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Polyacrolein by Polymerization

Submitted by: R. C. Schulz 1 and H. Cherdron 2 Checked by: V. T. Kagiya and S. Morita 3

Acrolein undergoes redox polymerization4 in the presence of to form a polymer in which aldehyde groups are hydrated or form hemiacetals. Several tetrahydropyran rings may be fused.5,6,7

1. Procedure In a 2 l, round-bottomed flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer, and inlet, 500 ml of water is heated under reflux in a nitrogen atmosphere o for 30 min. After cooling to 20 , 4.75 g of K2S2O8 and 100 ml of destabilized (Note 1) are added. Caution! Acrolein is an extremely active lachrymator. All operations should be conducted in an efficient hood. When the monomer is dissolved, a solution of 2.96 g of AgNO3 in 60 ml of water is allowed to drip into the flask over a period of 10 min accompanied by vigorous stirring; nitrogen is passed through the apparatus during this time. After several minutes, the mixture becomes turbid and the polymer precipitates. The temperature should not rise above 20o (Note 2). After 2.5 h; 500 ml of water is added. The polymer is filtered with suction and washed twice with 500 ml of water. To remove the silver salts, the filter cake is dispersed in a solution of 5 g of

Na2S2O3 in 500 ml of water and stirred for 1 h. It is filtered with suction, washed several times, o dried under vacuum at 20 , then over CaCl2, and lastly over concentrated H2SO4 (Note 3); yd 68 g (80%).

2. Characterization Polyacrolein prepared by redox polymerization is insoluble in all organic at room temperature. The masked aldehyde groups of these polyacroleins are quite reactive5,6,7 (Note 4) and numerous derivatives of the polymer with good are available through chemical modifications. For many purposes, it is advantageous to convert the polyacrolein into the water- soluble bisulfite or sulfurous acid derivatives.8,9,10 Polyacroleins prepared radically have no softening points; they discolor above 170o and sinter at 220o. 4 For determination, 100 mg of polyacrolein is mixed with 5 ml of a 10% aqueous SO2 solution (d = 1.0493) in a 10 ml volumetric flask. This is allowed to stand for 24 h at room temperature and is then filled to the mark with 10% NaCl solution. Using this solution, the flow time is measured in an Ostwald viscometer (capillary diameter 0.43 mm) by the usual method. The flow time of the is determined with a 1:1 mixture of SO2 solution and NaCl solution.

177 178 Macromolecular Syntheses, Collective Volume 1 A generally valid viscosity-molecular weight relationship has not yet been derived. The osmotic molecular weight of several polyacrolein derivatives has been measured.11 The approximate molecular weights for specific measured at 1 g/dl in H2SO3/NaCl are as follows: 5,600 for 0.01dl/g; 56,000 for 0.05 dl/g; and 140,000 for 0.10 dl/g.

The polyacrolein obtained from the polymerization described above has çsp/c = 0.03 (dl/g) and thus a molecular weight of ca 28,000.

3. Notes 1. Immediately before use, acrolein is distilled under nitrogen through a 50 cm packed column to remove the stabilizer, bp 52-53o/760 torr. The monomer should be at least 96% pure.12 2. If reaction mass becomes viscous, the flask is cooled with ice water. 3. Drying continues for several days. The total water content (bound and unbound) may be determined from the carbon analysis. Unbound water can be determined by the Karl Fischer method. 4. The checkers obtained a 97.5 mol-% aldehyde group content by the phenylhydrazine method.13,14

4. Methods of Preparation Polyacrolein with higher viscosity numbers can be obtained by redox polymerizations in aqueous emulsions.9,15 A polyacrolein-sulfurous acid solution is a particularly good emulsifier for this purpose. The polymerization of acrolein can also be initiated by light16 or ã-irradiation.17,18 Initiation by azobis(isobutyronitrile) or peroxides in the presence of organic solvents is also possible.19,20 Ionic catalysts such as trifluoride, boron trifluoride-etherate, sodium , n-butyl , sodium alcoholate, or phosphine also initiate the polymerization of acrolein. However, the structure and properties of these polymers differ fundamentally from those of polymers from radical polymerization.7 Additional references on homo- and copolymerization of acrolein are available,21,22 and polymerization by electrochemical processes has been described.23

5. References 1. Organisch-Chemisches Institut der Universität, 65 Mainz, Germany. 2. Farbwerke Hoechst, Frankfurt-Hoechst, Germany. 3. Department of Chemistry, Faculty of Engineering, Kyoto University, Kyoto, Japan. 4. Schulz, R. C.; Cherdron, H.; Kern, W. Makromol. Chem. 1957, 24, 141. 5. Schulz, R. C.; Kern, W. Makromol. Chem. 1956, 18/19, 4. 6. Schulz, R. C. Kunstoffe 1957, 47, 303. 7. Schulz, R. C. Angew. Chem. Intern. Ed. Engl. 1964, 3, 416. 8. Schulz, R. C.; Löflund, I. Angew. Chem. 1960, 72, 771. 9. Cherdron, H. Kunststoffe 1960, 50, 568. 10. Dawson, T. L.; Welch, F. J. J. Am. Chem. Soc. 1964, 86, 4791. 11. Schulz, R. C.; Müller, E.; Kern, W. Makromol. Chem. 1959, 30, 39. 12. Peters, E. D. In Acrolein; Smith, C. W., Ed.; John Wiley & Sons, Inc.: New York, 1962; p 240. 13. Schulz, R. C.; Holländer, R.; Kern, W. Makromol. Chem. 1960, 40, 16. 14. Schulz, R. C.; Passmann, W. Makromol. Chem. 1963, 60, 139. 15. Chedron, H.; Schulz, R. C.; Kern, W. Makromol. Chem. 1959, 32, 197. 16. Blacet, F. E.; Fielding, G. H.; Roof, J. G. J. Am. Chem. Soc. 1937, 59, 2375. 17. Henglein, A.; Schnabel, W.; Schulz, R. C. Makromol. Chem. 1959, 31, 181. 18. Toi, Y.; Hachihama, Y. J. Chem. Soc. Jap., Ind. Chem. Sect. 1959, 62, 1924. 19. Schulz, R. C.; Suzuki, S.; Cherdron, H.; Kern, W. Makromol. Chem. 1962, 53, 145. Polyacrolein by Redox Polymerization 179 20. Fisher, R. F. U.S. Patent 3,079,357, 1963. 21. Schulz, R. C. In Encyclopedia of Polymer Science and Technology; Interscience Publishers: New York, 1964; Vol. 1, p 160. 22. Schulz, R. C. "Polymerization of Acrolein," in Ham, G. E., Ed., Vinyl Polymerization, Vol. 1, Part 1, Marcel Dekker: New York, 1967, p. 403. 23. Schulz, R. C.; Strobel, W. Monatsh., 1968, 99, 1724; Strobel, W.; Schulz, R. C. Makromol. Chem., 1970, 133, 303.