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Modification of linear triblock copolymer SBS via olefinic per(poly)fluoroalkylation by per(poly)fluorodiacyl peroxides
Journal of Fluorine Chemistry 104 (2000) 285±290
Modi®cation of linear triblock copolymer SBS via ole®nic per(poly)¯uoroalkylation by per(poly)¯uorodiacyl peroxides Zhi-bin Zhou*, Hai-ying He, Zhong-yuan Weng, Cheng-xue Zhao
Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074, Hubei, PR China Received 5 January 2000; accepted 23 February 2000
Abstract Facile electron transfer reactions between linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) and per(poly)¯uorodiacyl peroxides at room temperature (208C) in dichloromethane produced high yields of olefmic per(poly)¯uoroalkylated SBS with excellent water and oil repellency, chemical resistance and much lowered refractive indices. # 2000 Elsevier Science S.A. All rights reserved. Keywords: Per(poly)¯uorodiacyl peroxiaes; Fluoroalkylation; SBS; Surface modi®cation
1. Introduction To obtain the unique properties of organo¯uorine compounds and polymers including excellent water- and oilrepellency, chemical resistance, and much lower refractive indices for some of the most widely used polymers by introducing per(poly)¯uoroalkyl groups, has long been an aim in organic chemistry and polymer science [1,12]. Since the improved synthesis and kinetic studies of thermal decomposition of per(poly)¯uorodiacyl peroxides[(RFCO2)2, FAP] [2], and the reactions of FAP as per(poly)¯uoroalkylating agents with arenes succeeded [3,13], FAP have been found to be clean and highly effective per(poly)¯uoroalkylating and per(poly)¯uoroacyloxylating agents for arenes [4,14,15], aromatic heterocycles [5,16,17], ole®ns [6,18], fullerenes [7] and many other substrates with a variety of structures. As novel radical initiators, FAP were used to synthesize oligomeric or polymeric acrylic acid, acrylic esters, and vinyl silianes with end-capped per(poly)¯uoroalkyl groups. The resulting products were found to be excellent surfactants [8,19,20]. For polymeric substrates, we have succeeded in introducing per(poly)¯uoroalkyl groups onto the phenyl rings of polystyrene with high yields by homogeneous reactions [9]. Consequently, the chemistry of FAP plays an increasingly important role in the synthesis of organo¯uorine functional materials. * Corresponding author. E-mail address: [email protected] (Z.-b. Zhou)
In this work, we carefully designed the reaction systems, characterized the products, and proposed a mechanism of the reactions of linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) with FAP. The contact angles of water and paraf®n oil (n-dodecane), and the refractive indices of the resulting ¯uoroalkylated polymer ®lms on glass slides or quartz plates were determined. 2. Results and discussion 2.1. Homogeneous reactions of linear triblock copolymer SBS with FAP at 208C In the reactions of the representative FAP (RFH(CF2)4, n-C3F7, and n-C7F15) with linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) (20% styrene in weight), the molar ratio of FAP/B (butadiene unit in SBS) was ®xed at 0.05, 0.10, 0.15, 0.20, 0.30 and 0.4, respectively. The reactions was usually complete in 2 h at room temperature (208C) under mild conditions and no precipitate was observed in the ®nal mixture. 2.2. Product characterization The IR, and 19F NMR characterization of the products were summarized in Table 1. As shown in Table 1, strong absorption peaks at 1800 cmÿ1, which are presumably characteristic absorptions of carbonyl groups, occurred in
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Table 1 Reactions of SBS with (RFCO2)2 (FAP) in CH2Cl2 at 208C RF
H(CF2)4
n-C3F7
n-C7F15
(RFCO2)2/Butadienea
RF-ratiob (%)
RF group yieldsc (%)
IR (cmÿ1)
19
0.05:1 0.1:1 0.2:1 0.3:1 0.4:1 0.05:1 0.1:1 0.2:1 0.3:1 0.4:1 0.05:1 0.1:1 0.2:1 0.3:1 0.4:1
3 7 16 22 30 3 6 13 20 28 3 7 13 20 25
60 70 80 72 75 60 60 65 68 70 60 70 65 68 63
1775 (C=O) 1265, 1 260 (CF2) 1165 (C±O±C)
ÿ65.5 (a, 4F, JHF52.6 Hz) ÿ58.0 (b, 4F) ÿ51 to ±54 (c, m, 4F) ÿ46.5 (d, 2F) ÿ41.0 (e, 2F) ÿ3.0 (a, 6F) ÿ47 to ÿ50 (b, m, 4F) ÿ41.7 (c, 2F) ÿ35.5 (d, 2F)
1778 (C=O) 1352 (CF3) 1260, 1230 (CF2) 1150 (C±O±C) 1778 (C=O) 1350 (CF3) 1240, 1210 (CF2) 1150 (C±O±C)
F NMRd (ppm)
ÿ3.5 (a, 6F) ÿ48.6 (b, 4F) ÿ44.5 (c, 16F) ÿ41.0 (d, 2F) ÿ35.5 (e, 2F)
a
Molar ratio. Fluoroalkylation ratio of C=C bonds in SBS chain. c Based on (RFCO2)2. d RFH(CF2)4: HCF2aCF2bCF2cCF2d, HCF2aCF2bCF2cCF2eCO2; RFn-C3F7: CF3aCF2bCF2c, CF3aCF2bCF2dCO2; RFn-C7F15: CF3aCF2b(CF2)4cCF2d, a CF3 CF2b(CF2)4cCF2eCO2. b
the IR spectra of all the products. The characteristic absorption bands for uCF3 at 1350 cmÿ1, and 1260 cmÿ1 for uCF2 , indicate the success in introducing RF groups into the SBS polymer. The 19F NMR spectra of the isolated products clearly show that two kinds of RF groups were introduced into the structure of SBS. For example, in the 19F NMR spectra of the isolated products (RFn-C3F7), absorption peaks showed at ÿ3.0 (2CF3), ÿ35.5 (CF2), 41.7 (CF2), and ÿ47 to ÿ50 ppm (2 CF2), respectively. Compared with the previous results of FAP reacted with polystyrene (PS) [9], the absorption peaks of RF (RFn-C3F7) groups which were introduced onto the phenyl rings in PS revealed at ÿ8.0 (CF3), ÿ39.5 (CF2), and ÿ54.0 ppm (CF2), no detectable absorption peaks of RF groups introduced onto the phenyl rings of the linear triblock copolymer SBS polymer in the side chains were observed from 19F NMR spectra of any of the products. Moreover, no detectable RFCO2H was detected by acid-base titration method in the reaction systems. All these results show that RF- and RFCO2-groups were only added onto the ole®nic bonds of the SBS polymer chains, and the ¯uoroalkylated products of SBS polymers can be expressed as RF-SBS-OCORF. The ¯uoroalkylation ratios (RF-ratio) of C=C bonds in SBS chains and the yields of RF-SBS-OCORF based on FAP added were calculated from 19F NMR integrations (mtri¯uoromethylaniline used as internal standard for quantitative analysis) described in the literature [9], and summarized in Table 1. The yields of RF-ratio are in the range of 3± 30%. The yields of the products based on FAP added for all the runs are fairly high (60±80%). All the matter given above shows that FAP are effective, regioselective, and convenient per(poly)¯uoroalkylating agents for ole®niccontaining polymers.
2.3. Mechanism The unimolecular decomposition of (RFCO2)2 (FAP) has been studied in detail in a previous study [2]. At 208C, the half-life time of (RFCO2)2 employed in this work are: 5.83 h (RFH(CF2)4), 8.78 h (RFn-C3F7), and 6.4 h (RFnC7F15), respectively. In the presence of SBS, the disappearance of FAP was signi®cantly accelerated, and FAP was usually completely consumed within 2 h. The ole®nic and phenyl groups in the polymer chain of SBS are suf®ciently reactive for transferring an electron to the highly effective one-electron oxidant FAP but it was shown from IR and 19F NMR spectra of the products that RF- and RFCO2-groups were only added onto the C=C bonds of the linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) chain. Moreover, no detectable RFCO2H was discovered in the ®nal reaction mixture by acid±base titration which is a strong indicator that no single electron transfer (SET) reaction takes place between FAP and phenyl rings in the polymer [9,11]. All results given above are strong indications of a SET reaction taking place between FAP and the ole®nic groups in the linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) chain as illustrated in Scheme 1. 2.4. Water and oil-repellency of RF-SBS-OCORF The contact angles of water (ywater) and n-dodecane (yoil) on the surface of the ®lms of RF-SBS-OCORF polymers cast on glass slides were used to determine water- and oilrepellent properties, and chemical resistance of the prepared polymers. The plots of contact angles vis yields of RF-ratio (the ¯uoroalkylation ratio of C=C bonds in SBS chains) are
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287
Scheme 1.
Fig. 2. The contact angles (ywater) of RF-SBS-OCORF (RFn-C3F7).
Fig. 1. The contact angles (ywater) of RF-SBS-OCORF (RFH(CF2)4).
shown in Figs. 1±4. From Table 2 and Figs. 1±4, the following trends are observed: For all the prepared RF-SBS-OCORF polymers, both the contact angles ywater and yoil increase with RF-ratio increase.
Especially, the contact angles (ywater) of RF-SBS-OCORF (RFn-C7F15) almost reached that of poly(tetra¯uoroethylene) (PTFE) (ywater1408). Moreover, at the RF-ratio of 6%, ywater reaches 1008 and over, this trend provides de®nitive evidence of the change of the surface composition by the surface distribution of RF groups [10]. At the same RF-ratio, the contact angles (ywater) of RFSBS-OCORF polymers containing longer RF groups such as n-C7F15 are higher than those bearing shorter RF groups (RFH(CF2)4, n-C3F7) with the order H(CF2)4
Fig. 3. The contact angles (ywater) of RF-SBS-OCORF (RFn-C7F15).
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Z.-b. Zhou et al. / Journal of Fluorine Chemistry 104 (2000) 285±290 Table 3 Refractive indices (nD) of RF-SBS-OCORF polymers RF
H(CF2)4
n-C3F-7
n-C7F15 SBS Fig. 4. The contact angles (yoil) of RF-SBS-OCORF.
improved from detected ywater. However, RF-SBS-OCORF polymers are less resistant than the corresponding RF-PS polymers [9], most likely, because the ester linkage RFCO2in the RF-SBS-OCORF side chain may be reactive under the acid or alkaline conditions. Furthermore, the large number of unreacted C=C bonds in RF-SBS-OCORF chains may also be reactive. 2.5. Optical properties of RF-SBS-OCORF Poly(tetra¯uoroethylene) (PTFE) is the most important commercially ¯uoropolymer with very low refractive index, but it is dif®cult to process by conventional compression, injection moulding or by extrusion. Accordingly, seeking for novel polymers with much lowered refractive indices,
a
RF-ratioa (%)
nD
3 7 16 22 30 3 6 13 20 28 3 7 13 20 0
1.5250 1.5109 1.5025 1.5111 1.4738 1.5357 1.5192 1.5056 1.5174 1.4805 1.5177 1.5048 1.4699 1.4434 1.5710
Fluoroalkylation ratio of C=C bonds in SBS chain.
which can be processed by conventional methods, is a major challenge in functional material ®eld. As shown in Table 3, all the RF-SBS-OCORF polymers have distinctly lowered refractive indices (nD) compared with the parent polymer SBS (nD1.5710). The plots of nD vis RF-ratio are shown in Fig. 5. From Fig. 5, an interestingly optical property, which was discovered in our previous study [9], was also observed for the RF-SBS-OCORF polymers. The refractive indices (nD) are not always decreased with RF-ratio increase. In the RFratio range of 0±22%, there exist a minimum and a maximum nD for RF-SBS-OCORF (RFH(CF2)4, n-C3F7). But the nD decrease signi®cantly with the increase of RF-ratio for RF-SBS-OCORF (RFn-C7F15). It is dif®cult for us to explain the relationships between such strange changes of
Table 2 Contact angles of SBS and RF-SBS-OCORF polymers RF
H(CF2)2
n-C3F7
n-C7F15 SBS a
RF-ratioa (%)
yoil (n-dodecane, 58C)
3 7 16 22 30 3 6 13 20 28 3 7 13 20 25 0
27 31 35 42 42 23 26 28 30 30 28 35 42 46 50 22
Fluoroalkylation ratio of C=C bonds in SBS chain.
ywater (208C) Before treatment
5% H2SO4
5% NaOH
98 103 105 107 110 95 101 107 114 114 111 113 117 131 131 93
95 98 101 103 103 91 97 103 109 110 98 103 108 117 122 83
90 92 94 97 100 87 88 93 97 100 95 99 101 107 110 80
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meter (Chengde). The refractive indices were determined with a TP-77 elliposmeter (Beijing). 3.3. Reactions of FAP with linear triblock copolymer SBS
Fig. 5. Refractive indices (nD) of RF-SBS-OCORF.
nD with the chain length of RF for synthetic RF-SBS-OCORF at present. Nevertheless, the RF-SBS-OCORF polymers with much lowered refractive indices, which may be useful as surface coating of plastic ®ber were successfully prepared in our study. 3. Experiment 3.1. Materials Linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) (20% styrene in weight) supplied by Yueyang General Petrochemical Works (Hunan Province, China), was dissolved in CH2Cl2, precipitated with methanol and dried at 408C under vacuum for 24 h before use. Commercial Freon 113 (CCl2F±CClF2) was carefully washed in turn with concentrated H2SO4, 5% NaHCO3, and water, and dried over anhydrous MgSO4 and distilled, bp 47.5±488C. FAP were prepared from the corresponding acyl chloride (RFCOCl) and hydrogen peroxide (30%) in the presence of aqueous sodium hydroxide (10%) according to our previously reported method [2], the concentrations of FAP were determined by standard iodometry. All other solvents were dried, and redistilled before use. 3.2. Instruments IR spectra were obtained with Shimadazu IR-435 and IR408 spectrometers. Fluoroalkylated polymer samples were prepared in dichloromethane and cast onto NaCl plates for recording IR spectra. 19F NMR were recorded on a Bruker FT-AC 80 NMR spectrometer. Tri¯uoroacetic acid was used as an external standard; m-tri¯uoromethylaniline was used as internal standard in the quantitative analysis of products. Fluoroalkylated polymer samples were weighed and dissolved in CDCl3 for quantitative analysis by 19F NMR. The contact angles were measured with a JY-82 contact angle
In an typical reaction at room temperature (208C), SBS (2.0 g, 30 mmol of butadiene units) was dissolved in dichloromethane (50 ml) with gently magnetic stirring in a reactor with a ¯at bottom. After ¯ushing with nitrogen, FAP (2 mmol) dissolved in Freon 113 (usually at a concentration of 0.2 M) was dropped into the SBS solution over 30 min. The reaction was continued for an additional 2 h. A few milliliter of the reaction mixture were removed for determination of the yield of RFCO2H by acid±base titration. The reaction mixture was washed in turn with 5% NaHCO3, distilled water, and dried over anhydrous NaSO4. The mixture was concentrated to a volume of 10 ml, then added to 100 ml of methanol. The crude polymeric precipitate was ®ltrated, redissolved in dichloromethane, reprecipitated with methanol, and dried at 458C under vacuum for 24 h. Parent polymer SBS and ¯uoroalkylated SBS from solutions in CH2Cl2 were cast uniformly on glass slides (7.5 cm2.5 cm) or thin quartz plates (5 mm3 mm) to form thin ®lms by solvent evaporation, and dried under vacuum. The polymeric ®lms were used for the measurement of contact angles and refractive indices. 3.4. Measurement of contact angle About 0.05 ml water or n-dodecane from a syringe was dropped carefully onto the surface of the ®lms coated on the glass slides (7.5 cm2.5 cm). The contact angles of water (ywater) or n-dodecane (yoil) on the surface of the polymeric ®lms were read out directly by the contact angle meter. 3.5. Tests of chemical resistance The polymeric ®lms coated on the glass slides (7.5 cm2.5 cm) were immersed in a sealed glass vial containing 5% H2SO4, or 5% NaOH solutions at room temperature for 7 days. After carefully washing with distilled water, and drying under vacuum, contact angles were measured. 3.6. Determination of refractive indices The re¯ecting angles of the polymeric ®lms coated on thin quartz plates (5 mm3 mm) were measured by an Ê , inciellipsometer equipped with He-Ne laser(l6234 A dent angle708). Refractive indices were calculated from the detected re¯ecting angles by data processing software in a computer system described in the literature [9].
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Acknowledgements Funding by NSF of China is gratefully acknowledged. In addition, the authors also thank Professor Jin Nie for critical reading of the manuscript. References [1] R.E. Banks, Organofluorine Chemicals and Their Industrial Applications, Ellis Horwood, London, 1979. [2] C.X. Zhao, R.M. Zhou, H.Q. Pan, Y.L. Qu, X.K. Jiang, J. Org. Chem. 47 (1982) 2009. [3] C.X. Zhao, M. Gamil, C. Walling, J. Org. Chem. 48 (1983) 4908. [4] M. Yoshida, M. Amemiya, M. Kobayashi, H. Sawada, H. Haggi, K. Aoshima, J. Chem. Soc., Chem. Commun. (1985) 234. [5] M. Yoshida, K. Moriya, H. Sawada, M. Kobayashi, Chem. Lett. (1985) 755. [6] H. Sawada, M. Nakayama, J. Fluor. Chem. 46 (1990) 423. [7] P.J. Fagan, P.J. Crussic, C.N. McEwen, J. Lazar, D.H. Parker, N. Herron, E. Wasserman, Science 262 (1993) 404.
[8] X.D. Luo, R.X. Li, D.C. Wu, H.S. Ling, Acta Polym. Sinica (1999) 623. [9] Z.B. Zhou, H.Y. He, Z.Y. Weng, C.X. Zhao, J. Fluor. Chem. 79 (1996) 1. [10] J.P. Badyal, R.D. Chambers, A.K. Jeol, J. Fluor. Chem. 60 (1993) 297. [11] H. Sawada, M. Mitani, M. Nakayama, M. Yosbida, N. Kamigata, Polymer 31 (1990) 63. [12] RF. Brady, Chem. Brit. (1990) 427. [13] C.X. Zhao, X.K. Jiang, J.Y. Zhang, J. Fluor. Chem. 27 (1985) 401. [14] X.K. Jiang, C.X. Zhao, Y.F. Gong, J. Phys. Org. Chem. 4 (1991) 1. [15] M. Yoshida, Y. Morinaga, M. Ueda, N. Kamigata, M. Iyoda, Chem. Lett. (1992) 227. [16] H. Sawada, M. Yoshida, H. Haggi, K. Aoshima, M. Kobayashi, Bull. Chem. Soc. Jpn. 59 (1986) 215. [17] H. Sawada, M. Nakayama, J. Fluor. Chem. 51 (1991) 117. [18] H. Sawada, Y.F. Gong, T. Matsunoto, M. Nakayama, M. Kosugi, T. Migita, J. Jpn. Oil Chem. Soc. 40 (1991) 730. [19] H. Sawada, A. Ohashi, M. Oue, M. Baba, M. Abe, M. Mitani, H. Nakajima, J. Fluor. Chem. 81 (1997) 215. [20] H. Sawada, Y.F. Gong, Y. Minoshima, T. Matsunoto, M. Nakayama, M. Kosugi, T. Migita, J. Chem. Soc., Chem. Commun. (1992) 537.
Modi®cation of linear triblock copolymer SBS via ole®nic per(poly)¯uoroalkylation by per(poly)¯uorodiacyl peroxides Zhi-bin Zhou*, Hai-ying He, Zhong-yuan Weng, Cheng-xue Zhao
Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074, Hubei, PR China Received 5 January 2000; accepted 23 February 2000
Abstract Facile electron transfer reactions between linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) and per(poly)¯uorodiacyl peroxides at room temperature (208C) in dichloromethane produced high yields of olefmic per(poly)¯uoroalkylated SBS with excellent water and oil repellency, chemical resistance and much lowered refractive indices. # 2000 Elsevier Science S.A. All rights reserved. Keywords: Per(poly)¯uorodiacyl peroxiaes; Fluoroalkylation; SBS; Surface modi®cation
1. Introduction To obtain the unique properties of organo¯uorine compounds and polymers including excellent water- and oilrepellency, chemical resistance, and much lower refractive indices for some of the most widely used polymers by introducing per(poly)¯uoroalkyl groups, has long been an aim in organic chemistry and polymer science [1,12]. Since the improved synthesis and kinetic studies of thermal decomposition of per(poly)¯uorodiacyl peroxides[(RFCO2)2, FAP] [2], and the reactions of FAP as per(poly)¯uoroalkylating agents with arenes succeeded [3,13], FAP have been found to be clean and highly effective per(poly)¯uoroalkylating and per(poly)¯uoroacyloxylating agents for arenes [4,14,15], aromatic heterocycles [5,16,17], ole®ns [6,18], fullerenes [7] and many other substrates with a variety of structures. As novel radical initiators, FAP were used to synthesize oligomeric or polymeric acrylic acid, acrylic esters, and vinyl silianes with end-capped per(poly)¯uoroalkyl groups. The resulting products were found to be excellent surfactants [8,19,20]. For polymeric substrates, we have succeeded in introducing per(poly)¯uoroalkyl groups onto the phenyl rings of polystyrene with high yields by homogeneous reactions [9]. Consequently, the chemistry of FAP plays an increasingly important role in the synthesis of organo¯uorine functional materials. * Corresponding author. E-mail address: [email protected] (Z.-b. Zhou)
In this work, we carefully designed the reaction systems, characterized the products, and proposed a mechanism of the reactions of linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) with FAP. The contact angles of water and paraf®n oil (n-dodecane), and the refractive indices of the resulting ¯uoroalkylated polymer ®lms on glass slides or quartz plates were determined. 2. Results and discussion 2.1. Homogeneous reactions of linear triblock copolymer SBS with FAP at 208C In the reactions of the representative FAP (RFH(CF2)4, n-C3F7, and n-C7F15) with linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) (20% styrene in weight), the molar ratio of FAP/B (butadiene unit in SBS) was ®xed at 0.05, 0.10, 0.15, 0.20, 0.30 and 0.4, respectively. The reactions was usually complete in 2 h at room temperature (208C) under mild conditions and no precipitate was observed in the ®nal mixture. 2.2. Product characterization The IR, and 19F NMR characterization of the products were summarized in Table 1. As shown in Table 1, strong absorption peaks at 1800 cmÿ1, which are presumably characteristic absorptions of carbonyl groups, occurred in
0022-1139/00/$ ± see front matter # 2000 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 2 - 1 1 3 9 ( 0 0 ) 0 0 2 5 3 - 0
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Table 1 Reactions of SBS with (RFCO2)2 (FAP) in CH2Cl2 at 208C RF
H(CF2)4
n-C3F7
n-C7F15
(RFCO2)2/Butadienea
RF-ratiob (%)
RF group yieldsc (%)
IR (cmÿ1)
19
0.05:1 0.1:1 0.2:1 0.3:1 0.4:1 0.05:1 0.1:1 0.2:1 0.3:1 0.4:1 0.05:1 0.1:1 0.2:1 0.3:1 0.4:1
3 7 16 22 30 3 6 13 20 28 3 7 13 20 25
60 70 80 72 75 60 60 65 68 70 60 70 65 68 63
1775 (C=O) 1265, 1 260 (CF2) 1165 (C±O±C)
ÿ65.5 (a, 4F, JHF52.6 Hz) ÿ58.0 (b, 4F) ÿ51 to ±54 (c, m, 4F) ÿ46.5 (d, 2F) ÿ41.0 (e, 2F) ÿ3.0 (a, 6F) ÿ47 to ÿ50 (b, m, 4F) ÿ41.7 (c, 2F) ÿ35.5 (d, 2F)
1778 (C=O) 1352 (CF3) 1260, 1230 (CF2) 1150 (C±O±C) 1778 (C=O) 1350 (CF3) 1240, 1210 (CF2) 1150 (C±O±C)
F NMRd (ppm)
ÿ3.5 (a, 6F) ÿ48.6 (b, 4F) ÿ44.5 (c, 16F) ÿ41.0 (d, 2F) ÿ35.5 (e, 2F)
a
Molar ratio. Fluoroalkylation ratio of C=C bonds in SBS chain. c Based on (RFCO2)2. d RFH(CF2)4: HCF2aCF2bCF2cCF2d, HCF2aCF2bCF2cCF2eCO2; RFn-C3F7: CF3aCF2bCF2c, CF3aCF2bCF2dCO2; RFn-C7F15: CF3aCF2b(CF2)4cCF2d, a CF3 CF2b(CF2)4cCF2eCO2. b
the IR spectra of all the products. The characteristic absorption bands for uCF3 at 1350 cmÿ1, and 1260 cmÿ1 for uCF2 , indicate the success in introducing RF groups into the SBS polymer. The 19F NMR spectra of the isolated products clearly show that two kinds of RF groups were introduced into the structure of SBS. For example, in the 19F NMR spectra of the isolated products (RFn-C3F7), absorption peaks showed at ÿ3.0 (2CF3), ÿ35.5 (CF2), 41.7 (CF2), and ÿ47 to ÿ50 ppm (2 CF2), respectively. Compared with the previous results of FAP reacted with polystyrene (PS) [9], the absorption peaks of RF (RFn-C3F7) groups which were introduced onto the phenyl rings in PS revealed at ÿ8.0 (CF3), ÿ39.5 (CF2), and ÿ54.0 ppm (CF2), no detectable absorption peaks of RF groups introduced onto the phenyl rings of the linear triblock copolymer SBS polymer in the side chains were observed from 19F NMR spectra of any of the products. Moreover, no detectable RFCO2H was detected by acid-base titration method in the reaction systems. All these results show that RF- and RFCO2-groups were only added onto the ole®nic bonds of the SBS polymer chains, and the ¯uoroalkylated products of SBS polymers can be expressed as RF-SBS-OCORF. The ¯uoroalkylation ratios (RF-ratio) of C=C bonds in SBS chains and the yields of RF-SBS-OCORF based on FAP added were calculated from 19F NMR integrations (mtri¯uoromethylaniline used as internal standard for quantitative analysis) described in the literature [9], and summarized in Table 1. The yields of RF-ratio are in the range of 3± 30%. The yields of the products based on FAP added for all the runs are fairly high (60±80%). All the matter given above shows that FAP are effective, regioselective, and convenient per(poly)¯uoroalkylating agents for ole®niccontaining polymers.
2.3. Mechanism The unimolecular decomposition of (RFCO2)2 (FAP) has been studied in detail in a previous study [2]. At 208C, the half-life time of (RFCO2)2 employed in this work are: 5.83 h (RFH(CF2)4), 8.78 h (RFn-C3F7), and 6.4 h (RFnC7F15), respectively. In the presence of SBS, the disappearance of FAP was signi®cantly accelerated, and FAP was usually completely consumed within 2 h. The ole®nic and phenyl groups in the polymer chain of SBS are suf®ciently reactive for transferring an electron to the highly effective one-electron oxidant FAP but it was shown from IR and 19F NMR spectra of the products that RF- and RFCO2-groups were only added onto the C=C bonds of the linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) chain. Moreover, no detectable RFCO2H was discovered in the ®nal reaction mixture by acid±base titration which is a strong indicator that no single electron transfer (SET) reaction takes place between FAP and phenyl rings in the polymer [9,11]. All results given above are strong indications of a SET reaction taking place between FAP and the ole®nic groups in the linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) chain as illustrated in Scheme 1. 2.4. Water and oil-repellency of RF-SBS-OCORF The contact angles of water (ywater) and n-dodecane (yoil) on the surface of the ®lms of RF-SBS-OCORF polymers cast on glass slides were used to determine water- and oilrepellent properties, and chemical resistance of the prepared polymers. The plots of contact angles vis yields of RF-ratio (the ¯uoroalkylation ratio of C=C bonds in SBS chains) are
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Scheme 1.
Fig. 2. The contact angles (ywater) of RF-SBS-OCORF (RFn-C3F7).
Fig. 1. The contact angles (ywater) of RF-SBS-OCORF (RFH(CF2)4).
shown in Figs. 1±4. From Table 2 and Figs. 1±4, the following trends are observed: For all the prepared RF-SBS-OCORF polymers, both the contact angles ywater and yoil increase with RF-ratio increase.
Especially, the contact angles (ywater) of RF-SBS-OCORF (RFn-C7F15) almost reached that of poly(tetra¯uoroethylene) (PTFE) (ywater1408). Moreover, at the RF-ratio of 6%, ywater reaches 1008 and over, this trend provides de®nitive evidence of the change of the surface composition by the surface distribution of RF groups [10]. At the same RF-ratio, the contact angles (ywater) of RFSBS-OCORF polymers containing longer RF groups such as n-C7F15 are higher than those bearing shorter RF groups (RFH(CF2)4, n-C3F7) with the order H(CF2)4
Fig. 3. The contact angles (ywater) of RF-SBS-OCORF (RFn-C7F15).
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Z.-b. Zhou et al. / Journal of Fluorine Chemistry 104 (2000) 285±290 Table 3 Refractive indices (nD) of RF-SBS-OCORF polymers RF
H(CF2)4
n-C3F-7
n-C7F15 SBS Fig. 4. The contact angles (yoil) of RF-SBS-OCORF.
improved from detected ywater. However, RF-SBS-OCORF polymers are less resistant than the corresponding RF-PS polymers [9], most likely, because the ester linkage RFCO2in the RF-SBS-OCORF side chain may be reactive under the acid or alkaline conditions. Furthermore, the large number of unreacted C=C bonds in RF-SBS-OCORF chains may also be reactive. 2.5. Optical properties of RF-SBS-OCORF Poly(tetra¯uoroethylene) (PTFE) is the most important commercially ¯uoropolymer with very low refractive index, but it is dif®cult to process by conventional compression, injection moulding or by extrusion. Accordingly, seeking for novel polymers with much lowered refractive indices,
a
RF-ratioa (%)
nD
3 7 16 22 30 3 6 13 20 28 3 7 13 20 0
1.5250 1.5109 1.5025 1.5111 1.4738 1.5357 1.5192 1.5056 1.5174 1.4805 1.5177 1.5048 1.4699 1.4434 1.5710
Fluoroalkylation ratio of C=C bonds in SBS chain.
which can be processed by conventional methods, is a major challenge in functional material ®eld. As shown in Table 3, all the RF-SBS-OCORF polymers have distinctly lowered refractive indices (nD) compared with the parent polymer SBS (nD1.5710). The plots of nD vis RF-ratio are shown in Fig. 5. From Fig. 5, an interestingly optical property, which was discovered in our previous study [9], was also observed for the RF-SBS-OCORF polymers. The refractive indices (nD) are not always decreased with RF-ratio increase. In the RFratio range of 0±22%, there exist a minimum and a maximum nD for RF-SBS-OCORF (RFH(CF2)4, n-C3F7). But the nD decrease signi®cantly with the increase of RF-ratio for RF-SBS-OCORF (RFn-C7F15). It is dif®cult for us to explain the relationships between such strange changes of
Table 2 Contact angles of SBS and RF-SBS-OCORF polymers RF
H(CF2)2
n-C3F7
n-C7F15 SBS a
RF-ratioa (%)
yoil (n-dodecane, 58C)
3 7 16 22 30 3 6 13 20 28 3 7 13 20 25 0
27 31 35 42 42 23 26 28 30 30 28 35 42 46 50 22
Fluoroalkylation ratio of C=C bonds in SBS chain.
ywater (208C) Before treatment
5% H2SO4
5% NaOH
98 103 105 107 110 95 101 107 114 114 111 113 117 131 131 93
95 98 101 103 103 91 97 103 109 110 98 103 108 117 122 83
90 92 94 97 100 87 88 93 97 100 95 99 101 107 110 80
Z.-b. Zhou et al. / Journal of Fluorine Chemistry 104 (2000) 285±290
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meter (Chengde). The refractive indices were determined with a TP-77 elliposmeter (Beijing). 3.3. Reactions of FAP with linear triblock copolymer SBS
Fig. 5. Refractive indices (nD) of RF-SBS-OCORF.
nD with the chain length of RF for synthetic RF-SBS-OCORF at present. Nevertheless, the RF-SBS-OCORF polymers with much lowered refractive indices, which may be useful as surface coating of plastic ®ber were successfully prepared in our study. 3. Experiment 3.1. Materials Linear triblock copolymer SBS (polystyrene±polybutadiene±polystyrene) (20% styrene in weight) supplied by Yueyang General Petrochemical Works (Hunan Province, China), was dissolved in CH2Cl2, precipitated with methanol and dried at 408C under vacuum for 24 h before use. Commercial Freon 113 (CCl2F±CClF2) was carefully washed in turn with concentrated H2SO4, 5% NaHCO3, and water, and dried over anhydrous MgSO4 and distilled, bp 47.5±488C. FAP were prepared from the corresponding acyl chloride (RFCOCl) and hydrogen peroxide (30%) in the presence of aqueous sodium hydroxide (10%) according to our previously reported method [2], the concentrations of FAP were determined by standard iodometry. All other solvents were dried, and redistilled before use. 3.2. Instruments IR spectra were obtained with Shimadazu IR-435 and IR408 spectrometers. Fluoroalkylated polymer samples were prepared in dichloromethane and cast onto NaCl plates for recording IR spectra. 19F NMR were recorded on a Bruker FT-AC 80 NMR spectrometer. Tri¯uoroacetic acid was used as an external standard; m-tri¯uoromethylaniline was used as internal standard in the quantitative analysis of products. Fluoroalkylated polymer samples were weighed and dissolved in CDCl3 for quantitative analysis by 19F NMR. The contact angles were measured with a JY-82 contact angle
In an typical reaction at room temperature (208C), SBS (2.0 g, 30 mmol of butadiene units) was dissolved in dichloromethane (50 ml) with gently magnetic stirring in a reactor with a ¯at bottom. After ¯ushing with nitrogen, FAP (2 mmol) dissolved in Freon 113 (usually at a concentration of 0.2 M) was dropped into the SBS solution over 30 min. The reaction was continued for an additional 2 h. A few milliliter of the reaction mixture were removed for determination of the yield of RFCO2H by acid±base titration. The reaction mixture was washed in turn with 5% NaHCO3, distilled water, and dried over anhydrous NaSO4. The mixture was concentrated to a volume of 10 ml, then added to 100 ml of methanol. The crude polymeric precipitate was ®ltrated, redissolved in dichloromethane, reprecipitated with methanol, and dried at 458C under vacuum for 24 h. Parent polymer SBS and ¯uoroalkylated SBS from solutions in CH2Cl2 were cast uniformly on glass slides (7.5 cm2.5 cm) or thin quartz plates (5 mm3 mm) to form thin ®lms by solvent evaporation, and dried under vacuum. The polymeric ®lms were used for the measurement of contact angles and refractive indices. 3.4. Measurement of contact angle About 0.05 ml water or n-dodecane from a syringe was dropped carefully onto the surface of the ®lms coated on the glass slides (7.5 cm2.5 cm). The contact angles of water (ywater) or n-dodecane (yoil) on the surface of the polymeric ®lms were read out directly by the contact angle meter. 3.5. Tests of chemical resistance The polymeric ®lms coated on the glass slides (7.5 cm2.5 cm) were immersed in a sealed glass vial containing 5% H2SO4, or 5% NaOH solutions at room temperature for 7 days. After carefully washing with distilled water, and drying under vacuum, contact angles were measured. 3.6. Determination of refractive indices The re¯ecting angles of the polymeric ®lms coated on thin quartz plates (5 mm3 mm) were measured by an Ê , inciellipsometer equipped with He-Ne laser(l6234 A dent angle708). Refractive indices were calculated from the detected re¯ecting angles by data processing software in a computer system described in the literature [9].
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