Alternative Fluoropolymers to Avoid the

according to the Centers for Disease Control and Prevention. (DCP), ∼95% of .... By measuring the contact angles of the polymers against two differe...
10 downloads 4 Views 209KB Size
Download PDF
502

Ind. Eng. Chem. Res. 2008, 47, 502-508

Alternative Fluoropolymers to Avoid the Challenges Associated with Perfluorooctanoic Acid Ji Guo,†,‡ Paul Resnick,*,§ Kirill Efimenko,| Jan Genzer,| and Joseph M. DeSimone*,†,‡,| Department of Chemistry and the Institute for AdVanced Materials, Nanoscience and Technology, UniVersity of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599; NSF Science and Technology Center for EnVironmentally Responsible SolVents and Processes, UniVersity of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599; Fluoroscience LLC, 104 RiVerside CT, Cary, North Carolina 27518; and Department of Chemical and Biomolecular Engineering, North Carolina State UniVersity, Raleigh, North Carolina 27695

The degradation of stain-resistant coating materials leads to the release of biopersistent perfluorooctanoic acid (PFOA) to the environment. In order to find the environmentally friendly substitutes, we have designed and synthesized a series of nonbiopersistant fluorinated polymers containing perfluorobutyl groups in the side chains. The surface properties of the new coating materials were characterized by static and dynamic contact angle measurements. The new coating materials demonstrate promising hydrophobic and oleophobic properties with low surfaces tensions. The wetting properties and surface structure of the polymers were tuned by varying the “spacer” structures between the polymer backbones and the perfluorinated groups of the side chains. The relationship between orientations of the fluorinated side chains and performances of polymer surfaces were further investigated by near-edge X-ray fine absorption structure (NEXAFS) experiments and differential scanning calorimetry (DSC). I. Introduction The widespread occurrence, biopersistance, and unexpected toxicity of long-chain perfluorinated acids, notably perfluorooctanoic acids (PFOA), have raised worldwide environmental concerns. The U.S. EPA found that PFOA is very persistent and has a long half-life in the environment.1,2 Moreover, according to the Centers for Disease Control and Prevention (DCP), ∼95% of the population in the United States has the PFOA in their blood, albeit at very low levels. Toxicity and exposure studies indicate that PFOA can cause developmental issues and other adverse effects in laboratory animals and is a “likely” carcinogen. It is envisioned that long-chain perfluorocarboxylic acids, such as PFOA and materials that may degrade to them in the environment, will be severely restricted by the EPA and comparable agencies worldwide in the near future. Thus, it is imperative that alternative materials be found in order to replace these conventional fluorinated repellents. There are two major sources of PFOA in the environment. Perfluorinated acids are directly used as the surfactants in the manufacture of polytetrafluoroethylene (PTFE). However, most of the PFOA found in the environment is believed to arise from the gradual degradation of products derived from fluorinated telomers, short-chain fluorinated alcohols used as stain- and grease-resistant coatings on carpets, textiles, and paper.2-5 Fluorinated repellents are acrylates or methacrylates that contain long perfluoroalkyl groups (>8 fluorocarbons) as a portion of the pendant side chains. The fluorinated components form a protective layer on fabrics but are slowly and partially degraded to PFOA by oxidization in the environment. Potential substitute coating materials for the fluorinated repellent include silicones and perfluoropolyethers. Though * To whom correspondence should be addressed. E-mail: presnick@ earthlink.net, [email protected]. † University of North Carolina at Chapel Hill. ‡ NSF Science and Technology Center for Environmentally Responsible Solvents and Processes. § Flouroscience LLC. | North Carolina State University.

polysiloxanes have a cost advantage over fluorinated polymers, they are not ideal as substitute repellents for the fluorine-based materials. Polysiloxanes do not provide the oil repellency and stain resistance associated with fluorinated repellents.6-14 PFPEbased polymers have limited solubility in water and common organic solvents that prevent the wide applicability of these materials in the textile industry. Moreover, the cost of these materials is comparably high. At the 14th European Symposium on Fluorine Chemistry, the 3M Company reported a systematic study of the biopersistance of perfluorinated chemicals.15 It was found that perfluorinated carboxylic and sulfonic acids containing chains of four or less perfluorinated carbon atoms do not bioaccumulate in the human body and are not biopersistent. In order to find environmentally friendly and nontoxic alternative fluoropolymers to avoid the challenges associated with PFOA, a series of fluorinated comblike polymers containing the shorter and nonbiopersistant perfluorobutyl group as the fluorinated component of the side chains, called as C4 polymers, have been prepared starting from perfluorobutyl iodide.16-23 The new compounds are analogous to conventional textile-treating materials and are processed and characterized by similar methods. The properties of the C4 polymers are tuned by changing the “spacers” between the polymer backbones and the perfluorinated groups of the side chains. The spacer may include flexible methylene groups and stiff phenyl groups. Various characterization techniques were applied to investigate the thermal properties and surface performance of the new C4 materials, especially the wetting properties and the special side chain organization on the uppermost surfaces. II. Experimental Section II.1. Polymer Preparation. All the monomers (see Supporting Information) were purified and any inhibitors were removed by passing through an alumina column. The initiator 2,2′-azobis(isobutyronitrile) (AIBN, Kodak, 99%) was recrystallized twice from methanol (Aldrich). All purification solvents were pur-

10.1021/ie0703179 CCC: $40.75 © 2008 American Chemical Society Published on Web 08/18/2007

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008 503 Chart 1. Chemical Structures and Labels of Fluorinated Alkyl Methacrylate Polymers and Styrene Derivative Polymers

Table 1. Contact Angle (θ), Critical Surface Tension (γc), and Free Surface Energy (γs) of the Fluorinated Polymers θ

surface energy (mN/m)

pol ym ers H2O n-C16H34 CH2I2 γc (mN/m) PH2F4 PH4F4 PH6F4 PH4F6 PH2F8 PSI-F4 PSII-F4

111 109 108 114 118 109 109

69 67 66 75 80 60 60

96 95 94 98 100 70 75

13.2 14.2 15.1 11.7 9.8 18.1 18.3

γs

γsd

γsp

11.1 11.8 12.2 9.8 8.8 17.6 17.3

9.1 9.4 10.0 8.6 8.1 17.5 17.3

2.0 2.4 2.2 1.2 0.7 0.1 0

to the value of cos(θ) ) 1 in order to obtain the critical surface tension (γc). The free surface energies (γs) of the polymers were measured using water and hexadecane as the testing liquids. By measuring the contact angles of the polymers against two different liquids, γs can be calculated through the following equation. chased from Aldrich and used as received. Monomers containing AIBN (0.5-1 wt %) were purged with argon for ∼15 min prior to transfer to a 25 mL high-pressure view cell. The contents of the high-pressure cell were purged with argon for an additional 15 min. The reaction cell was heated to 60 °C while CO2 was added via an Isco syringe pump over a period of ∼15 min to a pressure of 345 bar. The polymerization proceeded for 24 h at 60 °C and 345 bar. The polymers and any unreacted monomer were removed from the reaction cell by solution in trifluorotoluene. The polymers were precipitated by addition of a large excess of methanol, isolated by suction filtration, washed several times with methanol, and dried in a vacuum oven overnight under reduced pressure. The polymer structures are listed and labeled in Chart 1. For convenience, all the polymers with perfluorobutyl groups in the side chain are named C4 polymers. The C4 polymers are both C4 methacrylates and C4 styrenes. Polymers PH4F6 and PH2F8 were synthesized and characterized similarly. II.2. Thermal Analysis. The thermal stability of polymers was measured using a Perkin-Elmer Pyris 1 thermogravimetric analyzer (TGA). The fluorinated polymethacrylate samples were heated from room temperature to 500 °C with a heating rate of 10 °C/min under a nitrogen atmosphere. The temperature for onset of rapid weight loss (5 wt %) was defined as the decomposition temperature. The thermal physical behavior of polymers was recorded using a Seiko-Haake differential scanning calorimeter (DSC) 220. Samples (∼5 mg) were placed in aluminum pans that were crimped shut. Thermograms of polymers were collected from a second heat under a nitrogen atmosphere with a heating rate of 10 °C/min from -100 to 200 °C. The thermograms of the fluorinated alcohols were collected from the first heating cycle with a heating rate of 5 °C/min from -150 to 150 °C. II.3. Wetting Properties. Static contact angles were measured using a KSV Instrument LTD CAM 200 Optical Contact Angle Meter. A screw-top Fisher syringe was used to deposit a liquid drop onto silicon wafers coated with the polymers. Water, diiodomethane, hexadecane, and n-alcohols (n ) 4, 6, 8, 10, 12) were used as testing liquids (see surface tensions in the Supporting Information).24 Each sample was measured in triplicate and averaged. Two methods were used to calculate the surface tensions from the static contact angles: Zisman analysis (critical surface tension) and the Owen-WendtFowkes method (free surface energy). From the contact angles (θ) of a homologous series of alcohols on low-energy surfaces, a typical Zisman plot of cos(θ) versus the surface tensions of the liquids was obtained. The linear plot was then extrapolated

(

) (

)

(γsdγld)0.5 (γspγlp)0.5 1 + cos(θ) ) 2 +2 γl γl

(1)

where θ is the static contact angle; γl is the surface tension of a liquid; and γld and γlp are the dispersion component and the polar component of the liquid surface tension, respectively. The free surface energy is the sum of the dispersion contribution (γsd) and the polar component contribution (γsp). Dynamic tensiometry measurements were performed using a NIMA Technologies DST 9005 dynamic surface tensiometer, based on the Wilhelmy Plate method.25,26 Glass cover-slips were dip-coated with polymer. The stage speeds for the immersion and receding measurements were 50 µm/s. Each experiment included multiple immersions and receding measurements to ensure consistent and reproducible data. II.4. Surface Structure Analysis. The surface roughness was measured by a Veeco Metrology group multimode atomic force microscope (AFM) equipped with a Nanoscope IIIA control station and silicon cantilevers (Mikromasch). The resonance frequencies were ∼160 kHz, with spring constants of 5.0 N/m. Radii < 10 nm were used for visualization of the prepared films in the tapping mode. Near-edge X-ray absorption fine structure experiments (NEXAFS) was ued to identify different chemical bonds (including their relative densities) and their molecular orientation on the polymer surfaces.27 The NEXAFS experiments were carried out using the U7A NIST/Dow materials characterization end-station at the National Synchrotron Light Source at Brookhaven National Laboratory.28 The detailed description of the experiments may be found elsewhere.27-30 III. Results and Discussions III.1. Thermal Properties. The thermal stability of the polymers was investigated by TGA. All C4 polymers exhibit a similar onset of decomposition, 5% weight loss, at ∼260 °C, indicating that possible cleavage of hydrocarbon units occurred before any degradation of the fluorine side chain.31 The maximum decomposition temperatures of C4 styrene polymers, PSI-F4 and PSII-F4, were higher than those of the C4 methacrylates, due to the presence of the stiff phenyl groups. The glass transitions (Tg) of the C4 polymers were above the room temperature, as measured by DSC spectra. No melting transitions were observed for C4 materials, indicating lack of side-chain crystallization. III.2. Surface Properties. The static contact angles of C4 materials in water and hexadecane are summarized in Table 1.

504

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008

Figure 1. Dynamic contact angles of the methacrylate polymers PH2F4, PH4F4, PH6F4, PH4F6, and PH2F8 (A) in water and (B) in hexadecane.

Hexadecane was chosen to obtain the oleophobic index. Both water and hexadecane static contact angles of the C4 methacrylate decreased with increasing methylene spacer length. Polymers PH2F8 and PH4F6 with longer perfluorinated groups had higher contact angles than the C4 materials.31,32 The contact angles of the C4 styrene polymers with water and hexadecane were similar to those collected on C4 methacrylates. The critical surface tensions (γc) of C4 methacrylates increased from 13 to 15 mN/m with the increasing length of the methylene spacer, which is consistent with the contact angle results. These values were considerably lower than the surface tensions of silicone-based repellents (∼22 mN/m) and PTFE (18 mN/m).33 In contrast, γc increased with the decreasing fluorine content of the side chain, as shown by the critical surface tensions of the polymers with an equal number of carbon atoms in their side chains (PH6F4, PH2F8, and PH4F6). Substitution of two CF2 groups by two CH2 groups increased γc by 5.3 mN/m. The C4 styrene polymers with phenyl spacers exhibited higher values of γc, 18 mN/m, due to the lower fluorine content of the side chains. The results of the critical surface tension agreed with the observations of static contact angles for C4 polymers. Although C4 polymers display apparently higher critical surface tensions than conventional C8 polymer, they are still considered to be hydrophobic and oleophobic, since their critical surface tensions are well-below those of water (72.8 mN/m) and hydrocarbon oil (20-30 mN/m). The surface energies for C4 polymers were found to be slightly lower than the critical surface tensions, but the two surface tension values are in reasonable agreement. The difference may result from the curvature of Zisman plots for critical surface tension measurements due to the incompatibility between the highly fluorinated surfaces and the hydrocarbon alcohols. The polar surface energy component was ∼16-19% of the total free surface energy and made an important contribution to the surface behavior of the C4 methacrylates. This polar component contribution suggested hydrogen bonding interactions on the uppermost surface. It is interesting to note that there was little or no polar component contribution to the free surface energies of the C4 styrenes. It is possible that the absence of carboxyl groups in the C4 styrenes results in the lack of oxygen moieties that form hydrogen bonds upon contact with polar liquids. The surface properties of comblike polymers were found to be strongly dependent on the composition and segregation of side chains on the topmost surface region.34 The constituent surface tension of the -CF3 group is extremely low (6 mN/m).

Hence, a surface covered with the closely packed -CF3 groups exhibits the lowest critical surface tension.35-38 Fluorinated polymers with long perfluorinated alkyl side chains, such as polymer PH2F8, can undergo side-chain crystallization as a result of the inter-side-chain interactions of the perfluoro groups. The side chains of these polymers are forced to pack tightly on the topmost surface, providing a dense layer of -CF3 groups that repel liquid. Therefore, they exhibit excellent repellency to water and oil.31,32,37,39 C4 materials lack side-chain crystallization, and the perfluorinated alkyl groups are distributed in a disordered fashion on the surface with a loose packing of the -CF3 end groups, hence resulting in higher critical surface tensions. Furthermore, the introduction of longer hydrocarbon spacers increases the free space between the side chains, thus increasing the possibility of wetting and penetration of liquids. III.3. Contact Angle Hysteresis. Contact angle hysteresis represents the difference between the advancing and receding contact angles, providing information about the chemical and physical homogeneity of the surface.24,40 The parameters, which affect contact angle hysteresis, include surface roughness, chemical heterogeneity, chain reorientation, and mobility.24 AFM observations of the tested film surfaces revealed a roughness of 0.5 nm (rms) that was considered to have no effect on the contact angle measurements. In addition, no change in morphology was observed before and after the dynamic contact angle measurements. Hence, the major contribution to the contact angle hysteresis is thought to arise from the reorientation and mobility of the side chains residing on the topmost polymer surface. As shown in Figure 1, the contact angle hysteresis of C4 methacrylates increased both in water and hexadecane when the number of methylene groups in the side chain was varied from 2 to 6. Chibowski24 and Lam et al.40 concluded that the thin liquid film remaining after the receding liquid line was responsible for the observed contact angle hysteresis. The high mobility of the longer spacers enables easier side-chain reorientation, thus increasing exposure of the hydrocarbon spacers and their interaction with the liquid. The contact angle hysteresis decreased by 15 degrees when the side chains contained eight perfluorocarbon groups (cf. Figure 1B). This is attributed to the existence of side-chain crystallization in PH2F8,37 prohibiting the movement of the perfluoro groups resulting in an extremely low hysteresis both in water and hexadecane. Figure 2 shows the effect of a stiff spacer, the phenyl group, on the contact angle hysteresis. C4 styrene demonstrated much higher water receding contact angles than the C4 methacrylates,

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008 505

Figure 2. Dynamic contact angles of C4 styrene polymers PSI-F4 and PSII-F4 (A) in water and (B) in hexadecane.

leading to a significantly lower hysteresis of 20 degrees. This value is even lower than the hysteresis of the C8 polymer PH2F8 (cf. Figure 1A), indicating that the introduction of the bulky phenyl spacer might confine the mobility and reorientation of the side chains. Additionally, the zero polar component contribution to the free surface energy in Table 1 suggests that no hydrogen bonding exists between the polymer surface and the water because of the absence of the carboxyl function. Hence, the interactions between the polymer surface and the polar solvent, water, are significantly weaker for the C4 styrene in comparison with the C4 methacrylate. III.4. Surface Segregation. The surface segregation of polymer thin films was investigated using near-edge X-ray absorption fine structure (NEXAFS) experiments. The NEXAFS spectra enable the identification of the chemical bonds (including their relative population density) and the molecular orientation on the samples.28,41 Figure 3A displays the partial electron yield (PEY) spectrum at the fluorine K-edge of polymer PH2F4. The difference between the preedge and postedge signals in the PEY spectrum (so-called edge-jump), set arbitrarily at 680 and 730 eV, respectively, provides information about the concentration of fluorine per unit area of the incident beam on the sample.42 Figure 3B summarizes the PEY NEXAFS spectra collected at θ ) 50° of all the fluorinated polymers, where θ is the angle between the surface normal and the electric vector of the polarized X-ray beam. We note that, at this geometry, NEXAFS is insensitive to any molecular orientation present in the sample; the PEY NEXAFS spectra can, thus, be used to identify the concentration of fluorine in the sample. The rather high values of the edge-jump indicate that all polymer surfaces are rich in fluorine. The concentration of fluorine on the surface increases with increasing the number of fluoroalkyl units and decreases with increasing the number of methylene units in the spacer. Note that polymer PSII-F4 displays a slightly lower fluorine density on the surface than other C4 polymers. Figure 4A shows PEY signals of the carbon K-edge NEXAFS from polymer PH2F4, collected at three different orientations (θ ) 20°, 50°, 90°) of the polymer sample with respect to the X-ray beam. In this setup, the PEY NEXAFS signals provide important information about the orientation of the pendant side chains on the surface. The overlapped intensities from three angles show the element population density of C, F, and O in different orientations. The three characteristic peaks correspond to the 1s f σ* transitions of the C-H bond (E ) 288.7 eV), C-F bond (E ) 292.8 eV), and C-C bond (E ) 295.7 eV). The signal at E ) 285.2 eV corresponds to the 1s f π*

Figure 3. (A) Fluorine K-edge PEY NEXAFS spectra from sample PH2F6 collected at θ ) 50°; and (B) overlap of fluorine K-edge PEY NEXAFS spectra for the polymers PH4F4, PH4F4, PH6F4, PH4F6, PH2F8, PSI-F4, and PSII-F4, collected at θ ) 50°. θ is the angle between the surface normal and the electric vector of the polarized X-ray beam.

transitions of the CdO bond of the methacrylate or CdC bond of the phenyl rings in the case of the styrene polymers. The difference PEY NEXAFS spectra were obtained by subtracting the PEY NEXAFS signal measured at θ ) 20° from that measured at θ ) 90°. The angular dependence of the intensities / / and 1s f σC-C were used as for transitions of 1s f σC-F evidence of the side-chain orientation. The difference PEY NEXAFS spectra of the fluorinated polymers are summarized in Figure 4B. For the ordered surface in the semicrystalline polymer PH2F8,28-30 the increase in θ corresponds to an increase and decrease in the intensity of the C-F and C-C bond transitions, respectively. Hexagonal packing of the long fluorinated side chains was confirmed by X-ray photoelectron spectroscopy (XPS) and DSC.32,39 This is the result of the inter-side-chain interactions of the fluoroalkyl groups. Polymer PH4F6 also displayed a certain ordered structure of the side chains even without side-chain crystalliza/ tion. However, the intensities for the 1s f σC-F transitions and

506

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008

Figure 5. DSC thermographs of different semifluorinated alcohols C4F9(CH2)2OH, C4F9(CH2)4OH, C4F9(CH2)6OH, C6F13(CH2)4OH, and C8F17(CH2)2OH.

Figure 4. (A) Normalized PEY signals and differential PEY signals of the carbon K-edge NEXAFS for sample PH2F4; and (B) the difference PEY NEXAFS spectra from the polymer samples PH4F4, PH4F4, PH6F4, PH4F6, PH2F8, PSI-F4, and PSII-F4, by subtracting the signals at θ ) 20° from that at θ ) 90°. θ is the angle between the surface normal and the electric vector of the polarized X-ray beam. / the 1s f σC-C transitions for C4 polymers were independent of the detection angles, suggesting there was no orientation of the perfluoro groups on the topmost surfaces. This is in agreement with the observations of Genzer et al., who reported that at least six perfluoroalkyl groups are needed to initiate the ordered segregation of semifluorinated side chains.27 The perfluoroalkyl groups adapt a helical structure due to electrostatic repulsion of fluorine atoms in the relative 1,3-positions of the crystalline state.43,44 This helical structure of perfluroalkyl groups determines the length of side chains needed to initiate ordered packing. The intensity corresponding to the CdC bond for C4 styrene varied with the different detection angles, indicating that the phenyl ring might adopt an orientation roughly parallel to the substrate surfaces. This special surface construction might result in the low mobility of the side chains, resulting in the observed low hysteresis in water. The side-chain segregation of these semifluorinated polymers was further studied by the thermal physical behavior of analogous fluorinated alcohols. A semifluorinated alkyl chain could be regarded as a miniblock oligomer (mesogen), because the pefluorocarbon segment (CF2) is strongly immiscible with its hydrocarbon analog. In Figure 4B, it is obvious that surface properties of polymers strongly depend on the length of the “hard” segment, i.e., the fluoroalkane groups. In addition, the content of the “soft” segment, the methylene spacer, might affect the segregation of the side chains by varying the enthalpy by disordering the highly orientated liquid crystal structure of these semifluorinated compounds.45,46 The DSC spectra of the fluorinated alcohols, presented in Figure 5, show the four-phase transitions of typical liquid crystals: crystal, smectic B (SB), smectic A (SA), and isotropic (I). The smetic B mesophase is a highly ordered liquid-liquid transition.47-49 The existence of either the SA, SB, or I phases is a function of the content of the

fluoroalkyl groups and the methylene groups.46,50 The melting peak is associated with SB-to-SA or crystal-to-SA phase transitions. The thermographs of C4F9(CH2)2OH were not complete because of its rapid volatization at higher temperature. Upon heating, the melting temperature of the semifluorinated alcohols increased with either increasing number of methylene groups in the spacer or the length of the perfluoroalkyl chain. The melting temperatures of the alcohols were all below zero, except for C8F17(CH2)2OH, which melted at 45 °C. Hence, only the ordered SB phase of C8F17(CH2)2OH was thermally stable above room temperature. The perfluoro groups of the polymers exhibit similar high mobility in the SA phase, while forming ordered structures in the SB phase with a close packing of the -CF3 groups due to crystallization. This special side-chain packing provides high resistance to water and oil, as well as the low contact angle hysteresis. The thermal stability of the SB phase for fluorinated alcohols represents a critical factor in the formation of the side-chain construction that results in properties such as crystallization. Ober and co-workers have studied the unique mesophase, SB, in fluorinated block polymers and attributed the high stability of this phase to the high enthalpy needed to destroy the ordered structure.45,51 IV. Conclusions Short-chain perfluorinated carboxylic acids containing a chain of four or less perfluorinated carbon atoms do not bioaccumulate in the enviroment. In order to find environmentally benign and nontoxic alternative fluoropolymers to avoid the challenges associated with PFOA, new fluorinated polymers (C4 polymers) containing perfluorobutyl side chains have been successfully prepared starting from perfluorobutyl iodide. The properties of the polymers were tuned by varying the length of the hydrocarbon spacer of the side chains located between the polymer backbones and the perfluorinated side-chain tails. In addition, the relationship between the surface properties and the lengths of both the spacer and the perfluoro groups of the polymers was investigated. C4 polymers are hydrophobic and oleophobic with surface energies ranging from 10 to 18 mN/m. The surface energy and the contact angle hysteresis of the polymers increase with increasing methylene spacer length, while decreasing when the perfluoro group is lengthened. The introduction of phenyl

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008 507

spacers improves dynamic performance of the polymers in polar solvents. The different surface behavior is attributed to the segregation of the side chains that vary with the spacer and length of the perfluoroalkyl and hydrocarbon segments. The further investigation of semifluorinated alcohols indicated that the thermal stability of the smectic B phase is the critical factor in the formation of side-chain crystallization. Acknowledgment This work is supported by the NSF Science and Technology Center for Environmentally Responsible Solvents and Process (No. CHE-9876674). The NEXAFS experiments were carried out at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences. The authors thank Dr. Daniel A. Fischer (NIST) for his assistance with the NEXAFS experiments. Supporting Information Available: The Supporting Information includes additional information about synthesis of fluorinated monomers, methacrylates, and alcohols. This material is available free of charge via the Internet at http:// pubs.acs.org. Literature Cited (1) Renner, R. Growing Concern Over Perfluorinated Chemicals. EnViron. Sci. Technol. 2001, 35 (7), 154A. (2) Renner, R. Scientist hail PFOA reduction plan. EnViron. Sci. Technol. 2006, 40 (7), 2083. (3) Ellis, D. A.; Martin, J. W.; Silva, A. O. d.; Mabury, S. A.; Hurley, M. D.; Andersen, M. P. S.; Wallington, T. J. Degradation of Fluorotelomer alcohols: A likely atmospheric source of perfluorinated carboxylic acids. EnViron. Sci. Technol. 2004, 38, 3316. (4) Dinglasan-Panlilio, M. J. A.; Mabury, S. A. Significant Residual fluorinated alcohols present in various fluorinated materials. EnViron. Sci. Technol. 2006, 40, 1447. (5) Renner, R. Canada bans fluoropolymer stain repellents. EnViron. Sci. Technol. 2005, 39 (3), 56A. (6) Grajeck, E. J.; Petersen, W. H. Oil and Water Repellent Fluorochemical Finishes for Cotton. Text. Res. J. 1962, 32, 320. (7) Yoerger, W. E.; McCabe, J. M.; Wright, J. F. Repellent compositions and elements containing the same. U.S. Patent 3859090 19750107, 1975. (8) Pentz, L. Textile treating compositions for increasing water and oil repellency of textiles. U.S. Patent 4070152 19780124, 1978. (9) Koda, Y.; Ona, I.; Takeda, A. Fluorosilicone-containing compositions for treatment of fibers. U.S. Patent 4417024 A 19831122, 1983. (10) Waratani, K.; Saito, Y.; Seki, M.; Asakawa, S. Manufacture of permselective membranes from polyfunctional polymer, fluorinated end group-functional polymer and difunctional polysiloxane. JP 01143621 A2 19890606 Heisei, 1989. (11) Ono, I.; Uehara, H.; Ichinohe, S. Fluorine-containing titanosiloxanes and their water-repellent films with hard surface. JP 06271679 A2 19940927 Heisei, 1994. (12) Kobayashi, H.; Masatomi, T. Oil- and water-repellent coatings containing fluorinated silicones. JP 09151357 A2 19970610 Heisei, 1997. (13) Mignani, G.; Olier, P.; Priou, C. Crosslinkable silicone composition useful for coating and/or impregnating to produce water and/or oil repellency with low surface energy. WO 2000000559 A1 20000106, 2000. (14) Sato, K.; Yamaya, M.; Asai, M.; Matsumura, K. Fluorine-containing silsesquioxane coating compositions and their manufacture and use. EP 1178071 A2 20020206, 2002. (15) Dams, R. In 14th European Symposium on Fluorine Chemistry, Poznan, Poland, July 2004; Paper c-O-07. (16) Huang, W. Perfluoroalkylation initiated with sodium dithionite and related reagent systems. J. Fluorine Chem. 1992, 58, 1. (17) Huang, X.; Long, Z.; Chen, Q. Fluoroalkylation of aromatic compounds with per(poly)fluoroalkyl chlorides initiated by sodium dithionate in DMSO. J. Fluorine Chem. 2001, 111, 107. (18) Xiao, F.; Wu, F.; Shen, Y.; Zhou, L. Synthesis of R,R-difluoro-γbutylrolactones via ethyl iododifluoroacetate. J. Fluorine Chem. 2005, 126, 63.

(19) Brace, N. O.; Van Elswyk, E. Evidence for free-radical reductive dehalogenation in reaction of zinc and acid with 1-perfluoroalkyl-2iodoalkanes and with 1-perfluoroalkyl-2-iodoalkenes. J. Org. Chem. 1976, 41 (5), 766. (20) Leebrick, J. R.; Ramsden, H. E. Synthesis and reactions of p-vinylphenylmagnesium chloride. J. Org. Chem. 1958, 23, 953. (21) Banks, A. R.; Fibiger, R. F.; Jones, T. A convenient synthesis of methacrylates. J. Org. Chem. 1977, 42 (24), 3965. (22) Audenaert, F.; Elst, P. J. v. d.; Rolly, D. G. Fluoropolymer of fluorinated short chain acrylates and oil- and water-repellent compositions based thereon. 05.01.2005, 2005. (23) Kostov, G.; Ameduri, B.; Boutevin, B. New appraches to the synthesis of functionlized fluorine-containing polymers. J. Fluorine Chem. 2002, 114, 171. (24) Chibowski, E. Surface free engery of a solid from from contact angle hysteresis. AdV. Colloid Interface Sci. 2003, 103, 149. (25) Johnson, R. E.; Dettre, R. H. Surfactant Science; Marcel Dekker: New York, 1997. (26) Adamson, A. W.; Gast, A. P. Physical Chemistry of Surfaces; John Wiley and Sons: New York, 1993; Vol. 49, pp 1-73. (27) Genzer, J.; Sivaniah, E.; Kramer, E. J.; Wang, J.; Xiang, M.; Char, K.; Ober, C. K.; Bubeck, R. A.; Fischer, D. A.; Graupe, M.; Colorado, R., Jr.; Shmakova, O. E.; Lee, T. R. Molecular Orientation of single and twoarmed monodendron semifluorinated chains on “soft” and “hard” surfaces studies using NEXAFS. Macromolecules 2000, 33, 6068. (28) Fischer, D. A.; Efimenko, K.; Bhat, R. R.; Sambasivan, S.; Genzer, J. Mapping surface chemistry and molecular orientation with combinational near-edge X-ray absorption fine structure spectroscopy. Macromol. Rapid Commun. 2004, 25, 141. (29) Genzer, J.; Efimenko, K.; Fischer, D. A. Molecular orientation and grafting density in semifluorinated monolayers of mono-, di-, and trichloro silanes and silica substrates. Langmuir 2002, 18, 9307. (30) Genzer, J.; Sivaniah, E.; Kramer, E. J.; Wang, J.; Korner, H.; Xiang, M.; Char, K.; Ober, C. K.; DeKoven, B. M.; Bubeck, R. A.; Chaudhury, M. K.; Sambasivan, S.; Fischer, D. A. The Orientation of semifluroinated alkanes attached to polymers at the surface of polymer films. Macromolecules 2000, 33, 1882. (31) Saidi, S.; Guittard, F.; Guimon, C.; Geribaldi, S. Fluorinated comblike homopolymers: the effect of spacer length on surface properties. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 3737. (32) Tsibouklis, J.; Graham, P.; Eaton, P. J.; Smith, J. R.; Nevell, T. G.; Smart, J. D.; Ewen, R. J. Poly(perfluoro methacrylate) film strutures: Surface organization phenomena, surface energy setermination, and force of adhesion measurements. Macromolecules 2000, 33, 8460. (33) Rossier, J.; Reymond, F.; Michel, P. E. Polymer microfluidic chips for electrochemical and biochemical analyses. Electrophoresis 2002, 23 (6), 858. (34) Owens, M. J. Low Surface Energy Inorganic Polymers. Comments Inorg. Chem. 1988, 7, 195. (35) Lau, Y. W.; Burns, C. M. Effect of temperature and molecular weight on the rate of spreading of polystyrene melts on plane soda lime glass surfaces. J. Polym. Sci., Polym. Phys. Ed. 1974, 12, 431. (36) Bernett, M. K.; Zisman, W. A. Wetting properties of tetrafluoroethylene and hexafluoropropylene copolymers, J. Phys. Chem. 1960, 64, 1292. (37) Honda, K.; Morita, M.; Otsuka, H.; Takahara, A. Molecular aggregation struture and surface properties of poly(fluoroalkyl acrylate) thin films. Macromolecules 2005, 38, 5699. (38) Luning, J.; Yoon, D. Y.; Stohr, J. Importance of structural order for the low surface energy of perfluoroalkyl substituted polymethacrylates. J. Electron Spectrosc. Relat. Phenom. 2001, 121, 265. (39) Shimizu, T.; Tanaka, Y.; Kutsumizu, S.; Yano, S. Ordered structure of poly(fluoroalkyl a-fluoroacrylate)s. Macromolecules 1993, 26, 6694. (40) Lam, C. N. C.; Kim, N.; Hui, D. K. D. Y.; Hair, M. L. The effects of liquid properties to contact angle hysteresis. Colloids Surf., A 2001, 189, 265. (41) Hayakawa, T.; Wang, J.; Xiang, M.; Li, X.; Ueda, M.; Ober, C. K.; Genzer, J.; Sivaniah, E.; Kramer, E. J.; Fischer, D. A. Effect of changing molecular end groups on surface properties: synthesis and characterization of poly(styrene-b-semifluorinated isoprene) block copolymers with -CF2H end groups. Macromolecules 2000, 33, 8012. (42) Stohr, J. NEXAFS Spectrascopy; Springer-Verlag: Berlin, 1992. (43) Bunn, C. W.; Howells, E. R. Structures of Molecules and Crystals of Fluoro-Carbons. Nature 1954, 174, 549. (44) Kirsch, P. Fluoroorganic chemistry; Wiley-VCH: Weinheim, Germany, 2004; p 1. (45) Wang, J.; Ober, C. K. Self-organizing materials with low surface energy: The synthesis and solid-state properties of semifluorinated sidechain ionenes. Macromolecules 1997, 30, 7560.

508

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008

(46) Vilalta, P. M.; Weiss, R. G. Smectic liquid-crystalline phases of F(CF2)7(CHOH)(CH2)8H and F(CF2)9(CHOH)(CH2)10H: Comparison with other partially fluorinated molecules. Liq. Cryst. 1992, 12 (4), 531. (47) Rabolt, J. F.; Russell, T. P.; Siemens, R.; Twieg, R. J.; Farmer, B. In ObserVations of a gel-like phase in two-component mixtures of semifluorinated n-alkanes and hydrocarbon liquids; American Chemical Society, Division of Polymer Chemistry, Polymer Preprints: Washington, DC, 1986; p 1135. (48) Mahler, W.; Guillon, D.; Skoulios, A. Mol. Cryst. Liq. Cryst. Lett. 1985, 2, 111. (49) Viney, C.; Twieg, R. J.; Russell, T. P.; Depero, L. E. The structural basis of transitions between highly ordered smectic phases in semifluorinated alkanes. Liq. Cryst. 1989, 5 (6), 1783.

(50) McGrath, K. J.; Weiss, R. G. Kinetics of Isothermal Crystallization of a Smectic Partially Fluorinated Alcohol by 2H NMRl. J. Phys. Chem. 1993, 97, 11115. (51) Wang, J.; Mao, G.; Ober, C. K.; Kramer, E. J. Liquid crystalline, semifluorinated side group block copolymers with stable low energy surafces: Synthesis, liquid crystalline structure, and critical surfce tension. Macromolecules 1997, 30, 1906.

ReceiVed for reView March 1, 2007 ReVised manuscript receiVed July 3, 2007 Accepted July 10, 2007 IE0703179