© Copyright 1996 American Chemical Society
JULY 24, 1996 VOLUME 12, NUMBER 15
Letters Synthesis and Surface Properties of Novel Fluoroalkylated Flip-Flop-Type Silane Coupling Agents Hideo Sawada,*,† Yuka Ikematsu,† Tokuzo Kawase,‡ and Yoshio Hayakawa§ Department of Chemistry, Nara National College of Technology, Yata, Yamatokoriyma-city, Nara 639-11, Japan, Faculty of Human Life Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan, and National Industrial Research Institute of Nagoya, Kita-ku, Nagoya 462, Japan Received November 16, 1995. In Final Form: May 28, 1996X New fluoroalkylated oligomeric silane coupling agents containing morpholino groups were prepared by the reactions of fluoroalkanoyl peroxides with trimethoxyvinylsilane and acryloylmorpholine. The modified glass surface treated with these silane coupling agents was shown to have a strong hydrophilicity with good oil repellency, and these fluoroalkylated oligomers are applicable to new flip-flop-type silane coupling agents.
Recently, there has been a great interest in fluorosilicon compounds as new functional materials possessing excellent properties imparted by both fluorine and silicon. From such points of view, silane coupling agents having some perfluoroalkyl groups [RF-CH2CHSi(OMe)3; RF ) perfluoroalkyl groups] were prepared by the use of hydrosilylation of fluorine-containing alkenes promoted by a platinum catalyst, and were found to have a high modification ability (water and oil repellency) against a modified glass surface.1 Similarly, we reported the * To whom all correspondence should be addressed. † Nara National College of Technology. ‡ Osaka City University. § National Industrial Research Institute of Nagoya. X Abstract published in Advance ACS Abstracts, July 1, 1996. (1) (a) Yoshino, N.; Yamamoto, Y.; Seto, T.; Tominaga, S.; Kawase, T. Bull. Chem. Soc. Jpn. 1993, 66, 472. (b) Yoshino, N.; Yamamoto, Y.; Hamano, K.; Kawase, T. Bull. Chem. Soc. Jpn. 1993, 66, 1754. (c) Yoshino, N.; Yamamoto, Y.; Teranaka, T. Chem. Lett. 1993, 821. (d) Yoshino, N. Chem. Lett. 1994, 735. (e) Teranaka, T.; Iwamoto, T.; Yoshino, N. Bull. Kanagawa Dent. Col. 1994, 22, 151. (f) Yoshino, N.; Nakaseko, H.; Yamamoto, Y. Reactive Polym. 1994, 23, 157. (g) Yoshino, N.; Tomita, J.; Hirai, H. Bull. Chem. Soc. Jpn. 1989, 62, 2208. (h) Kobayashi, H. Makromol. Chem. 1993, 194, 2569. (i) Zhao, Q.; Mark, J. E. Macromol. Rep. 1992, A29, 221. (j) Owen, M. J.; Kobayashi, H. Macromol. Symp. 1994, 82, 115. (k) Yoshino, N.; Yamaguchi, E.; Yamamoto, Y.; Itagaki, T.; Matsumoto, T.; Sawada, H.; Kondo, Y.; Abe, M. Nippon Kagaku Kaishi 1993, 995. (l) Owen, M. J.; Williams, D. E. Adhes. Sci. Technol. 1991, 5, 307.
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preparation of numerous oligomeric silane coupling agents with two fluoroalkylated end groups [RF-(CH2-CR1R2)nRF, R1 ) H, R2 ) Si(OMe)3; R1 ) H, Me, R2 ) CO2CH2CH2CH2Si(OMe)3; RF ) perfluoroalkyl, perfluorooxaalkyl groups] by using fluoroalkanoyl peroxides as intermediates, and the modified surface with these compounds was shown to have a good water and oil repellency.2 Recently, we have prepared amphiphilic fluoroalkylated silane coupling agents, in which the hydrophobic tail is a fluoroalkyl group and the hydrophilic moiety is a poly(oxyethylene) unit.3 However, these silane coupling agents, even though possessing long poly(oxyethylene) chains, failed to show a good hydrophilic property. The development of fluorinated silane coupling agents possessing not only a oleophobic property imparted by fluorine but also a strong hydrophilic property, namely, flip-floptype silane coupling agents, is very desirable but the synthesis of such compounds had hitherto been very limited. Now, we have found that fluoroalkylated silane coupling agents containing morpholino groups can be prepared by using fluoroalkanoyl peroxide, and the (2) (a) Sawada, H.; Nakayama, M. J. Chem. Soc., Chem. Commun. 1991, 677. (b) Sawada, H.; Minoshima, Y.; Matsumoto, T.; Gong, Y.-F.; Kosugi, M.; Migita, T. J. Fluorine Chem. 1992, 59, 275. (3) Sawada, H.; Mitani, M.; Nishida, M.; Gong, Y.-F.; Kosugi, M.; Migita, T.; Kawase, T. J. Jpn. Oil Chem. Soc. 1994, 43, 65.
© 1996 American Chemical Society
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Langmuir, Vol. 12, No. 15, 1996
Letters
Table 1. Reactions of Fluoroalkanoyl Peroxides with Acryloylmorpholine (ACMO) and Trimethoxyvinylsilane (VMOSi)
Table 2. Contact Angles of Dodecane and Water Treated with RF-(ACMO)x-(VMOSi)y-RF contact angle (deg)
RF-(ACMO)x-(VMOSi)y-RF RF in peroxide (mmol)
ACMO (mmol)
VMOSi (mmol)
yield (%)a
C3F7 5 15 15 CF(CF3)OC3F7 5 15 15 CF(CF3)OCF2CF(CF3)OC3F7 5 15 15 CF(CF3)OCF2CF(CF3)OCF2CF(CF3)OC3F7 6 18 18
water
M h nb (x:y)c
51
2720 (34:66)
25
3520 (28:72)
27
5060 (71:29)
28
6420 (39:61)
h n] RF [M
C 3F 7 [2720] 39 70 68 48 CF(CF3)OC3F7 [3520] 49 78 68 48 CF(CF3)OCF2CF(CF3)OC3F7 [5060] 57 79 67 49 CF(CF3)OCF2CF(CF3)OCF2CF(CF3)OC3F7 [6420] 60 72 60 50 a
a The yields are based on the starting materials (acryloylmorpholine, trimethoxyvinylsilane, and the decarboxylated peroxide unit (RF-RF)). b M h n indicates number-average molecular weight. c Co-oligomerization was determined by 1H NMR.
modified glass surface treated with these silane coupling agents shows a strong hydrophilic property and a good oil repellency.
A typical experiment for the synthesis of fluoroalkylated trimethoxyvinylsilane-acryloylmorpholine co-oligomers is as follows. Perfluorobutyryl peroxide (5 mmol) in 1:1 mixed solvents (AK-225) of 1,1-dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,2,2,3,3-pentafluoropropane (21 g) was added to a mixture of trimethoxyvinylsilane (15 mmol), acryloylmorpholine (15 mmol), and AK-225 (62 g). The solution was stirred at 45 °C for 3 h under nitrogen. After the solvent was evaporated, the obtained crude product was purified by dissolution in AK225 and reprecipitation with n-hexane to give bis(perfluoropropylated) trimethoxyvinylsilane-acryloylmorpholine co-oligomer (3.11 g). This co-oligomer showed the following spectral data: IR (ν/cm-1) 1631 (CdO), 1335 (CF3), 1230 (CF2), 1115 (-O-); 19F NMR (CDCl3, ext. CF3CO2H) δ -1.58 (6F), -36.73 (4F), -44.53 (4F); 1H NMR (CDCl3) δ 0.77-2.80 (CH2, CH), 1.96 (CH3), 3.20-3.98 h n) ) 2720, M h n/M h w ) 1.49 (CH2); average molar mass (M (determined by a gel permeation chromatography calibrated with standard polystyrenes). Similarly, the reactions of fluoroalkanoyl peroxides with acryloylmorpholine and trimethoxyvinylsilane were carried out, and the results are summarized in Table 1. As shown in Table 1, not only perfluoropropylated materials but also a series of perfluorooxaalkylated acryloylmorpholine-trimethoxyvinylsilane co-oligomers was obtained in 25-51% isolated yields. In these cooligomers, the molecular weights of perfluorooxaalkylated oligomers are higher than that of the perfluoropropylated one under the degree of oligomerization. This is because perfluorooxaalkyl radicals are more stable than perfluoropropyl radicals as we previously reported in the preparation of fluoroalkylated acrylic acid oligomers [RF(CH2CHCO2H)n-RF].4
0 5 10 15 20 25 30 dodecane min min min min min min mina 30
18
0
30
18
0
32
13
0
42
23
8
0
b
Time dependence of contact angle. The contact angles of dodecane and water on nontreated glass are 0° and 49°, respectively.
Fluoroalkylated silicon co-oligomers containing morpholino groups thus obtained are expected to be useful as surface-active substances since these co-oligomers possess reactive groups such as methoxysilanes. In fact, these silicon co-oligomers were tested for surface activity as a new type of fluorosilane coupling agent. As shown in Table 2, the contact angles for dodecane on the glass treated with these co-oligomers [1% (m/m)]5 showed a significantly large value (39-60°) compared with that of nontreated glass, indicating that our silane coupling agents possess a good oil repellency. In each fluoroalkylated silane coupling agent, time dependence of contact angle of dodecane was not observed. The contact angles of dodecane increased with the co-oligomers bearing longer perfluorooxaalkyl groups in a similar manner to the usual fluoroalkylated oligomeric silane coupling agents (RF[CH2CHSi(OMe)3]n-RF, RF ) perfluoroalkyl, perfluorooxaalkyl groups).6 More interestingly, a steep time dependence of contact angle of water was observed in these silane coupling agents as shown in Table 2. The contact angles decreased dramatically from about 75° to 0° over 25 or 30 min with each silane coupling agent. Therefore, these silane coupling agents exhibit a markedly strong hydrophilicity above their surface, though these materials have fluoroalkyl groups. This finding suggests that at the interface with water, hydrophobic fluoroalkyl segments are replaced by the strongly hydrophilic morpholino segments. The morpholino segments in fluoroalkylated co-oligomers are also likely to be arranged more regularly at the water interface. It takes about 30 min to replace the fluoroalkyl segments by morpholino segments when the environment is changed from air to water. Thus, our new fluoroalkylated co-oligomers are expected to behave as novel flipflop-type silane coupling agents. To our knowledge, this is the first example which shows that fluorosilane coupling agents can exhibit not only oleophobicity but also extremely strong hydrophilicity. Further studies are now in progress. LA951041P (4) Sawada, H.; Minoshima, Y.; Nakajima, H. J. Fluorine Chem. 1993, 65, 169. (5) With respect to the thickness of siloxane layer, we studied the depth profile by X-ray photoelectron spectroscopy using Ar gas ion etching at the condition of 0.5 kV and 10 µA, at which condition the ion etching rate has been said to be about 50 Å/min. Even after 30 min of etching (∼1500 Å), though fairly small, there existed the N1s peak at 401 eV, while the peak of F1s disappeared after 10 min of etching. Therefore, the thickness of the siloxane layer is reasonably estimated at about 0.2 µm or above. (6) Sawada, H.; Gong, Y.-F.; Matsumoto, T.; Nakayama, M.; Kosugi, M.; Migita, T. J. Jpn. Oil Chem. Soc. 1991, 40, 730.
