Chapter 10
Grafting of Functionalized Water Soluble Downloaded by NORTH CAROLINA STATE UNIV on September 24, 2012 | http://pubs.acs.org Publication Date: November 28, 2000 | doi: 10.1021/bk-2001-0780.ch010
Polymers on Gold Surfaces Stable Stimuli-responsive Thin Hydrogel Films Exhibiting a LCST or a UCST 1
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B. S.Heinz ,A.Laschewsky ,E.D.Rekaï ,Ε. Wischerhoff , T. Zacher2 1
Université catholique de Louvain, Dept. of Chemistry, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium BioTuL AG, Gollierstrasse 70, D-80339 München, Germany 2
Stimuli-responsive water soluble acrylamide polymers which exhibit a lower critical solution temperature (LCST), or an upper critical solution temperature (UCST) were prepared by free radical polymerization, or by chemical modification of precursor polymers. The obtained nonionic thermosensitive polymers are employed for the preparation of thin hydrogel films on gold surfaces. Two different strategies were studied. The first one consists of the immobilization of polymers functionalized with disulfide end-groups onto gold (grafting to). The second strategy consists of the immobilization of a disulfide functionalized initiator followed by the polymeriza tion in situ from gold surfaces (grafting from). The grafting reactions in water or in ethanol were followed by surface plasmon resonance (SPR), ellipsometry and contact angle measurements.
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© 2001 American Chemical Society
In Stimuli-Responsive Water Soluble and Amphiphilic Polymers; McCormick, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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INTRODUCTION Polymers responding to external stimuli, such as temperature, are discussed by virtue of their potential applications in various fields (7,2). Many polymers and hydrogels show thermoresponsive behavior in aqueous systems, undergoing a phase separation at a lower critical solution temperature (LCST), or at an upper critical solution temperature (UCST). The LCST is a critical temperature beyond which polymer and solvent separate into two phases; whereas, the UCST is the critical temperature below which the polymer and solvent separate. LCST and UCST are linked, within other parameters, to the balance of hydrophilic and hydrophobic groups in the polymer (3). The occurence of a LCST is widespread for nonionic polymers in water (4). Poly(JV-vinyl caprolactam) (5), polyethyleneoxide, polyvinylmethylether and poly(AT-isopropylacrylamide) (PNIPAM) (6) are notorious examples. Typically, the LCST is adapted by varying the chemical structure of the monomer employed (an approach which is limited) or by copolymerization (7). The latter approach suffers in general from the inherent chemical heterogeneity of the statistical copolymers obtained, which broadens the thermal transition. This problem may be overcome by the chemical modification of nonionic precursor polymers, resulting in most cases in random copolymers. But this approach has been rarely used so far (8). Within this line of reasoning, we synthesized copolymers of N-isopropyl acrylamide and iV-tris(hydroxymethyl)methylacrylamide (P-NIPAM-co-THMA) by free radical copolymerization (Figure 1). Additionally, we have employed chemical modification, namely the acylation of the water soluble poly[iV-tris(hydroxymethyl)methylacrylamide] (P-THMA) and poly[^-2-hydroxypropylmethacrylamide] (P-HPMA) that do not exhibit a LCST under atmospheric pressure themselves. Appropriately acetylated and cinnamoylated copolymers however exhibit a LCST in water which can be tailored in the full temperature range between 0°C and 100°C by controlling the extent of esterification (9). Instead of a LCST, thermoresponsive water soluble polymers can exhibit a UCST. UCSTs are frequently observed for sulfobetaine polymers such as poly[iV'-(3-sulfopropyl)-Ar-methacryloyloxyethyl]-A^-dim ammonium betaine] (10) or poly[iV,#-dimethyl-i^ ammonium betaine] (P-SPM) 10 (//). UCSTs are exhibited by more complex structures, too, such as poly [iV^-dimethyl-i^-ll-metfiacryloyl oxyundecylammonio propanesulfonate] (12), or as naphtalene-labeled copolymers of styrene and JV^-dimethylmaleimido propylammonium propanesulfonate (13). We used P-SPM 10 which has a UCST of about 70°C in pure water for our investigations. This polymer contains an amide moiety and is therefore relatively stable towards hydrolysis.
In Stimuli-Responsive Water Soluble and Amphiphilic Polymers; McCormick, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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Downloaded by NORTH CAROLINA STATE UNIV on September 24, 2012 | http://pubs.acs.org Publication Date: November 28, 2000 | doi: 10.1021/bk-2001-0780.ch010
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