Stimuli responsive microfiltration membranes and surfaces from copolymers with grafted functional side chains

STIMULI-RESPONSIVE MICROFILTRATION MEMBRANES AND SURFACES FROM COPOLYMERS WITH GRAFTED FUNCTIONAL SIDE CHAINS YING LEI NATIONAL UNIVERSITY OF SINGAPORE 2004 STIMULI-RESPONSIVE MICROFILTRATION MEMBRANES AND SURFACES FROM COPOLYMERS WITH GRAFTED FUNCTIONAL SIDE CHAINS YING LEI (M.Eng., BUCT) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2004 ACKNOWLEDGEMENT First of all, I would like to express my cordial gratitude to my supervisors, Prof. E. T. Kang and Prof. K. G. Neoh, for their invaluable guidance, suggestion and discussion throughout this work. Their enthusiasm and active research interests are a constant source of inspiration to me in carrying out this project. I have learnt invaluable knowledge from them on how to research work and how to enjoy doing research. I would like to thank Dr. Li Sheng for his help in XPS operation training and sample analysis. I am also grateful to all my colleagues for their kind help and support. In particular, thanks to Dr. Ling Qidan, Dr. Yang Guanghui, Mr. Yu Weihong, Mr. Wang Wencai, Mr. Zhao Luping and Miss Cen Lian for sharing with me the invaluable experience on the research field. In addition, special thanks go to Madam Chow Pek, Madam Liu Suxia, and other lab technologists of Department of Chemical and Biomolecular Engineering, for their assistance and help. The financial support provided by the National University of Singapore in the form of a research scholarship is gratefully acknowledged. Finally, but not least, I would like to thank my wife, Wan Xue, and my parents for their continuous love, support, and encouragement. i TABLE OF CONTENTS Page Acknowledgement i Table of Contents ii Summary iv Nomenclature vi Lists of Figures viii Lists of Tables xiv Chapter Introduction Chapter Literature Survey 2.1 Preparation of Microporous Membranes 10 2.2 Preparation of Stimuli-responsive Microporous Membranes 21 2.3 Smart Surface for Enzyme Immobilization and Cell Culture 35 Chapter Synthesis and Characterization of Acid/Base PolymerGrafted Poly(vinylidene fluoride) Copolymers and pHSensitive Microfiltration Membranes 44 3.1 Synthesis and Characterization of Poly(acrylic acid)-grafted Poly(vinylidene fluoride) Copolymers and pH-sensitive Microfiltration Membranes 45 3.1.1 Experimental Section 45 3.1.2 Results and Discussion 51 3.1.3 Conclusion 71 3.2 pH Effect of the Coagulation Bath on the Characteristics of Poly(acrylic acid)-grafted and Poly(4-vinylpyridine)-graftedPoly(vinylidene fluoride) Microfiltration Membranes 72 3.2.1 Experimental Section 72 3.2.2 Results and Discussion 74 3.2.3 Conclusion 90 ii Chapter Synthesis and Characterization of Poly(N-isopropylacrylamide)-grafted-Poly(vinylidene fluoride) Copolymers and Temperature-Sensitive Microfiltration Membranes 91 4.1 Experimental Section 92 4.2 Results and Discussion 95 4.3 Conclusion Chapter Preparation of Temperature- and pH-Sensitive Microfiltration Membranes from Blends of Poly(acrylic acid)Grafted-Poly(vinylidene fluoride) (PAAc-g-PVDF) with Poly(N-isopropylacrylamide) 119 120 5.1 Experimental Section 121 5.2 Results and Discussion 123 5.3 Conclusion 144 Chapter Preparation of Polymeric ‘Smart Surface’ for Enzyme Immobilization and Cell Culture 145 6.1 Covalent Immobilization of Glucose Oxidase on Microporous Membranes Prepared From Poly(vinylidene fluoride) with Grafted Poly(acrylic acid) Side Chains 146 6.1.1 Experimental Section 146 6.1.2 Results and Discussion 150 6.1.3 Conclusion 164 6.2 Immobilization of Galactose Ligands on Acrylic Acid GraftCopolymerized Poly(ethylene terephthalate) Film and Its Application to Hepatocyte Culture 165 6.2.1 Experimental Section 165 6.2.2 Results and Discussion 172 6.2.3 Conclusion 192 Chapter Conclusion 193 Chapter References 198 List of publications 219 iii SUMMARY In this work, molecular graft polymerization (bulk modification) was carried to synthesize stimuli-responsive polymeric materials. New graft copolymers, PAAc-gPVDF, P4VP-g-PVDF and PNIPAAM-g-PVDF, were successfully synthesized through the molecular graft copolymerization of acrylic acid (AAc), 4-vinylpyridine (4VP), N-isopropylacrylamide (NIPAAM) with the ozone-preactivated poly(vinylidene fluoride) (PVDF) backbone. The microporous membranes prepared from these stimuliresponsive polymeric materials by phase inversion technique exhibit strongly pH- or temperature-sensitive properties. For the pH-sensitive PAAc-g-PVDF microfiltration (MF) membranes, the flux of the aqueous solution through the membranes exhibited a strong and reversible dependence on solution pH in the pH range of to 6. The rate of permeation through the PAAc-gPVDF MF membranes changed reversibly in response to pH variation of the aqueous solution, with the most drastic change in permeation rate occurring between pH to 4. For the temperature-sensitive PNIPAAM-g-PVDF MF membranes cast below the lower critical solution temperature (LCST) of the NIPAAM polymer (~ 32°C), the rate of water permeation increased substantially at a permeate temperature above 32°C. A reverse permeate temperature dependence was observed for the flux of isopropanol through the membrane cast above the LCST of the NIPAAM polymer. For the PAAcg-PVDF/PNIPAAM MF blend membranes, on the other hand, XPS analyses of the blend membranes revealed a substantial surface enrichment of the grafted AAc polymer and blended PNIPAAM. The copolymer blend membranes exhibited both pHdependent and temperature-sensitive permeability to the aqueous solutions, with the iv most drastic change in permeability being observed at permeate pH between to and temperature around 32°C. The present studies have shown that molecular functionalization by graft copolymerization prior to membrane fabrication is a relatively simple approach for the preparation of membranes with uniform surface (including the pore surfaces) properties. Furthermore, the smart polymer brushes (PAAc and PNIPAAM side chains) can be used as physicochemical gates to control the permeability through the porous PVDF membranes. The ‘smart membranes’ can be also used as a polymeric matrix for enzyme immobilization. It was also demonstrated that the PAAc-g-PVDF MF membrane could be further functionalized by covalent immobilization of an enzyme, glucose oxidase (GOD). The immobilized GOD exhibited good chemical resistance, thermal and storage stability in a phosphate buffer solution (pH 7.4), and still retained substantial activity. On the other hand, UV-induced surface graft copolymerization of the Ar plasmapretreated PET films with AAc was carried out to generate the PAAc-g-PET surfaces. Immobilization of the galactose ligand on the PAAc-g-PET surface gave rise to a hepatocyte-specific surface with a high surface concentration of the flexible galactose ligands. Surface modification of PET substrates with galactose ligands allows a good control of the hepatocyte attachment, the cell-substrate interactions, and the physiological functions of the attached hepatocytes. v NOMENCLATURE α XPS photoelectron take-off angle AAc Acrylic acid AAm Acrylamide AFM Atomic force microscopy AHG 1-O-(6’-aminohexyl)-D-galactopyranoside BE Binding energy BSA Bovine serum albumin DSC Differential scanning calorimetry EGF Epidermal growth factor FTIR Fourier transform infrared FWHM Full width at half maximum -g- -graft- GA Galactose ligands GOD Glucose oxidase Km Michaelis constant MES 2-(N-morpholino)-ethanesulfonic acid MF Microfiltration NaSS Na salt of styrenesulfonic acid NIPAAM N-isopropylacrylamide OD Optical density PBS Phosphate-buffered solution pKa The logarithmic scale of acidity PET Poly(ethylene terephthalate) PVDF Poly(vinylidene fluoride) vi Ra Average surface root-mean-square roughness RF Radio-frequency SEM Scanning electron microscopy sulfo-NHS N-hydroxysulfosuccinimide TBO Toluidine blue O TG Thermogravimetric TIPS Thermally-induced phase separation TMB 1-Step Turbo 3, 3, 5, 5-tetramethylbenzidine UF Ultrafiltration Vmax Maximum reaction velocity of the enzyme reaction 4VP 4-vinylpyridine WSC Water-soluble carbodiimide XPS X-ray photoelectron spectroscopy XRD X-ray diffraction vii LIST OF FIGURES Figure 2.1 Phase diagram of a ternary system showing a one-phase region and a two-phase region (shaded area). Figure 3.1 Schematic representation of the process of thermally-induced graft copolymerization of AAc with the ozone-preactivated PVDF backbone. Figure 3.2 FT-IR spectra of (a) the pristine PVDF film, and three thin films cast from the acetone solution of PAAc-g-PVDF copolymers prepared from [AAc] to [-CH2CF2-] feed (weight) ratios of (b) 3, (c) and (d) 6. Figure 3.3 XPS C1s core-level spectra of four MF membranes cast by phase inversion from 12 wt% NMP solutions of: (a) the pristine PVDF and the PAAc-g-PVDF copolymers prepared from [AAc] to [-CH2CF2-] feed (weight) ratios of: (b) 3, (c) and (d) 6. Figure 3.4 Effect of the [AAc] to [-CH2CF2-] feed (weight) ratio on the bulk graft concentration of the PAAc-g-PVDF copolymer. Figure 3.5 TG analysis curves of (1) the PVDF homopolymer; the PAAc-g-PVDF copolymers of graft concentrations of (2) [C]/[F]bulk=1.01 or 0.7 wt% AAc polymer, (3) [C]/[F]bulk=1.09 or 5.7 wt% AAc polymer, (4) [C]/[F]bulk=1.25 or 14.3 wt% AAc polymer, (5) [C]/[F]bulk=1.33 or 18 wt% AAc polymer; and (6) the AAc homopolymer. Figure 3.6 Effect of surface graft concentration on the water contact angle of the PAAc-g-PVDF film. Figure 3.7 SEM micrographs of the MF membranes cast with phase inversion from 12 wt% NMP solutions of (a) the pristine PVDF, and the PAAc-gPVDF copolymers of graft concentrations (([C]/[F])surface ratios) of (b) 1.20, (c) 2.03 , and (d) 2.46. Figure 3.8 Effect of the [AAc]/[-CH2CF2-] weight ratio in the feed on the surface graft concentration of the PAAc-g-PVDF copolymer membranes. 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Polym. J., 29, pp.301-303. 1993. Zsigmondy, R. and W. Bachmann. Ueber Neue Filter, Z. Anorg. Alg. Chem., 103, pp.119-28. 1918. 218 PUBLICATIONS Journal Papers: (1). Ying L., G.Q. Zhai, A.Y. Winata, E.T. Kang and K.G. Neoh. Preparation of Temperature- and pH-Sensitive Microfiltration Membranes From Blends of Poly(acrylic acid)-graft-Poly(vinylidene fluoride) with Poly(N-isopropylacrylamide), J. Membr. Sci., 224 (1-2): 93-106 Oct 2003. (2). Ying L., E.T. Kang, and K.G. Neoh. pH Effect of Coagulation Bath on the Characteristics of Poly(acrylic acid)-grafted and Poly(4-vinylpyridine)-grafted Poly(vinylidene fluoride) Microfiltration Membranes, J. Colloid Interf. Sci., 265 (2): 396-403 Sep 2003. (3). Ying L., E.T. Kang, K.G. Neoh, K. Kato and H. Iwata. Novel Poly(Nisopropylacrylamide)-graft-Poly(vinylidene fluoride) Copolymers for TemperatureSensitive Microfiltration Membranes, Macromol. Mater. Eng., 288 (1): 11-16 Jan 31 2003. (4). Ying L., C. Yin, R.X. Zhuo, K.W. Leong, H.Q. Mao, E.T. Kang and K.G. Neoh. Immobilization of Galactose Ligands on Acrylic Acid Graft-Copolymerized Poly(ethylene terephthalate) Film and Its Application to Hepatocyte Culture, Biomacromolecules, 4(1): 157-165 Jan-Feb 2003. (5). Zhai, G.Q., L. Ying, E.T. Kang and K.G. Neoh. Synthesis and Characterization of Poly(vinylidene fluoride) with Grafted Acid/Base Polymer Side Chains, Macromolecules, 35 (26): 9653-9656 Dec 17 2002. (6). Zhai, G.Q., L. Ying, E.T. Kang and K.G. Neoh. Poly(vinylidene fluoride) with Grafted 4-vinylpyridine Polymer Side Chains for pH-Sensitive Microfiltration Membranes, J. Mat. Chem., 12 (12): 3508-3515 Nov 29 2002. (7). Ying L., E.T. Kang and K.G. Neoh. Covalent Immobilization of Glucose Oxidase on Microporous Membranes Prepared From Poly(vinylidene fluoride) with Grafted Poly(acrylic acid) Side Chains, J. Membr. Sci., 208 (1-2): 361-374 Oct 2002. (8). Ying L., E.T. Kang and K.G. Neoh. Synthesis and Characterization of Poly(Nisopropylacrylamide)-graft-Poly(vinylidene fluoride) Copolymers and TemperatureSensitive Membranes, Langmuir, 18 (16): 6416-6423 Aug 2002. (9). Ying L., P. Wang, E.T. Kang and K.G. Neoh. Synthesis and Characterization of Poly(acrylic acid)-graft-Poly(vinylidene fluoride) Copolymers and pH-Sensitive Membranes, Macromolecules, 35 (3): 673-679 Jan 29 2002. 219 [...]... membrane fabrication The membranes prepared from the new functional polymeric materials by phase inversion exhibit stimuli- responsive properties The work in this thesis is an attempt to prepare ‘smart membranes and ‘smart surfaces via surface and molecular grafting techniques 3 The applications of the ‘smart membranes and ‘smart surfaces on controlled permeation, enzyme immobilization and cell culture... literature It starts with the definition and the preparation methods of microporous membranes It then goes into the preparation of stimuli- responsive membranes (smart membranes) Finally, it focuses on the applications of smart membranes and smart surfaces In Chapter 3, molecular modification of ozone-pretreated poly(vinylidene fluoride) (PVDF) via thermally-induced graft copolymerization with acrylic acid... PAAc-g-PET film with surface carboxyl group concentrations of (c) 0.03 µmol/cm2, (d) 0.56 µmol/cm2, and (e) the GA-PAAc-g-PET film with a surface galactose ligand concentration of 0.51 µmol/cm2 Figure 6.15 Hepatocyte attachment on different surfaces: (1) the pristine PET surface; the PAAc-g-PET surfaces with a COOH concentration of (2) 0.03 µmol/cm2 and (3) 0.56 µmol/cm2; the GA-PAAc-g-PET surfaces with galactose... and temperature-sensitive microfiltration (MF) membranes from blends of the PAAc-g-PVDF copolymer and poly(N-isopropylacrylamide) (PNIPAAM) in NMP solution were prepared by phase inversion in water at 25°C The bulk and surface compositions of the membranes were obtained by elemental analysis and XPS, respectively XPS analyses of the blend membranes revealed a substantial surface enrichment of the grafted. .. well known from reverse 11 osmosis and ultrafiltration membranes; for example higher flux values and lower rate of flux decay are obtained generally Highly asymmetric microfiltration membranes have become available since 1980s (Kesting et al., 1981; Wrasidlo and Hofmann, 1984; Le et al., 1984) As new applications began to emerge, the need for membranes with improved chemical resistance and heat stability... GA-PAAc-g-PET surfaces with galactose ligand concentrations of (1) 0.47×10-3 µmol/cm2, (2) 0.02 µmol/cm2, (3) 0.51 µmol/cm2, and on (4) the collagen-coated PET film xiii LIST OF TABLES Table 2.1 A Survey of Materials for Commercial Polymer Membranes Table 2.2 Preparation Techniques for Microfiltration Membranes Table 3.1 Peroxides Content, Intrinsic Viscosity and Water Contact Angle of Pristine and Ozone-treated... spectroscopy, elemental analysis, and thermogravimetric (TG) analysis In general, the graft concentration increased with the NIPAAM monomer concentration used for graft copolymerization Microfiltration (MF) membranes were prepared from the PNIPAAM-g-PVDF copolymers by the phase inversion method The bulk and surface graft concentrations of the membranes were obtained by elemental analysis and XPS, respectively... liquid) and inorganic (ceramic, metal, etc.) membranes Here the synthetic polymeric membranes are emphasized Secondly, membranes can be distinguished by their morphology Roughly, two types of membrane structures can be distinguished: ⎯ porous membrane ⎯ non-porous membrane In porous membranes, fixed pores are present Microfiltration, ultrafiltration and nanofiltration membranes are all porous membranes. .. (([-AAc-]/[CH2CF2-])surface) of 0.97, and the PAAc-g-PVDF/PNIPAAM blend membranes with ([-NIPAAM-]/[-CH2CF2-])surface blend (mole) ratios of (c) 4.88, (d) 2.57, (e) 2.47, and (f) 2.11 Figure 5.7 pH- and temperature-dependent permeability of aqueous solutions of pH 1-6 and temperature 4-55°C through the PAAc-g-PVDF/PNIPAAM blend membranes with ([-NIPAAM-]/[-CH2CF2-])surface blend (mole) ratios of (a) 2.11, (b) 2.57, and (c) 4.63... above its melting point) and by cooling demixing will take place (Lloyd et al., 1990; Lloyd et al., 1991) TIPS has been used to form microporous polymeric membranes of controlled pore characteristics from a variety of crystalline and thermoplastic polymers, including polyolefins, condensation and oxidation polymers, copolymers, and blends (Vitzthum and Davis, 1984; Caneba and Soong, 1985) Commercially . STIMULI- RESPONSIVE MICROFILTRATION MEMBRANES AND SURFACES FROM COPOLYMERS WITH GRAFTED FUNCTIONAL SIDE CHAINS YING LEI . NATIONAL UNIVERSITY OF SINGAPORE 2004 STIMULI- RESPONSIVE MICROFILTRATION MEMBRANES AND SURFACES FROM COPOLYMERS WITH GRAFTED FUNCTIONAL SIDE CHAINS YING LEI (M.Eng., BUCT). Polymer- Grafted Poly(vinylidene fluoride) Copolymers and pH- Sensitive Microfiltration Membranes 44 3.1 Synthesis and Characterization of Poly(acrylic acid) -grafted Poly(vinylidene fluoride) Copolymers