Synthesis, characterization and swelling behaviour of poly(methacrylic acid) brushes synthesized using atom transfer radical polymerization

abstract Poly(methacrylic acid) brushes have been prepared utilizing the ‘‘grafting from’’ technique and a livingradical synthesis route using a two stage process. Firstly a poly(1-ethoxyethyl methacrylate) brush wassynthesized by atom transfer radical polymerization and then thermally decomposed to poly-(methacrylic acid). The swelling behaviour of the weak polyacid brush was investigated as a function ofpH and salt concentration in aqueous solutions using atomic force microscopy. Force pulling measure-ments were used to establish the molecular weight and the grafted chain density. The swelling transitionwas found to be at pH 9; which is significantly different to the pK a (5.5) of untethered poly(methacrylicacid). We attribute this large shift in pK a to the high grafting density of these brushes. This can beexplained as a resultof the Coulombic repulsion of neighbouring charges. High salt concentrations (0.3 MNa þ ) also collapse the brush layer. Conversely low salt concentrations cause an increase in the thicknessof the brush, a behaviour expected for osmotic brushes. 2008 Elsevier Ltd. All rights reserved.

[1]  S. Kawaguchi,et al.  Conformation of poly(methacrylic acid) in acidic aqueous solution studied by small angle X-ray scattering. , 1999, Biophysical chemistry.

[2]  L. Névot,et al.  Caractérisation des surfaces par réflexion rasante de rayons X. Application à l'étude du polissage de quelques verres silicates , 1980 .

[3]  R. Jones,et al.  Mechanical Actuation by Responsive Polyelectrolyte Brushes and Triblock Gels , 2005 .

[4]  William J. Brittain,et al.  Polymer brushes : synthesis, characterization, applications , 2004 .

[5]  G. J. Fleer,et al.  Analytical Self-Consistent-Field Model of Weak Polyacid Brushes , 1995 .

[6]  Hongwei Ma,et al.  Stimulus-Responsive Poly(N-isopropylacrylamide) Brushes and Nanopatterns Prepared by Surface-Initiated Polymerization , 2004 .

[7]  J. Lahann,et al.  A Reversibly Switching Surface , 2003, Science.

[8]  D. Brooks,et al.  Evaluation of an atomic force microscopy pull-off method for measuring molecular weight and polydispersity of polymer brushes: effect of grafting density. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[9]  K. Matyjaszewski,et al.  Development of novel attachable initiators for atom transfer radical polymerization. Synthesis of block and graft copolymers from poly(dimethylsiloxane) macroinitiators , 1998 .

[10]  N. Ayres,et al.  A Facile Route to Poly(acrylic Acid) Brushes Using Atom Transfer Radical Polymerization , 2006 .

[11]  S. Alexander,et al.  Adsorption of chain molecules with a polar head a scaling description , 1977 .

[12]  John Lekner,et al.  Theory of reflection , 1987 .

[13]  J. Genzer,et al.  Behavior of Surface-Anchored Poly(acrylic acid) Brushes with Grafting Density Gradients on Solid Substrates: 1. Experiment , 2007 .

[14]  William J. Brittain,et al.  Polymer brushes––surface immobilized polymers , 2004 .

[15]  M. Ward,et al.  Self-assembled thiol monolayers with carboxylic acid functionality: measuring pH-dependent phase transitions with the quartz crystal microbalance , 1992 .

[16]  J. Bechhoefer,et al.  Calibration of atomic‐force microscope tips , 1993 .

[17]  W. Brittain,et al.  Polymer brushes: surface-immobilized macromolecules , 2000 .

[18]  O. Borisov,et al.  Theory of Ionizable Polymer Brushes , 1995 .

[19]  Richard A. L. Jones,et al.  Polymers at Surfaces and Interfaces , 1999 .

[20]  P. Topham,et al.  Controlled growth of poly(2-(diethylamino)ethyl methacrylate) brushes via atom transfer radical polymerisation on planar silicon surfaces , 2006 .

[21]  A. Ryan,et al.  Direct visualization of the real time swelling and collapse of a poly(methacrylic acid) brush using atomic force microscopy , 2009 .

[22]  G. J. Fleer,et al.  On the Theory of Grafted Weak Polyacids , 1994 .

[23]  K. Matyjaszewski,et al.  Atom transfer radical polymerization. , 2001, Chemical reviews.

[24]  N A Peppas,et al.  Water, solute and protein diffusion in physiologically responsive hydrogels of poly (methacrylic acid-g-ethylene glycol). , 1996, Biomaterials.

[25]  D. Brooks,et al.  Attractive bridging interactions in dense polymer brushes in good solvent measured by atomic force microscopy. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[26]  S. Martin,et al.  Responsive brushes and gels as components of soft nanotechnology. , 2005, Faraday discussions.

[27]  M. Joanicot,et al.  Water-dispersed lamellar phases of symmetric poly(styrene)-block-poly(acrylic acid) diblock copolymers: Model systems for flat dense polyelectrolyte brushes , 2004, The European physical journal. E, Soft matter.

[28]  M. Tirrell,et al.  A Study of Polyelectrolyte Brushes Formed from Adsorption of Amphiphilic Diblock Copolymers Using the Surface Forces Apparatus , 2002 .

[29]  W. Huck,et al.  AFM study of cationically charged polymer brushes: switching between soft and hard matter. , 2005, Soft matter.

[30]  A. Karim,et al.  Interfacial segment density profiles of end-anchored polymers in a melt , 1992 .

[31]  A. Ryan,et al.  Chemically induced oscillations in a pH-responsive hydrogel , 2002 .

[32]  E. Ruckenstein,et al.  Living Anionic Polymerization of 1-(Alkoxy)ethyl Methacrylates and the Preparation of Well-Defined Poly(methacrylic acid) , 1998 .

[33]  G. Battaglia,et al.  Conformation of Poly(methacrylic acid) Chains in Dilute Aqueous Solution , 2008 .

[34]  Krzysztof Matyjaszewski,et al.  The Synthesis of Densely Grafted Copolymers by Atom Transfer Radical Polymerization , 1998 .

[35]  Shiping Zhu,et al.  Atom Transfer Radical Polymerization of Methyl Methacrylate Mediated by Copper Bromide−Tetraethyldiethylenetriamine Grafted on Soluble and Recoverable Poly(ethylene-b-ethylene glycol) Supports , 2001 .

[36]  S. Bon,et al.  Atom transfer radical polymerization of 1-ethoxyethyl (meth)acrylate: Facile route toward near-monodisperse poly((meth) acrylic acid) , 2004 .

[37]  S. Minko,et al.  Stimuli-responsive hydrogel thin films , 2009 .

[38]  Christine Ortiz,et al.  Direct Measurement of Glycosaminoglycan Intermolecular Interactions via High-Resolution Force Spectroscopy , 2002 .

[39]  J. Rühe,et al.  Synthesis and swelling behavior of a weak polyacid brush , 2002 .

[40]  O. Borisov,et al.  Screening effects in a polyelectrolyte brush: Self-consistent-field theory , 2000 .

[41]  Jochen S. Gutmann,et al.  Synthesis and Characterization of Polymer Brushes on Micromechanical Cantilevers , 2004 .

[42]  Wenmiao Shu,et al.  Highly reversible and multi-stage cantilever actuation driven by polyelectrolyte brushes. , 2006, Journal of the American Chemical Society.

[43]  D. Brooks,et al.  Molecular weight and polydispersity estimation of adsorbing polymer brushes by atomic force microscopy. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[44]  R. Golestanian,et al.  The pH-induced swelling and collapse of a polybase brush synthesized by atom transfer radical polymerization. , 2006, Soft matter.

[45]  A. Chiche,et al.  Controlling network-brush interactions to achieve switchable adhesion. , 2007, Angewandte Chemie.

[46]  M. C. Stuart,et al.  Polyacrylic Acid Brushes: Surface Pressure and Salt-Induced Swelling , 2000 .

[47]  B. Akhremitchev,et al.  Study of the Polydispersity of Grafted Poly(dimethylsiloxane) Surfaces Using Single-Molecule Atomic Force Microscopy† , 2001 .

[48]  J. Rühe,et al.  Swelling of Poly(methacrylic acid) Brushes: Influence of Monovalent Salts in the Environment , 2005 .

[49]  O. Chyan,et al.  Comparative Studies of Hydrogen Termination on Single-Crystal Silicon Surfaces by FT-IR and Contact-Angle Measurements , 1997 .