- Email: [email protected]
Synthesis and characterization of a novel difunctional fluorinated acrylic oligomer used for UV-cured coatings
Journal of Fluorine Chemistry 147 (2013) 49–55
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of a novel difunctional fluorinated acrylic oligomer used for UV-cured coatings Zhenlong Yan a,b, Weiqu Liu a,*, Nan Gao a,b, Ziqi Ma a,b, Minjian Han a,b a b
Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 September 2012 Received in revised form 11 January 2013 Accepted 15 January 2013 Available online 23 January 2013
A novel dimethacrylate terminated, poly(2,2,3,4,4,4-hexafluorobutyl acrylate (MATHFA), was synthesized in four-step procedure, and the structures were characterized by FT-IR and 1H NMR spectra. The fluorinated acrylic oligomer was employed as reactive surface additives and copolymerized with bisphenol-A epoxy methacrylate (EMA) in UV-curable formulation to improve the surface properties of UV-cured films. The influence of MATHFA concentration and length, i.e. the number of repeat units on the bulk and surface properties of the films were investigated. Contact angle measurements showed that the high hydrophobic surfaces on the air side of films were obtained by the introduction of fluorinated oligomers in very low amount (less than 1.3 wt.%) in the UV-curable mixed formulation, while the glass side did not changed. The surface composition and the surface enrichment factors measured by X-ray photoelectron spectroscopy (XPS) confirmed the selective enrichment of fluorinated moieties at the outermost surface of cured films and also proved the longer MATHFA was easier to concentrate on the air side than that of shorter MATHFA. ß 2013 Elsevier B.V. All rights reserved.
Keywords: Surface segregation Surface property Hydrophobic coating Photopolymerization Fluorinated films
1. Introduction UV-curable techniques are of high interest in industrial applications due to the advantages of high cure speed, high efficiency, solvent free formulations, and low energy consumption [1–4]. These advantages afforded by UV-curable systems have led to rapid growth in their use in different fields, including the production of films and coatings on a variety of substrates, such as paper, metal, fibers [5–7]. The fluorinated materials have received much attention because of their unique performances provided by the presence of fluorine atoms, such as chemical and thermal stability, excellent surface energy, release properties and low refractive indices [8– 10]. Therefore, the fluorinated polymers have been widely used in the field of hydrophobic coatings, mechanical devices and electronic components [11–13]. Especially, in the following years the fluorinated coatings have been designed in uses for selfcleaning surfaces [14], reversibly switching surfaces [15] and surperhydrophobic surfaces [16] in controlled methods. Thus, the incorporated fluorinated additives into the UV-curable systems are well-known to combine the properties of fluorinated groups and the advantages of UV-curing technology [17]. There are two main
* Corresponding author. Tel.: +86 20 85231660; fax: +86 20 85231660. E-mail address: [email protected] (W. Liu). 0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jfluchem.2013.01.014
approaches used to modify the surface properties: first, blended unreactive fluorinated additives with UV-cured formulations are common approach to modify the coatings where the surfaces properties are controlled by the fluorinated groups through surface segregation [18]. The other technique, functional fluorinated monomers or reactive fluorinated oligomers are introduced in to the cured formulations where the fluorinated segments dominate the surface [19–22]. In most previous reports, low amount of reactive fluorinated surface additives mixed into coatings can not only generate very low surface energy surface by fluorinated segments enrichment towards to the outermost layer but also maintain or improve the bulk properties [21,23]. Recently, much attention has been paid to the long perfluoroalkyl groups resulted in exciting hydrophobic surface as fluorine groups are enriched on the air surfaces [24–26]. For instance, Lin et al. have synthesized a novel UV-curable fluorinated epoxy acrylate (FEA) oligomers using 1 H,1H-perfluorohexan-1-ol (PFHOL), 1,6-hexamethylene diisocyanate (TDI) and epoxy acrylate. Because the functional oligomer contained a spacer linking the side perfluoroalkyl chains, superhydrophobic films were obtained with the water contact angle (1518) [27]. Miao et al. prepared two perfluoroalkyl phosphate acrylates (PFPA 1 and PFPA 2) monomers used as reactive additives to modify the surface properties of UV-curable polyurethane coatings [17]. The result showed that a small amount of PFPA 1 and PFPA 2 (no more than 1 wt.%) led to high hydrophobic surface (1148). Bongiovanni et al. reported a series of fluorinated
50
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
monomers and oligomes bearing either radical or cationic UVcurable formulations to produce hydrophobic surface duo to the selective enrichment of fluorinated groups towards the air-surface [21,26,28]. All the results showed that the long fluorinated groups in the tail of monomers can significantly lower the energy surface of coatings as the fluorinated polymer chains segregates up to the polymer-air interface. Considering these points, the present work was focused on the synthesis of a novel functional acrylic oligomer with long fluorinated segments. Two kinds of molecular weight bearing the repeating fuorinated unit, –CF2–CHF–CF3–, which made it possible to investigate the effect of the length of fluorinated moiety on the surface properties of UV-cured films. First, di-tert-butyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (BTHFA) and dicarboxyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (CTHFA) were synthesized with the metal-free anionic polymerization and hydrolysis reaction as reported in previous literature [29]. Then well-defined dimethacrylate terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomers (MATHFA) were prepared by the reaction of CTHFA and hydroxyethyl methyacrylate (HEMA). The specifically designed oligomer was used as an effective surface additive because of its unique ability to produce high hydrophobic surface of the UVcured films as well as thermal and chemical stabilities. The effects of chain length and content of MATHFA on the surface properties of UV-cured films were specifically investigated by changing the ratio of oligomers used. Contact angle measurements and surface energy were used to assess the wettability of the UV-cured films and the surface composition was evaluated by X-ray photoelectron spectroscopy (XPS). In addition, the bulk properties of the films, such as the thermal properties were also discussed in details.
2. Results and discussion 2.1. Synthesis and characterization of fluorinated oligomer MATHFA MATHFA was synthesized in a four-step procedure. Firstly, the BTHMA was synthesized by the metal-free anionic polymerization in THF at room temperature. GPC data showed the molecular weight distributions were fairly narrow. In this work, BTHFA of 2000 and 3000 g/mol was synthesized to investigate the effect of length of fluorinated chain on the properties of UV-cured coatings. Then the di-tert-butyl esters at the end of BTHMA were hydrolyzed under mild conditions in present of anhydrous sodium iodide and trimethylchlorosilane as previously reported [29]. Next, the CTHMA was reacted with SOCl2 to give diacyl chloride terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate). Finally, diacyl chloride terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) was functionalized by the reaction with HEMA to generate MATHFA. The synthetic route of MATHFA was shown in Scheme 1. The chemical structures of MATHFA were confirmed by FTIR and 1H NMR spectra. As shown in Fig. 1, the characterization absorption peaks at 812 and 1635 cm1 in trace b represented the bending and stretching vibration of C5 5C groups, which indicates the existence the methyacrylic groups. Fig. 2 shows the 1H NMR spectra of MATHFA in DMSO solvent. The resonance signals of methane proton of –CHF– and methylene protons of –CH2–CF2– appear in the region of 5.98–6.11 ppm and 4.54–4.62 ppm, respectively. The chemical shift of 4.25–4.33 ppm represents the methylene protons of –CH2–CH2– groups affected by the two ester C5 5O groups. The peaks at chemical shift of 5.64–5.68 ppm and 5.98–6.11 ppm belong to the protons of C5 5C double bonds. These results confirm that the pure MATHFA is successfully prepared.
Scheme 1. Synthetic route of difunctional fluorinated acrylic oligomer MATHFA.
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
Fig. 1. FT-IR absorption spectra of (a) CTHFA-3000 and (b) MATHFA-3000.
Fig. 2. 1H NMR spectra of MATHFA-3000.
51
Fig. 4. Contact angles on the UV-cured films with different concentrations of MATHFA-2000 and pure MEA.
Fig. 5. Surface energy of UV-cured films with different concentrations of MATHFA2000 and MATHFA-3000.
2.2. Surface properties of the UV-cured films The water contact angles and surface energies were measured to determine the wettability of the fluorinated films. Firstly, all the UV-cured films were peeled off form the glass substrates and the surface properties were investigated on the two sides of cured films. The contact angles and the surface energies of the cured films are shown in Figs. 3–5. As shown in the Figures, the water contact
Fig. 3. Contact angles on the UV-cured films with different concentrations of MATHFA-2000 and pure MEA.
angle of pure MEA acrylic resin is around 648 on both sides. When a small amount of difunctional fluorinated oligomer is added to the mixture, the water contact angles of the air side of the composited film are greatly changed [21,30]. It can be seen from the Figs. 3 and 4, the contact angles of the films on the air side depend on the fluorinated oligomer content: the contact angles increases upon increasing the amount of fluorinated oligomer [22]. By comparing with the two sides of the films, the fluorinated oligomer MATHFA is only effective to modify surface properties at air side [19]. It can be seen from Fig. 5, when the concentration of fluorinated oligomers in the sample is up to 1.3 wt.%, the surface energy lowered the minimum value and similar data measured by a fully fluorinated surface [31]. This phenomenon may be attributed the fluorinated moieties produce ordered surface structure, allowing fluorocarbons to be exposed to the outermost surface of the films [9,17,28]. In addition, the long tail-like fluorinated moieties in the welldefined difunctional oligomer has stronger thermodynamic driving force for fluorinated groups migration and concentration on the outermost layer, so a little amount of MATHFA can result in a completely hydrophobic surface. For further comparing the data of different additives MATHFA2000 and MATHFA-3000, it can be clearly seen that the contact angle in the case of MATHFA-3000 are slightly higher than for MATHFA-2000 at the same concentration. This result suggests that besides concentration, the length of fluorinated oligomer also influences the surface properties [9,27].
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
52
Fig. 6. XPS curves of UV-cured films with 0.2 wt.% MATHFA-2000 and MATHFA3000, and 1.3 wt.% MATHFA-2000 and MATHFA-3000.
2.3. Surface composition characterization The contact angle measurements could provide the indirect information that there is a change in the surface composition of the film and fluorinated group migration takes place at the outermost layer. XPS analysis can provide quantitative and qualitative analysis on the surface composition of the surface. Therefore, XPS was used to investigate the surface composition to confirm the surface enrichment of fluorine atom. Fig. 6 shows the XPS curves of UV-cured films with 0.2 wt.% MATHFA-2000 and MATHFA-3000, and 1.3 wt.% MATHFA-2000 and MATHFA-3000. The peaks at 282.8, 530.9 and 686.6 eV are attributed to C1s, O1s and F1s, respectively. As shown in Fig. 6, the fluorine signal at 686.6 eV strongly increases when the MATHFA concentration goes form 0.2 wt.% to 1.3 wt.%, which indicates the fluorine atoms at the surface of the film increase upon increasing the MATHFA concentration [17]. This result can explain the sharp change of water contact angles of the MATHFA modified UV-cured films shown in Figs. 3 and 4. In addition, at the same concentration, the fluorine signal of MATHFA-3000 is bigger than that of MATHFA2000, which demonstrates the shorter MATHFA is less effective enrichment at the surface than the corresponding films containing the longer MATHFA. In this paper, we define a new surface enrichment factor, Smf, which is the ratio of mass content of fluorine atoms at the top surface of the UV-cured films (Fm), to the mass content of fluorine atoms in bulk of the UV-cured formulation (Fmb): the equation is summarized below:
Smf ¼
Fm : F mb
Table 1 shows the fluorine atomic content, mass content and surface enrichment factors (SF and Smf) of the UV-cured films measured by XPS, respectively. As seen from the Table 1, the surface fluorine contents of all the samples are much higher than
calculated in bulk, which significantly illustrates the fluorine atom migrate to the outermost surface. In the bulk, the four samples have two mass content of fluorine of 0.096 wt.% and 0.624 wt.%, while at the surface the fluorine mass content are 14.50, 30.70, 20.35, 35.15 wt.%, respectively. The two surface enrichment factors, SF and Smf, range from 50 to 208-fold and 56 to 490fold with respect to the bulk concentration, respectively. All the four samples exhibit higher fluorine atom and mass concentrations at the outermost surface at the air side than in the bulk of UVcured formulations. These results can be explained as following: during the UV-curing process, the difunctional vinyl groups at the end of MATHFA react with the MEA to generate three-dimensional networks; because of the low surface tension and strong thermodynamic driving force of fluorinated moieties, the perfluoroalkyl segments of MATHFA float on the surface from the bulk. The F/C atom ratios at the surface of the UV-cured films with different concentration of fluorinated oligomer are listed in Table 2. As shown in the Table 2, the F/C atom ratios increase with adding more MATHFA, which implied the fluorine atoms enrichment at the surface of the films [21]. In addition, the values of F/C atom ratios of films incorporated with MATHFA-2000 from 0.2 wt.% to 1.3 wt.% are 0.1462 to 0.3823, while the values of the F/ C atom ratios of films incorporated with MATHFA-3000 from 0.2 wt.% to 1.3 wt.% are 0.2208 and 0.4506. This demonstrates that at the same concentration the longer MATHFA-3000 is more efficient in migrating to the air-polymer surface at extremely low concentration, which is in agreement with the results obtained from the contact angle measurements. 2.4. Bulk properties of the UV-cured films The surface modified films were obtained by introducing functional MATHFA to bisphenol-A epoxy methacrylate resin (MEA) at a concentration ranging from 0.2 to 1.3 wt.%. The gel contents of UV-cured films shown in Table 3 containing different MATHFA concentrations are quite high, which is the similar to that of the pure MEA [28]. The surface hardness of the films was measured using the pencil test method. The hardness of the films in presence of fluorinated groups is not changed in such low amount [32] (Table 3). The adhesion property, which takes part in a protective function in the coatings, is one of important issues to assess the high performance coatings. Because the fluorinated groups have different surface tension from other composition in the UV-cured formulations, the fluorinated coatings exhibit poor adhesion property [33]. However, the MATHFA modified films shown 97% adhesion on the glass substrate as well as the pure MEA. This phenomenon can be explained as follows: during the curing process, the fluorinated groups of MATHFA selectively migrate to the outermost layer of UV-cured film, which lead to the side of film in contact with glass substrate free of fluorinated groups [26,32]. Glass transition temperature (Tg) of the UV-cured films were investigated by differential scanning calorimetry (DSC). Fig. 7 shows the DSC thermograms of the pure BMA film and modified films by introduction of MATHFA-2000 and MATHFA-3000 at the
Table 1 The fluorine content on the surface of the UV-cured films. Samples
wt.% of fluorine in bulka
Estimated atom % of fluorine in bulk
Atomic conc % of fluorine
Mass conc wt.% of fluorine
SF
Smf
0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
0.096 0.624 0.096 0.624
0.071 0.46 0.071 0.46
10.30 23.10 14.75 26.70
14.50 30.70 20.35 35.15
145 50 208 58
151 490 286 56
a
The ratio as fluorine mass content in MATHFA to the whole UV-cured formulation.
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
53
Table 2 The surface composition and F/C atom ratio of the UV-cured films measured by XPS. Samples
C1s
O1s
F1s
F/C
0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
70.44 60.77 66.79 59.25
19.26 16.13 18.46 14.05
10.30 23.10 14.75 26.70
0.1462 0.3823 0.2208 0.4506
Table 3 The main bulk properties of the UV-cured films. Samples
Gel content %
Pencil hardness
Adhesion (%)
EMA 0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
98 98 98 97 98
4H 4H 5H 4H 4H
98 97 98 98 98 Fig. 8. TGA thermograms of the MATHFA-2000 and MATHFA-3000 samples.
Table 4 Thermal properties of the UV-cured films.
change significantly the thermal stability of pure MEA due to the low concentrations.
Samples
T5% (8C) T50% (8C) Tmax (8C) wt.% at 600 8C Tg (8C)
EMA 0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
296.8 295.9 294.0 295.7 296.3
416.1 416.6 419.9 418.1 417.9
415.0 420.0 420.0 422.0 421.0
7.95 8.86 9.40 9.84 9.11
63.7 62.9 63.5 63.3 64.1
0.2 and 1.3 wt.% concentrations. The Tg values of all the samples are summarized in Table 4. No obvious change of Tg is found between MATHFA modified UV-cured films and the pure EMA resins [19]. The thermal decomposition behaviors of the films modified by MATHFA were analyzed by TGA under N2 atmosphere and compared with the pure MEA resin. The TGA curves are reported in Fig. 8, while the thermal parameters such as their decomposition temperatures at weight loss of 5, 50 wt.%, the maximum rate of weight loss and residual weight percent at 600 8C (Td5%, Td50%, Tmax and wt.% at 600 8C), are also listed in Table 4. The residual weight values of UV-cured films at 600 8C containing MATHFA-2000 and MATHFA-3000 are slightly higher than the pure MEA. This result can be contributed to the excellent thermal stability properties of fluorinated groups, which decelerates the thermal decomposition [34]. The Td5%, Td50%, and Tmax values of the UV-cured films containing MATHFA are similar to that of pure MEA resin, which indicates the MATHFA added in UV-cured formulations does not
Fig. 7. DSC thermograms of the MATHFA-2000 and MATHFA-3000 samples.
3. Conclusion The well-defined fluorinated acrylic oligomer MATHFA, was prepared successfully in four steps and characterized by FTIR and 1 H NMR spectroscopy. This reactive fluorinated oligomer was employed as an effective surface additive into UV-cured epoxy acrylic resin formulations at different concentrations (ranging from 0.2 wt.% to 1.3 wt.%). Contact angle measurements showed that completely hydrophobic surfaces of the UV-cured films at the air side were obtained even at low amount of MATHFA. XPS analysis confirmed that the fluorinated groups selectively migrate to the outermost layer of the films. In addition, by comparing to the MATHFA-2000 and MATHFA-3000 series, the length of fluorinated oligomers also influence the surface properties of the films. The longer MATHFA oligomers can float on the air-side surface easier than that of shorter MATHFA oligomers. The bulk properties of the films measured by DSC, TGA etc. were the similar to that of pure MEA due to low amount of fluorinated additives. In brief, tailored high hydrophobic surfaces of UV-cured films were obtained and there was no change in bulk properties. 4. Experimental 4.1. Materials THF (Purity: 99.0%, Shanghai Chemical Co., Ltd, China) and 2,2,3,4,4,4-hexafluorobutyl acrylate (HFA, Purity: 96%; Harbin Xeogia Fluorine-Silicon Chemical Co., Ltd, China) were purified using procedures reported earlier [29]. Tetrabutylammonium hydroxide (TBAOH; Purity: 25% in H2O, Aladdin Chemistry Co., Ltd, China), methylacrylic acid (Purity: 99.0%, Aladdin Chemistry Co., Ltd, China), 2-hydroxy-2-methylpropiophenone (Darocur 1173; Purity: 97.0% Lianyungang Shennan Chemical Co., Ltd, China), di-tert-butyl malonate (Purity: 98.0%, ChangZhou XiaQing Chemical Co., Ltd. China), diglycidyl ether of bisphenol A (DGEBA, the epoxide equivalent weight (EEW): 196 g/epoxide, Shell Chemical Co., Ltd, Holland), were used as received. 2hydroxyethyl methacrylate (HEMA; Purity: 98.0%, Aladdin Chemistry Co., Ltd, China) was dried over 4 A˚ molecular sieve prior to use. Sodium iodide (NaI; Purity: 99.5% Shanghai Lingfeng Chemical Reagent Co., Ltd, China) was dried at 160 8C for 8 h to use. Bisphenol-A epoxy methacrylate (EMA, 98.0%) was synthesized according to a procedure reported in literature [34]. Trimethylchlorosilane ((TMS)Cl, Purity: 99.0%), triethylamine
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
54
(Purity: 99.0%), acetonitrile (Purity: 99.0%) and chloroform (Purity: 99.0%) were supplied by Shanghai Chemical Co., Ltd, China and were distilled prior to use, respectively.
SF ¼
4.2. Characterization The 1H NMR spectra was record with a 400 MHZ NMR spectrometer (Bruker, Germany) using DMSO as a solvent. The Fourier transform infrared (FT-IR) spectra were obtained using a TENSOR27 (Bruker, Germany) spectrometer over the range 400– 4000 cm1. Gel permeation chromatography (GPC) was performed with Waters 2410 (USA) equipped with two Styragel HR columns (7.8 mm 300 mm). The molecular weight and molecular weight distribution of the functional oligomer were determined from a calibration curve established using polystyrene standards (PS, Shodex, SM-105, Japan). THF was used as the eluent at a flow rate of 1 mL min1 at 25 8C. The gel content was performed with the following procedure. The UV-cured films were extracted with chloroform for 24 h at room temperature. The equation summarized below: Wt Gel content % ¼ W 100% where, W0 is the initial weight of the 0 UV-cured film. Wt is the final weight after extraction. The hardness of the cured films was evaluated using the Stander test method ASTM D3363. The adhesion of the films was measured using the ‘‘Lattice notch method’’. The measured films were divided in to small squares (1 mm 1 mm) by razor blade. The insulating tape is used to place over the surface of the films, squeezed with finger in order to completely contact with these squares and pulled form the films. A portion of small squares is separated from the substrate. The equation was calculated as [35]:
Adhesion ¼
ab 100% a
where, a represented the total number of squares, b represented the number of squares separated from the substrate. The contact angles of water were performed with an optical contact angle meter (Shanghai Zhongchen, China) at room temperature (25 8C). The air-side and glass-side of the UV-cured films were measured using sessile drop technique to avoid vibration and distortion of the drops. The average contact angle of each sample was measured more than five times at different locations. In this study, the surface energy from the contact angle was calculated based on the equation derived by Li and Neumann [36].
1 þ cosu ¼ 2ðg S =g L Þ1=2 exp½bðg L g S Þ
used to represent the ability of the surface segregation of fluorinated groups.
2
gS and gL were the surface energy of the solid and the test liquid, respectively. b was a constant with a value of 0.0001247 (m2 mj1)2. u was the test water contact angle date. X-ray photoelectron spectroscopy (XPS) results were obtained using an X-ray Photoelectron Spectroscopy/ESCA (Axis Ultra DLD, Kratos Analytical Ltd, UK) with a Mono Al Ka source. The take-off angle was 908 with respect to the surface of all the UV-cured films. The surface enrichment factor given by Levine et al., SF [37,38], was
F surface F bulk
where, Fsurface was the atom fluorine content at the surface of the UV-cured films measured by XPS; Fbulk was the atom fluorine content in the bulk of the UV-cured formulation estimated assuming a uniform and random distribution. The differential scanning calorimetry (DSC) measurements were performed on DSC204 (NETZSCH Germany) under N2 atmosphere. Each sample (about 10 mg) was scanned from 70 to 200 8C at a heating rate of 20 8C/min and held at 200 8C for 5 min to remove the thermal history. Glass transition temperature (Tg) values were recorded during the second heating scan taken as the midpoint of the heat capacity change. Thermogravimetric analysis (TGA, TG209F3 NETZSCH Germany) was performed on a TG209F3 to study the thermal stability of fluorinated UV-cured films under N2 atmosphere. Each sample was about 5 mg and heated at the heating rate of 10 8C/min from 30 8C to 800 8C. 4.3. Synthesis of fluorinated acrylic oligomer The synthetic routes for preparing di-tert-butyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (BTHFA) and dicarboxyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (CTHFA) have been reported in our previous work [29]. In summary, using tetrabutylammonium salt of di-tert-butyl malonate as anionic initiator, BTHFA was prepared by metal-free anionic polymerization of HFA in a controlled manner at room temperature. The molecular weight and molecular weight distribution of BTHFA were estimated by GPC and shown in Table 5. CTHFA was synthesized by the hydrolysis of BTHFA under argon atmosphere for 3 h in presence of sodium iodide and the (TMS)Cl. CTHFA 5 g and thionyl chloride (SOCl2) 30 ml were added in a two-neck round bottomed flask equipped with a reflux condenser and thermometer. The mixture was refluxed for 24 h at 60 8C, removed the excessive SOCl2 under reduced pressure. The obtained compound, diacyl chloride terminated poly(2,2,3,4,4,4hexafluorobutyl acrylate), dried in vacuum at 50 8C for 24 h and stored under an argon atmosphere. The diacyl chloride terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (3 g), 50 ml purified THF, DMAP (0.02 g) and Triethylamine (0.4 g) were placed in a three-neck round bottomed flask equipped with an argon inlet tube and reflux condenser and thermometer, and then immersed in an ice bath at 0 8C. Then HEMA (0.52 g) dissolved in 10 ml THF and added drop by drop to the reactor via syringe over a period of 10 min. The mixture was stirred at 0 8C for 2 h and kept at 60 8C for 24 h. The precipitate of triethylamine hydrochloride was filtrated by Buchner funnel. THF was removed under reduced pressure, and the obtained product was dissolved in ethyl acetate (50 ml), and washed with 5% aqueous hydrochloric acid (20 ml) three times and distilled water (20 ml) repeatedly to remove the excessive HEMA and DMAP. The ethyl acetate layer was evaporated to obtained difunctional
Table 5 The molecular weight and molecular weight distribution of BTHFA prepared using metal-free anionic polymerization in THF solvent. Sample
[I]/[M]a molar ratio
T (8C)
Mn,GPC (g mol1)
PDIb (Mw/Mn)
Mn,NMc (g mol1)
State
Yield (%)
BTHFA-2000 BTHFA-3000
1:8 1:12
25 25
1947 2993
1.14 1.11
1735 2771
Liquid Liquid
94.7 95.2
a b c
[I]/[M] = initiator/monomer; [I] = 2 mmol. obtained from GPC. Molecular weight measured by 1H NMR.
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
55
Table 6 The weight composition of UV-cured formulations. Sample
a
b
Darocur 1173 (g)
EMA (g)
EMA 0.2MATHFA-2000/EMA 0.5MATHFA-2000/EMA 0.8MATHFA-2000/EMA 1.0MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 0.5MATHFA-3000/EMA 0.8MATHFA-3000/EMA 1.0MATHFA-3000/EMA 1.3MATHFA-3000/EMA
— 0.01 0.025 0.04 0.05 0.065 — — — — —
— — — — — — 0.01 0.025 0.04 0.05 0.065
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 4.99 4.975 4.6 4.95 4.935 4.99 4.975 4.6 4.95 4.935
a b
MATHFA-2000 (g)
Obtained from BTHFA-2000. Obtained from BTHFA-3000.
fluorinated acrylic oligomer (MATHFA) and dried in vacuum oven at 60 8C for 24 h. 4.4. Preparation of UV-curable coatings The UV-curing formulations were prepared by mixing different amount of MATHFA to bisphenol-A epoxy methacrylate (MEA) by adding 4 wt.% of 2-hydroxy-2-methylphenylpropanone (Darocur 1173) and the relative weight compositions for the mixtures were listed in Table 6. The obtained mixtures were stirred for 30 min and coated on glass substrate by means of a wire-wound applicator. The coated films were exposed to UV irradiation by using a highpressure mercury lamp (500 W) for 30 s with a distance of 20 cm from lamp to the surface of samples in the air atmosphere. The cured films about of 100 mm were obtained. Acknowledgements The work was financially supported by the Program Key Laboratory of Cellulose and Lignocellulosics, Guangzhou Institute of Chemistry, Chinese Academy of Sciences - ‘‘Research on fiber fabric modified by waterborne fluorosilicone polymer finishing agent’’. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
MATHFA-3000 (g)
S.J. Choi, K.Y. Suh, H.H. Lee, J. Am. Chem. Soc. 130 (2008) 6312–6313. B. Mu˝ ller, U. Poth, Coatings Formulation, Vincentz, Hannover, 2006. H.D. Hwang, H.J. Kim, React. Funct. Polym. 71 (2011) 655–665. P. Roose, I. Fallais, C. Vandermiers, M.G. Olivier, M. Poelman, Prog. Org. Coat. 64 (2009) 163–170. R. Bongiovanni, F. Montefusco, A. Priola, N. Macchioni, S. Lazzeri, L. Sozzi, B. Ameduri, Prog. Org. Coat. 45 (2002) 359–363. G. Hougham, K. Johns, P.E. Cassidi, J. Davidson, Floropolymers, Plenum Press, New York, 1999. C.G. Roffey, Photopolymerization of Surface Coatings, Wiley, New York, 1982. J.R. Lee, F.L. Jin, S.J. Park, J.M. Park, Surf. Coat. Technol. 180–181 (2004) 650–654. R.D. van de Grampel, W. Ming, W.J.H. van Gennip, F. van der Velden, J. Laven, J.W. Niemantsverdriet, R. van der Linde, Polymer 46 (2005) 10531–10537.
[10] L. Valtola, S. Hietala, H. Tenhu, P. Denifl, C.E. Wilen, Polym. Adv. Technol. 20 (2009) 225–234. [11] T. Imae, Curr. Opin. Colloid. Interface Sci. 8 (2003) 307–314. [12] H.S. Sundaram, Y. Cho, M.D. Dimitriou, J.A. Finlay, G. Cone, S. Williams, D. Handlin, J. Gatto, M.E. Callow, J.A. Callow, E.J. Kramer, C.K. Ober, Appl. Mater. Interfaces 3 (2011) 3366–3374. [13] Z.Q. Tao, S.Y. Yang, Z.Y. Ge, J.S. Chen, L. Fan, Eur. Polym. J. 43 (2007) 550–560. [14] J. Wang, Y. Xu, L. Zhu, J. Li, B. Zhu, Polymer 49 (2008) 3256–3264. [15] K. Reihs, M. Voetz, Langmuir 21 (2005) 10573–10580. [16] S.J. Yuan, S.O. Pehkonen, B. Liang, Y.P. Ting, K.G. Neoh, E.T. Kang, Corros. Sci. 53 (2011) 2738–2747. [17] H. Miao, Z.G. Huang, L.L. Cheng, W.F. Shi, Prog. Org. Coat. 64 (2009) 365–370. [18] H. Miao, F.F. Bao, L.L. Cheng, W.F. Shi, J. Fluorine Chem. 131 (2010) 1356–1361. [19] M. Sangermano, R. Bongiovanni, G. Malucelli, A. Priola, A. Pollicino, A. Recca, J. Appl. Polym. Sci. 89 (2003) 1524–1529. [20] M. Sangermano, W. Carbonaro, R. Bongiovanni, R.R. Thomas, C.M. Kausch, Macromol. Mater. Eng. 295 (2010) 469–475. [21] R. Bongiovanni, G. Malucelli, M. Sangermano, A. Priola, J. Fluorine. Chem. 125 (2004) 345–351. [22] H.K. Kim, J.G. Kim, J.D. Cho, J.W. Hong, Polym. Test. 22 (2003) 899–906. [23] B.S. Shemper, L.J. Mathias, J. Appl. Polym. Sci. 91 (2004) 3301–3314. [24] J.M. Corpart, S. girault, D. Juhue´, Langmuir 17 (2001) 7237–7244. [25] E. Barbu, R.A. Pullin, P. Graham, P. Eaton, R.J. Ewen, J.D. Smart, T.G. Nevell, J. Tsibouklis, Polymer 43 (2002) 1727–1734. [26] R. Bongiovanni, A. Medici, A. Zompatori, S. Garavaglia, C. Tonelli, Polym. Int. 61 (2012) 65–73. [27] Y.H. Lin, K.H. Liao, C.K. Huang, N.K. Chou, S.S. Wang, S.H. Chu, K.H. Hsieh, Polym. Int. 59 (2010) 1205–1211. [28] M. Sangermano, R. Bongiovanni, G. Malucelli, A. Priola, R.R. Thomas, C.M. Kausch, Y. Kim, J. Polym. Sci: Part. A: Polym. Chem. 44 (2006) 6943–6951. [29] Z.L. Yan, W.Q. Liu, N. Gao, Y. Sun, H.S. Chen, Iran. Polym. J., http://dx.doi.org/ 10.1007/s13726-012-0074-6. [30] B. Ameduri, R. Bongiovanni, V. Lombardi, A. Pollicino, A. Priola, A. Recca, J. Polym. Sci.: Part A: Polym. Chem. 39 (2001) 4227–4235. [31] M.K. Chaudhury, G.M. Whitesides, Langmuir 7 (1991) 1013–1025. [32] M. Sangermano, A.D. Gianni, R. Bongiovanni, A. Priola, B. Voit, D. Pospiech, D. Appelhans, Macromol. Mater. Eng. 290 (2005) 721–725. [33] R. Bongiovanni, A.D. Gianni, A. Priola, A. Pollicino, Eur. Polym. J. 43 (2007) 3787–3794. [34] C.Y. Tang, W.Q. Liu, S.Q. Ma, Z.F. Wang, C.H. Hu, Prog. Org. Coat. 69 (2010) 359–365. [35] G. Ahmetli, H. Deveci, U. Soydal, A. Seker, R. Kurbanli, Prog. Org. Coat. 75 (2012) 97–105. [36] D. Li, A.W. Neumann, J. Colloid Interf. Sci. 148 (1992) 190–200. [37] F. Levine, J.L. Scala, W. Kosik, Prog. Org. Coat. 69 (2010) 63–72. [38] H.D. Hwang, H.J. Kim, J. Colloid. Interf. Sci. 362 (2011) 274–284.
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of a novel difunctional fluorinated acrylic oligomer used for UV-cured coatings Zhenlong Yan a,b, Weiqu Liu a,*, Nan Gao a,b, Ziqi Ma a,b, Minjian Han a,b a b
Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 15 September 2012 Received in revised form 11 January 2013 Accepted 15 January 2013 Available online 23 January 2013
A novel dimethacrylate terminated, poly(2,2,3,4,4,4-hexafluorobutyl acrylate (MATHFA), was synthesized in four-step procedure, and the structures were characterized by FT-IR and 1H NMR spectra. The fluorinated acrylic oligomer was employed as reactive surface additives and copolymerized with bisphenol-A epoxy methacrylate (EMA) in UV-curable formulation to improve the surface properties of UV-cured films. The influence of MATHFA concentration and length, i.e. the number of repeat units on the bulk and surface properties of the films were investigated. Contact angle measurements showed that the high hydrophobic surfaces on the air side of films were obtained by the introduction of fluorinated oligomers in very low amount (less than 1.3 wt.%) in the UV-curable mixed formulation, while the glass side did not changed. The surface composition and the surface enrichment factors measured by X-ray photoelectron spectroscopy (XPS) confirmed the selective enrichment of fluorinated moieties at the outermost surface of cured films and also proved the longer MATHFA was easier to concentrate on the air side than that of shorter MATHFA. ß 2013 Elsevier B.V. All rights reserved.
Keywords: Surface segregation Surface property Hydrophobic coating Photopolymerization Fluorinated films
1. Introduction UV-curable techniques are of high interest in industrial applications due to the advantages of high cure speed, high efficiency, solvent free formulations, and low energy consumption [1–4]. These advantages afforded by UV-curable systems have led to rapid growth in their use in different fields, including the production of films and coatings on a variety of substrates, such as paper, metal, fibers [5–7]. The fluorinated materials have received much attention because of their unique performances provided by the presence of fluorine atoms, such as chemical and thermal stability, excellent surface energy, release properties and low refractive indices [8– 10]. Therefore, the fluorinated polymers have been widely used in the field of hydrophobic coatings, mechanical devices and electronic components [11–13]. Especially, in the following years the fluorinated coatings have been designed in uses for selfcleaning surfaces [14], reversibly switching surfaces [15] and surperhydrophobic surfaces [16] in controlled methods. Thus, the incorporated fluorinated additives into the UV-curable systems are well-known to combine the properties of fluorinated groups and the advantages of UV-curing technology [17]. There are two main
* Corresponding author. Tel.: +86 20 85231660; fax: +86 20 85231660. E-mail address: [email protected] (W. Liu). 0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jfluchem.2013.01.014
approaches used to modify the surface properties: first, blended unreactive fluorinated additives with UV-cured formulations are common approach to modify the coatings where the surfaces properties are controlled by the fluorinated groups through surface segregation [18]. The other technique, functional fluorinated monomers or reactive fluorinated oligomers are introduced in to the cured formulations where the fluorinated segments dominate the surface [19–22]. In most previous reports, low amount of reactive fluorinated surface additives mixed into coatings can not only generate very low surface energy surface by fluorinated segments enrichment towards to the outermost layer but also maintain or improve the bulk properties [21,23]. Recently, much attention has been paid to the long perfluoroalkyl groups resulted in exciting hydrophobic surface as fluorine groups are enriched on the air surfaces [24–26]. For instance, Lin et al. have synthesized a novel UV-curable fluorinated epoxy acrylate (FEA) oligomers using 1 H,1H-perfluorohexan-1-ol (PFHOL), 1,6-hexamethylene diisocyanate (TDI) and epoxy acrylate. Because the functional oligomer contained a spacer linking the side perfluoroalkyl chains, superhydrophobic films were obtained with the water contact angle (1518) [27]. Miao et al. prepared two perfluoroalkyl phosphate acrylates (PFPA 1 and PFPA 2) monomers used as reactive additives to modify the surface properties of UV-curable polyurethane coatings [17]. The result showed that a small amount of PFPA 1 and PFPA 2 (no more than 1 wt.%) led to high hydrophobic surface (1148). Bongiovanni et al. reported a series of fluorinated
50
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
monomers and oligomes bearing either radical or cationic UVcurable formulations to produce hydrophobic surface duo to the selective enrichment of fluorinated groups towards the air-surface [21,26,28]. All the results showed that the long fluorinated groups in the tail of monomers can significantly lower the energy surface of coatings as the fluorinated polymer chains segregates up to the polymer-air interface. Considering these points, the present work was focused on the synthesis of a novel functional acrylic oligomer with long fluorinated segments. Two kinds of molecular weight bearing the repeating fuorinated unit, –CF2–CHF–CF3–, which made it possible to investigate the effect of the length of fluorinated moiety on the surface properties of UV-cured films. First, di-tert-butyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (BTHFA) and dicarboxyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (CTHFA) were synthesized with the metal-free anionic polymerization and hydrolysis reaction as reported in previous literature [29]. Then well-defined dimethacrylate terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomers (MATHFA) were prepared by the reaction of CTHFA and hydroxyethyl methyacrylate (HEMA). The specifically designed oligomer was used as an effective surface additive because of its unique ability to produce high hydrophobic surface of the UVcured films as well as thermal and chemical stabilities. The effects of chain length and content of MATHFA on the surface properties of UV-cured films were specifically investigated by changing the ratio of oligomers used. Contact angle measurements and surface energy were used to assess the wettability of the UV-cured films and the surface composition was evaluated by X-ray photoelectron spectroscopy (XPS). In addition, the bulk properties of the films, such as the thermal properties were also discussed in details.
2. Results and discussion 2.1. Synthesis and characterization of fluorinated oligomer MATHFA MATHFA was synthesized in a four-step procedure. Firstly, the BTHMA was synthesized by the metal-free anionic polymerization in THF at room temperature. GPC data showed the molecular weight distributions were fairly narrow. In this work, BTHFA of 2000 and 3000 g/mol was synthesized to investigate the effect of length of fluorinated chain on the properties of UV-cured coatings. Then the di-tert-butyl esters at the end of BTHMA were hydrolyzed under mild conditions in present of anhydrous sodium iodide and trimethylchlorosilane as previously reported [29]. Next, the CTHMA was reacted with SOCl2 to give diacyl chloride terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate). Finally, diacyl chloride terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) was functionalized by the reaction with HEMA to generate MATHFA. The synthetic route of MATHFA was shown in Scheme 1. The chemical structures of MATHFA were confirmed by FTIR and 1H NMR spectra. As shown in Fig. 1, the characterization absorption peaks at 812 and 1635 cm1 in trace b represented the bending and stretching vibration of C5 5C groups, which indicates the existence the methyacrylic groups. Fig. 2 shows the 1H NMR spectra of MATHFA in DMSO solvent. The resonance signals of methane proton of –CHF– and methylene protons of –CH2–CF2– appear in the region of 5.98–6.11 ppm and 4.54–4.62 ppm, respectively. The chemical shift of 4.25–4.33 ppm represents the methylene protons of –CH2–CH2– groups affected by the two ester C5 5O groups. The peaks at chemical shift of 5.64–5.68 ppm and 5.98–6.11 ppm belong to the protons of C5 5C double bonds. These results confirm that the pure MATHFA is successfully prepared.
Scheme 1. Synthetic route of difunctional fluorinated acrylic oligomer MATHFA.
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
Fig. 1. FT-IR absorption spectra of (a) CTHFA-3000 and (b) MATHFA-3000.
Fig. 2. 1H NMR spectra of MATHFA-3000.
51
Fig. 4. Contact angles on the UV-cured films with different concentrations of MATHFA-2000 and pure MEA.
Fig. 5. Surface energy of UV-cured films with different concentrations of MATHFA2000 and MATHFA-3000.
2.2. Surface properties of the UV-cured films The water contact angles and surface energies were measured to determine the wettability of the fluorinated films. Firstly, all the UV-cured films were peeled off form the glass substrates and the surface properties were investigated on the two sides of cured films. The contact angles and the surface energies of the cured films are shown in Figs. 3–5. As shown in the Figures, the water contact
Fig. 3. Contact angles on the UV-cured films with different concentrations of MATHFA-2000 and pure MEA.
angle of pure MEA acrylic resin is around 648 on both sides. When a small amount of difunctional fluorinated oligomer is added to the mixture, the water contact angles of the air side of the composited film are greatly changed [21,30]. It can be seen from the Figs. 3 and 4, the contact angles of the films on the air side depend on the fluorinated oligomer content: the contact angles increases upon increasing the amount of fluorinated oligomer [22]. By comparing with the two sides of the films, the fluorinated oligomer MATHFA is only effective to modify surface properties at air side [19]. It can be seen from Fig. 5, when the concentration of fluorinated oligomers in the sample is up to 1.3 wt.%, the surface energy lowered the minimum value and similar data measured by a fully fluorinated surface [31]. This phenomenon may be attributed the fluorinated moieties produce ordered surface structure, allowing fluorocarbons to be exposed to the outermost surface of the films [9,17,28]. In addition, the long tail-like fluorinated moieties in the welldefined difunctional oligomer has stronger thermodynamic driving force for fluorinated groups migration and concentration on the outermost layer, so a little amount of MATHFA can result in a completely hydrophobic surface. For further comparing the data of different additives MATHFA2000 and MATHFA-3000, it can be clearly seen that the contact angle in the case of MATHFA-3000 are slightly higher than for MATHFA-2000 at the same concentration. This result suggests that besides concentration, the length of fluorinated oligomer also influences the surface properties [9,27].
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
52
Fig. 6. XPS curves of UV-cured films with 0.2 wt.% MATHFA-2000 and MATHFA3000, and 1.3 wt.% MATHFA-2000 and MATHFA-3000.
2.3. Surface composition characterization The contact angle measurements could provide the indirect information that there is a change in the surface composition of the film and fluorinated group migration takes place at the outermost layer. XPS analysis can provide quantitative and qualitative analysis on the surface composition of the surface. Therefore, XPS was used to investigate the surface composition to confirm the surface enrichment of fluorine atom. Fig. 6 shows the XPS curves of UV-cured films with 0.2 wt.% MATHFA-2000 and MATHFA-3000, and 1.3 wt.% MATHFA-2000 and MATHFA-3000. The peaks at 282.8, 530.9 and 686.6 eV are attributed to C1s, O1s and F1s, respectively. As shown in Fig. 6, the fluorine signal at 686.6 eV strongly increases when the MATHFA concentration goes form 0.2 wt.% to 1.3 wt.%, which indicates the fluorine atoms at the surface of the film increase upon increasing the MATHFA concentration [17]. This result can explain the sharp change of water contact angles of the MATHFA modified UV-cured films shown in Figs. 3 and 4. In addition, at the same concentration, the fluorine signal of MATHFA-3000 is bigger than that of MATHFA2000, which demonstrates the shorter MATHFA is less effective enrichment at the surface than the corresponding films containing the longer MATHFA. In this paper, we define a new surface enrichment factor, Smf, which is the ratio of mass content of fluorine atoms at the top surface of the UV-cured films (Fm), to the mass content of fluorine atoms in bulk of the UV-cured formulation (Fmb): the equation is summarized below:
Smf ¼
Fm : F mb
Table 1 shows the fluorine atomic content, mass content and surface enrichment factors (SF and Smf) of the UV-cured films measured by XPS, respectively. As seen from the Table 1, the surface fluorine contents of all the samples are much higher than
calculated in bulk, which significantly illustrates the fluorine atom migrate to the outermost surface. In the bulk, the four samples have two mass content of fluorine of 0.096 wt.% and 0.624 wt.%, while at the surface the fluorine mass content are 14.50, 30.70, 20.35, 35.15 wt.%, respectively. The two surface enrichment factors, SF and Smf, range from 50 to 208-fold and 56 to 490fold with respect to the bulk concentration, respectively. All the four samples exhibit higher fluorine atom and mass concentrations at the outermost surface at the air side than in the bulk of UVcured formulations. These results can be explained as following: during the UV-curing process, the difunctional vinyl groups at the end of MATHFA react with the MEA to generate three-dimensional networks; because of the low surface tension and strong thermodynamic driving force of fluorinated moieties, the perfluoroalkyl segments of MATHFA float on the surface from the bulk. The F/C atom ratios at the surface of the UV-cured films with different concentration of fluorinated oligomer are listed in Table 2. As shown in the Table 2, the F/C atom ratios increase with adding more MATHFA, which implied the fluorine atoms enrichment at the surface of the films [21]. In addition, the values of F/C atom ratios of films incorporated with MATHFA-2000 from 0.2 wt.% to 1.3 wt.% are 0.1462 to 0.3823, while the values of the F/ C atom ratios of films incorporated with MATHFA-3000 from 0.2 wt.% to 1.3 wt.% are 0.2208 and 0.4506. This demonstrates that at the same concentration the longer MATHFA-3000 is more efficient in migrating to the air-polymer surface at extremely low concentration, which is in agreement with the results obtained from the contact angle measurements. 2.4. Bulk properties of the UV-cured films The surface modified films were obtained by introducing functional MATHFA to bisphenol-A epoxy methacrylate resin (MEA) at a concentration ranging from 0.2 to 1.3 wt.%. The gel contents of UV-cured films shown in Table 3 containing different MATHFA concentrations are quite high, which is the similar to that of the pure MEA [28]. The surface hardness of the films was measured using the pencil test method. The hardness of the films in presence of fluorinated groups is not changed in such low amount [32] (Table 3). The adhesion property, which takes part in a protective function in the coatings, is one of important issues to assess the high performance coatings. Because the fluorinated groups have different surface tension from other composition in the UV-cured formulations, the fluorinated coatings exhibit poor adhesion property [33]. However, the MATHFA modified films shown 97% adhesion on the glass substrate as well as the pure MEA. This phenomenon can be explained as follows: during the curing process, the fluorinated groups of MATHFA selectively migrate to the outermost layer of UV-cured film, which lead to the side of film in contact with glass substrate free of fluorinated groups [26,32]. Glass transition temperature (Tg) of the UV-cured films were investigated by differential scanning calorimetry (DSC). Fig. 7 shows the DSC thermograms of the pure BMA film and modified films by introduction of MATHFA-2000 and MATHFA-3000 at the
Table 1 The fluorine content on the surface of the UV-cured films. Samples
wt.% of fluorine in bulka
Estimated atom % of fluorine in bulk
Atomic conc % of fluorine
Mass conc wt.% of fluorine
SF
Smf
0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
0.096 0.624 0.096 0.624
0.071 0.46 0.071 0.46
10.30 23.10 14.75 26.70
14.50 30.70 20.35 35.15
145 50 208 58
151 490 286 56
a
The ratio as fluorine mass content in MATHFA to the whole UV-cured formulation.
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
53
Table 2 The surface composition and F/C atom ratio of the UV-cured films measured by XPS. Samples
C1s
O1s
F1s
F/C
0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
70.44 60.77 66.79 59.25
19.26 16.13 18.46 14.05
10.30 23.10 14.75 26.70
0.1462 0.3823 0.2208 0.4506
Table 3 The main bulk properties of the UV-cured films. Samples
Gel content %
Pencil hardness
Adhesion (%)
EMA 0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
98 98 98 97 98
4H 4H 5H 4H 4H
98 97 98 98 98 Fig. 8. TGA thermograms of the MATHFA-2000 and MATHFA-3000 samples.
Table 4 Thermal properties of the UV-cured films.
change significantly the thermal stability of pure MEA due to the low concentrations.
Samples
T5% (8C) T50% (8C) Tmax (8C) wt.% at 600 8C Tg (8C)
EMA 0.2MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 1.3MATHFA-3000/EMA
296.8 295.9 294.0 295.7 296.3
416.1 416.6 419.9 418.1 417.9
415.0 420.0 420.0 422.0 421.0
7.95 8.86 9.40 9.84 9.11
63.7 62.9 63.5 63.3 64.1
0.2 and 1.3 wt.% concentrations. The Tg values of all the samples are summarized in Table 4. No obvious change of Tg is found between MATHFA modified UV-cured films and the pure EMA resins [19]. The thermal decomposition behaviors of the films modified by MATHFA were analyzed by TGA under N2 atmosphere and compared with the pure MEA resin. The TGA curves are reported in Fig. 8, while the thermal parameters such as their decomposition temperatures at weight loss of 5, 50 wt.%, the maximum rate of weight loss and residual weight percent at 600 8C (Td5%, Td50%, Tmax and wt.% at 600 8C), are also listed in Table 4. The residual weight values of UV-cured films at 600 8C containing MATHFA-2000 and MATHFA-3000 are slightly higher than the pure MEA. This result can be contributed to the excellent thermal stability properties of fluorinated groups, which decelerates the thermal decomposition [34]. The Td5%, Td50%, and Tmax values of the UV-cured films containing MATHFA are similar to that of pure MEA resin, which indicates the MATHFA added in UV-cured formulations does not
Fig. 7. DSC thermograms of the MATHFA-2000 and MATHFA-3000 samples.
3. Conclusion The well-defined fluorinated acrylic oligomer MATHFA, was prepared successfully in four steps and characterized by FTIR and 1 H NMR spectroscopy. This reactive fluorinated oligomer was employed as an effective surface additive into UV-cured epoxy acrylic resin formulations at different concentrations (ranging from 0.2 wt.% to 1.3 wt.%). Contact angle measurements showed that completely hydrophobic surfaces of the UV-cured films at the air side were obtained even at low amount of MATHFA. XPS analysis confirmed that the fluorinated groups selectively migrate to the outermost layer of the films. In addition, by comparing to the MATHFA-2000 and MATHFA-3000 series, the length of fluorinated oligomers also influence the surface properties of the films. The longer MATHFA oligomers can float on the air-side surface easier than that of shorter MATHFA oligomers. The bulk properties of the films measured by DSC, TGA etc. were the similar to that of pure MEA due to low amount of fluorinated additives. In brief, tailored high hydrophobic surfaces of UV-cured films were obtained and there was no change in bulk properties. 4. Experimental 4.1. Materials THF (Purity: 99.0%, Shanghai Chemical Co., Ltd, China) and 2,2,3,4,4,4-hexafluorobutyl acrylate (HFA, Purity: 96%; Harbin Xeogia Fluorine-Silicon Chemical Co., Ltd, China) were purified using procedures reported earlier [29]. Tetrabutylammonium hydroxide (TBAOH; Purity: 25% in H2O, Aladdin Chemistry Co., Ltd, China), methylacrylic acid (Purity: 99.0%, Aladdin Chemistry Co., Ltd, China), 2-hydroxy-2-methylpropiophenone (Darocur 1173; Purity: 97.0% Lianyungang Shennan Chemical Co., Ltd, China), di-tert-butyl malonate (Purity: 98.0%, ChangZhou XiaQing Chemical Co., Ltd. China), diglycidyl ether of bisphenol A (DGEBA, the epoxide equivalent weight (EEW): 196 g/epoxide, Shell Chemical Co., Ltd, Holland), were used as received. 2hydroxyethyl methacrylate (HEMA; Purity: 98.0%, Aladdin Chemistry Co., Ltd, China) was dried over 4 A˚ molecular sieve prior to use. Sodium iodide (NaI; Purity: 99.5% Shanghai Lingfeng Chemical Reagent Co., Ltd, China) was dried at 160 8C for 8 h to use. Bisphenol-A epoxy methacrylate (EMA, 98.0%) was synthesized according to a procedure reported in literature [34]. Trimethylchlorosilane ((TMS)Cl, Purity: 99.0%), triethylamine
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
54
(Purity: 99.0%), acetonitrile (Purity: 99.0%) and chloroform (Purity: 99.0%) were supplied by Shanghai Chemical Co., Ltd, China and were distilled prior to use, respectively.
SF ¼
4.2. Characterization The 1H NMR spectra was record with a 400 MHZ NMR spectrometer (Bruker, Germany) using DMSO as a solvent. The Fourier transform infrared (FT-IR) spectra were obtained using a TENSOR27 (Bruker, Germany) spectrometer over the range 400– 4000 cm1. Gel permeation chromatography (GPC) was performed with Waters 2410 (USA) equipped with two Styragel HR columns (7.8 mm 300 mm). The molecular weight and molecular weight distribution of the functional oligomer were determined from a calibration curve established using polystyrene standards (PS, Shodex, SM-105, Japan). THF was used as the eluent at a flow rate of 1 mL min1 at 25 8C. The gel content was performed with the following procedure. The UV-cured films were extracted with chloroform for 24 h at room temperature. The equation summarized below: Wt Gel content % ¼ W 100% where, W0 is the initial weight of the 0 UV-cured film. Wt is the final weight after extraction. The hardness of the cured films was evaluated using the Stander test method ASTM D3363. The adhesion of the films was measured using the ‘‘Lattice notch method’’. The measured films were divided in to small squares (1 mm 1 mm) by razor blade. The insulating tape is used to place over the surface of the films, squeezed with finger in order to completely contact with these squares and pulled form the films. A portion of small squares is separated from the substrate. The equation was calculated as [35]:
Adhesion ¼
ab 100% a
where, a represented the total number of squares, b represented the number of squares separated from the substrate. The contact angles of water were performed with an optical contact angle meter (Shanghai Zhongchen, China) at room temperature (25 8C). The air-side and glass-side of the UV-cured films were measured using sessile drop technique to avoid vibration and distortion of the drops. The average contact angle of each sample was measured more than five times at different locations. In this study, the surface energy from the contact angle was calculated based on the equation derived by Li and Neumann [36].
1 þ cosu ¼ 2ðg S =g L Þ1=2 exp½bðg L g S Þ
used to represent the ability of the surface segregation of fluorinated groups.
2
gS and gL were the surface energy of the solid and the test liquid, respectively. b was a constant with a value of 0.0001247 (m2 mj1)2. u was the test water contact angle date. X-ray photoelectron spectroscopy (XPS) results were obtained using an X-ray Photoelectron Spectroscopy/ESCA (Axis Ultra DLD, Kratos Analytical Ltd, UK) with a Mono Al Ka source. The take-off angle was 908 with respect to the surface of all the UV-cured films. The surface enrichment factor given by Levine et al., SF [37,38], was
F surface F bulk
where, Fsurface was the atom fluorine content at the surface of the UV-cured films measured by XPS; Fbulk was the atom fluorine content in the bulk of the UV-cured formulation estimated assuming a uniform and random distribution. The differential scanning calorimetry (DSC) measurements were performed on DSC204 (NETZSCH Germany) under N2 atmosphere. Each sample (about 10 mg) was scanned from 70 to 200 8C at a heating rate of 20 8C/min and held at 200 8C for 5 min to remove the thermal history. Glass transition temperature (Tg) values were recorded during the second heating scan taken as the midpoint of the heat capacity change. Thermogravimetric analysis (TGA, TG209F3 NETZSCH Germany) was performed on a TG209F3 to study the thermal stability of fluorinated UV-cured films under N2 atmosphere. Each sample was about 5 mg and heated at the heating rate of 10 8C/min from 30 8C to 800 8C. 4.3. Synthesis of fluorinated acrylic oligomer The synthetic routes for preparing di-tert-butyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (BTHFA) and dicarboxyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (CTHFA) have been reported in our previous work [29]. In summary, using tetrabutylammonium salt of di-tert-butyl malonate as anionic initiator, BTHFA was prepared by metal-free anionic polymerization of HFA in a controlled manner at room temperature. The molecular weight and molecular weight distribution of BTHFA were estimated by GPC and shown in Table 5. CTHFA was synthesized by the hydrolysis of BTHFA under argon atmosphere for 3 h in presence of sodium iodide and the (TMS)Cl. CTHFA 5 g and thionyl chloride (SOCl2) 30 ml were added in a two-neck round bottomed flask equipped with a reflux condenser and thermometer. The mixture was refluxed for 24 h at 60 8C, removed the excessive SOCl2 under reduced pressure. The obtained compound, diacyl chloride terminated poly(2,2,3,4,4,4hexafluorobutyl acrylate), dried in vacuum at 50 8C for 24 h and stored under an argon atmosphere. The diacyl chloride terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (3 g), 50 ml purified THF, DMAP (0.02 g) and Triethylamine (0.4 g) were placed in a three-neck round bottomed flask equipped with an argon inlet tube and reflux condenser and thermometer, and then immersed in an ice bath at 0 8C. Then HEMA (0.52 g) dissolved in 10 ml THF and added drop by drop to the reactor via syringe over a period of 10 min. The mixture was stirred at 0 8C for 2 h and kept at 60 8C for 24 h. The precipitate of triethylamine hydrochloride was filtrated by Buchner funnel. THF was removed under reduced pressure, and the obtained product was dissolved in ethyl acetate (50 ml), and washed with 5% aqueous hydrochloric acid (20 ml) three times and distilled water (20 ml) repeatedly to remove the excessive HEMA and DMAP. The ethyl acetate layer was evaporated to obtained difunctional
Table 5 The molecular weight and molecular weight distribution of BTHFA prepared using metal-free anionic polymerization in THF solvent. Sample
[I]/[M]a molar ratio
T (8C)
Mn,GPC (g mol1)
PDIb (Mw/Mn)
Mn,NMc (g mol1)
State
Yield (%)
BTHFA-2000 BTHFA-3000
1:8 1:12
25 25
1947 2993
1.14 1.11
1735 2771
Liquid Liquid
94.7 95.2
a b c
[I]/[M] = initiator/monomer; [I] = 2 mmol. obtained from GPC. Molecular weight measured by 1H NMR.
Z. Yan et al. / Journal of Fluorine Chemistry 147 (2013) 49–55
55
Table 6 The weight composition of UV-cured formulations. Sample
a
b
Darocur 1173 (g)
EMA (g)
EMA 0.2MATHFA-2000/EMA 0.5MATHFA-2000/EMA 0.8MATHFA-2000/EMA 1.0MATHFA-2000/EMA 1.3MATHFA-2000/EMA 0.2MATHFA-3000/EMA 0.5MATHFA-3000/EMA 0.8MATHFA-3000/EMA 1.0MATHFA-3000/EMA 1.3MATHFA-3000/EMA
— 0.01 0.025 0.04 0.05 0.065 — — — — —
— — — — — — 0.01 0.025 0.04 0.05 0.065
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 4.99 4.975 4.6 4.95 4.935 4.99 4.975 4.6 4.95 4.935
a b
MATHFA-2000 (g)
Obtained from BTHFA-2000. Obtained from BTHFA-3000.
fluorinated acrylic oligomer (MATHFA) and dried in vacuum oven at 60 8C for 24 h. 4.4. Preparation of UV-curable coatings The UV-curing formulations were prepared by mixing different amount of MATHFA to bisphenol-A epoxy methacrylate (MEA) by adding 4 wt.% of 2-hydroxy-2-methylphenylpropanone (Darocur 1173) and the relative weight compositions for the mixtures were listed in Table 6. The obtained mixtures were stirred for 30 min and coated on glass substrate by means of a wire-wound applicator. The coated films were exposed to UV irradiation by using a highpressure mercury lamp (500 W) for 30 s with a distance of 20 cm from lamp to the surface of samples in the air atmosphere. The cured films about of 100 mm were obtained. Acknowledgements The work was financially supported by the Program Key Laboratory of Cellulose and Lignocellulosics, Guangzhou Institute of Chemistry, Chinese Academy of Sciences - ‘‘Research on fiber fabric modified by waterborne fluorosilicone polymer finishing agent’’. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
MATHFA-3000 (g)
S.J. Choi, K.Y. Suh, H.H. Lee, J. Am. Chem. Soc. 130 (2008) 6312–6313. B. Mu˝ ller, U. Poth, Coatings Formulation, Vincentz, Hannover, 2006. H.D. Hwang, H.J. Kim, React. Funct. Polym. 71 (2011) 655–665. P. Roose, I. Fallais, C. Vandermiers, M.G. Olivier, M. Poelman, Prog. Org. Coat. 64 (2009) 163–170. R. Bongiovanni, F. Montefusco, A. Priola, N. Macchioni, S. Lazzeri, L. Sozzi, B. Ameduri, Prog. Org. Coat. 45 (2002) 359–363. G. Hougham, K. Johns, P.E. Cassidi, J. Davidson, Floropolymers, Plenum Press, New York, 1999. C.G. Roffey, Photopolymerization of Surface Coatings, Wiley, New York, 1982. J.R. Lee, F.L. Jin, S.J. Park, J.M. Park, Surf. Coat. Technol. 180–181 (2004) 650–654. R.D. van de Grampel, W. Ming, W.J.H. van Gennip, F. van der Velden, J. Laven, J.W. Niemantsverdriet, R. van der Linde, Polymer 46 (2005) 10531–10537.
[10] L. Valtola, S. Hietala, H. Tenhu, P. Denifl, C.E. Wilen, Polym. Adv. Technol. 20 (2009) 225–234. [11] T. Imae, Curr. Opin. Colloid. Interface Sci. 8 (2003) 307–314. [12] H.S. Sundaram, Y. Cho, M.D. Dimitriou, J.A. Finlay, G. Cone, S. Williams, D. Handlin, J. Gatto, M.E. Callow, J.A. Callow, E.J. Kramer, C.K. Ober, Appl. Mater. Interfaces 3 (2011) 3366–3374. [13] Z.Q. Tao, S.Y. Yang, Z.Y. Ge, J.S. Chen, L. Fan, Eur. Polym. J. 43 (2007) 550–560. [14] J. Wang, Y. Xu, L. Zhu, J. Li, B. Zhu, Polymer 49 (2008) 3256–3264. [15] K. Reihs, M. Voetz, Langmuir 21 (2005) 10573–10580. [16] S.J. Yuan, S.O. Pehkonen, B. Liang, Y.P. Ting, K.G. Neoh, E.T. Kang, Corros. Sci. 53 (2011) 2738–2747. [17] H. Miao, Z.G. Huang, L.L. Cheng, W.F. Shi, Prog. Org. Coat. 64 (2009) 365–370. [18] H. Miao, F.F. Bao, L.L. Cheng, W.F. Shi, J. Fluorine Chem. 131 (2010) 1356–1361. [19] M. Sangermano, R. Bongiovanni, G. Malucelli, A. Priola, A. Pollicino, A. Recca, J. Appl. Polym. Sci. 89 (2003) 1524–1529. [20] M. Sangermano, W. Carbonaro, R. Bongiovanni, R.R. Thomas, C.M. Kausch, Macromol. Mater. Eng. 295 (2010) 469–475. [21] R. Bongiovanni, G. Malucelli, M. Sangermano, A. Priola, J. Fluorine. Chem. 125 (2004) 345–351. [22] H.K. Kim, J.G. Kim, J.D. Cho, J.W. Hong, Polym. Test. 22 (2003) 899–906. [23] B.S. Shemper, L.J. Mathias, J. Appl. Polym. Sci. 91 (2004) 3301–3314. [24] J.M. Corpart, S. girault, D. Juhue´, Langmuir 17 (2001) 7237–7244. [25] E. Barbu, R.A. Pullin, P. Graham, P. Eaton, R.J. Ewen, J.D. Smart, T.G. Nevell, J. Tsibouklis, Polymer 43 (2002) 1727–1734. [26] R. Bongiovanni, A. Medici, A. Zompatori, S. Garavaglia, C. Tonelli, Polym. Int. 61 (2012) 65–73. [27] Y.H. Lin, K.H. Liao, C.K. Huang, N.K. Chou, S.S. Wang, S.H. Chu, K.H. Hsieh, Polym. Int. 59 (2010) 1205–1211. [28] M. Sangermano, R. Bongiovanni, G. Malucelli, A. Priola, R.R. Thomas, C.M. Kausch, Y. Kim, J. Polym. Sci: Part. A: Polym. Chem. 44 (2006) 6943–6951. [29] Z.L. Yan, W.Q. Liu, N. Gao, Y. Sun, H.S. Chen, Iran. Polym. J., http://dx.doi.org/ 10.1007/s13726-012-0074-6. [30] B. Ameduri, R. Bongiovanni, V. Lombardi, A. Pollicino, A. Priola, A. Recca, J. Polym. Sci.: Part A: Polym. Chem. 39 (2001) 4227–4235. [31] M.K. Chaudhury, G.M. Whitesides, Langmuir 7 (1991) 1013–1025. [32] M. Sangermano, A.D. Gianni, R. Bongiovanni, A. Priola, B. Voit, D. Pospiech, D. Appelhans, Macromol. Mater. Eng. 290 (2005) 721–725. [33] R. Bongiovanni, A.D. Gianni, A. Priola, A. Pollicino, Eur. Polym. J. 43 (2007) 3787–3794. [34] C.Y. Tang, W.Q. Liu, S.Q. Ma, Z.F. Wang, C.H. Hu, Prog. Org. Coat. 69 (2010) 359–365. [35] G. Ahmetli, H. Deveci, U. Soydal, A. Seker, R. Kurbanli, Prog. Org. Coat. 75 (2012) 97–105. [36] D. Li, A.W. Neumann, J. Colloid Interf. Sci. 148 (1992) 190–200. [37] F. Levine, J.L. Scala, W. Kosik, Prog. Org. Coat. 69 (2010) 63–72. [38] H.D. Hwang, H.J. Kim, J. Colloid. Interf. Sci. 362 (2011) 274–284.