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The influence of phase-transfer catalysts on alkaline hydrolysis of acrylonitrile-divinylbenzene copolymers
Fur. Polym. J. Vol. 28, No. 12, pp. 1593-1595, 1992 Printed in Great Britain.All rights reserved
0014-3057/92$5.00+0.00 Copyright © 1992PergamonPress Ltd
THE INFLUENCE OF PHASE-TRANSFER CATALYSTS ON ALKALINE HYDROLYSIS OF ACRYLONITRILE-DIVINYLBENZENE COPOLYMERS ANDRZEJ W. TROCHIMCZUK* and BOZENAN. KOLARZ Institute of Organic and Polymer Technology, Technical University of Wroclaw, Poland (Received 6 March 1992) Abstract--Some organic solvents and phase-transfer catalysts, made as macrocyclic ethers and poly(ethylene glycols), were used to facilitate the alkaline hydrolysis of the nitrile groups in acrylonitriledivinylbenzene copolymer with l0 wt% of the crosslinking agent. The dependences of the reaction yield on the type of solvent and catalyst are discussed. By using good solvents such as dioxane or DMF, it is possible to obtain relatively high contents carboxyl groups up to 5.4 mmol/g of dry resin.
INTRODUCTION
Polymeric resin with carboxyl groups can be obtained directly by copolymerization of an appropriate m o n o m e r with the crosslinking agent or by chemical modification of resins that contain hydroxyl, ester or nitrile groups. The latter can be hydrolysed to carboxyl groups and this reaction was investigated for linear polymer [1-4] as well as for crosslinked systems [5]. Hydrolysis was carried out under both acidic and alkaline conditions. In the case of polyacrylonitrile, the following acids were used: acetic, sulphuric, phosphoric, nitric and benzene sulphonic at temperatures ranging from - 1 0 to 210 °. In the alkaline hydrolysis, the reagents were: potassium hydroxide, sodium carbonate and sodium hydroxide. For polymers containing acrylonitrile (AN), the dependences of the rate of the reaction on type and a m o u n t of comonomers were reported [6, 7]. The aim of this work was to check the influence of various solvents on the alkaline hydrolysis of AH-divinylbenzene (DVB) copolymer. In order to increase the conversion of nitrile groups to carboxyl, phase-transfer catalysts like macrocyclic ethers and poly(ethylene glycols) were used. EXPERIMENTAL PROCEDURES
The copolymer of AN and DVB was synthesized according to the procedure reported earlier [8]. The main characteristics of the copolymer are: specific surface area 58 m2/g, pore volume 1.21 ml/g, porosity 59%, crystallinity degree 25% and particle size 0.1-0.2 mm. 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) was synthesized by a published method [9], dibenzo-18-crown-6 (2, 3, I 1,12- dibenzo- 1,4, 7,10,13,16- hexaoxacyclooctadeca2,11-diene) and dipyridylo-18-crown-6 (l,4,7,14,23-pentaoxa/7,2/orthocyclo/2/(2,6)pyridinophan) were obtained from Merck and poly(ethylene glycols) 600 and 2000 from Loba Chemic. Other reagents and solvents were analytical grade materials. Hydrolysis was carried out in sealed glass *To whom all correspondence should be addressed at: Department of Chemistry, University of Tennessee, 575 Buebler Hall, Knoxville, TN 37996, U.S.A.
vials using 0.5 g of the dry polymer, 3 ml of an appropriate solvent, 210 mg of powdered KOH and 1 mol% of catalysts with respect to the amount of the nitrile groups. They were placed in a water bath at 60° and shaken occasionally for 6 hr. Then the samples were separated by filtration and washed with acetone, water, I M HC1 solution and again with water until CI- ions were absent from the eluate. The samples were then centrifugated and placed in stoppered flasks together with 50 ml of 0.1 M NaOH solution for 5 days. Then 10 ml aliquots of the supernatant were titrated with 0.I M HCI to determine the content or carboxyl groups in each sample. RESULTS
Using water as a solvent, 1.25 mmol of carboxyl groups can be obtained per 1 g of dry sample. However, hydrolysis is in this case time-consuming since the A N - D V B copolymer used does not swell in water. Additional pretreatment is required; polymer must be preswollen in methanol then washed with a mixture of methanol and water and finally with water and an aqueous solution of KOH. It seemed that the best way to improve the reaction efficiency was to change the solvation conditions. This procedure is known in the modification of polymers, for example dioxane and l-methoxyethanol were used in hydrolysis of copolymers crosslinked with ethylene glycol dimethacrylate [10] and various organic solvents were used in alkaline hydrolysis of slightly crosslinked poly(methyl methacrylate) [11]. It is evident from Table 1 (samples 1-6) that only in the mixture of dioxane/water (2: 1) was the reaction yield twice that when water was used. Solvents like dioxane and D M F were of the same effectiveness as water whereas toluene was inefficient. This result can be explained by the large differences between solubility parameters for polyacrylonitrile (25-26 MPa I/2) and toluene (18.2 MPa t/2) as well as by the low concentration of K O H in organic solvents (except dioxane). Solubility parameters for other systems are: dioxane 20.5, D M F 24.8, dioxane/water 29.3, DMF/water 32.2 and water 47.9 MPa t/2. The addition of water had a positive influence on the course of hydrolysis in the case of dioxane/water
1593
ANDRZF..J W. TROCmMCZUK and BO~NA N. KOLARZ
1594
Table 1. Phase-transfer catalysed hydrolysis of AN-DVB copolymer in various solvents
No.
Solvent
I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Water Toluene DM F/water(2:1) Dioxane/water(2 : 1) DMF Dioxane Toluene DMF/water(2:1) Dioxane/water(2 : 1) DMF Dioxane Toluene DMF/water(2:1) Dioxane/water(2:1) DMF Dioxane Toluene DMF/water(2 : 1) Dioxane/water(2 : 1) DMF Dioxane Toluene DMF/water(2:1) Dioxane/water(2: I) DMF Dioxane Toluene DMF/water(2 : I) Dioxane/water(2:1) DMF Dioxane
Catalyst
Carboxyl groups content (mmol/g)
Solubility parameter (MPa I/2)
None None None None None None 18-Crown-6 18-Crown-6 18-Crown-6 18-Crown-6 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000
1.25 0.40 0.45 2.30 1.25 1.20 1.20 1.95 4.15 4.75 1.45 0.95 1.20 5.40 3.00 0.95 0.40 0.25 2.70 0.60 0.30 0.70 0.45 1.05 1.25 1.00 0.60 0.40 2.80 0.65 0.40
47.9 18.2 32.2 29.3 24.8 20.5
mixture and had a negative effect on hydrolysis in the mixture with DMF. The hydrolysis in DMF must take place in a short time since DMF reacts with KOH to form dimethylamine and potassium formate. Thus, the explanation of inferior hydrolysis in DMF/water might be the acceleration of the above reaction of DMF in the presence of water. In order to increase the content of carboxyl groups in the resulting polymer, some phase-transfer catalysts like macrocyclic polyethers and poly(ethylene glycols) were used. Addition of 18-crown-6, 1 mol% with respect to the number of nitrile groups, resulted in increase of the content of carboxyl groups (samples 7-11). However, this increase was not significant in the case of the best solvent-dioxane. It seemed that good swelling of polymer in this solvent and relatively high concentration of alkali in it were the most important factors influencing the hydrolysis. The AN-DVB copolymer used had a dioxane regain 3.3 g/g; for the other solvents regains were: 1.3, 1.2, and 2.9g/g for water, toluene and DMF, respectively. When dibenzo 18-crown-6 (samples 12-16) and dipyridylo 18-crown-6 (samples 17-21) were used, decrease of reaction efficiency is found. The most probable reason for this effect is the more rigid structure of these molecules and their larger size and hence some difficulties for diffusion into the polymer. Another explanation could be inferior complexing properties towards potassium ion than in the case of unsubstituted crown. Relatively good results were obtained when dioxane/water or DMF was used as solvents (samples 14.15 and 19). In these solvents, swelling of polymer is greatest and diffusion into the polymer is improved.
Poly(ethylene glycols) 600 and 2000 are not as good catalysts as 18-crown-6 but only slightly worse than substituted crowns (samples 22-26 and 27-31). Also in this case, the best results were obtained for samples in which dioxane/water and DMF were used. For the former system, poly(ethylene glycol) 2000 (sample 29) was better whereas poly(ethylene glycol) 600 was better in other solvents. In solution, both glycols can form cyclic structures of dimension and shape similar to crown ethers. The probability of such structure formation increases with increase of the polyglycol length. Thus, it seems that better results should be obtained in the presence of poly(ethylene glycol) 2000. Such an effect was observed but only in a good solvent in which the polymer is well swollen. For the other solvents studied, poly(ethylene glycol) 600 was better because of its lower molecular weight and hence improved diffusion in polymer. Thus, AN-DVB copolymer can be hydrolysed with KOH in the presence of small amounts of phase-transfer catalysts under mild conditions. The best catalysts for this reaction are 18-crown-6 and its dibenzo derivative, which can function in all solvents used in hydrolysis. The highest reaction yields were obtained when reaction was carried out in DMF or dioxane/water. It should be pointed out that, in all cases, results obtained for hydrolysis in DMF were good despite the possibility of decomposition of DMF in the presence of KOH. This finding can be explained by the possibility of this solvent dissolving the crystalline part of AN-DVB copolymer [12]. This part of the polymer is not accessible to poor solvents such as water or toluene.
Alkaline hydrolysis of AN-DVB copolymers
Acknowledgement--This work was done with financial support from CPBP 04.11.
REFERENCES
1. G. Smets and W. de Locker. J. Polym. Sci. 41, 375 (1959). 2. F. C. Baines and J. C. Bevington. J. Polym. Sci., A-I 2433 (1968). 3. P. Bajaj and M. S. Kumar. Fur. Polym. J. 24, 275 (1988). 4. Y. N. Zilberman, A. A. Starkov and E. G. Pomarantseva. Vysokomolek. Soedin. A-19, 2714 (1977). 5. J. Seidl et al. Patent CS 215 740, 10.04.1984 Invs.
EPJ 28/12--J
1595
6. A. A. Geller, A. G. Yerschenko, Zh. A. Zgibnieva and M, V. Polovnikova. J. Polym. Sci.; Polym. Chem. Edn 12, 2327 (1974). 7. P. Bajaj, P. B. Chavan and B. Manjeet. J. Maeromolec. $ci., Chem. A22, 1219 (1985). 8. M. Wojaczynska and B. N. Kolarz. J. Chromatogr. 358, 129 (1986). 9. L. F. Fieser and K. L. Williams. In Organic Experiments, 3rd edn, p. 386. D. C. Heath and Co., Lexington (1975). I0. J. Hradil and F. Svec. Reactive Polym. 3, 91 (1985). 11. A. S. G6~d~. Makromolek. Chem.; Rapid Commun. 2, 443 (1981). 12. A. Trochimczuk, M. Ilavsky and B. N. Kolarz (unpublished results).
0014-3057/92$5.00+0.00 Copyright © 1992PergamonPress Ltd
THE INFLUENCE OF PHASE-TRANSFER CATALYSTS ON ALKALINE HYDROLYSIS OF ACRYLONITRILE-DIVINYLBENZENE COPOLYMERS ANDRZEJ W. TROCHIMCZUK* and BOZENAN. KOLARZ Institute of Organic and Polymer Technology, Technical University of Wroclaw, Poland (Received 6 March 1992) Abstract--Some organic solvents and phase-transfer catalysts, made as macrocyclic ethers and poly(ethylene glycols), were used to facilitate the alkaline hydrolysis of the nitrile groups in acrylonitriledivinylbenzene copolymer with l0 wt% of the crosslinking agent. The dependences of the reaction yield on the type of solvent and catalyst are discussed. By using good solvents such as dioxane or DMF, it is possible to obtain relatively high contents carboxyl groups up to 5.4 mmol/g of dry resin.
INTRODUCTION
Polymeric resin with carboxyl groups can be obtained directly by copolymerization of an appropriate m o n o m e r with the crosslinking agent or by chemical modification of resins that contain hydroxyl, ester or nitrile groups. The latter can be hydrolysed to carboxyl groups and this reaction was investigated for linear polymer [1-4] as well as for crosslinked systems [5]. Hydrolysis was carried out under both acidic and alkaline conditions. In the case of polyacrylonitrile, the following acids were used: acetic, sulphuric, phosphoric, nitric and benzene sulphonic at temperatures ranging from - 1 0 to 210 °. In the alkaline hydrolysis, the reagents were: potassium hydroxide, sodium carbonate and sodium hydroxide. For polymers containing acrylonitrile (AN), the dependences of the rate of the reaction on type and a m o u n t of comonomers were reported [6, 7]. The aim of this work was to check the influence of various solvents on the alkaline hydrolysis of AH-divinylbenzene (DVB) copolymer. In order to increase the conversion of nitrile groups to carboxyl, phase-transfer catalysts like macrocyclic ethers and poly(ethylene glycols) were used. EXPERIMENTAL PROCEDURES
The copolymer of AN and DVB was synthesized according to the procedure reported earlier [8]. The main characteristics of the copolymer are: specific surface area 58 m2/g, pore volume 1.21 ml/g, porosity 59%, crystallinity degree 25% and particle size 0.1-0.2 mm. 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) was synthesized by a published method [9], dibenzo-18-crown-6 (2, 3, I 1,12- dibenzo- 1,4, 7,10,13,16- hexaoxacyclooctadeca2,11-diene) and dipyridylo-18-crown-6 (l,4,7,14,23-pentaoxa/7,2/orthocyclo/2/(2,6)pyridinophan) were obtained from Merck and poly(ethylene glycols) 600 and 2000 from Loba Chemic. Other reagents and solvents were analytical grade materials. Hydrolysis was carried out in sealed glass *To whom all correspondence should be addressed at: Department of Chemistry, University of Tennessee, 575 Buebler Hall, Knoxville, TN 37996, U.S.A.
vials using 0.5 g of the dry polymer, 3 ml of an appropriate solvent, 210 mg of powdered KOH and 1 mol% of catalysts with respect to the amount of the nitrile groups. They were placed in a water bath at 60° and shaken occasionally for 6 hr. Then the samples were separated by filtration and washed with acetone, water, I M HC1 solution and again with water until CI- ions were absent from the eluate. The samples were then centrifugated and placed in stoppered flasks together with 50 ml of 0.1 M NaOH solution for 5 days. Then 10 ml aliquots of the supernatant were titrated with 0.I M HCI to determine the content or carboxyl groups in each sample. RESULTS
Using water as a solvent, 1.25 mmol of carboxyl groups can be obtained per 1 g of dry sample. However, hydrolysis is in this case time-consuming since the A N - D V B copolymer used does not swell in water. Additional pretreatment is required; polymer must be preswollen in methanol then washed with a mixture of methanol and water and finally with water and an aqueous solution of KOH. It seemed that the best way to improve the reaction efficiency was to change the solvation conditions. This procedure is known in the modification of polymers, for example dioxane and l-methoxyethanol were used in hydrolysis of copolymers crosslinked with ethylene glycol dimethacrylate [10] and various organic solvents were used in alkaline hydrolysis of slightly crosslinked poly(methyl methacrylate) [11]. It is evident from Table 1 (samples 1-6) that only in the mixture of dioxane/water (2: 1) was the reaction yield twice that when water was used. Solvents like dioxane and D M F were of the same effectiveness as water whereas toluene was inefficient. This result can be explained by the large differences between solubility parameters for polyacrylonitrile (25-26 MPa I/2) and toluene (18.2 MPa t/2) as well as by the low concentration of K O H in organic solvents (except dioxane). Solubility parameters for other systems are: dioxane 20.5, D M F 24.8, dioxane/water 29.3, DMF/water 32.2 and water 47.9 MPa t/2. The addition of water had a positive influence on the course of hydrolysis in the case of dioxane/water
1593
ANDRZF..J W. TROCmMCZUK and BO~NA N. KOLARZ
1594
Table 1. Phase-transfer catalysed hydrolysis of AN-DVB copolymer in various solvents
No.
Solvent
I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Water Toluene DM F/water(2:1) Dioxane/water(2 : 1) DMF Dioxane Toluene DMF/water(2:1) Dioxane/water(2 : 1) DMF Dioxane Toluene DMF/water(2:1) Dioxane/water(2:1) DMF Dioxane Toluene DMF/water(2 : 1) Dioxane/water(2 : 1) DMF Dioxane Toluene DMF/water(2:1) Dioxane/water(2: I) DMF Dioxane Toluene DMF/water(2 : I) Dioxane/water(2:1) DMF Dioxane
Catalyst
Carboxyl groups content (mmol/g)
Solubility parameter (MPa I/2)
None None None None None None 18-Crown-6 18-Crown-6 18-Crown-6 18-Crown-6 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dibenzo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Dipyridylo 18-Crown-6 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)600 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000 Poly(ethylene glycol)2000
1.25 0.40 0.45 2.30 1.25 1.20 1.20 1.95 4.15 4.75 1.45 0.95 1.20 5.40 3.00 0.95 0.40 0.25 2.70 0.60 0.30 0.70 0.45 1.05 1.25 1.00 0.60 0.40 2.80 0.65 0.40
47.9 18.2 32.2 29.3 24.8 20.5
mixture and had a negative effect on hydrolysis in the mixture with DMF. The hydrolysis in DMF must take place in a short time since DMF reacts with KOH to form dimethylamine and potassium formate. Thus, the explanation of inferior hydrolysis in DMF/water might be the acceleration of the above reaction of DMF in the presence of water. In order to increase the content of carboxyl groups in the resulting polymer, some phase-transfer catalysts like macrocyclic polyethers and poly(ethylene glycols) were used. Addition of 18-crown-6, 1 mol% with respect to the number of nitrile groups, resulted in increase of the content of carboxyl groups (samples 7-11). However, this increase was not significant in the case of the best solvent-dioxane. It seemed that good swelling of polymer in this solvent and relatively high concentration of alkali in it were the most important factors influencing the hydrolysis. The AN-DVB copolymer used had a dioxane regain 3.3 g/g; for the other solvents regains were: 1.3, 1.2, and 2.9g/g for water, toluene and DMF, respectively. When dibenzo 18-crown-6 (samples 12-16) and dipyridylo 18-crown-6 (samples 17-21) were used, decrease of reaction efficiency is found. The most probable reason for this effect is the more rigid structure of these molecules and their larger size and hence some difficulties for diffusion into the polymer. Another explanation could be inferior complexing properties towards potassium ion than in the case of unsubstituted crown. Relatively good results were obtained when dioxane/water or DMF was used as solvents (samples 14.15 and 19). In these solvents, swelling of polymer is greatest and diffusion into the polymer is improved.
Poly(ethylene glycols) 600 and 2000 are not as good catalysts as 18-crown-6 but only slightly worse than substituted crowns (samples 22-26 and 27-31). Also in this case, the best results were obtained for samples in which dioxane/water and DMF were used. For the former system, poly(ethylene glycol) 2000 (sample 29) was better whereas poly(ethylene glycol) 600 was better in other solvents. In solution, both glycols can form cyclic structures of dimension and shape similar to crown ethers. The probability of such structure formation increases with increase of the polyglycol length. Thus, it seems that better results should be obtained in the presence of poly(ethylene glycol) 2000. Such an effect was observed but only in a good solvent in which the polymer is well swollen. For the other solvents studied, poly(ethylene glycol) 600 was better because of its lower molecular weight and hence improved diffusion in polymer. Thus, AN-DVB copolymer can be hydrolysed with KOH in the presence of small amounts of phase-transfer catalysts under mild conditions. The best catalysts for this reaction are 18-crown-6 and its dibenzo derivative, which can function in all solvents used in hydrolysis. The highest reaction yields were obtained when reaction was carried out in DMF or dioxane/water. It should be pointed out that, in all cases, results obtained for hydrolysis in DMF were good despite the possibility of decomposition of DMF in the presence of KOH. This finding can be explained by the possibility of this solvent dissolving the crystalline part of AN-DVB copolymer [12]. This part of the polymer is not accessible to poor solvents such as water or toluene.
Alkaline hydrolysis of AN-DVB copolymers
Acknowledgement--This work was done with financial support from CPBP 04.11.
REFERENCES
1. G. Smets and W. de Locker. J. Polym. Sci. 41, 375 (1959). 2. F. C. Baines and J. C. Bevington. J. Polym. Sci., A-I 2433 (1968). 3. P. Bajaj and M. S. Kumar. Fur. Polym. J. 24, 275 (1988). 4. Y. N. Zilberman, A. A. Starkov and E. G. Pomarantseva. Vysokomolek. Soedin. A-19, 2714 (1977). 5. J. Seidl et al. Patent CS 215 740, 10.04.1984 Invs.
EPJ 28/12--J
1595
6. A. A. Geller, A. G. Yerschenko, Zh. A. Zgibnieva and M, V. Polovnikova. J. Polym. Sci.; Polym. Chem. Edn 12, 2327 (1974). 7. P. Bajaj, P. B. Chavan and B. Manjeet. J. Maeromolec. $ci., Chem. A22, 1219 (1985). 8. M. Wojaczynska and B. N. Kolarz. J. Chromatogr. 358, 129 (1986). 9. L. F. Fieser and K. L. Williams. In Organic Experiments, 3rd edn, p. 386. D. C. Heath and Co., Lexington (1975). I0. J. Hradil and F. Svec. Reactive Polym. 3, 91 (1985). 11. A. S. G6~d~. Makromolek. Chem.; Rapid Commun. 2, 443 (1981). 12. A. Trochimczuk, M. Ilavsky and B. N. Kolarz (unpublished results).