<p> Poly(N-isopropylacrylamide) (PNIPAM) has attracted much attention as a thermo-responsive polymer. However, the molecular weight (MW) dependence of its phase transition temperature is still controversial. This situation is largely due to the difficulty in synthesizing narrow-disperse PNIPAM. We have addressed the challenge and developed an atom transfer radical polymerization (ATRP) method to prepare narrow-disperse PNIPAM with moderate to high conversions, using branched alcohols as solvents. Aqueous solutions of these narrow-disperse PNIPAMs showed a dramatic decrease of the phase transition temperature with increasing molecular weight, as measured by turbidimetry and differential scanning calorimetry. Four other series of narrow-disperse PNIPAM with well-controlled molecular weights and with end groups of varying hydrophobicity were also synthesized by ATRP using the corresponding initiators, which enabled us to resolve the MW and end group effects. All the four series of samples showed an inverse molecular weight (MW) dependence of their phase transition temperature. The magnitude of the MW dependence decreased when using more hydrophobic end groups. The end groups were observed to have effects on the cloud point temperature, on the shape of the cloud point curves, and on the enthalpy of the phase transition.</p> / Thesis / Master of Science (MSc)

When a biomaterial is inserted into the body, the interaction of the surface with the surrounding biological environment is crucial. Given the importance of the surface, the ability to alter the surface properties to support a compatible environment is therefore desirable. Silicone hydrogel contact lenses (CL) allow for improved oxygen permeability through the incorporation of siloxane functional groups. These groups however are extremely surface active and upon rotation, can impart hydrophobicity to the lens surface, decreasing lens wettability and increasing protein and lipid deposition. Lens biofouling may be problematic and therefore surface modification of these materials to increase compatibility is exceedingly recognized for importance in both industry and research. The current work focuses on the creation of a novel anti-fouling polymer surface by the incorporation of 2-methacryoyloxyethyl phosphorylcholine (MPC), well known for its biomimetic and anti-fouling properties. A controlled polymerization method was used to generate a unique double-grafted architecture to explore the effect of increasing surface density of polyMPC chains on corresponding anti-fouling properties. The novel free polymer was synthesized by a 3-step atom transfer radical polymerization (ATRP). First, poly(2-hydroxyethyl methacrylate) (polyHEMA) was polymerized by ATRP, where the hydroxyl (OH) groups of the polymer then underwent an esterification to create macroinitiating sites. From these sites, a second ATRP of poly(MPC) varying in length occurred, yielding the double-grafted polymer poly(2(2-bromoisobutyryloxy-ethyl methacrylate)-graft-poly(2-methacryloyloxyethyl phosphorylcholine (pBIBEM-g-pMPC). The polymer was designed for resistance to protein adsorption through a possible synergistic effect between the surface induced hydration layer by surrounding PC groups coupled with steric repulsion of the densely grafted chains. To test its potential as a surface modifier, the polymer was grafted from model silicone hydrogel CL through a 4-step surface initiated ATRP (SI-ATRP) in a similar manner to the free polymer. First, the ATRP initiator was immobilized from the HEMA OH groups of the unmodified CL, generating Intermedate-1. A polyHEMA brush was grafted from the initiating sites yielding pHEMA-50, followed by the generation of a second initiator layer (Intermediate- 2). A sequential ATRP of poly(MPC) then generated the target pMPC-50/pMPC-100 surfaces. For the free pBIBEM-g-pMPC polymer analysis, 1H-NMR and GPC determined polymers formed with a predictable MW and low polydispersity (PDI). For surface grafting, using a sacrificial initiator, 1H-NMR and GPC indicated that the pHEMA-50 and pMPC-50/pMPC-100 polymers were well-controlled, with a MW close to the theoretical and a low PDI. For surface chemical composition, ATR-FTIR showed the presence of the ATRP initiator (Intermediate-1 and 2) by the appearance of a C-Br peak and disappearance of the OH peak. XPS confirmed the chemical composition of the 4-step synthesis by a change in the fraction of expected surface elements. Both the surface wettability and EWC of the materials increased upon pMPC modification, further improving upon increasing pMPC chain length. The contact angle was as low as 16.04 ± 2.37º for pMPC-50 surfaces and complete wetting for pMPC-100. Finally, the single protein adsorption using lysozyme and bovine serum albumin (BSA) showed significantly decreased protein levels for pMPC-50/100 lenses, as much as 83% (p 0.00036) for lysozyme and 73% (p 0.0076) for BSA, with no significant difference upon chain length variation. The aforementioned data demonstrates that the novel polymer has potential in providing an anti-fouling and extremely wettable surface, specifically regarding silicone hydrogel CL surfaces. / Thesis / Master of Applied Science (MASc)

In this thesis, acrylic polymers (methyl methacrylate, MMA; N,N' -dimethylamino ethyl methacrylate, DMAEMA; oligo-ethylene glycol methacrylate, OEGMA; trifluoroethyl methacrylate, TFEMA) were grafted from various metal surfaces such as cold rolled steel (CRS), stainless steel (SS), aluminum (Al) and nickel (Ni) through surface-initiated atom transfer radical polymerization (s-ATRP). The purpose is to improve corrosion resistance and to introduce multi-functionality to metal surface. The metal substrates were precisely polished and were facile for characterization by ellipsometry. 3-((alpha)-Bromo-2-methyl) propylamide propyltriethoxysilane was synthesized and immobilized on the metal surfaces under a simple and workplace-friendly condition. Grafting density was estimated to be 0.58 chains/nm^2 for CRS-gPMMA, 0.55 chains/nm^2 for Ni-g-PMMA and 0.18 chains/nm^2 for SS-g-DMAEMA and 0.66 chains/nm^2 for SS-g-PDMAEMA. Two strategies, i.e., "adding free initiator" and "adding deactivator", were adopted for the control over polymer molecular weight and grafting density in the CRS-g-PMMA system. The polymer thicknesses up to 80 nm were obtained within 80 min using the "adding deactivator" strategy. Copper and iron catalyst systems were compared on different metal substrates. A severe deactivation of copper catalyst was observed on the metal substrates. Controlled polymerization with relatively low polydispersity was obtained using the iron catalyst. The metal surfaces at various stages of modification were characterized by X-ray photoelectron spectroscopy, ellipsometry, goniometry, and atomic force microscopy (AFM). Electrochemical experiments were also carried out to measure the polarization resistance and corrosion potential of CRS-g-PMMA substrates. This thesis work demonstrated that the surface-initiated ATRP is a versatile means for the surface modification of metals with well-defined and functionalized polymer brushes. / Thesis / Master of Applied Science (MASc)

Amphiphilic polymers are a class of polymers that self-assemble into different types of microstructure, depending on the solvent environment and external stimuli. Self assembly structures can exist in many different forms, such as spherical micelles, rod-like micelles, bi-layers, vesicles, bi-continuous structure etc. Most biological systems are basically comprised of many of these organised structures arranged in an intelligent manner, which impart functions and life to the system. We have adopted the atom transfer radical polymerization (ATRP) technique to synthesize various types of block copolymer systems that self-assemble into different microstructure when subject to an external stimuli, such as pH or temperature. The systems that we have studied are: (1) pH responsive fullerene (C60) containing poly(methacrylic acid) (PMAA-b-C60); (2) pH and temperature responsive fullerene containing poly[2-(dimethylamino)ethyl methacrylate] (C₆₀-b-PDMAEMA); (3) other responsive water-soluble fullerene systems. By varying temperature, pH and salt concentration, different types microstructure can be produced. In the presence of inorganic salts, fractal patterns at nano- to microscopic dimension were observed for negatively charged PMAA-b-C60, while such structure was not observed for positively charged PDMAEMA-b-C60. We demonstrated that negatively charged fullerene containing polymeric systems can serve as excellent nano-templates for the controlled growth of inorganic crystals at the nano- to micrometer length scale and the possible mechanism was proposed. The physical properties and the characteristics of their self-assembly properties will be discussed, and their implications to chemical and biomedical applications will be highlighted. / Singapore-MIT Alliance (SMA)

Liquid chromatography is an analytical technique that is constantly facing new challenges in the separation of small molecules and large biomacromolecules. Recently the development of ultra high pressure liquid chromatography has increased the demand on sturdy particles as stationary phase. At the same time the particle size has decreased to sub-2 µm and packed into shorter analytical columns. This thesis deals with the development of new ways of preparing particulate polymer materials using divinylbenzene (DVB) as crosslinker. It includes a novel procedure for synthesizing monodisperse polymer particles by photoinitiated precipitation polymerization. A 150 W short arc xenon lamp was used to initiate the polymerizations. The synthesized particles are monodisperse and have an average particle size ranging from 1.5 to 4 μm depending on reaction conditions and have subsequently been used as grafting templates. The surface of DVB particles contains residual vinyl groups that serve as anchoring points for further functionalization via a variety of grafting schemes. Copolymerization with incorporation of 2,3-epoxypropyl methacrylate yielded pendant oxirane groups on the particle surface. Atom transfer radical polymerization (ATRP) was used to graft methacrylates from the surface resulting in a core-shell type material. A “grafting to” scheme was used to attach pre-made sulfopropyl methacrylate telomers onto particles containing oxirane rings. / Populärvetenskaplig sammanfattning på svenska: Vätskekromatografi är en analytisk kemisk teknik som ständigt står inför nya utmaningar när det gäller att separera allt från små organiska föreningar till stora makro¬molekyler. Denna avhandling beskriver tillverkning av polymera partiklar med exceptionellt jämn storleksfördelning och ytmodifiering av dessa, för användning som stationärfas i kromatografi¬kolonner. Polymeriserings¬tekniken som används är utfällnings¬polymerisering där lösningen UV-bestrålas av en 150 W xenonlampa. Monomeren (byggstenen) löses tillsammans med en intiator i ett lösningsmedel och efterhand som polymeriseringen fortskrider faller polymerpartiklarna ut. Polymerpartiklarna är gjorda av monomeren divinylbensen som fungerar som en tvärbindare, dvs att den länkar ihop flera kedjor till ett hårt litet nystan. Partiklarna växte till en storlek på 1,5 till 4 µm under två till fyra dygn. Efter tillverkningen är partiklarnas yta täckta av vinylgrupper som kan användas för att fästa funktionella polymerkedjor. Genom att tillföra monomeren 2,3-epoxipropyl¬metakrylat i polymeriseringen kunde man desutom få en partikelyta som innehöll epoxigrupper. Epoxigrupperna användes för att fästa positivt laddade polymerkedjor av bestämd längd. Materialet packades i en kromatografikolonn och användes för att separera en testlösning bestående av fyra proteiner. Partiklarna användes även som bas för ymppolymerisering där den vinyltäckta ytan fått reagera med vätebromid. Detta gör att partiklarna blir stora makroinitiatorer som kan användas för att på ett kontrollerat sätt låta polymerkedjor växa från ytan. I en undersökning ympades 2,3-epoxypropylmetakrylat från ytan på partiklarna och resultatet blev ett tjockt ytskikt. Epoxigrupperna kunde sedan hydrolyseras till dioler vilket gjorde partiklarna mer hydrofila.

The potential use of renewable, bio-based polymers in high-technological applications has attracted great interest due to increased environmental concern. Cellulose is the most abundant biopolymer resource in the world, and it has great potential to be modified to suit new application areas. The development of controlled polymerization techniques, such as atom transfer radical polymerization (ATRP), has made it possible to graft well-defined polymers from cellulose surfaces. In this study, graft-modification of cellulose substrates by ATRP was explored as a tool for tailoring surface properties and for the fabrication of functional cellulose surfaces. Various native and regenerated cellulose substrates were successfully graft-modified to investigate the effect of surface morphology on the grafting reactions. It was found that significantly denser polymer brushes were grafted from the native than from the regenerated cellulose substrates, most likely due to differences in surface area. A method for detaching the grafted polymer from the substrate was developed, based on the selective cleavage of silyl ether bonds with tetrabutylammonium fluoride. The results from the performed kinetic study suggest that the surface-initiated polymerization of methyl methacrylate from cellulose proceeds faster than the concurrent solution polymerization at low monomer conversions, but slows down to match the kinetics of the solution polymerization at higher conversions. Superhydrophobic and self-cleaning bio-fiber surfaces were obtained by grafting of glycidyl methacrylate using a branched graft-on-graft architecture, followed by post-functionalization to obtain fluorinated polymer brushes. AFM analysis showed that the surface had a micro-nano-binary structure. It was also found that superhydrophobic surfaces could be achieved by post-functionalization with an alkyl chain, with no use of fluorine. Thermo-responsive cellulose surfaces have been prepared by graft-modification with the stimuli responsive polymer poly(N-isopropylacrylamide) (PNIPAAm). Brushes of poly(4-vinylpyridine) (P4VP) rendered a pH-responsive cellulose surface. Dual-responsive cellulose surfaces were achieved by grafting block-copolymers of PNIPAAm and P4VP. / QC 20100804

We reported a non-crosslinking approach to synthesize nitroxide radical polymer brushes for thin-film electrodes via surface-initiated atom transfer radical polymeization (SI-ATRP), which was effective to yield the organic radical polymer brushes with high grafting density and to attain a uniform surface. As mentioned above, the covalent bonding of nitroxide polymer brushes to the conducting substrate not only prevented the polymer dissolution into organic electrolyte solution but improved the cycle life performance of batteries. Moreover, they can be the potential application in microbatteries by using microcontact printing to produce the patterned nitroxide polymer brushes on a conducting substrate. Even though the organic radical polymer brushes provided a new approach to syn-thesize thin-film electrodes, they still existed many problems that needed to study and to figure out. We discussed the morphology and electrochemical performance about ni-troxide radical polymer in the thesis. In the measurement of surface properties, we used the contact angle, electron spectroscopy for chemical analysis (ESCA) and atomic force microscopic (AFM) to proceed. Another, in the measurement of electrochemical analysis, we used the cyclic voltammetry(CV), alternating current (AC) impedance and charge-discharge to understand the regarding mechanism in this polymer layer during the electrochemical reaction. In chapter 4, we discussed the oxidative problem in the polymer brushes. It should be well controlled during the oxidation reaction, because the oxidation level may affect the diffusion of electron that resulted the capacity better or not. In chapter5, we controlled the density of polymer brushes to construct the possible mechanism during the electro-chemical reaction, and found out the possible factors that affected the electrochemistry. In chapter 6, we applied the better results from the front chapter to the organic radical battery, and compared their electrical performance.

In this study, ethyl methacrylate was polymerized by free radical polymerization at 600C, 700C, 800C at open atmosphere / atom transfer radical polymerization, (ATRP), at 800C in vacuum and in gamma irradiation in vacuum. The polymer obtained was white, hard material. The kinetic curves for free radical polymerization and ATRP by gamma radiation were S-type. However, the curve for polymerization by gamma irradiation raises more smoothly. For ATRP by thermal initiation gives a lineer change of conversion with time. It was observed that the molecular weight can be controlled and low molecular weight polymer could be obtained by ATRP method. The characterization of polymers were made by FTIR, DSC, 1H and 13C NMR techniques.

No description available.

In this study, dendronization and grafting via controlled polymerization techniques, atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP), have been explored. Modification of surfaces and cellulose using these techniques, which enable grafting of well-defined polymer architectures, has been investigated. The interest in using cellulose stems from its renewability, biocompatibility, high molecular weight, and versatile functionalization possibilities. Dendronization was performed using disulfide-cored didendrons of 2,2-bis(methylol)propionic acid (bis-MPA) on gold surfaces, for the formation of self-assembled monolayers. It was found that the height of the monolayer increased with increasing dendron generation and that the end-group functionality controlled the wettability of the modified surface. Superhydrophobic cellulose surfaces could be obtained when a ‘graft-on-graft’ architecture was obtained using ATRP from filter paper after subsequent post-functionalized using a perfluorinated compound. The low wettability could be explained by a combination of a high surface roughness and the chemical composition. Biobased dendronized polymers were synthesized through the ‘attach to’ route employing dendronization of soluble cellulose, in the form of hydroxypropyl cellulose (HPC). The dendronized polymers were studied as nanosized objects using atomic force microscopy (AFM) and it was found that the dendron end-group functionality had a large effect on the molecular conformation on surfaces of spun cast molecules. ATRP of vinyl monomers was conducted from an initiator-functionalized HPC and an initiator-functionalized first generation dendron, which was attached to HPC. The produced comb polymers showed high molecular weight and their sizes could be estimated via AFM of spun cast molecules on mica and from dynamic light scattering in solution, to around 100-200 nm. The comb polymers formed isoporous membranes, exhibiting pores of a few micrometers, when drop cast from a volatile solvent in a humid environment. HPC was also used to initiate ROP of ε-caprolactone, which was chain extended using ATRP to achieve amphiphilic comb block copolymers. These polymers could be suspended in water, cross-linked and were able to solubilize a hydrophobic compound. / QC 20100826