Langmuir 2002, 18, 3767-3772
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Articles Unusual Hofmann Elimination under Mild Conditions in Polymerizable Cationic Surfactant Systems R. M. Jime´nez,† J. F. A. Soltero,† R. Manrı´quez,‡ F. A. Lo´pez-Dellamary,‡ G. Palacios,§ and J. E. Puig*,† Departamentos de Ingenierı´a Quı´mica, de Madera, Celulosa y Papel, y de Quı´mica, Universidad de Guadalajara, Boulevard Marcelino Garcı´a Barraga´ n #1451, Guadalajara, Jalisco 44430, Mexico
M. Morini and P. C. Schulz Departamento de Quı´mica y de Ingenierı´a Quı´mica, Universidad Nacional del Sur, Bahı´a Blanca 8000, Argentina Received July 13, 2001. In Final Form: November 7, 2001 Hofmann elimination and nucleophilic substitution reactions have been simultaneously observed at relatively low temperatures in a family of polymerizable alkyltrimethylammonium methacrylate surfactants, as well as in dodecyltrimethylammonium hydroxide. In concentrated aqueous solutions of the latter surfactant, Hofmann elimination occurs at room temperature. These reactions have been verified by IR, 1H NMR, and 13C NMR spectroscopies; differential scanning calorimetry; gas chromatography coupled to mass spectroscopy; and other techniques. A possible explanation of this phenomenon is provided.
Introduction Research on polymerizable surfactants has increased notably in the past 15 years because of the possibility of “freezing” the complex fluid microstructures that these surfactants form in polar and nonpolar solvents. This freezing procedure can provide polymers with novel structures and properties.1-4 Also, more stable emulsionmade lattices with improved adhesive properties can be obtained with polymerizable surfactants.2 For these reasons, surfactants with polymerizable groups in the head or in the tail, or even in the counterion, have been synthesized.5-17 * To whom correspondence should be addressed. E-mail address:
[email protected] or
[email protected]. † Departamento de Ingenierı´a Quı´mica. ‡ Departamento de Madera, Celulosa y Papel. § Departamento de Quı´mica. (1) Paleos, C. M., Ed. Polymerization in Organized Media; Gordon & Breach Science Publishers: Langhorne, PA, 1992. (2) Guyot, A. Curr. Opin. Colloid Interface Sci. 1996, 5, 580. (3) Chew, C. H.; Li, T. D.; Gan, L. H.; Quek, C. H.; Gan, L. M. Langmuir 1998, 14, 6068. (4) Gan, L. M.; Li, T. D.; Chew, C. H.; Ten, W. K.; Gan, L. H. Langmuir 1995, 11, 3316. (5) Paleos, C. M.; Voliotis, S.; Margomenou-Leonidopoulou, G. J. Polym. Sci. 1980, 18, 3463. (6) Paleos, C. M.; Christias, C.; Evangelatos, G. P. J. Polym. Sci. 1982, 20, 2565. (7) Paleos, C. M.; Dais, P.; Malliaris, A. J. Polym. Sci. 1984, 22, 3383. (8) Babilis, D.; Dais, P.; Margaritis, L. H.; Paleos, C. M. J. Polym. Sci. 1985, 23, 1089. (9) Paleos, C. M.; Margomenou-Leonidopoulou, G.; Malliaris, A. J. Cryst. Liq. Cryst. Nonlinear Opt. 1988, 161, 385. (10) Paleos, C. M.; Rashkov, I. B.; Gitsov, I. J. Polym. Sci. A: Polym. Chem. 1994, 24, 155. (11) McGrath, K. M.; Drummond, C. J. Colloid Polym. Sci. 1996, 274, 316. (12) McGrath, K. M. Colloid Polym. Sci. 1996, 274, 399. (13) McGrath, K. M. Colloid Polym. Sci. 1996, 274, 499.
Several years ago, the synthesis of the polymerizable cationic surfactant cetyltrimethylammonium methacrylate (CTAM) by ion exchange from its bromide counterpart surfactant, CTAB, was reported, as well as its formation of micelles in water and the polymerization of these micelles.15-17 In the course of establishing the phase diagram of mixtures of water with CTAM or DTAM (dodecyltrimethylammonium methacrylate), an anomalous thermal behavior of the pure surfactants was detected by differential scanning calorimetry (DSC). The thermograms of successive heating-and-cooling cycles performed on the same sample were not reproducible, and a gradual transformation was observed. We show here by a battery of techniques including NMR and IR spectroscopies that this anomalous behavior is caused by a Hofmann elimination reaction and a nucleophilic substitution reaction. Moreover, we demonstrate that the Hofmann elimination reaction takes place at room temperature in concentrated aqueous solutions of alkyltrimethylammonium hydroxide surfactants. Usually, Hofmann elimination reactions in alkyltrimethylammonium salts take place in the presence of strong bases and at temperatures up to 400 °C.18-24 (14) McGrath, K. M.; Drummond, C. J. Colloid Polym. Sci. 1996, 274, 612. (15) Lerebours, B.; Perly, B.; Pileni, M. P. Chem. Phys. Lett. 1988, 147 (5), 503. (16) Lerebours, B.; Perly, B.; Pileni, M. P. Prog. Colloid Polym. Sci. 1989, 79, 239. (17) Hammouda, A.; Gulik, Th.; Pileni, M. P. Langmuir 1995, 11, 3656. (18) Doering, W.; Meislich, H. J. Chem. Sci. 1952, 7, 2099. (19) Shiner, V. J.; Morris, J. R.; Smith, L. J. Chem. Sci. 1958, 5, 4095. (20) Stanley, J.; Stermitz, F. R. J. Chem. Sci. 1960, 82, 4692. (21) Feit, I. N.; Saunder, W. H., Jr.; William, H. J. Am. Chem. Soc. 1970, 82, 5615.
10.1021/la011077j CCC: $22.00 © 2002 American Chemical Society Published on Web 04/12/2002
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Experimental Section DTAB (dodecyltrimethylammonium bromide) and CTAB, both 99% pure from Aldrich, were used without further purification. Analytical-grade methacrylic acid and deuterium oxide (>99%) were also from Aldrich. Doubly distilled and deionized water was used. DTAM and CTAM were produced from DTAB and CTAB by ion exchange in a column packed with AG1-X2 resin (Amberlite) according to the procedure described elsewhere15 followed by neutralization with methacrylic acid. The resulting aqueous solutions were freeze-dried in a Labconco system. The DTAOH aqueous solution was made by passing a DTAB aqueous solution through an ion-exchange column packed with Amberlite IRA400 (OH-) from Carlo Erba under N2 atmosphere. The water employed in this procedure was doubly distilled and free of CO2. The complete conversion of DTAB to DTAOH was verified with a titration-and-conductometric analytical method described elsewhere.25 The DTAOH aqueous solutions (0.18 M) were stored in closed jars at room temperature under N2 atmosphere. These solutions were analyzed by conductimetry after 1-3 months of storage to verify the concentration of DTAOH. The DTAOH solutions were concentrated by evaporation and then allowed to dry in a desiccator jar containing P2O5 at room temperature. After 3 days, the samples were yellowish and translucent, with a sticky glue-like consistency. Upon addition of excess CO2-free water, part of the material dissolved, and the rest retained the appearance described above. The water-soluble portion was analyzed by conductimetry to determine the amount of the original surfactant lost by decomposition. This procedure was repeated with DTAOH samples left for 1 and 2 weeks in the desiccator jar. Other desiccation methods were used such as a desiccator jar without P2O5 under vacuum and a desiccator jar subjected to a water-free N2 flow. In every case, DTAOH was lost in different proportions. The water-insoluble residue was desiccated until its weight was constant, and its molar mass was estimated by measuring the variation of the melting point in camphor. Also, an IR spectrum of the residue was obtained. Samples were examined with a Meopta microscope equipped with cross polarizers, a heating-and-cooling stage (-15 to 300 °C), and a digital temperature controller ((0.2 °C). Thermograms were obtained in a Perkin-Elmer DSC-7 calorimeter at heating and cooling rates of 10 °C/min. Dried surfactants, as well as DTAM and CTAM aqueous solutions (in the concentration range of 5-95 wt %), were examined. Pure DTAM and CTAM samples for studies using IR, 1H NMR, and 13C NMR spectroscopies and gas chromatography coupled to mass spectroscopy (GC-MS) were subjected to a preheating treatment. Dried surfactant samples were heated to 60, 100, 150, or 200 °C and maintained at this temperature for 10 min, 1 h, or 24 h in a laboratory oven. The temperature was monitored during the preheating treatment by insertion of a thermocouple in the sample. Preheated samples were also mixed with water, and the water-soluble and water-insoluble portions were separated, dried, and examined by IR spectroscopy in a 5ZDA Nicolet FT-IR spectrometer. 1H and 13C NMR spectra of the water-soluble and -insoluble portions of the pretreated samples in CDCl3 were carried out at room temperature. Volatile releases from the samples heated at 100, 150, or 200 °C were collected by bubbling them through a 5% HCl-methanol mixture and ice-cooled decalin. These solutions were analyzed with a Varian Gemini 2000 broadband 200-MHz NMR spectrometer and a Perkin-Elmer Autosystem Q-Mass 900 instrument (GC-MS).
Figure 1. Photograph of a 30 wt % CTAM sample taken through cross polarizers in a polarizing microscope at 30 °C.
Results Figure 1 shows a photograph of a 30 wt % CTAM sample taken through cross polarizers in the polarizing microscope at 30 °C. The sample is birefringent with textures typical of the hexagonal phase.
Figure 2. DSC thermograms of pure CTAM obtained during consecutive heating-and-cooling runs: (A) first run, (B) second run, (C) fifth run, and (D) eighth run. Inset: Thermogram of pure CTAB.
(22) Coke, J. L.; Smith, G. D.; Britton, M., Jr.; George, H. J. Am. Chem. Soc. 1974, 82, 4323. (23) Kaiser, C.; Weinstock, J. Org. Synth. 1976, 55, 3. (24) Seuron, P.; Solladie, G. J. Am. Chem. Soc. 1980, 45, 715. (25) Schulz, P. C.; Morini, M. E.; Minardi, R. M.; Puig, J. E. Colloid Polym. Sci. 1995, 273, 959.
The thermograms of CTAB and CTAM, subjected to consecutive heating-and-cooling cycles, are shown in Figure 2 (only the heating part is displayed). The thermogram of CTAB does not change upon consecutive cycles, and it depicts a single sharp peak starting at ca.
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Figure 3. Thermograms of a 30 wt % CTAM aqueous sample obtained during consecutive heating-and-cooling runs: (A) first run, (B) seventh run.
98 °C, which corresponds to the melting of the hydrocarbon tail (inset in Figure 2). By contrast, the thermogram of CTAM changes upon consecutive cycles. In the first cycle (curve A in Figure 2), a single broad peak is detected at about 53 °C with a small shoulder at ca. 42 °C, which corresponds to the melting of the hydrocarbon tail. The reduction of the melting transition from CTAB to CTAM might be due to the looser packing of the polar layers in the crystalline structure of CTAM compared to that in CTAB, caused by the presence of hydration water (see the IR spectrum in Figure 5) and methacrylate ion. The weakening of the cohesion of the ionic double layer in the surfactant crystals decreases the melting temperature and enthalpy of the hydrocarbon tails.26 On the other hand, water of hydration is not detectable by DSC.27 However, upon cooling, some free water could form and give rise to the small peak at ca. 0 °C observed in the second run (curve B in Figure 2). This peak is not detected in further cycles (curves C and D in Figure 2), presumably because of water evaporation. After the first cycle, several other peaks appear in the following cycles (curves B-D in Figure 2). The peaks that are observed at temperatures above 100 °C might be due to decomposition products. Each cooling-and heating cycle shown in Figure 2 was performed immediately after the previous cycle had been completed, with each cycle lasting about 35 min. When the next cycle was performed 24 h, rather than immediately, after the previous cycle on the same sample, the results were identical to those reported in Figure 2. Figures 3 and 4 display the thermograms of two aqueous solutions of CTAM subjected to consecutive heating-andcooling cycles. The thermogram of the less concentrated sample (30% CTAM) includes the melting peak of the water and another smaller peak at ca. 20 °C that is related to the fusion of the hydrocarbon tail (Figure 3). Notice that this peak is shifted to lower temperatures than the melting peak of the hydrocarbon tail in pure CTAM because, at this concentration, CTAM and water form a hexagonal liquid-crystalline phase in which the hydrocarbon tails are more loosely packed. Hence, the tails can “melt” at lower temperatures in the liquid-crystalline form than in the crystalline form. After consecutive heating-and-cooling cycles, the thermograms remained unchanged (curve B in Figure 3). Also, the thermogram of a 30 wt % CTAM sample stored for 1 month was found to be identical to that shown in Figure 3. By contrast, the thermograms of (26) Schulz, P. C.; Abrameto, M.; Puig, J. E.; Soltero-Martı´nez, J. F. A.; Gonza´lez-Alvarez, A. Langmuir 1996, 12, 3082. (27) Schulz, P. C. Therm. Anal. 1998, 51, 135.
Figure 4. Thermograms of a 80 wt % CTAM aqueous sample obtained during consecutive heating-and-cooling runs: (A) first run, (B) seventh run.
an 85 wt % CTAM aqueous solution changed upon consecutive heating-and-cooling cycles (Figure 4). The thermogram taken during the first cycle (curve A in Figure 4) is similar to that of pure CTAM, that is, it includes a broad peak at about 53 °C with a small shoulder at ca. 38 °C, due to the melting of the hydrocarbon tail. Notice that no water signal is detected inasmuch as most of the water in this sample is bound (i.e., not free). Upon consecutive cycles, the thermograms change, and several peaks appear at lower temperatures, indicating chemical changes in the sample (curve B in Figure 4). The IR spectra of freeze-dried CTAM (inset) and of CTAM preheated for 10 min at 100, 150, 200, and 250 °C are displayed in Figure 5. No important changes occurred in the spectra after varying heating times. All samples exhibited a broad band typical of the OH group around 3400 cm-1. The OH band might be due to water absorbed from the humidity in the air during the handling of the samples, as all samples were previously freeze-dried. The presence of water in the samples can cause the partial hydrolysis of CTAM to yield CTA+, OH-, and methacrylic acid, as the alkyltrimethylammonium hydroxides are stronger bases (pKb ≈ 2.89 for dodecyltrimethylammonium hydroxide)28 than the weak methacrylic acid (pKa ≈ 4.25).29 Inasmuch as the OH group from water, the OH-, and the COOH group absorb strongly around 3400 cm-1, this band might arise from any of these groups in these spectra. The IR spectra of Figure 5 also include a band at 3020 cm-1, due to the -CHdCH2 group, whose intensity diminished as the preheating temperature became higher. However, the variation in intensity of the -CHdCH2 band is difficult to detect because it is partially superimposed on the bands of the OH, methyl, and methylene groups. Moreover, the intensities of the latter two bands increase as a result of the decomposition of CTAM to yield 1-hexadecene; as will be demonstrated later, this causes an increase in the band of the -CdC- group at 1650 cm-1. However, as the preheating temperature is increased, there is a small decrease in the intensities of the methyl and methylene bands as a result of the loss of (28) Morini, M. A.; Minardi, R. M.; Schulz, P. C.; Puig, J. E.; Hernandez-Vargas, M. E. Colloids Surf. A. 1995, 37, 103. (29) Lide, D. R. Handbook of Physics and Chemistry., 76th ed.; CRC Press: Boca Raton, FL, 1995.
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Figure 5. FTIR spectra of pure CTAM subjected to a preheating treatment at different temperatures: (A) 100, (B) 150, (C) 200, and (D) 250 °C. Inset: FTIR spectrum of a freeze-dried CTAM sample without the preheating treatment.
methacrylic acid by evaporation, which is evident by the decrease in intensity of the carbonyl band (1720 cm-1). In fact, the spectrum of the sample preheated at 250 °C indicates that the methacrylic acid band has almost completely vanished. Also, the bands corresponding to the trimethylammonium ion, located between 2600 and 2800 cm-1, become more intense as the decomposition of the CTAM increases as a result of the formation of trimethylamine. Even though, this compound is a gas, it is partially retained as trimethylammonium methacrylate. Notice that the spectrum of the sample preheated to 150 °C, which has lost almost all the water, clearly shows the bands of this salt. DTAM exhibited similar behavior. 1H NMR spectra of CTAM and of the preheated samples dissolved in CDCl3 are shown in Figure 6. The spectrum of CTAM (spectrum A) is identical to that reported in the literature.15 A comparison of the areas under the peaks corresponding to the cetyltrimethylammonium ion at 3.45 (br s, 2H), 3.38 (s, 9H), 1.66 (br s, 2H), 1.2 (br s, 26H) and 0.8 ppm (t, 3H) with the areas under the peaks corresponding to methacrylic acid at 6.1 (s, 1H), 5.57 (s, 1H), and 1.85 ppm (s, 3H) indicates a 1:1 relationship. Similar conclusions were drawn from the 13C NMR spectrum. On the other hand, a singlet at around 2.5 ppm in 1H NMR spectra (spectra B-E in Figure 6) and at 42.22 ppm in the 13C NMR spectra (not shown) is observed in the samples preheated at 150 °C for 1 h and at 250 °C for 10 min. This peak, which gradually appears and becomes more intense as the preheating temperature increases, might be due to the formation of cetyltrimethylamine or trimethylammonium ion. This peak appeared gradually in all cases and became more intense as the preheating temperature increased. It is noteworthy that the characteristic smell of amines was perceived from these samples during their manipulation. Also, the vinyl hydrogen peaks of the methacrylate ion at 5.57 and 6.1 ppm gradually vanished.
GC-MS experiments on the preheated samples of DTAM and CTAM dissolved in CH2Cl2 revealed two main peaks. One of these peaks corresponds to the alkyldimethylammonium ion at 269 m/e for CTAM or 213 m/e for DTAM. The other peak at 224 m/e for CTAM or 168 m/e for DTAM corresponds to 1-hexadecene or 1-dodecene, respectively. Integration of these peaks indicates that the decomposition increases as the temperature of the preheating treatment increases. The surfactant decomposition is noticeable even at temperatures as low as 60 °C (1 wt % of the total); at 200 °C, more than 20 wt % of the original surfactant decomposes. Moreover, freeze-dried CTAM kept at roomtemperature revealed signs of decomposition after 6 months. However, aqueous samples of CTAM or DTAM kept at room temperature did not show evidence of decomposition after 6 months. Headspace GC-MS of CTAM at 150 °C demonstrated that methacrylic acid, methyl methacrylate, and cetyldimethylamine were the decomposition products of CTAM. The 1H NMR spectra in D2O of the volatile products from the heating of CTAM at 150 °C for 30 min, absorbed in a mixture of HCl and methanol, included a singlet at 3.19 ppm that corresponds to trimethylamine hydrochloride. Conductometric analysis of the DTAOH samples desiccated for 3 days by the different methods described in the Experimental Section and redissolved in CO2-free distilled water, indicates that only 39.5% ( 1.5% of the original surfactant remained. A sample left in the desiccator jar for 1 week had only 25% of the original surfactant, whereas that left for 2 weeks contained only 13% of the original DTAOH. The variation in the desiccation method did not significantly alter these results. The molar mass of the water-insoluble material was 168 ( 1 g mol-1. The IR spectrum of this residue depicted methyl bands plus four consecutive bands of methylene groups and a vinyl group. Also, a small band due to the OH group was detected, which might come from traces of water or from DTAOH
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Figure 6. 1H NMR spectra of (A) freeze-dried CTAM and CTAM subjected to preheating treatments at (B) 100, (C) 150, (D) 200, and (E) 250 °C.
in the material. Other than this OH band, this spectrum was identical to the literature spectrum of dodecene. The 0.18 M DTAOH solutions did not undergo detectable changes in the surfactant concentration at ambient temperature after 3 months of storage. However, a slight amine odor was always detected. Discussion and Conclusions As described above, DSC detected an anomalous behavior in scans of pure CTAM and DTAM (Figure 2) and their concentrated aqueous solutions (Figure 4). This anomalous behavior, however, was not observed for more dilute solutions (Figure 3). The appearance of new thermal transitions in consecutive heating-and-cooling cycles makes us suspect that possible polymerization or degradation reactions occur at relatively low temperatures (e200 °C). That no polymerization reactions take place during the treatment and handling of CTAM and DTAM is supported by (1) the disappearance of the characteristic peaks of the methacrylate ion in the FTIR (Figure 5), 1H NMR (Figure 6), and 13C NMR (not shown) spectra; (2) the high solubility in chloroform; (3) the low viscosity; and (4) the physical appearance of the material. The results obtained during the process of drying DTAOH from a dilute solution demonstrated that, when the system is highly concentrated, in fact, when a hexagonal liquid-crystalline phase forms, a Hofmann elimination reaction occurs at room temperature.30,31 This reaction does not take place in relatively dilute solutions. The kinetics of the reaction is difficult to follow because the elimination reaction occurs simultaneously with the desiccation process. Hence, it is not possible to control the experimental conditions accurately enough to study the kinetics of decomposition reliably. (30) Minardi, R. M.; Schulz, P. C.; Vuano, B. Colloid Polym. Sci. 1989, 267, 589. (31) Morini, M. A. Ph.D. Thesis, Universidad Nacional del Sur, Bahı´a Blanca, Argentina, 1998.
That the decomposition of DTAOH occurs when crystals or liquid crystals (i.e., concentrated systems) are present suggests that this process is highly facilitated by the close proximity of the polar groups and the strong bonding of the OH groups in the Stern layer in these phases.32 The increasing packing density of the polar groups in the Stern layer as spherical micelles change into cylindrical ones, which change into hexagonal liquid crystals and then into crystals as the surfactant concentration is increased can be visualized by calculating the area occupied by the polar group at the interface. According to Tanford,33 the volume (V) of the hydrocarbon tails in a given aggregate and the length (L) of the hydrocarbon chain for a surfactant with nc carbon atoms in the tail can be calculated from
V(Å3) ) 27.4 + 26.9nc
(1)
L(Å) ) 1.5 + 1.265nc
(2)
respectively. With these two formulas and Schulz’s model for spherical and cylindrical micelles,34 the area occupied by a polar group at the interface (S) can be estimated. For DTAOH (as well as for CTAOH), Ssphere ) 63.3 Å2, Shexa lc ) 42.0 Å2, and Scrystal ) 21.5 Å2. On the basis of the structure of the trimethylammonium group, a degree of micellar ionization (R) equal to 0.225 and a thickness of the Stern layer of 2.5 Å can be used. With these data, it is possible to estimate the local concentration of OH- at the Stern layer, giving values of 8.3 mol/dm3 for spherical micelles (for both DTAOH and CTAOH) and of 31.3 and 40.4 mol/dm3 for the hexagonal mesophases of DTAOH and CTAOH, respectively. Hence, even in relatively dilute surfactant solutions, the concentration of OH- in the neighborhood (32) Morini, M. A.; Schulz, P. C.; Puig, J. E. Colloid Polym. Sci. 1996, 274, 662. (33) Tanford, C. The Hydrophobic Effect: Formation of Micelles and Biological Membranes; Wiley: New York, 1974; p 75. (34) Schulz, P. C. Colloid Polym. Sci. 1991, 269, 612.
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of the reactive groups (i.e., the alkyltrimethylammonium groups) is extremely high. In fact, it is higher than the concentrations that can be obtained in common alkali solutions. These factors can then act as the driving forces for the Hofmann elimination at room temperature in concentrated solutions of alkyltrimethylammonium hydroxide surfactants. In the case of CTAM and DTAM, these molecules rapidly absorb water from humidity in the air. This is evident in the IR spectra where the presence of small amounts of water in the freeze-dried and preheated samples was always observed (Figure 5). This water can then induce the partial hydrolysis of CTAM (or DTAM) to produce small amounts of CTAOH (or DTAOH) and methacrylic acid inasmuch as it is a weak acid whereas the alkyltrimethylammonium hydroxides are stronger bases. Hence, the presence of OH- ions in CTAM and DTAM can induce the Hofmann elimination reaction to produce 1-alkene, trimethylamine, and methacrylic acid. However, as the concentration of OH- ions in the ionic layers of the crystals and concentrated solutions are lower than in the DTAOH
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or CTAOH surfactants, the Hofmann elimination occurs at higher temperatures. Also, for solid DTAM and CTAM, there is another reaction competing with the Hofmann elimination, mainly a nucleophilic reaction that yields alkyldimethylamine. That the dilute solutions of DTAM, CTAM, and DTAOH do not show evidence of decomposition suggests that less crowded packing and smaller local concentrations of OHions, which occur for spherical micelles, hinder Hofmann elimination reactions. This phenomenon has to be taken into account when polymerization reactions with these type of surfactants are studied. Acknowledgment. The Council of Science and Technology of Mexico supported this work through Grant 3343P-E9607. One of us (P.C.S.) acknowledges the Visiting Professor position granted by the Universidad de Guadalajara. LA011077J
