THS ||||”Hill”llllIllHIMllllllllllllllllllilllllllllllllllli 3 1293 02080 102 7 LEBRARY Michigan State University This is to certify that the thesis entitled SYNTHESIS AND CHARACTERIZATION OF ULTRATHIN POLY(STYRENE) FILMS GRAFTED FROM HYPERBRANCHED POLY(ACRYLIC ACID) presented by Anika A. Odukale has been accepted towards fulfillment of the requirements for MS degree in mm Major professor Date (33/219 /9‘i 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution PLACE IN RETURN BOX to remove this checkout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE is)” 2912903 11/00 chlRC/DatoDmpfiS-p“ SYNTHESIS AND CHARACTERIZATION OF ULTRATHIN POLY(STYRENE) FILMS GRAFTED FROM HYPERBRANCHED POLY(ACRYLIC ACID) By Anika A. Odukale A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemistry 1999 ABSTRACT SYNTHESIS AND CHARACTERIZATION OF ULTRATHIN POLY(STYRENE) FILMS GRAFTED FROM HYPERBRANCHED POLY(ACRLYLIC ACID) By Anika Assata Odukale Imprinting of polymer films can produce recognition sites whose selectivity rivals that of natural antibodies. One challenge in applying imprinted polymers for chemical detection is that they equilibrate with analyte molecules very slowly. This project reports on the development of ultrathin polymer films (<100 nm) which are “grafted from” a gold substrate and could be used for imprinting to make a highly selective sensor. The minimal thickness of these films should allow rapid response time to analyte molecules. Using polystyrene as a model system, we address whether the polymer can be successfully grafted from a gold substrate and what conditions are required for this grafting. FTIR and ellipsometry show that styrene polymers cannot be thermally grown from a substrate using a monolayer of thiol-initiator compound, due to the instability of the thiol-gold bonds. However, results indicate that polymerization from a gold substrate is possible utilizing azo-initiators linked to poly(acrylic acid) films. To Eddie Lloyd Jr. and Constance Fabunmi ACKNOWLEDGMENTS First and foremost I would like to thank GOD, whose blessings upon me have been infinite during the course of my graduate studies. Dr. Merlin Bruening, my advisor, for providing the resources and opportunity to expand on my scientific knowledge, and for seeing me through the completion of this degree. I would like to acknowledge my Committee: Dr. Crouch, Dr. Hunt and Dr. Rathke, for taking the time to answer all of my “little questions” and being understanding. I am extremely grateful to Dr. Crouch and Dr. Hunt for all of their wisdom, guidance and support. Both have truly altered the course of my life by supplying insight and inspiration in more areas than they will ever know. Special appreciation is extended to my family, especially my mother, Jabari, who is truly the most beautiful woman I will ever have the pleasure to know, and the best “little bro” a sister could have, Kao. Thank you for always being in my comer, regardless of the situation. And to my extended family, Shalia Lindsey, Christal Spence, T. M. Portis and Dionne Townsend, who could always feel my spirit across the miles. I am extremely grateful to my best friend, Jesse Edwards III, for the constant support, advice and comfort. I would finally like to thank Michigan State University and NSF MRSEC for funding provided for this project. TABLE OF CONTENTS LIST OF TABLES ........................................................................ vii LIST OF FIGURES ...................................................................... viii LIST OF ABBREVIATIONS ............................................................ ix INTRODUCTION .......................................................................... 1 CHAPTER 1 BACKGROUND ............................................................................ 3 1.1 Molecular Imprinting ........................................................ 3 1.2 Self-Assembled Monolayers .............................................. 5 1.3 Grafting Technique ......................................................... 8 1.3.1 “Grafting To” technique ......................................... 8 1.3.2. “Grafting From” technique ..................................... 9 1.4 Initiator ......................................................................... 9 CHAPTER 2 EXPERIMENTAL ......................................................................... 11 2.1 Ellipsometry .................................................................. 11 2.2 Infrared Spectroscopy ..................................................... 12 2.3 Experimental Materials ................................................... 13 2.4 Synthesized Chemicals ................................................... 14 CHAPTER 3 POLYMERIZATION OF STYRENE ................................................. 15 3.1 Experimental ................................................................ 16 3.2 Results ........................................................................ 19 3.2.1 Grafting PAA to Surfaces ................................. 19 3.2.2 Attempt to Use lnitiator-Derivatized MUA SAMs for “ Grafting From” Polymerization ..................... 22 3.2.3 Using Hyperbranched PAA Monolayers for Surface Stabilization ....................................... 23 CHAPTER 4 TEMPERATURE CONTROL STUDIES ............................................ 29 4.1 Experimental ................................................................ 29 4.2 Results ........................................................................ 30 CHAPTER 5 CONCLUSIONS ......................................................................... 34 CHAPTER 6 FUTURE PROJECTS ................................................................... 36 6.1 Improving Current Technique and Reproducibility ........................................................ 36 6.1.1 Chemical Purification ................................................ 37 6.1.2 Oxygen ................................................................. 37 6.1.3 Using Low —Temperature Initiators .............................. 39 6.1.4 Exposure to Light ..................................................... 39 6.1.5 Controlled Temperature ............................................ 39 6.2 Application of Current Technique to Other Polymers ............. 39 6.3 Decreasing Reaction Times ............................................. 4O BIBLIOGRAPHY ......................................................................... 41 vi 4.1 4.2 6.1 LIST OF TABLES Poly(styrene) layer thickness of 1PAA derivatized samples over a range of various temperatures. Reported values are averages of three samples ............................................................ 32 Poly(styrene) layer thickness of 2PAA derivatized samples over a range of various temperatures. Reported values are averages of three samples ............................................................ 33 Polymerizations of samples using styrene that was freeze-thawed in comparison to samples polymerized with styrene purified through nitrogen purging. Values with standard deviations are averages of three samples ......................................... 38 vii 1.1 1.2 3.1 3.2 3.3 3.4 3.5 3.6 3.7 LIST OF FIGURES Concept of molecular imprinting of polymers ....................................... 6 Adsorption of an MUA SAM on an Au substrate .................................. 7 Formation of 1PAA layer on an Au substrate ..................................... 18 FTIR-ERS spectra of a MUA monolayer on Au Before (bottom) and after (top) activation to form a mixed anhydride ............................ 2O FTIR-ERS spectra of MUA(bottom), PTBA(middle), and PAA(top) films on an Au surface ............................................... 21 FTIR-ERS of polystyrene precipitated on an Au substrate .................... 24 FTIR spectra of a bare, MUA without initiator and MUA with initiator on Au surface, after exposure to styrene/toluene for 24 hours at 80-82°C ................................................................ 25 FTIR spectra of MUA, 1PAA and 2PAA samples without initiator on an Au surface after exposing to styrene for 24 hours at 80-82°C ..................................................................... 26 FTIR spectra of MUA, 1PAA and 2PAA substrates derivatized with initiator and exposed to styrene/toluene for 24 hours at 80-82°C ................................................................ 28 viii SAM MIP PTBA LIST OF ABBREVIATIONS Self-Assembled Monolayer Molecular Imprinted Polymer a , w-diaminopoly(tert-butylacrylate) 10-Hour thermal half-life of initiator Angstrom INTRODUCTION The ability to distinguish among molecules in solutions is central to many areas of research and plays a vital role in important technologies ranging from biotechnology to materials science.1 One example of a particularly exciting area of chemical recognition involves monitoring levels of drugs in the blood stream using “plastic” rather than natural antibodies.2 This new technology will be especially valuable if it can be used in the development of real-time sensors that are capable of highly selective chemical recognition. “Plastic antibodies” are based on the use of imprinted polymers, which serve as a medium for molecular recognition. Basic characteristics of a functional imprinted polymer are stiff structure, good accessibility of binding sites, mechanical and thermal stability, and the ability to distinguish between molecules, even enantiomers.3 In order to minimize diffusion distances and reduce response times of imprinted materials, we are focusing on synthesizing ultrathin films that are <1OO nm thick. Ultrathin polymers are what will likely enable imprinted sensors to have fast response times. The main focus of this thesis is to develop a stable system in which an ultrathin polymer film can be thermally grafted from a gold substrate. An imprinted polymer film of this type can eventually be used in conjunction with a piezoelectric detector to develop a real-time sensor. The reason for developing a model system on gold is that, upon modification of polymer type and other process parameters, it can be applied to the evolution of many different ultrathin polymer substrate systems. Gold is a convenient substrate for electrochemical as well as piezoelectric detection. The “grafting from” technique, which involves growing polymers from surface-bound initiators, leads to higher graft densities and stronger adhesion of the polymer film to the substrate than does adsorption or end group attachment.4 Though extensive studies have been performed on the development of stable systems for “grafting from” highly scattered particles such as carbon black 5 and substrates like silica,6 l have found no prior studies of thermal grafting on gold surfaces. The purpose of this research is to define the parameters necessary for this polymerization. A good deal of interest has been directed towards the field of terminally grafted polymers on substrates because of the significant role that they play in surface modification and stability.7 Extensive studies show that one way to successfully achieve stable formation of grafted polymers is by means of grafting them from covalently bound radical polymerization initiators.8 The background of these studies is outlined in Chapter 1, and Chapter 2 describes experimental techniques and materials used for polymerization. Development of a stable, initiator-containing film on gold is the subject of Chapter 3. The effect that temperature has on the optimization of polymers grafted from surfaces is analyzed in Chapter 4. Conclusions are made involving the stability of 1PAA and 2PAA substrates with and without initiators, and their response to temperature in Chapter 5. Lastly, future projects are discussed in Chapter 6. Chapter 1 BACKGROUND For many years scientist have been interested in molecular recognition and the ability to mimic natural binding phenomena. The ability to synthesize a system that mimics processes found in living organisms has great scientific appeal. One way to achieve such a system is via the use of highly stable, ultrathin, imprinted polymer films that possess selective binding properties because of recognition sites within the polymer matrix.9 This chapter presents important previous work that has led to the conceptualization of this project. The ultimate reason for making these ultrathin polymer films is their ability to be molecularly imprinted. First, I review progress in molecular imprinting. I then review the use of self-assembled monolayers (SAMs) which form the basis for our polymer grafting system. Finally, I discuss previous work in grafting polymers from surfaces, and the type of initiators used in this process. 1.1 Molecular Imprinting The concept of using molecular imprinted polymers (MlPs) for chemical recognition originated from Linus Pauling’s template-and-cast theory.10 In the early 1940’s, Pauling speculated that when an antigen is introduced into a blood system, it is recognized as a foreign object. The system creates antibodies that surround the antigen and form a rigid structure, thus holding the antigen in place and rendering it ineffective. He described possible bonding that allows the antibodies to encase the antigen in a 3-dimensional configuration, and proposed that the antigen can eventually dissociate from the antibody structure, thus leaving behind a well-defined antigen-binding cavity. When the antigen is re- introduced to the system, it can be selectively recognized and re-trapped by the same antibody structure. Though Pauling’s theory was not correct for antibodies, his idea eventually found fulfillment in the synthesis of molecular imprints. The challenge in molecular imprinting has been to determine which materials are best suited for a molecular cast for desired template molecules and subsequent release of the template for future recognition. Many researchers began to address this challenge in the 1970’s. Gunter Wulff and his group were among these, and in 1972 Wulff’s group was the first to report the imprinting of cross-linked organic polymers as a method to synthesize molecular recognition sites.3 Over the past 20 years there have been many advances in the development of MlPs, as their practical applications have far-reaching appeal.11 These include non-covalent imprinting and catalysis using imprinted polymers. Progression in the field has continued through the work of many researchers like Mosbach and Shea. Collectively, these groups have come up with a basic reaction scheme for developing highly selective, imprinted polymers. The overall concept is very simple, as shown in Figure 1.1.2 A template molecule is introduced into a solution containing functionalized monomer, and functional groups of the monomer bind to reactive sites on the template molecule. A cross-linking agent is added to the solution and polymerization occurs around the template molecule. When the template is removed, a well- defined cavity remains in the rigid cross-linked polymer. Once re-introduced to the polymer, the template molecule is capable of selectively binding to the site and thus is “recognized “. 1.2 Self-Assembled Monolayers When a gold substrate is placed in a solution of long-chain thiols, the thiols adsorb at the surface and self-organize as the system approaches equilibrium”:13 The resulting surface film is described as a SAM (Figure 1.2). SAMs are fairly stable, highly ordered and can be prepared with constituents containing a range of chain composition and terminal end groups.14 These features make SAMs very popular in terms of their applications to corrosion studies 15, biotechnology 15 and electrochemical based sensors.17 Previously, Langmuir-Blodgett films 18,19 were extensively used for the formation of monolayers on substrates. Though they are capable of forming multilayers, as well as monolayers, they are only physically adsorbed to substrates, and therefore are very unstable.20 Because SAMs are covalently attached to the surface and highly stable, much of the focus of monolayer formation has turned to SAMs.21 \// Cross-linking Polymerizatif/ Figure 1.1 Concept of molecular imprinting of polymers. OH OH SH SH V MUA in Solution OH OH OH OH fag/2% '90- Cr»; 'V-II‘.‘ -. __~ r. 7._‘€ 1.23.. 21 Du"? ."--t Figure 1.2 Adsorption of an MUA SAM on an Au substrate. SAMs are ideal systems for making initiation sites on surfaces. Alkanethiol SAMs have been extensively studied over that past 15 years due to their highly stable and ordered formation on gold. This is mainly due to the powerful adsorption of sulfur to metals:22 Because the end of this chain can be functionally modified, an alkanethiol can be suitable for attaching a wide array of chemicals to its terminal group. 1.3 Grafting Technique Once it was established that one of the major components of this research would be the formation of ultrathin polymer films on substrates, we had to address which method would be best suited for grafting a dense polymer film from a SAM. Two methods were considered for this purpose: the “grafting to” and “grafting from” technique. 1.3.1 “Grafting To” technique Grafting polymers to substrates can be done in a variety of ways, which all include either physical or covalent attachment to surface sites}:3 Block- copolymers, or polymer chains, can contain functional and groups that attach to the substrate when it is placed in the solution. The reactive surface sites on the substrate behave as anchors and attach to the functional end groups on the polymer, thus attaching the polymer “to” the surface.24 One discouraging factor associated with grafting block-copolymers is that less than 5mg/m2 of polymer can be immobilized on the substrate surface, which may not be a dense enough layer to secure a sufficient amount of template molecules for detection}?5 The main disadvantage of this technique is that most polymerization occurs in solution, and attachment to the surface can not be well controlled. 1.3.2 “Grafting From” technique A more feasible approach for grafting polymers to substrates is through the “grafting from” technique. In this case, initiators are attached directly to the surface and polymer chains grow from the substrate. This increases the amount of possible reaction sites that the cross-linking agent, monomer and template molecules, which are mixed in solution, can attach to when the substrate is placed in this solution. As the polymer begins to form from a number of sites, it is attached to the surface at many different places. Advantages are that this system can be used with many types of monomers, and more of the polymer should be immobilized on the surface.26 Control over the number of initiators on the surface should also yield control over the film thickness and density. 1.4 Initiator In developing films for sensing applications, it is necessary to be able to control immobilized film thickness. In the “grafting from” technique, temperature 27, duration of polymerization, and altering the type 23 and amount of initiator on the surface affect polymer thickness. The amount of initiator should influence the number of attachment sites and hence the film thickness.29 The type of initiator is important because the amount of film decreases as the rate of decomposition of initiator decreases.30 Because they decompose at relatively low temperatures (40-90°C), azo-initiators 31 with a low 10-hour thermal half-life 25 have received a good deal of attention for radical polymerization of vinyl monomers. SAMs of initiators can be prepared through immersing gold slides, which already have a MUA SAM, in an azo-initiator solution. These immobilized initiator “chains” can be thermally activated and the polymer can subsequently be covalently attached,.or “grafted from” 32,33 the substrate. 10 Chapter 2 EXPERIMENTAL The techniques used to characterize the polymer are first discussed. Then the materials and chemicals used are presented. Finally, syntheses of chemicals are explained. 2.1 Ellipsometry Optical ellipsometry is a highly sensitive technique that measures the change in polarization in light reflected from a sample. Using a model based on the Fresnel Equations,34 the thickness and refractive index of thin films can be calculated from the polarization measurement. The change in polarization upon reflection is measured in terms of psi (‘1’) and delta (A), which represent the amplitude ratios and phase difference of p and s polarized light.35 The p and 5 components have electric field vectors parallel and normal to the plane of incidence, respectively. Measurements of ‘I’ and A are very sensitive to the thickness of thin films. As the thickness and/or roughness of surface films increase, sensitivity and accuracy of measurements decrease due to deviation from ideal behavior. A J. A. Wollam Co. ellipsometer was used to measure changes in polarization upon reflection and the WinVASE (variable angle spectroscopic ellipsometry) software calculated the optical constants of substrates and layer 11 thickness (t) of thin films on surfaces.35 The beam comes through an optical fiber from a xenon lamp source and reflects from the surface at a 75° angle. A diffraction grating allows simultaneous polarization measurements at 44 different wavelengths. The assumed index of refraction used for organic films was 1.5. We had to assume a refractive index for these films because ‘1’ and A are not very sensitive to refractive indices of ultrathin films. The absorption coefficient (k) is presumed to be zero because these polymers do not absorb visible light. 2.2 Infrared Spectroscopy FTIR-ERS (external reflection spectroscopy) measures the infrared absorption at a reflective substrate using a single reflection mode. A Nicolet FT IR spectrometer, MAGNA-IR 560 model, was used in conjunction with an external reflection attachment to measure infrared spectra. Spectra were taken in a dry nitrogen environment, which was achieved through the design of a plexi- glass glovebox, along with standard sample compartment purging. Measurements were taken using 128 scans and a spectral resolution of 4 cm'1 using p-polarized light. The ideal incident angle of z87°, 35 which provides maximum absorbance, is difficult to work with so an 80° angle of incidence was used. The FTIR contained an Ever-Glo source and MCT detector. All spectra are recorded as absorbance, which is defined in this instance as -log(R/Ro) where R is the reflectivity of the monolayer on gold and R0 is the reflectivity of a bare Au substrate.37 12 2.3 Experimental Materials Gold substrates were prepared by evaporating 200 nm of gold on silicon wafers. The (100) Si wafers are doped with boron, have diameters of 100+/-0.5 mm, thickness’ of 380-580 um and resistivities of 1-20 ohm/cm. Prior to evaporation of Au, 20 nm of Ti was deposited to promote adhesion. Gold substrates are used for attaching polymers because they will eventually allow electrochemical characterization of films. In addition, their chemically homogenous surfaces are easy to clean, practically contaminant free, and suitable for forming well-organized monolayers of organic thiols and disulfides through spontaneous adsorption.38 The 11-Bromoundecanoic acid, 4-(Dimethylamino)—pyridine (DMAP), sodium hydroxide, hexanes, dimethylfonnamide, 4-methylmorpholine, ethyl acetate, tetrahydrofuran (THF), chloroform, ethanol (EtOH), methanol, styrene inhibited with a 4-tert-butylcatechol, and ethyl chloroforrnate were all purchased from Aldrich Chemical Company. Sodium sulfate, triethylamine (N(Et)3), and p- toluenesulfonic acid were purchased from Spectrum. Hydrochloric acid came from Columbus Chemical Industries, thiourea from Mallinkrodt, N, N- dimethylforrnamide (DMF) from Fisher Chemical, and VA-086 initiator (2,2’- azobis[2-methyl 1-N-(2-hydroxyethyl)propionamide]) was purchased from Wako Chemicals. Further purification was required for styrene and toluene only. Styrene (100 mL) was purified by first extracting the inhibitor in 50 mL sodium hydroxide, followed by washing with three 50 mL portions of Millipore water. The extracted portion was dried over sodium sulfate and run through a 13 silica or alumina gel column. Nitrogen was blown over the collected solution until it was clear (approximately 24 hours). Toluene was degassed with the same nitrogen purging method. 2.4 Synthesized Chemicals The 11-mercaptoundecanoic acid (MUA) was synthesized in the following fashion: A mixture of 49.74 g (0.18 mol) 11-bromoundecanoic acid, 14.84 g thiourea (0.19 mol), and 165 mL of methanol was refluxed for 4 hours under nitrogen. The solution was slightly heated with an oil bath and 63 mL of 8 M sodium hydroxide was added dropwise, while stirring. The solution was allowed to reflux for 3 hours. The thick precipitate was acidified to a pH of 3 with concentrated hydrochloric acid and washed with hexanes. There were two phases: an aqueous top layer and a thick, semi-solid bottom. The aqueous portion was collected and dried over sodium sulfate. The solution was concentrated to a precipitate via rotovap, then pump dried. Recrystallization of the precipitate in hexanes gave a product that was pure by 1H NMR, and confirmed by mass spectrometry. 1H NMR (CDCI3) 5 2.49 (q, 2H), 2.33 (t, 2H), 1.57 (m, 4H), 1.3 (s, 1H), 1.25 (m, 12H). Group members synthesized the H2NR-(PTBA)-RNH2, referred to simply as PTBA, according to a literature procedure.39 PTBA: poly(tert-butylacrylate), and R: (CH2)2NHCO(CH2)2C(CN) CH3. 14 Chapter 3 POLYMERIZATION OF STYRENE Spontaneous adsorption of long chain alkanethiols for the formation of SAM’s on gold is a widely used strategy for developing interfaces with tailored properties.40 This includes modification of wetting 41' 42 and bioadhesion, and introduction of functional groups.43 In addition to being more stable than traditional Langmuir-Blodgett films,44 SAM’s composed of long-chain thiols 45 where n>10 (TI-CH2), could play a multifunctional role in the stabilization of polymers grafted from gold substrates. First, the structure of the SAM is very uniform and dense on the substrate,42 thus serving as a stable base for further derivatization. Secondly, functionalized terminal groups of SAM’s can present reactive sites for attachment of a large number of initiators to the surface.20 11- Mecrapto undecanioc acid is a useful thiol for surface modification for two reasons. One is that the 10 methyl groups provide stability,46 but do not render the molecule insoluble. Another is that the carboxylic acid group at the tail end of the MUA provides a reactive functional group. This carboxylic acid group does not hinder the coordination of the thiol to the Au substrate, but is what ultimately determines the surface properties of the spontaneously adsorbed monolayer. Grafting of hyperbranched poly (acrylic acid) (PAA) to MUA SAMs provides a way to further stabilize the SAM on the Au substrate. The increase in film thickness, as well as cross-linking, can induce stabilization that is desired 15 before grafting from the substrate. The hyperbranched PAA contains many -COOH groups that can be utilized for further surface modification.47 This chapter examines the process of forming styrene films on gold substrates. This involves evaluating the stability of the MUA SAM, studying stabilization due to derivatized PAA layers, proving that azo-initiators induce polymerization from the surface and establishing temperature ranges for optimal polymerization. 3.1 Experimental Gold substrates were placed in a Boekel ozone cleaner, model 135500, for 15 minutes and then immersed in Millipore water for 20 minutes. Using ellipsometric measurements, n and k values were calculated for the bare substrate. These are required in the model used to determine film thickness. The substrate was placed in a solution containing 0.001 M MUA in EtOH for 30 minutes, rinsed with EtOH followed by Millipore water and dried with a N2 stream. The MUA SAM was activated in a solution containing 10 mL dry DMF, 80 uL 4-methylmorpholine and 100 uL ethyl chloroforrnate for 10 minutes, rinsed with ethyl acetate and dried with N2. This created a mixed anhydride intermediate. To graft PTBA films to this substrate, the activated monolayer was submerged in a solution containing 200 mg PTBA in 4 mL DMF for one hour, rinsed with EtOH and dried with N2. This film was hydrolyzed by immersing the substrate in benzene saturated with p-Toluenesulfonic acid monohydrate at 55°C, for one hour. The slide was removed, rinsed with EtOH and dried with N2 16 to yield one monolayer of PAA (1 PAA). This process is illustrated in Figure 3.1. To graft a 2PAA film, activation of the —COOH groups of 1PAA, followed by reaction with PTBA and hydrolysis were repeated. To attach the initiator to a film, the PAA-grafted substrate was activated as previously described, and placed in a solution containing 10 mL DMF, 70 uL N(Et)3, 28 mg DMAP (0.25 mmol) and 124 mg VA-086 initiator (0.43 mmol) for one hour, removed and dried with N2. For polymerization, the substrate was placed in a vial and sealed with a septum. The vial was evacuated via suction and filled with N2. This process was repeated three times. Equal volumes of degassed toluene and styrene were cannula transferred to the vial. The vial was placed in an oil bath at 80-82°C for a period of 24 hours. The substrate was removed, rinsed with toluene and subsequently chloroform, and dried with N2. Ellipsometric and IR measurements of the substrate were taken after each surface modification. All data was generated from a pool of 82 samples which were polymerized as either bare gold, 1PAA, 1PAA + initiator, 2PAA, or 2PAA + initiator derivatized substrates. 17 CH CH CHCH 4343(343 O O OH OH OAovooA / o o 0’ 0’ / / / chloroforrnate O O O N-methyl morpholine ‘I’ 2 ans-51‘s; '.P!-’.'.:‘:‘.r '1-."',......'_ :1: Q" ‘zgct’yqqajviyq; “- 24,-. ‘— PAA = {CH-CH3];I PTBA = HZNR—£H2-SF:5——RNH2 $=0 0 CH3 OH _ H3O>