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International Journal of Polymer Science

Volume 2014, Article ID 464806, 11 pages

http://dx.doi.org/10.1155/2014/464806
Research Article

Synthesis of Fluorinated Amphiphilic Block Copolymers Based on PEGMA, HEMA, and MMA via ATRP and CuAAC Click Chemistry

1Department of Chemistry, Faculty of Arts and Science, Yildiz Technical University, Davutpasa Campus, Esenler, 34220 Istanbul, Turkey

2Department of Chemistry, Faculty of Arts and Science, Fatih University, Buyukcekmece, 34500 Istanbul, Turkey

3Department of Chemistry, Medical Laboratory Techniques, Vocational School of Medical Sciences, Fatih University, Maltepe, 34840 Istanbul, Turkey

4Department of Chemical Engineering, Faculty of Chemical and Metallurgical Engineering, Yildiz Technical University, Davutpasa Campus, Esenler, 34220 Istanbul, Turkey

Received 6 May 2014; Accepted 27 July 2014; Published 19 August 2014

Academic Editor: Ali Akbar Entezami

Copyright © 2014 Fatime Eren Erol et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Synthesis of fluorinated amphiphilic block copolymers via atom transfer radical polymerization (ATRP) and Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) was demonstrated. First, a PEGMA and MMA based block copolymer carrying multiple side-chain acetylene moieties on the hydrophobic segment for postfunctionalization was carried out. This involves the synthesis of a series of P(HEMA-co-MMA) random copolymers to be employed as macroinitiators in the controlled synthesis of P(HEMA-co-MMA)-block-PPEGMA block copolymers by using ATRP, followed by a modification step on the hydroxyl side groups of HEMA via Steglich esterification to afford propargyl side-functional polymer, alkyne-P(HEMA-co-MMA)-block-PPEGMA. Finally, click coupling between side-chain acetylene functionalities and 2,3,4,5,6-pentafluorobenzyl azide yielded fluorinated amphiphilic block copolymers. The obtained polymers were structurally characterized by 1H-NMR, 19F-NMR, FT-IR, and GPC. Their thermal characterizations were performed using DSC and TGA.

1. Introduction

The perfluoroalkyl moieties in amphiphilic molecules provide distinct properties, such as hydrophobicity and lipophobicity, high thermal and chemical stability, excellent mechanical properties at extreme temperatures, low refractive index, and a strong tendency to self-assemble [16]. A great deal of attention has been paid to the incorporation of fluorinated groups into synthetic materials, which combine the advantages of both fluorinated groups and other polymers [710]. Controlled radical polymerization (CRP) can serve as a powerful synthetic tool in the production of well-defined fluorinated polymers with various architectures having predetermined chain lengths and low polydispersities. Fluorinated block copolymers have been synthesized previously via CRPs, involving nitroxide mediated radical polymerization (NMP) [11, 12], reversible addition fragmentation chain transfer polymerization (RAFT) [13, 14], and atom transfer radical polymerization (ATRP) [1519].

Amphiphilic block copolymers consisting of hydrophobic fluorinated blocks and hydrophilic poly[poly(ethylene glycol)methyl ether methacrylate] (P(PEGMA)) have been synthesized [2023]. P(PEGMA) block, prepared by CRPs, is a versatile polymer in fine-tuning hydrophobic/hydrophilic balance of the amphiphile since lengths of both P(PEGMA) and PEG side-chains can be altered. Besides, P(PEGMA) segments may introduce favorable characteristics to the copolymers including water solubility, low toxicity, and high biocompatibility [2426]. 2,3,4,5,6-Pentafluorobenzyl containing segments have been employed as the hydrophobic part in several studies and have accounted for the abovementioned properties stemming from perfluoroalkyl moieties [2729]. The overall macromolecules have potential in applications involving nonlinear optics, rheology modifiers, and antifouling coatings.

Quite recently, click reactions have attracted considerable attention in synthetic polymer chemistry owing to their high specificity, high tolerance of functional groups, and quantitative reaction yields. Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC), which occurs between an azide and an alkyne to give 1,2,3-triazole ring [30, 31], has emerged as a powerful tool in the preparation of versatile macromolecular structures when used in conjunction with controlled/living radical polymerization techniques [9, 32].

Herein, we report the synthesis of a fluorinated amphiphilic block copolymer on the basis of combined ATRP and Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) methods. To the best of our knowledge, this is the first study to report the preparation of perfluoroalkylated amphiphilic block copolymer brushes by this approach. Furthermore, the method allows for facile adaptation of a variety of other click moieties and fine-tunes their concentration without altering the size of hydrophobic segment.

2. Experimental

2.1. Materials

Methyl methacrylate (MMA, 99%, Aldrich) and 2-hydroxyethyl methacrylate (HEMA, 99%, Aldrich) were distilled before use. Poly(ethylene glycol) methyl ether acrylate (PEGMA, = 480 g/mol, Aldrich) was passed through basic alumina column to remove the inhibitor. Ethylα-bromoisobutyrate (EBIB, 98%, Aldrich), 2,3,4,5,6-pentafluorobenzyl chloride (Aldrich 99%), CuCl (≥99.99%, Aldrich), CuBr (98%, Aldrich), sodium azide (NaN3, Sigma-Aldrich), 2,2-bipyridine (bpy, 99%, Fluka), -pentamethyldiethylenetriamine (PMDETA, 99%, Aldrich), methanol (≥99.9, Aldrich), -dicyclohexylcarbodiimide (DCC, 99%, Aldrich), 4-(dimethylamino) pyridine (DMAP, ≥99.99%, Aldrich), propiolic acid (99%, Aldrich), and -dimethylformamide (DMF, 99%, Aldrich) were used as received.

2.2. Typical Procedure for the Random Copolymerization of HEMA with MMA via ATRP (1a–d)

Molar ratio of MMA and HEMA was varied to get random copolymers with different HEMA contents. For instance, to obtain P(HEMA(20)-co-MMA(80)), in which the numbers in parenthesis refer to v/v percentages, reagents at the molar ratio of [HEMA]/[MMA]/[EBIB]/[CuCl]/[bpy]: 18/82/1/1/2.5 were added. HEMA (1.72 g, 1.60 mL, 13 mmol), MMA (6.01 g, 6.40 mL, 60 mmol), CuCl (0.072 g, 0.72 mmol), ethylα-bromoisobutyrate (EBIB, 0.142 g, 0.72 mmol), and bipyridine (bpy, 0.145 g, 0.093 mmol) were mixed in a Schlenk tube equipped with a magnetic stirring bar, to which 5.3 mL of methanol ([monomer]/solvent = 1.5 : 1 v/v) was added. The tube was degassed by three freeze-pump-thaw cycles. The polymerization flask was placed on a magnetic stirrer and kept there for a given period at room temperature, after which the reaction was terminated by dipping the tube into liquid nitrogen. The mixture was diluted with THF and passed through a silica gel column to remove the complex salts. The solution was then concentrated and precipitated into 10-fold excess hexane. The precipitate was collected by filtration and dried in a vacuum oven at 30°C overnight. (68 % conv., 1H-NMR (CDCl3, ppm): δ = 0.88–1.36 (s, α-CH3, MMA and HEMA), 1.5–2.1 (s, –CH2, MMA and HEMA), 3.55 (s, –OCH3, MMA), 3.78 (t, –CH2OH, HEMA), 4.05 (t, –OCH2, HEMA). FT-IR (cm−1): 3540 (–OH stretching), 2957 (–CH aliphatic stretching), 1726 (–C=O stretching), and 1151 (–C–O–C– stretching).

2.3. Block Copolymerization of PEGMA Using Poly(HEMA-co-MMA) Macroinitiator via ATRP (2b, 2d)

In a typical procedure, P(HEMA(20)-co-MMA(80)) (1b) macroinitiator (0.41 g, 0.045 mmol), PEGMA (8.72 g, 18 mmol) monomer, CuBr (0.007 g, 0.045 mmol), and PMDETA (0.016 g, 0.09 mmol) were dissolved in methanol/water mixture (MeOH/water = 2 : 1 v/v) in a Schlenk tube equipped with a magnetic stirring bar. The reaction mixture was degassed by three freeze-pump-thaw cycles, backfilled with nitrogen, and kept in a magnetic stirrer at room temperature. After the given period, the Schlenk tube was immersed into liquid nitrogen to terminate the reaction. Upon reaching room temperature, the mixture was diluted with THF and passed through a silica gel column to remove the copper salt. The solution was completely dried in a rotary evaporator and then subjected to dialysis against regularly replaced distilled water to remove PEGMA monomer (spectra/Por membranes, cut-off 1,000 Da). The solution was again evaporated to dryness in a rotary evaporator. The residue was dissolved in THF and precipitated into 10-fold excess hexane. The precipitate was collected by filtration and dried in vacuo overnight. Yield: 75%. 1H-NMR (CDCl3, ppm): δ = 0.84–1.4 (s, α-CH3, MMA and HEMA), 1.8–2.1 (s, –CH2, MMA and HEMA), 2.3–2.5 (d, –CH2, PEGMA), 3.38 (s, CH3O–, PEGMA), 3.55 (s, CH3O–, MMA), 3.65 (t, –CH2O–, PEGMA), 3.84 (t, –OCH2–, HEMA), 4.1-4.2 (t, –CH2OH and –CH2CH2O, HEMA and PEGMA). FT-IR (cm−1): 3550 (–OH stretching), 2870 (–CH aliphatic stretching), 1733 (–C=O stretching), and 1095 (–C–O–C– stretching).

2.4. Synthesis of Alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b, 3d)

The reagents were used according to the following molar ratios: [side-chain OH]/[DCC]/[DMAP]/[propiolic acid]: 1/1.6/0.16/1.5. To obtain alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b, 3d), P(HEMA-co-MMA)-block-PPEGMA (2b, 2d) (0.5 g, 0.008 mmol), DCC (0.053 g, 0.256 mmol), DMAP (0.003 g, 0.0256 mmol), and propiolic acid (0.017 g, 0.24 mmol) were added in a round-bottom flask and dissolved in 50 mL CH2Cl2 under stirring at room temperature. Then, the mixture was concentrated in the rotary evaporator and precipitated in 10-fold excess hexane. Yield: 87 %. 1H-NMR (CDCl3, ppm): δ = 0.84–1.4 (s,α-CH3, MMA and HEMA), 1.8–2.1 (s, –CH2, MMA and HEMA), 2.3-2.4 (d, –CH2, PEGMA), 2.57 (s, –OCCH) 3.38 (s, CH3O–, PEGMA), 3.55 (s, CH3O–, MMA), 3.63 (t, –CH2O, PEGMA), 3.82 (t, –OCH2, HEMA), 4.1-4.2 (t, –CH2OH and –CH2CH2O, HEMA and PEGMA). FT-IR (cm−1): 3320 (–CCH stretching), 2875 (–CH aliphatic stretching), 2350 (–CCH stretching), 1735 (–C=O stretching), and 1099 (–C–O–C– eter stretching).

2.5. Synthesis of 2,3,4,5,6-Pentafluorobenzyl Azide

NaN3 (0.65 g, 0.01 mol) and 2,3,4,5,6-pentafluorobenzyl chloride (2 g, 0.008 mol) were dissolved in 50 mL -dimethylformamide in a round-bottomed flask equipped with a magnetic stirrer. The reaction solution was stirred for 24 h at room temperature [3336]. Then, DMF was removed under reduced pressure in a rotary evaporator and the remaining solid was dissolved in CH2Cl2. The mixture was washed thoroughly with water. The organic layer was removed and recovered solid was dried under vacuum at 25°C. Yield: 80%. 1H-NMR (CDCl3, ppm): δ = 3.67 (s, –CH2). FT-IR (cm−1): 2110 (–N3 stretching), 1650–1500 (–C=C– stretching), and 1235 (–CF stretching). 19F-NMR (CDCl3, ppm): δ = o: –142 (2F), p: –151 (1F), m: –161 (2F).

2.6. Click Coupling Reaction of Alkyne-P(HEMA-co-MMA)-block-PPEGMA with 2,3,4,5,6-Pentafluorobenzyl Azide (4)

The reagents were used according to the following molar ratios: [side-chain acetylene]/[–N3]/[CuBr]/[PMDETA]: 1/1/2.5/2.5. Alkyne-P(HEMA-co-MMA)-block-PPEGMA (0.3 g, 0.005 mmol) (3b) was dissolved together with 2,3,4,5,6-pentafluorobenzyl azide (0.016 g, 0.07 mmol) in degassed DMF under nitrogen. To the reaction mixture CuBr (0.025 g, 0.176 mmol) and PMDETA (0.031 g, 0.176 mmol) were added, while the solution was being purged with nitrogen. Then, it was stirred for 48 h at room temperature, after which, the mixture was diluted with THF and passed through a silica gel column to remove the copper salt [3436]. Finally, excess solvent was removed in a rotary-evaporator and the resultant solution was poured into 10-fold excess hexane for precipitation. The solid was collected by filtration and dried in vacuo overnight. (For 2,3,4,5,6-pentafluorobenzyl functional P(HEMA-co-MMA)-block-PPEGMA, yield: 83%, 1H-NMR (CDCl3, ppm): δ = 0.84–1.58 (s, α-CH3, MMA and HEMA), 1.83 (s, –CH2, MMA and HEMA), 2.30 (d, –CH2, PEGMA), 3.38 (s, CH3O–, PEGMA), 3.56 (s, CH3O–, MMA), 3.65 (t, –CH2O, PEGMA), 3.90 (t, –OCH2, HEMA), 4.0–4.17 (t, –CH2CH2 and –CH2CH2O, HEMA and PEGMA), 4.47 (s, –CH2–N3), 7.64 (s, –CH, from triazole ring), FT-IR (cm−1): 2870 (–CH aliphatic stretching), 1733 (–C=O stretching), and 1095 (–C–O–C– stretching)).

2.7. Characterizations

FT-IR spectra were recorded using a Bruker Alpha-P in ATR in the range of 4000–400 cm−1. 1H-NMR spectra were recorded using a 400 MHz Bruker Avance spectrometer in CDCl3. Chemical shifts are reported in ppm relative to TMS as internal standard.

Thermal stabilities of the membranes were analyzed by a PerkinElmer STA 6000 Thermal Analyzer. The samples (~10 mg) were heated between 30–750°C under N2 atmosphere at a scanning rate of 10°C/min. PerkinElmer JADE Differential Scanning Calorimetry (DSC) was used to investigate the thermal transitions of the samples. The samples (~10 mg) were put into aluminum pans and then heated to the desired temperature at a rate of 10°C/min under nitrogen atmosphere.

Gel-permeation chromatography (GPC) measurements were performed on THF solutions of the polymers using an Agilent GPC 1100 instrument. The measurements were standardized against THF solutions of polystyrene standards.

3. Results and Discussion

A novel approach combining ATRP with Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) in the preparation of a fluorinated amphiphilic block copolymer has been demonstrated (Figure 1). Synthesis of polymers based on MMA and PEGMA carrying clickable moieties for further functionalization was carried out in a three-step strategy, as depicted in Figure 2. First, a series of precursor random copolymers (1a–1d) P(HEMA-co-MMA) were prepared via ATRP of MMA and HEMA. In the second step, the obtained polymer was employed as a macroinitiator in ATRP of PEGMA to afford the block copolymer (2b, 2d), P(HEMA-co-MMA)-block-PPEGMA.

464806.fig.001
Figure 1: Schematic illustration of click coupling between PEGMA based amphiphilic block copolymers bearing pendant clickable sites and azide-functional group.
464806.fig.002
Figure 2: Synthesis of alkyne-P(HEMA-co-MMA)-block-PPEGMA (3) and its click coupling reaction (4).

Finally, propargyl moieties were introduced via the Steglich esterification between the hydroxyl side-functionalities of HEMA and propiolic acid. Alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b, 3d) was then click-coupled with model compound, namely, 2,3,4,5,6-pentafluorobenzyl azide to yield (4). Copolymerization of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) was carried out via ATRP using ethylα-bromoisobutyrate (EBIB), CuCl, and bipyridine as initiator, catalyst, and ligand, respectively, at room temperature in methanol. Conditions and results are summarized in Table 1. Molar ratio of MMA and HEMA was varied to get random copolymers with different HEMA contents. For instance, to obtain P(HEMA(20)-co-MMA(80)), in which the numbers in parenthesis refer to v/v percentages, reagents at the molar ratio of [HEMA]/[MMA]/[EBIB]/[CuCl]/[bpy]: 18/82/1/1/2.5 were added.

tab1
Table 1: Conditionsa and results for the synthesis of P(HEMA--MMA).

Chemical structures of the copolymers were identified using several techniques. The FT-IR spectra of four different compositions of copolymers P(HEMA-co-MMA) are given in Figure 3. The broad band at 3540 cm−1 due to the –OH stretching, increasing with the HEMA content in the copolymers, was an apparent characteristic peak of the series. The –CH stretching appeared around 2957 cm−1. The characteristic –C=O stretching band in both HEMA and MMA units in the copolymer occurred at 1726 cm−1 [37, 38]. The strong –C–O–C– type ester stretching band appeared at 1151 cm−1 [38].

464806.fig.003
Figure 3: FT-IR spectra of P(HEMA-co-MMA) copolymers.

The 1H-NMR spectra of P(HEMA-co-MMA) copolymers are given in Figure 4. The signal for methyl protons of –OCH3 (a) in MMA units appeared at 3.55 ppm [38, 39]. The signals of α-CH3 protons were seen at 0.88–1.36 ppm in both MMA and HEMA units, while for methylene protons they were in the range of 1.5–2.1 ppm. The signals at 3.78 ppm (b) and 4.05 ppm (c) correspond to –CH2OH and –CH2O protons, respectively [38].

fig4
Figure 4: 1H-NMR spectra of P(HEMA-co-MMA) copolymers (1a–1d).

Copolymer compositions from 1H-NMR were calculated by integral area of the –OCH3 and –OCH2 protons using the following [38]:

The copolymer compositions obtained from 1H-NMR agreed well with the charged monomer ratio in feed as shown in Table 2.

tab2
Table 2: Compositions of P(HEMA--MMA) obtained from 1H-NMR data.

Polymerization of poly(ethylene glycol) methyl ether acrylate was carried out via ATRP using P(HEMA(20)-co-MMA(80)) (1b) and P(HEMA(50)-co-MMA(50)) (1d) as macroinitiator and CuBr/PMDETA as catalyst system at room temperature in methanol/water. Conditions and results are summarized in Table 3.

tab3
Table 3: Conditionsa and results for the synthesis of P(HEMA-co-MMA)-block-PPEGMA.

For both P(HEMA-co-MMA)-block-PPEGMA (2b, 2d) block copolymers, the 1H-NMR spectrum exhibited signals originating from α–CH3 protons and –CH2 protons between 0.84–1.4 ppm and 1.8–2.1 ppm, respectively, in both MMA and HEMA units [38], as depicted in Figure 5. The appearance of signals at 2.3–2.5 ppm and 3.38 ppm was attributed to –CH2 and CH3O– protons arising from PEGMA units [3941]. The methyl protons for –OCH3 in MMA units were at 3.55 ppm, while –CH2O protons in PEGMA units appeared at 3.65 ppm [24, 32, 34]. Methylene protons of –CH2OH in HEMA and –CH2 in PEGMA gave a sharp signal around 4.2 ppm [3841].

464806.fig.005
Figure 5: The 1H-NMR spectrum of P(HEMA-co-MMA)-block-PPEGMA (2b, 2d).

Figure 6 shows the DSC curves of P(HEMA-co-MMA) copolymers (1b and 1d), recorded between 0–180°C. A substantial decrease in the glass transition temperature with increasing HEMA content was observed, which agreed with the literature [38]. The of P(HEMA(20)-co-MMA(80)) (1b) and P(HEMA(50)-co-MMA(50)) (1d) were detected around 100°C and 57°C [38], respectively. PHEMA and PMMA homopolymers as well as their copolymers are amorphous and do not show any melting temperature, as expected. Figure 7 shows DSC analysis of P(HEMA-co-MMA)-block-PPEGMA (2b and 2d), evaluated during the heating process from –48 to 180°C. P(HEMA-co-MMA)-block-PPEGMA shows a due to the presence of crystalline domains originating from PPEGMA blocks. The presence of at around 0°C supports the block copolymer formation. It is also noteworthy that values for (2b) and (2d) are almost the same although different feed ratios of precursor P(HEMA-co-MMA) were employed in the block copolymer formation, which might have resulted in an evident shifting of since variation of HEMA and MMA content can possibly affect the crystallinity in the microstructure. However, a careful inspection reveals that the final copolymer content (in mol) of 2b (HEMA/MMA/PEGMA ~ 1/4/22) and 2d (HEMA/MMA/PEGMA ~ 4/4/22) is very close and the fact that values are nearly the same is just as expected.

464806.fig.006
Figure 6: The DSC curves of P(HEMA(20)-co-MMA(80)) (1b) and P(HEMA(50)-co-MMA(50)) (1d) copolymers.
464806.fig.007
Figure 7: The DSC of P(HEMA-co-MMA)-block-PPEGMA (2b, 2d).

The thermal stabilities of P(HEMA-co-MMA) copolymers (1b and 1d) and P(HEMA-co-MMA)-block-PPEGMA (2b and 2d) block copolymers were analyzed as well, as shown in Figure 8. The TGA curves of P(HEMA-co-MMA) copolymers with varying composition of HEMA indicated a thermal stability up to 340–350°C [38]. On the other hand, in the analysis of P(HEMA-co-MMA)-block-PPEGMA block copolymers, the decomposition temperatures are shifted to relatively lower values with the incorporation of PEGMA units.

464806.fig.008
Figure 8: TGA curves of P(HEMA-co-MMA) (1b, 1d) and P(HEMA-co-MMA)-block-PPEGMA (2b, 2d).

The temperature of 5% weight loss, the temperature of 10% weight loss, the temperature of the rapid weight loss () before 750°C, and the char yield at 750°C in nitrogen are summarized in Table 4.

tab4
Table 4: Temperatures of various decompositions and char yield in at 750°C.

Propargyl side-functional block copolymers, alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b and 3d), were prepared by the Steglich esterification between hydroxyl groups of HEMA and propiolic acid in the presence of DCC and DMAP at room temperature [35]. The GPC analysis provided evidence for the success of reaction. As expected, there was a slight increase in the values.

For P(HEMA(20)-MMA(80))-b-PPEGMA (2b), changed from 112620 to 113350 (PDI = 1.53), while, for P(HEMA(50)-MMA(50))-b-PPEGMA) (2d), there was a change from 58040 to 59514 (PDI = 1.39), which showed the incorporation of propargyl units.

Further proof was supplied by FT IR analysis as depicted in Figure 9. As compared to the spectrum of P(HEMA-co-MMA)-block-PPEGMA, two new bands (2b, 2d) appeared at around 2350 and 3320 cm−1 in the spectrum of alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b, 3d), which were assigned to the stretching vibration of the alkyne group [35].

fig9
Figure 9: The FT-IR spectra of P(HEMA-co-MMA)-block-PPEGMA (2b, 2d) and alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b, 3d).

Finally, to assess the applicability of alkyne-P(HEMA-co-MMA)-block-PPEGMA in postfunctionalization, 3b and 3d having different molecular weights were click coupled with 2,3,4,5,6-pentafluorobenzyl azide. For this purpose, first, 2,3,4,5,6-pentafluorobenzyl azide was prepared upon reaction between their halo-compounds and NaN3 in DMF at room temperature. The halogen atoms were substituted with azide groups via nucleophilic substitution. The FT-IR spectra are illustrated in Figure 10. The appearance of sharp –N3 stretching bands between 2110 cm−1 and 2090 cm−1 for 2,3,4,5,6-pentafluorobenzyl azide supported that azidation was successful [3236, 42, 43].

464806.fig.0010
Figure 10: The FT-IR spectra of 2,3,4,5,6-pentafluorobenzyl chloride and azido-2,3,4,5-pentafluorobenzene.

In the second step, Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) was carried out between propargyl side functionalities on the backbone and 2,3,4,5,6-pentafluorobenzyl azide. The 1H-NMR spectra of the click products are illustrated in Figure 11. The appearance of the new signals at 7.64 (f) and 5.59 (e) ppm, regarding the methine proton and the methylene protons adjacent to the triazole ring, respectively, were observed [32, 3436, 42, 43].

464806.fig.0011
Figure 11: The 1H-NMR spectra of the click product (4).

Further evidence for the incorporation of 2,3,4,5,6-pentafluorobenzene was provided by 19F-NMR analysis as presented in Figure 12. The signals which appeared in the spectrum of 2,3,4,5,6-pentafluorobenzyl azide also existed in that of click product. The signals detected at –142 ppm, –151 ppm, and –161 ppm originated from the aromatic fluorines: 2F at o-position, 1F at p-position, and 2F at m-position, respectively [44].

fig12
Figure 12: (a) The 19F-NMR spectra of click product; (b) the 19F-NMR spectra of 2,3,4,5,6-pentafluorobenzyl azide.

4. Conclusions

The strategy of combining ATRP with Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) in the preparation of a novel clickable amphiphilic block copolymer was demonstrated. First, P(HEMA-co-MMA) copolymers were prepared via ATRP. Molar ratio of MMA and HEMA was varied to get random copolymers with different HEMA contents. The copolymer compositions were obtained from 1H-NMR and agreed well with the charged monomer ratio in feed. Polymerization of poly(ethylene glycol) methyl ether acrylate was carried out via ATRP using P(HEMA(20)-co-MMA(80)) (1b) and P(HEMA(50)-co-MMA(50)) (1d) as macroinitiator to get block copolymers. GPC analysis of the obtained block copolymers was measured as = 112620 (PDI = 1.58) and = 58040 (PDI = 1.39), respectively. Both 1H-NMR and FT-IR spectra showed peaks associated with MMA, HEMA, and PEGMA repeating units. Thermal properties of the copolymers and the block copolymers were also studied by TGA and DSC. For the copolymers, a thermal stability of up to 340–350°C was detected. In the next step, alkyne-P(HEMA-co-MMA)-block-PPEGMA (3b, 3d) was prepared by the Steglich esterification between hydroxyl groups of HEMA and propiolic acid in the presence of DCC and DMAP at room temperature. Finally, Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) was employed as a tool for postfunctionalization. The click coupling between propargyl side functionalities on the backbone and 2,3,4,5,6-pentafluorobenzyl azide were evidenced by 1H-NMR and 19F-NMR. This synthetic route might be useful in tuning the lengths of the hydrophilic and hydrophobic segments in amphiphilic polymers as well as the average number of functionalities situated in the side chain.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgment

This work was supported by the Scientific Research Fund of Fatih University under the Project no. P50021002_2.

References

  1. B. Jiang, L. Zhang, J. Shi et al., “Synthesis, characterization and bulk properties of well-defined poly(hexafluorobutyl methacrylate)-block-poly(glycidyl methacrylate) via consecutive ATRP,” Journal of Fluorine Chemistry, vol. 153, pp. 74–81, 2013. View at Publisher · View at Google Scholar · View at Scopus
  2. M. P. Krafft, “Controlling phospholipid self-assembly and film properties using highly fluorinated components—fluorinated monolayers, vesicles, emulsions and microbubbles,” Biochimie, vol. 94, no. 1, pp. 11–25, 2012. View at Publisher · View at Google Scholar · View at Scopus
  3. E. Amado and J. Kressler, “Triphilic block copolymers with perfluorocarbon moieties in aqueous systems and their biochemical perspectives,” Soft Matter, vol. 7, no. 16, pp. 7144–7149, 2011. View at Publisher · View at Google Scholar · View at Scopus
  4. H. Nakahara, M. Tsuji, Y. Sato, M. P. Krafft, and O. Shibata, “Langmuir monolayer miscibility of single-chain partially fluorinated amphiphiles with tetradecanoic acid,” Journal of Colloid and Interface Science, vol. 337, no. 1, pp. 201–210, 2009. View at Publisher · View at Google Scholar · View at Scopus
  5. M. Broniatowski and P. Dynarowicz-Łatka, “Semifluorinated alkanes—primitive surfactants of fascinating properties,” Advances in Colloid and Interface Science, vol. 138, no. 2, pp. 63–83, 2008. View at Publisher · View at Google Scholar · View at Scopus
  6. M. P. Krafft, “Fluorocarbons and fluorinated amphiphiles in drug delivery and biomedical research,” Advanced Drug Delivery Reviews, vol. 47, no. 2-3, pp. 209–228, 2001. View at Publisher · View at Google Scholar · View at Scopus
  7. K. K. Goli, O. J. Rojas, and J. Genzer, “Formation and antifouling properties of amphiphilic coatings on polypropylene fibers,” Biomacromolecules, vol. 13, no. 11, pp. 3769–3779, 2012. View at Publisher · View at Google Scholar · View at Scopus
  8. H. Peng, K. J. Thurecht, I. Blakey, E. Taran, and A. K. Whittaker, “Effect of solvent quality on the solution properties of assemblies of partially fluorinated amphiphilic diblock copolymers,” Macromolecules, vol. 45, no. 21, pp. 8681–8690, 2012. View at Publisher · View at Google Scholar · View at Scopus
  9. P. Scholtysek, Z. Li, J. Kressler, and A. Blume, “Interactions of DPPC with semitelechelic poly(glycerol methacrylate)s with perfluoroalkyl end groups,” Langmuir, vol. 28, no. 44, pp. 15651–15662, 2012. View at Publisher · View at Google Scholar · View at Scopus
  10. Z. Zhao, H. Ni, Z. Han et al., “Effect of surface compositional heterogeneities and microphase segregation of fluorinated amphiphilic copolymers on antifouling performance,” ACS Applied Materials and Interfaces, vol. 5, no. 16, pp. 7808–7818, 2013. View at Publisher · View at Google Scholar · View at Scopus
  11. A. Bruno, “Controlled radical (Co)polymerization of fluoromonomers,” Macromolecules, vol. 43, no. 24, pp. 10163–10184, 2010. View at Publisher · View at Google Scholar · View at Scopus
  12. N. M. L. Hansen, K. Jankova, and S. Hvilsted, “Fluoropolymer materials and architectures prepared by controlled radical polymerizations,” European Polymer Journal, vol. 43, no. 2, pp. 255–293, 2007. View at Publisher · View at Google Scholar · View at Scopus
  13. A. Chakrabarty and N. K. Singha, “Tailor-made polyfluoroacrylate and its block copolymer by RAFT polymerization in miniemulsion; improved hydrophobicity in the core-shell block copolymer,” Journal of Colloid and Interface Science, vol. 408, pp. 66–74, 2013. View at Publisher · View at Google Scholar · View at Scopus
  14. J. M. Bak and H. Lee, “Novel thermoresponsive fluorinated double-hydrophilic poly{[N-(2,2- difluoroethyl)acrylamide]-b-[N-(2-fluoroethyl)acrylamide]} block copolymers,” Journal of Polymer Science A: Polymer Chemistry, vol. 51, no. 9, pp. 1976–1982, 2013. View at Publisher · View at Google Scholar · View at Scopus
  15. T. L. Bucholz and Y. Loo, “Phase behavior of near-monodisperse semifluorinated diblock copolymers by atom transfer radical polymerization,” Macromolecules, vol. 39, no. 18, pp. 6075–6080, 2006. View at Publisher · View at Google Scholar · View at Scopus
  16. G.-D. Fu, Z.-L. Yuan, E.-T. Kang, K.-G. Neoh, D. M. Lai, and A. C. H. Huan, “Nanoporous ultra-low-dielectric-constant fluoropolymer films via selective UV decomposition of poly(pentafluorostyrene)-block-poly(methyl methacrylate) copolymers prepared using atom transfer radical polymerization,” Advanced Functional Materials, vol. 15, no. 2, pp. 315–322, 2005. View at Publisher · View at Google Scholar · View at Scopus
  17. W. Guo, X. Tang, J. Xu et al., “Synthesis, characterization, and property of amphiphilic fluorinated abc-type triblock copolymers,” Journal of Polymer Science A: Polymer Chemistry, vol. 49, no. 7, pp. 1528–1534, 2011. View at Publisher · View at Google Scholar · View at Scopus
  18. E. Martinelli, S. Agostini, G. Galli et al., “Nanostructured films of amphiphilic fluorinated block copolymers for fouling release application,” Langmuir, vol. 24, no. 22, pp. 13138–13147, 2008. View at Publisher · View at Google Scholar · View at Scopus
  19. G. P. He, G. W. Zhang, J. P. Hu et al., “Low-fluorinated homopolymer from heterogeneous ATRP of 2,2,2-trifluoroethyl methacrylate mediated by copper complex with nitrogen-based ligand,” Journal of Fluorine Chemistry, vol. 132, no. 9, pp. 562–572, 2011. View at Publisher · View at Google Scholar · View at Scopus
  20. N. M. L. Hansen, M. Gerstenberg, D. M. Haddleton, and S. Hvilsted, “Synthesis, characterization, and bulk properties of amphiphilic copolymers containing fluorinated methacrylates from sequential copper-mediated radical polymerization,” Journal of Polymer Science A: Polymer Chemistry, vol. 46, no. 24, pp. 8097–8111, 2008. View at Publisher · View at Google Scholar · View at Scopus
  21. N. M. L. Hansen, D. M. Haddleton, and S. Hvilsted, “Fluorinated bio-acceptable polymers via an ATRP macroinitiator approach,” Journal of Polymer Science A: Polymer Chemistry, vol. 45, no. 24, pp. 5770–5780, 2007. View at Publisher · View at Google Scholar · View at Scopus
  22. Y. Chen, L. Chen, H. Nie, E. T. Kang, and R. H. Vora, “Fluorinated polyimides grafted with poly(ethylene glycol) side chains by the RAFT-mediated process and their membranes,” Materials Chemistry and Physics, vol. 94, no. 2-3, pp. 195–201, 2005. View at Publisher · View at Google Scholar · View at Scopus
  23. D. Burger, J. Gisin, and E. Bartsch, “Synthesis of sterically stabilized perfluorinated aqueous latices,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 442, pp. 123–131, 2014. View at Publisher · View at Google Scholar · View at Scopus
  24. Y. Liu, J. Y. Lee, E. T. Kang, P. Wang, and K. L. Tan, “Synthesis, characterization and electrochemical transport properties of the poly(ethyleneglycol)-grafted poly(vinylidenefluoride) nanoporous membranes,” Reactive and Functional Polymers, vol. 47, no. 3, pp. 201–213, 2001. View at Publisher · View at Google Scholar · View at Scopus
  25. P. Wang, K. L. Tan, and E. T. Kang, “Surface modification of poly(tetrafluoroethylene) films via grafting of poly(ethylene glycol) for reduction in protein adsorption,” Journal of Biomaterials Science, Polymer Edition, vol. 11, no. 2, pp. 169–186, 2000. View at Publisher · View at Google Scholar · View at Scopus
  26. Y. Nakayama, M. Miyamura, Y. Hirano, K. Goto, and T. Matsuda, “Preparation of poly(ethylene glycol)-polystyrene block copolymers using photochemistry of dithiocarbamate as a reduced cell-adhesive coating material,” Biomaterials, vol. 20, no. 10, pp. 963–970, 1999. View at Publisher · View at Google Scholar · View at Scopus
  27. G. D. Fu, Z. H. Shang, L. Hong, E. T. Kang, and K. G. Neoh, “Nanoporous, ultralow-dielectric-constant fluoropolymer films from agglomerated and crosslinked hollow nanospheres of poly(pentafluorostyrene)-block-poly(divinylbenzene),” Advanced Materials, vol. 17, no. 21, pp. 2622–2626, 2005. View at Publisher · View at Google Scholar · View at Scopus
  28. M. Paz-Pazos and C. Pugh, “Synthesis of optically active copolymers of 2,3,4,5, 6-pentafluorostyrene and β-pinene with low surface energies,” Journal of Polymer Science A: Polymer Chemistry, vol. 44, no. 9, pp. 3114–3124, 2006. View at Publisher · View at Google Scholar · View at Scopus
  29. A. M. Granville, S. G. Boyes, B. Akgun, M. D. Foster, and W. J. Brittain, “Thermoresponsive behavior of semifluorinated polymer brushes,” Macromolecules, vol. 38, no. 8, pp. 3263–3270, 2005. View at Publisher · View at Google Scholar · View at Scopus
  30. H. C. Kolb, M. G. Finn, and K. B. Sharpless, “Click chemistry: diverse chemical function from a few good reactions,” Angewandte Chemie—International Edition, vol. 40, no. 11, pp. 2004–2021, 2001. View at Google Scholar
  31. V. V. Rostovtsev, G. Green, V. V. Fokin, and K. B. Sharpless, “A stepwise huisgen cycloaddition process: copper(I)-catalyzed regioselective ligation of azides and terminal alkynes,” Angewandte Chemie International Edition, vol. 41, no. 14, pp. 2596–2599, 2002. View at Google Scholar
  32. M. Ergin, B. Kiskan, B. Gacal, and Y. Yagci, “Thermally curable polystyrene via click chemistry,” Macromolecules, vol. 40, no. 13, pp. 4724–4727, 2007. View at Publisher · View at Google Scholar · View at Scopus
  33. G. D. Fu, E. T. Kang, and K. G. Neoh, “Three-dimensionally ordered porous membranes prepared via self-assembly and reverse micelle formation from well-defined amphiphilic block copolymers,” Langmuir, vol. 21, no. 8, pp. 3619–3624, 2005. View at Publisher · View at Google Scholar · View at Scopus
  34. M. Degirmenci and N. Genli, “Synthesis of well-defined telechelic macrophotoinitiator of polystyrene by combination of ATRP and click chemistry,” Macromolecular Chemistry and Physics, vol. 210, no. 19, pp. 1617–1623, 2009. View at Publisher · View at Google Scholar · View at Scopus
  35. D. Sinirlioglu and A. E. Muftuoglu, “Synthesis of an inorganic-organic hybrid material based on polyhedral oligomeric silsesquioxane and polystyrene via nitroxide-mediated polymerization and click reactions,” Designed Monomers and Polymers, vol. 14, no. 3, pp. 273–286, 2011. View at Publisher · View at Google Scholar · View at Scopus
  36. O. Eren, M. Gorur, B. Keskin, and F. Yilmaz, “Synthesis and characterization of ferrocene end-capped poly(ε-caprolactone)s by a combination of ring-opening polymerization and “click” chemistry techniques,” Reactive and Functional Polymers, vol. 73, no. 1, pp. 244–253, 2013. View at Publisher · View at Google Scholar · View at Scopus
  37. S. Arifuzzaman, A. E. Özçam, K. Efimenko, D. A. Fischer, and J. Genzer, “Formation of surface-grafted polymeric amphiphilic coatings comprising ethylene glycol and fluorinated groups and their response to protein adsorption,” Biointerphases, vol. 4, no. 2, pp. FA33–FA44, 2009. View at Publisher · View at Google Scholar · View at Scopus
  38. E. Vargün, M. Sankir, B. Aran, N. D. Sankir, and A. Usanmaz, “Synthesis and characterization of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) l,” Journal of Macromolecular Science A: Pure and Applied Chemistry, vol. 47, no. 3, pp. 235–240, 2010. View at Publisher · View at Google Scholar · View at Scopus
  39. M. M. Ali and H. D. H. Stöver, “Well-defined amphiphilic thermosensitive copolymers based on poly(ethylene glycol monomethacrylate) and methyl methacrylate prepared by atom transfer radical polymerization,” Macromolecules, vol. 37, no. 14, pp. 5219–5227, 2004. View at Publisher · View at Google Scholar · View at Scopus
  40. B. H. Tan, H. Hussain, Y. Liu, C. B. He, and T. P. Davis, “Synthesis and self-assembly of brush-type poly[poly(ethylene glycol)methyl ether methacrylate]-block-poly(pentafluorostyrene) amphiphilic diblock copolymers in aqueous solution,” Langmuir, vol. 26, no. 4, pp. 2361–2368, 2010. View at Publisher · View at Google Scholar · View at Scopus
  41. B. Kim, H. Lee, S. Jeong, J. Lee, and H. Paik, “Amphiphilic gradient copolymer of [poly(ethylene glycol) methyl ether] methacrylate and styrene via atom transfer radical polymerization,” Macromolecular Research, vol. 19, no. 12, pp. 1257–1263, 2011. View at Publisher · View at Google Scholar · View at Scopus
  42. M. Degirmenci and N. Genli, “Synthesis of poly(cyclohexene oxide)-block-polystyrene by combination of radical-promoted cationic polymerization, atom transfer radical polymerization and click chemistry,” Polymer International, vol. 59, no. 6, pp. 859–866, 2010. View at Publisher · View at Google Scholar · View at Scopus
  43. O. Karagollu, M. Gorur, F. Gode, B. Sennik, and F. Yilmaz, “Phosphate ion sensors based on triazole connected ferrocene moieties,” Sensors and Actuators B, vol. 193, pp. 788–798, 2014. View at Google Scholar
  44. K. T. Powell, C. Cheng, K. L. Wooley, A. Singh, and M. W. Urban, “Complex amphiphilic networks derived from diamine-terminated poly(ethylene glycol) and benzylic chloride-functionalized hyperbranched fluoropolymers,” Journal of Polymer Science A: Polymer Chemistry, vol. 44, no. 16, pp. 4782–4794, 2006. View at Publisher · View at Google Scholar · View at Scopus