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Macromolecules 1986,19, 2472-2476
the bottom of the flask, 5.00 g of the polymer (8.31 mequiv/g) was swollen in 100 mL of chloroform under an argon atmosphere, and 400 mL of Clorox bleach (3.5% NaOCl solution, neutralized to pH 8.47 with concentrated HCl) was added to the flask. After addition of 1.899 g (8.34 mmol) of benzyltriethylammonium chloride, the reaction mixture was stirred a t 210 rpm at 25 "C under argon for 16.1 h. The reaction mixture was filtered. The beads were washed with methanol three times, water three times, dichloromethane followed by 3/2 dichloromethane/methanol, methanol, and water five times, and methanol three times. The beads were dried at 50 "C under vacuum to give 5.091 g of chlorinated poly(p-methylstyrene). (B) With 9.4% NaOCl (Run 49). The preceding method was modified to use just enough 1,2-dichloroethane (33 mL) to swell 5.00 g of the 1%cross-linked polymer. The rest of the procedure was identical with procedure A except 200 mL of the 9.4% NaOCl solution (swimming pool bleach) and 0.491 g (2.156 mmol) of benzyltriethylammonium chloride were used. (C) With SOzClz. To 5.00 g of 1% DVB cross-linked poly(p-methylstyrene) (8.31 mequiv/g) were added 50 mL of benzene and 70 mg of AIBN (azobis(isobutyronitri1e)). The mixture was stirred at room temperature under argon for 15 min and warmed to 60 "C. A solution of 104 mg of AIBN and 5.2 mL of S02C12 (Eastman Organic Chemicals) in 5 mL of benzene was added over a period of 1 h. The reaction mixture was stirred for another 1.5 h and cooled to room temperature. Cold methanol was added with stirring. The mixture was filtered and the beads were washed with methanol three times, dichloromethane twice, and methanol three times and dried a t 68 "C under vacuum for 15 h.
Acknowledgment. We are grateful to U S . Army Research Office for Contract DAAG29-82-K-0133 in support
of this research and to the National Science Foundation for a grant in support of the 300-MHz NMR spectrometer. Registry No. NaOCl, 7681-52-9; 4-H3CCsH4CH=CHz(homopolymer), 24936-41-2; (4-H3CCBH4CH=CH2).HzCHC6H$H= CHJ (copolymer), 39419-87-9;PhCH2NEt&l, 56-37-1;Bu4NHS04, 32503-27-8; Bu4NBr, 1643-19-2; SO2Cl2,7791-25-5. References and Notes (1) . , PeDDer. K. W.: Paislev. _ . H. M.: Young, -. M. A. J . Chem. Soc.
19ii, 4093.
(2) Merrifield. R. B. J . Am. Chem. SOC.1963, 85, 2149. (3) (a) Hodge; P.; Sherrington, D. C., Eds. Polymer-Supported Reactions in Organic Synthesis; Wiley-Interscience: New York, 1980. (b) Mathur, N. K.; Narang, C. K.; Williams, R. E. Polymers as Aids in Organic Chemistry; Academic: New York, 1980. (c) Ford, W. T., Ed. Polymeric Reagents and Catalysts;American Chemical Society: Washington, DC, 1986;
ACS Symp. Ser. No. 308. (4) Weiss, W. J. J . Occup. Med. 1976, 18, 194. ( 5 ) Olah, G.; Tolgyesi, W. S. In Friedel-Crafts and Related Reactions: Olah. G. A.. Ed.: Wilev-Interscience: New York. 1964: Vol. 2, pp 659-784. (6) (a) Warshawskv. A.: Deshe. A. J. Polvm. Sci.. Polvm. Chem. Ed. 1985, 23, f839. ' (b) Olah, G. A.; Beal, D.' A.; Olah, J. A. Synthesis 1974, 560. (7) Balakrishnan, T.; Ford, W. T. J . Appl. Polym. Sci. 1982, 27, 133. (8) Fonouni, H. E.; Krishnan, S.; Kuhn, D. G.; Hamilton, G. A. J . Am. Chem. Soc. 1983, 105, 7672. (9) Tarascon, R.; Hartney, Mi; Bowden, M. J. ACS Symp. Ser. 1984, 266, 361. (10) Christian, G. D. Analytical Chemistry, 3rd ed.; Wiley: New York, 1980; p 278. I
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270 nm), acrylamide gels having triphenylmethaneleucocyanide groups (1-4 mol %) dilated in water. The weight of the gel having 3.1 mol % leucocyanide groups increased by as much as 13 times and the size expanded approximately 2.2 times in each dimension. The dilated gel deswelled in the dark to the initial size. The cycles of dilation and contraction of the gel by photoirradiation could be repeated several times. The gel expansion was suppressed by the addition of salts such as NaCl or KBr. The salt effect and semiquantitative theoretical consideration of the behavior of ions suggested that the osmotic pressure differentials between the gel inside and the outer solution, which is produced by photodissociation of triphenylmethane leucocyanidegroups contained in the gel network, are the main driving force of the photostimulated gel dilation.
Introduction It is well-known that a polymer chain conformation depends on the solvent and temperature. In good solvents, polymers have an extended conformation, while they shrink in poor solvents a t low temperature. Polyelectrolytes change their conformation with changes in pH and salt concentration. Recently, several attempts have been reported to induce the conformational changes by “photochemistry” rather than “chemi~try”.~ Many photosensitive molecules are known to be transformed under photoirradiation into other isomers, which return to the initial state either thermally or photochemically. The isomerizations are always accompanied by certain physical and chemical property changes. The property changes of the chromophores, such as dipole moment and/or geometrical structure changes, have been utilized as the driving force to induce conformational changes of the polymer chains in solution by incorporating the chromophores into the polymers. The following three photochemical reactions are useful to control the chain conformations: (1)trans-cis isomerization of unsaturated linkages in the polymer backbone, (2) reversible photogeneration of strong dipoles in the polymer pendant groups, and (3) photoionization of the pendant groups. Representative examples of each system are polyamides with backbone azobenzene residue^,^ poly(methy1 methacrylate) with pendant spirobenzopyran groups? and poly(NJJ-dimethylacrylamide) with pendant triphenylmethane leucohydroxide.6 It seems possible to amplify the photostimulated conformational changes of the polymer chains in solution at the molecular level into shape changes of polymer gels or solids at the visible macro level. Attempts to use the structural changes of photoisomerizable chromophores at the molecular level for direct conversion of photon energy into mechanical work have been initiated by Meriar~.~ The system described by Merian was nylon filament fabric, 6
cm wide and 30 cm long, containing 15 mg/g of azo dye. After exposure to a xenon lamp, the dyed fabric was found to be 0.33 mm shorter. On the basis of Lovrien’s idea? van der Veen and Prins reported a photomechanical transd ~ c e r ,consisting ~ of water-swollen gels of poly(2hydroxyethyl methacrylate) mixed with a sulfonated bis(azostilbene) dye, The photostimulated contraction of the gel was 1.2%. Since then, many materials, most of which contained azobenzene chromophores in polymer, have been reported to show photostimulated deformation.1° The most recent study was polyquinoline with backbone stilbene gr0ups.l’ Till now, however, the reported deformations were limited to less than 10%. In addition, MatZijka et a1.12reported that in some cases a photoheating effect instead of photochemical reaction plays a dominant role in the photostimulated deformation. In the present study, we report large reversible photostimulated dilation of polyacrylamide gels by incorporating a small amount of triphenylmethane leuco derivatives in the gel network. Triphenylmethane leuco derivatives are well-known photochromic molecules which dissociate into ion pairs under ultraviolet irradiation, producing intensely colored trimphenylmethyl cations. The cations thermally recombine with counterions as follows:
According to eq 1, triphenylmethane leuco derivatives function as reversible ionizable groups by photoirradiation.I3 It is inferred from our previous experiments in solution6that the electrostatic force of repulsion between
0024-9297/86/2219-2476$01.50/0 0 1986 American Chemical Society
