematic studies of thermal oxidation of acid polycarbohydrates have not been carried out. Chromatographic paper (98-99% a-cellulose, the degree of polymerization being 1100) and the MCC obtained with different carboxyl group contents were used. Selective oxida$ion at Ce of the pyrane ring of a cellulose macromoleculo was carried out with N,O4 solution i n CC14 b y methods previously described [lJ. Heat treatment was carried out as follows. A * Vysokomol. soyed. AI7: ~o. 5, 1154-1160, 1975.
L.I.
BUTI~A et al.
4. V. B. GOLUBEV, V. P. ZUBOV, G. S. NAUMOV, L. 1. VALUYEV, V. A. KABANOV and V. A. KARGIN, Vysokomol. soyed. Al1: 2689, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 12, 3058, 1969) 5. Ye. T. DENISOV, Konstanty skorosti gomoliticheskikh zhidkofaznykh reaktsii (Rate Constants of Hemolytic Liquid-Phase Reactions). Izd. "Nauka", 1971 6. M. G. FOX, J. B. KINSINGER, H. F. MASON and E. M. SHUELE, Polymer 3: 72, 1962 7. W. H. STOCKMAYER, L. D. MOORE, M. FIXMAN and B. M. EPSTEIN, J. Polymer Sci. 16: 517, 1955 8. R. A. THOMSON and J. R. WALTERS, Trans. Faraday Soc. 67: 3046, 1971 9. N. FHURMAN and R. B. MESROBIAN, J. Amer. Chem. Soc. 76: 3281, 1954 10. Kh. S. BAGDASAR'YAN, Teoriya radikal'noi polimerizatsii (Theory of Radical Polymerization). Izd. "l~auka", 1969 11. N. G. GAYLORD, J. Polymer Sci. B7: 145, 1969
MECHANISM OF GRAFT COPOLYMERIZATION OF VINYL MONOMERS WITH SILK FIBROIN* L. I. BUTIIVA, M. V. SHISHKn~A,S. 1~. SADOVAand M. V. KORCHAGnv Moscow Textile Institute A. V. Topchiev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences
(Recsived 18 February 1974) In order to examine the mechanism of graft copolymerization to silk fibroin, polymethyhnethacrylate (PMMA) was synthesized using model systems of amino acid-ferrous iron-hydrogen peroxide. I t was shown that the phenol OH group of tyrosine and the indole N ~ group of tryptophan are the most active in chain transfer. The presence of amino acid residues in graft P M ~ A was established by I R spectroscopy.
THP. ferrous iron-hydrogen peroxide redox system was used for graft copolymerization with silk fibroin, as well as vinyl monomers: acrylonitrfle (AN), methyl methacrylate (MMA), styrene, aerylamine (AA). Graft copolymers were obtained with a variable weight increase (10-50%), according to the concentration of components of the redox system, monomer concentration, temperature and grafting time. Although the use of the ferrous iron-hydrogen peroxide redox system has been known for a long time for the modification of albumens (keratin in particular) by graft copolymerization [1], the reaction mechanism has not so far been studied. It has been assumed [2] that ferrous iron is combined with the carboxyl group of the polymer with a salt bond. During interaction of ferrous iron with * Vysokomol. soyod. AI7: No. 5, 1150-1153, 1975.
Graft copolymerization of vinyl monomers with silk fibroin
1323
hydrogen peroxide the following reaction takes place: Fe2+-4-H~O2-~Fe3++OH+OH. A graft polymer is formed when chain transfer to the albumen macromolecule is complete. The problem of the most likely places of localizing free radicals has so far not been studied in practice. To explain the mechanism of graft copolymerization of vinyl monomers with silk fibroin, an attempt was therefore made to synthesize vinyl monomers using systems which contain model compounds: ~-amino acid, ferrous iron-hydrogen peroxide redox system and a monomer. Freshly distilled MMA was u s e d as monomer.
I
8
I
I
1
28
3~ v,/O-~cm -I
I R absorption spectra of: the initial PMMA (1), PMMA graft to tyrosino (2) and t r y p t o p h a n (3). Conditions of carrying out experiments using model amino acid were similar to conditions of graft copolymerization using silk fibroin. An amino acid sample was used in which the proportion of carboxyl groups was equivalent to ,the carboxyl group content in 1 g fibre. An equimolecular amount of ferrous iron was used. Carefully weighed amino acid and ferrous iron samples were dissolved in 50 ml distilled water and a calculated amoun~ o f hydrogen peroxide added (0-008~/o). The reaction was carried out at 60 ° and lasted 60 rain. After the reaction th e residue was filtered, dried to constant weight and weighed. A control experiment without amino acid was carried out in parallel. A rust coloured residu~ was formed in this case which was readily soluble in 6 N hydrochloric acid. I t was establisheel
1324
L . I . B~rrnvA et al.
as a result that the residue contained ferric hydroxide. Bearing in m i n d the possibility of forming ferric hydroxide even in model experiments, the residues obtained were freed from ferric hydroxide by t r e a t m e n t in 6 z¢ hydrochloric acid. Final products were PMMA (Figure). Polymerization using model systems was carried out with fifteen amino acids contained in silk fibroin and with dipeptide (glycyl-glycine) (Table 1). TABLE
1. E F F E C T
O F T H E l q A T U R E O F A ~ I n q o A C I D O1~" T H E P O L Y M ~ R I Z A T I O I q
wt. Amino acid
Glycine DL-alanin D L -valine DL-serine D L -aspartic L-arginine HCl DL-phenylalanine DL-tyrosine Proline DL-tryptophane Dipeptide (glycyl-glycine) DL-leicine DL-threonine L-glutamic DL-lysine HC1 L-histidine HC1
Mol.
75.07 89.09 117.15 105.09 133.00 174.00 165-00 181-00 115.00 204.00 132-00 131.17 119.12 147-14 146-19 155.00
Amino acid sample, g
l~Iohr's salt sample, g
PlVIMA, g
0.027 0.032 0-042 0.037 0.047 0.062 0.058 0.064 0.041 0.072 0.047 0.047 0.042 0.052 0.052 0.058
0.0704 0.0704 0.0702 0.0690 0.0690 0-0800 0.0630 0.0690 0-0700 0-0691 0-0700 0.0700 0.0690 0.0693 0.0699 0.0704
0.0300 0.0121 Traces 0.0483 0.0418 0.0057 0.0216 0-1892 Traces 0.2105 0.0296 0.0252 0.0279 Traces 0.0061 0.0127
OF 1 ~
Monomer conversion,
% 6"00 2-42 9.66 8"36 1-14
4.32 37.84 42.10 5.92
5.04 5-58 1.12
2.54
As shown by Table 1, polymerization of MMA takes place to a very shght extent with practically all amino acids and dipeptide, monomer conversion varying up to 6 %. The result obtained using a model system with serine is somewhat different, where monomer conversion is 9.66%. In the presence of tyrosine-ferrous iron-hydrogen peroxide and tryptophanferrous iron-hydrogen peroxide model systems P~IMA is formed in significant proportions: monomer conversion is about 40%. Monomer conversion is 51.6% on silk fibroin under the same conditions. To verify further the possibility of chain transfer as a result of --CI-I2-- and ---CO--NH--, graft copolymerization was carried out with the redox system indicated using polyamide fibre (Kapron). Under conditions of reaction for a silk fibre, no graft copolymer had formed. These results indicate that chain transfer is most effective with phenol OH groups of tyrosine and indole NH groups oftryptophane, the aliphatic OI-I group of serine being much less effective in chain transfer. Chain transfer from aliphatie NH2 and CH groups (e.g. aspartic acid) is also possible. Considering the varying contents of amino acids in fibroin it should be borne in mind that the overall effect of each functional group on graft copolymeriza-
Graft copolymerization of vinyl monomers with silk fibroin
1325
tion varies and is determined not only b y activity, b u t also b y its quantitative content in fibroin. Knowing that the quantitative content in fibroin of tyrosine, one of the most active amino acids, is about 12.0~/o it m a y be assumed that it is precisely this amino acid which has the greatest effect on graft copolymerization. The mechanism of graft copolymerization involving OH groups of tyrosine as active centres m a y be as follows: R I
()It
nCH2=CH
fibroi,1 --CH2---, fibrom -- C H ~ I
T
OH
I 0
• fibroin--CH-. I
I i I O--(CIt~--CtI--)eth--Cff
Since tryptophan content in silk fibroin is low (0.6-1-2%), in spite of the highest activity of indole N H groups, the number of graft chains formed using tryptophyl residues cannot be significant. TABLE 2. OPTICAL DENSITY RATIO OF NI-I M.AXIM.AOF GRAFT P ~ k
Amino Acid Glycine Aspartic Serine
D1
D2
D
D
0.300 0.210 0.230
0.350 0.220 0-260
Amino acid Dipeptide Tyrosine Tryptophan
D1
Di
D
D
0.230 0.150 0.220
0.250 0.120 0.200
To confirm that PMMA obtained using model systems is chemically combined with amino acid residues, I R spectra were obtained of graft PMMA synthesized using model amino acids (glycine, aspartie acid, serine, dipeptide, tyrosine, tryptophan) and a spectrum of PMMA separated from graft copolymer b y alkaline hydrolysis of the albumen constituent [3]. I R absorption spectra were recorded using a UR-20 spectrophotometer with slot programme 4. To record the spectrum, PMMA was pelletized with potassium bromide (0.001-0.002 g for 0.200 g KBr). Spectra were recorded in the 400-4000 cm -1 range. These spectra are similar and are determined b y absorption of PMMA, end groups of amino acids being represented in spectra only with a double band of N H bond stretching vibrations in NH2 groups in the region of 3400 and 3500 cm -1 (e.g. using model amino acid, tyrosine, Figure). These bands represent the symmetrical and asymmetric forms of vibrations of N H groups, respectively. To evaluate the extent to which various amino acids are contained in PMMA, the optical density ratios of each of the N H maxima were calculated (D1 and D2)
1326
S . S . GusEv et al.
to the maximum of the band at 3000 cm-1 of PMMA (D), which characterizes the bond stretching vibration of C--H in the C(CH3)CO0 fragment. These ratios axe shown in Table 2 and their practically coincident values point to the absence of foreign absorption in this region. Translated by E. SEM.ERE REFERENCES 1. M. LIPSON a n d J. B. SPEAKMAN, J. Soc. I)yers and Colourists 65: 390, 1949 2. S. F. SADOVA a n d A. A. KONKtN, ZhVKhO ira. I). I. Mendeleyeva 11: 596, 1967 3. S. F. SADOVA a n d A. A. KONKIN, Vysokomol. soyed. BI0: 592, 1968 (l~ot translated in Polymer Sci. U.S.S.R.)
SPECTROSCOPIC AND CHEMICAL STUDY OF ATMOSPHERIC THERMAL CONVERSION OF CELLULOSE AND MONOCARBOXYL CELLULOSE* S. S. Gvsv.v, F. N. KAPVTSmI, V. Y~. KAPUTSK~ and E. P. KAI,UTSKAYA V. I. Lenin Byelorussian State University I n s t i t u t e of Physics, U.S.S.R. Academy of Sciences
(Received 20 February 1974) A study was made by spectroscopic, chemical and thermal methods of atmospheric oxidation of cellulose and monocarboxyl cellulose (IVICC)with different carboxyl group contents at temperatures of 80 to 400 ° . Two stages of decomposition were dis¢inguished and described using the information obtained. An auto-catalytic heterogeneous process of solid phase thermal oxidation b y atmospheric oxygen of cellulose a n d monocarboxyl cellulose is p u t forward as a hypothesis.
T~v. study deals with thermal conversions of cellulose and a polymeric acid, monocarboxylcellulose (MCC) obtained therefrom. The addition of ionogen groups to the polymer raised a further problem of studying variations of exchange adsorption properties under strict thermal conditions. Systematic studies of thermal oxidation of acid polycarbohydrates have not been carried out. Chromatographic paper (98-99% a-cellulose, the degree of polymerization being 1100) and the MCC obtained with different carboxyl group contents were used. Selective oxida$ion at Ce of the pyrane ring of a cellulose macromoleculo was carried out with N,O4 solution i n CC14 b y methods previously described [lJ. Heat treatment was carried out as follows. A * Vysokomol. soyed. AI7: ~o. 5, 1154-1160, 1975.