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PubMed2005

Dynamics of composite polymerization mediates the development of cuspal strain.

OBJECTIVES: In the current study, we used electronic speckle pattern interferometry (ESPI) to measure tooth deformation in response to polymerization of five resin composites with a range of polymerization shrinkage. Our hypothesis was that composites with higher polymerization shrinkage should cause more cuspal strain as measured by ESPI. METHODS: Standardized MOD cavities were prepared and placed into the ESPI apparatus before the cavities were filled with composites (n=10). The ESPI apparatus was constructed to measure the out-of-plane displacement of the lingual cusps of the teeth during the polymerization of the restorative material. A thermocouple was attached to the specimen to monitor thermal changes throughout the polymerization process. RESULTS: Experiments with empty preparations demonstrated that the ESPI technique was temporally responsive and sensitive to dimensional changes. However, the correlation between polymerization shrinkage of composite resins and ESPI-measured tooth deformation was not straightforward. In particular, a flowable material did not deform the tooth significantly more that a conventional hybrid. Further, an experimental silorane material (with the lowest axial shrinkage) induced the least tooth deformation. SIGNIFICANCE: We concluded that ESPI is a viable method for assessing cuspal strain induced by shrinkage of bonded composite restorations, but that polymerization shrinkage data may overestimate shrinkage-induced tooth deformation. The rate of polymerization shrinkage appeared to mediate the development of cuspal strain.

Composite Resins↗

PubMed2004

Influence of the microporosity and surface chemistry of polymeric resins on adsorptive properties toward phenol.

In this work, the effects of the microporosity and chemical surface of polymeric adsorbents on adsorptive properties of phenol were investigated. Textural parameters of four kinds of polymeric resins, namely AB-8, D4006, NKA-II and D16 resin, were separately measured by ASAP 2010. The surface chemistry of these polymeric resins was determined by means of inverse gas chromatography (IGC) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Static equilibrium adsorption experiments were carried out to obtain the isotherms of phenol on the polymeric resins. It was shown that NKA-II and AB-8 resin possessed relatively high BET surface areas and micropore volumes, while D4006 and D16 resin possessed comparatively low BET surface areas and micropore volumes. The results of IGC experiments revealed that NKA-II resin had extraordinary high specific component of the free energy of adsorption both for polar acetone and benzene probe, and thus extraordinary strong surface polarity compared to the other polymeric resins. It was also found that the isotherm of phenol on NKA-II was much higher than that on the other polymeric resins due to its strongest surface polarity and largest micropore volume among four kinds of resins. These experimental observations indicated that adsorption of phenol on the polymeric resins depended greatly on their microporosity and surface chemistry. The well-developed microporosity and the strong surface polarity would improve the adsorption of phenol on the polymeric resins.

Adsorption↗

PubMed2005

Extracellular polymeric substances mediate bioleaching/biocorrosion via interfacial processes involving iron(III) ions and acidophilic bacteria.

Extracellular polymeric substances seem to play a pivotal role in biocorrosion of metals and bioleaching, biocorrosion of metal sulfides for the winning of precious metals as well as acid rock drainage. For better control of both processes, the structure and function of extracellular polymeric substances of corrosion-causing or leaching bacteria are of crucial importance. Our research focused on the extremophilic bacteria Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, because of the "simplicity" and knowledge about the interactions of these bacteria with their substrate/substratum and their environment. For this purpose, the composition of the corresponding extracellular polymeric substances and their functions were analyzed. The extracellular polymeric substances of both species consist mainly of neutral sugars and lipids. The functions of the exopolymers seem to be: (i) to mediate attachment to a (metal) sulfide surface, and (ii) to concentrate iron(III) ions by complexation through uronic acids or other residues at the mineral surface, thus, allowing an oxidative attack on the sulfide. Consequently, dissolution of the metal sulfide is enhanced, which may result in an acceleration of 20- to 100-fold of the bioleaching process over chemical leaching. Experiments were performed to elucidate the importance of the iron(III) ions complexed by extracellular polymeric substances for strain-specific differences in oxidative activity for pyrite. Strains of A. ferrooxidans with a high amount of iron(III) ions in their extracellular polymeric substances possess greater oxidation activity than those with fewer iron(III) ions. These data provide insight into the function of and consequently the advantages that extracellular polymeric substances provide to bacteria. The role of extracellular polymeric substances for attachment under the conditions of a space station and resulting effects like biofouling, biocorrosion, malodorous gases, etc. will be discussed.

Acidithiobacillus↗

PubMed2001

On the role of oil-soluble initiators in the radical polymerization of micellar systems.

Polymerization in micellar systems is a technique which allows the preparation of ultrafine as well as coarse latex particles. This article presents a review of the current literature in the field of radical polymerization of classical monomers in micellar systems initiated by oil-soluble initiators. Besides a short introduction to some of the kinetic aspects of emulsion polymerization initiated by water-soluble initiators, we mainly focus on the kinetics and the mechanism of radical polymerization in o/w and w/o micellar systems initiated by classical oil-soluble initiators. The initiation of emulsion polymerization of an unsaturated monomer (styrene, butyl acrylate,...) by a water-soluble initiator (ammonium peroxodisulfate) is well understood. It starts in the aqueous phase and the initiating radicals enter the monomer-swollen micelle. The formed oligomeric radicals are surface active and increase the colloidal stability of the disperse system. Besides, the charged initiating radicals might experience the energetic barrier when entering the charged particle surface. The locus of initiation with oil-soluble initiators is more complex. It can partition between the aqueous-phase and the oil-phase. Besides, the surface-active oil-soluble initiator can penetrate into the interfacial layer. The dissolved oil-soluble initiator in the monomer droplet can experience the cage effect. The small fraction of the oil-soluble initiator dissolved in the aqueous phase takes part in the formation of radicals. The oligomeric radicals formed are uncharged and therefore, they do not experience the energetic barrier when entering the polymer particles. We summarize and discuss the experimental data of radical polymerization of monomers initiated by oil-soluble initiators in terms of partitioning an initiator among the different domains of the multiphase system. The inhibitor approach is used to model the formation of radicals and their history during the polymerization. The nature of the interfacial layer and the type of oil-soluble initiator including the surface active ones are related to the kinetic and colloidal parameters. The emulsifier type and reaction conditions in the polymerization are summarized and discussed.

Emulsions↗

PubMed1999

Deferoxamine: stimulation of hematin polymerization and antagonism of its inhibition by chloroquine.

The iron chelator deferoxamine enhances the clearance of Plasmodium falciparum parasitemia and may be useful in drug combinations for the treatment of cerebral malaria. However, the deferoxamine-chloroquine drug combination is antagonistic, or at best additive, against P. falciparum in vitro. As chloroquine is thought to exert its antimalarial activity by interacting with hematin released from the proteolytic degradation of hemoglobin in the parasite food vacuole, we hypothesized that deferoxamine might interfere with the ability of chloroquine to inhibit hematin polymerization, since it was reported that deferoxamine interacts with hematin. Therefore, we assessed deferoxamine-hematin binding in more detail and investigated the effect of deferoxamine on hematin polymerization in the presence and absence of chloroquine. Isothermal titration calorimetry (ITC) experiments demonstrated an enthalpy-driven deferoxamine:hematin mu-oxo dimer binding with an association constant of 2.8 x 10(4) M(-1) at pH 6.5, a binding affinity 14-fold lower than that measured for chloroquine. At least two of the three hydroxamic acid functional groups of deferoxamine must be unionized for effective binding. We also discovered that deferoxamine antagonized chloroquine-mediated inhibition of hematin polymerization. Unexpectedly, deferoxamine increased the concentration of soluble forms of hematin and enhanced the rate of hematin polymerization. Deferoxamine also could initiate hematin polymerization. In contrast, chloroquine decreased the concentration of soluble forms of hematin and inhibited hematin polymerization. This work supports the postulate that initiation of hematin polymerization requires a higher concentration of soluble hematin monomer than does the elongation phase of polymerization and provides one possible explanation for the observed antagonism between deferoxamine and chloroquine against parasites in culture.

Animals↗

PubMed2000

Solubility of fluoromethemoglobin S: effect of phosphate and temperature on polymerization.

The polymerization properties of the fully liganded fluoromet derivative of hemoglobin S (FmetHb S) were investigated by electron microscopy and absorption spectroscopy. Polymerization progress curves, as measured by increasing sample turbidity at 700 nm, exhibit a delay time (t(d)) consistent with the double nucleation mechanism. The pattern of fiber growth, as monitored by electron microscopy, is also indicative of a heterogeneous nucleation process, and dimensions of the fibers were found to be comparable to that of deoxyHb S. The polymerization rate constant (1/t(d)) depends exponentially on Hb S concentration, and the size of the homogeneous and heterogeneous nuclei also depend on FmetHb S concentration. As for deoxyHb S, higher concentrations of protein and phosphate favor fiber formation, while lower temperatures inhibit polymerization. Solubility experiments reveal, however, that eight times more FmetHb S is required for polymerization. The current studies further show that reaction order is independent of phosphate concentration if Hb S activity and not concentration is considered. The allosteric effector, inositol hexaphosphate (IHP), promotes fiber formation, and temperature-dependent reaggregation of FmetHb S suggests that IHP stabilizes pregelation aggregates. These studies show that FmetHb S resembles deoxyHb S in many of its polymerization properties; however, IHP-bound FmetHb S potentially provides a unique avenue for future studies of the early stages of Hb S polymerization and the effect of tertiary and quaternary protein structure on the polymerization process.

Allosteric Regulation↗

PubMed1999

pADPRT-2: a novel mammalian polymerizing(ADP-ribosyl)transferase gene related to truncated pADPRT homologues in plants and Caenorhabditis elegans.

Until recently, poly(ADP-ribosyl)ation was supposed to be confined only to polymerizing(ADP-ribosyl)transferase/(ADP-ribose)polymerase (E.C. 2.4.2.30). Here, we present novel polymerizing(ADP-ribosyl)transferase homologues from mouse and man that lack all of the N-terminal DNA binding and BRCA1 C-terminus domains and will be designated polymerizing(ADP-ribosyl)transferase-2 as distinguished from the classical polymerizing(ADP-ribosyl)transferase (polymerizing(ADP-ribosyl)transferase-1). The murine polymerizing(ADP-ribosyl)transferase-2 gene shares three identical intron positions with its Caenorhabditis elegans (EMBL nucleotide sequence database Z47075) and one with the Arabidopsis thaliana homologue ('APP', GenBank database AF069298). Expression of the murine polymerizing(ADP-ribosyl)transferase-2 gene was elevated in spleen, thymus and testis and the corresponding poly(ADP-ribosyl)ation activity might account for most of the residual poly(ADP-ribosyl)ation observed in polymerizing(ADP-ribosyl)transferase-1(-/-) mice.

Amino Acid Sequence↗

PubMed1999

Increased sialylation of polymeric immunoglobulin A1: mechanism of selective glomerular deposition in immunoglobulin A nephropathy?

Immunoglobulin A nephropathy (IgAN) is characterized by raised serum IgA and predominant mesangial IgA deposits of polymeric nature. The abnormal glycosylation of the carbohydrate moieties in the hinge region of the IgA molecule has recently attracted much attention. In this study we investigated the galactosylation and sialylation of monomeric and polymeric IgA1 isolated from patients with IgAN. Total IgA1 in serum samples from patients with IgAN or from healthy controls was isolated with a jacalin-agarose column as jacalin-bound protein (JBP). Monomeric and polymeric IgA1 were distinctly separated by fast protein liquid chromatography. Lectin binding assays were designed to examine the sialylation and the expression of terminal galactose and N-acetyl galactosamine of the O-linked carbohydrate in the hinge region of the IgA molecule. Reduced terminal galactosylation was demonstrated in serum IgA and monomeric IgA1 isolated from patients with IgAN as compared with results in healthy control subjects. However, a reduction in terminal galactosylation was not found in polymeric IgA1 isolated from patients with IgAN. Instead, increased sialylation of IgA1 (alpha2-3 linked to galactose) was demonstrated in polymeric IgA1. This abnormality of IgA1 could bear considerable implication on the pathogenesis of IgAN, because the masking effect of sialic acid may hinder the clearance of polymeric IgA1 by the asialoglycoprotein receptor (ASGP-R) of the liver cells. An increase in the sialylated content would also render the polymeric IgA from patients with IgAN more anionic. These immunochemical properties may contribute to the selective glomerular deposition of polymeric IgA1 in IgAN.

Adult↗

PubMed1999

Effect of water temperature on the fit of provisional crown margins during polymerization.

STATEMENT OF PROBLEM: When fabricating a provisional crown with the direct technique, dentists are concerned with margin discrepancies that result from polymerization shrinkage. PURPOSE: This in vitro study examined the effect of water temperature on the fit of provisional crown margins during resin polymerization. MATERIAL AND METHODS: The experiment was designed to simulate a direct technique to fabricate provisional crowns. After mixing autopolymerizing methyl methacrylate resin, the material was placed in a preformed polycarbonate crown. The crown was seated on a prepared premolar-shaped die with a shoulder margin. After 1 minute and 50 seconds, the crown was removed and polymerization was continued under the following conditions: 20 degrees C air, and water at 0 degrees C, 10 degrees C, 20 degrees C, 30 degrees C, 40 degrees C, 60 degrees C, and 80 degrees C. Six minutes after polymerization, the crown was trimmed and reseated on the die. Discrepancy of crown margin was measured with a 3-dimensional digitizer. RESULTS: Margin discrepancy varied with the condition during resin-polymerization (ANOVA, P <.001). The crowns polymerized in 20 degrees C and 30 degrees C water revealed the best margin fit, showing 3 times more accurate margin fit than those polymerized in 20 degrees C air (Bonferroni/Dunn procedure, P <.01). CONCLUSION: Conditions during resin polymerization were significant factors that affected margin fit of provisional crowns using the direct technique. Water temperatures of 20 degrees C and 30 degrees C produced the best fit at the margin of the provisional crown.

Analysis of Variance↗

PubMed2002

Polymerization kinetics of HEMA/DEGDMA: using changes in initiation and chain transfer rates to explore the effects of chain-length-dependent termination.

The effect of kinetic chain length and chain transfer on the polymerization kinetics and network structure in polymerizations of loosely crosslinked 2-hydroxyethyl methacrylate/di(ethylene glycol) dimethacrylate mixtures was explored. Polymerization behavior of the monomer mixture in the presence and absence of a chain transfer agent was monitored at various initiation rates and chain transfer agent concentration levels. Dependence of the polymerization rate on the initiation rate was found to deviate from the classical square-root relationship because of chain-length-dependent termination. This effect was further confirmed by addition of a chain transfer agent. The presence of a chain transfer agent led to the formation of shorter kinetic chains, which enhanced termination and slowed the polymerization. Investigation of the polymerization kinetics after cessation of irradiation yielded kt/kp[M] values for both systems. Prior to the onset of reaction diffusion-controlled termination, the system that included a chain transfer agent exhibited much higher kt/kp[M] values than the polymerization system without added chain transfer agent. In addition, the onset of reaction diffusion-controlled termination was delayed to higher conversions in the system containing chain transfer agent. The impact of a chain transfer agent on the polymerization behavior and kinetics demonstrates that the chain-length-dependent termination phenomenon is indeed important and must be considered in kinetic modeling of loosely crosslinked systems.

Calorimetry, Differential Scanning↗

PubMed1986

Clinical significance of polymeric and monomeric IgA complexes in patients with IgA nephropathy.

IgA nephropathy is currently considered an immune complex (IC) disease. However, though several groups have demonstrated the presence of IgA-IC in the sera of patients by various techniques, a correlation with clinical activity of the nephropathy has not always been found. Since these assays detect (simultaneously) polymeric and monomeric IgA-IC, the pathogenicity of these two classes of complexes could not be established. In this work, we have studied in 66 patients with IgA nephropathy the existence and significance of such IC, by means of a technique described in our laboratory, based on the specific binding of secretory component for polymeric IgA. Furthermore, IgG-ICs were also determined by the standard Raji cell assay in ELISA. The prevalence of these complexes was as follows: Multimeric (polymeric and monomeric) IgA-ICs were detected in 55% of 66 patients studied, polymeric IgA-ICs in 30%, monomeric IgA-ICs in 39%, and IgG-ICs in 46%. The intermittency of all these complexes was clearly noted in sequential examinations. A significant correlation (P less than .025) with hematuria was only found with polymeric IgA-IC, but not with multimeric IgA-IC, monomeric IgA-IC, or IgG-IC. Polymeric IgA-ICs were more frequently observed at the initial phases of the disease. Analytical ultracentrifugation showed that polymeric IgA-IC was of larger size than monomeric IgA-IC. The major pathogenicity of polymeric IgA-IC is in agreement with the finding of this immunoglobulin at the mesangial level in patients and animals with IgA nephropathy.

Adolescent↗

PubMed2000

Liposomes encapsulating polymeric chitosan based vesicles--a vesicle in vesicle system for drug delivery.

Drug delivery systems comprising vesicles prepared from one amphiphile encapsulating vesicles prepared from a second amphiphile have not been prepared previously due to a tendency of the bilayer components of the different vesicles to mix during preparation. Recently we have developed polymeric vesicles using the new polymer-palmitoyl glycol chitosan and cholesterol in a 2:1 weight ratio. These polymeric vesicles have now been encapsulated within egg phosphatidylcholine (egg PC), cholesterol (2:1 weight ratio) liposomes yielding a vesicle in vesicle system. The vesicle in vesicle system was visualised by freeze fracture electron microscopy. The mixing of the different bilayer components was studied by monitoring the excimer fluorescence of pyrene-labelled polymeric vesicles after their encapsulation within egg PC liposomes or hexadecyl diglycerol ether niosomes. A minimum degree of lipid mixing was observed with the polymeric vesicle-egg PC liposome system when compared to the polymeric vesicle-hexadecyl diglycerol ether niosome system. The polymeric vesicle-egg PC vesicle in vesicle system was shown to retard the release of encapsulated solutes. 28% of 5(6)-carboxyfluorescein (CF) encapsulated in the polymeric vesicle compartment of the vesicle in vesicle system was released after 4 h compared to the release of 62% of encapsulated CF from plain polymeric vesicles within the same time period.

Carbohydrate Sequence↗

PubMed1975

Ionic and nucleotide requirements for microtubule polymerization in vitro.

The ionic and nucleotide requirements for the in vitro polymerization of microtubules from purified brain tubulin have been characterized by viscometry. Protein was purified by successive cycles of a temperature dependent assembly-diassembly scheme. Maximal polymerization occurred at a concentration of 0.1 M Pipes (piperazine-N,N'-bis(2-ethanesulfonic acid)); increasing ionic strength by addition of NaCl to samples prepared in lower buffer concentrations did not result in an equivalent level of polymerization. Both Na-+ and K-+ inhibited microtubule formation at levels greater than 240 mM, withmaximal assembly occurring at physiological concentrations of 150 mM. Maximal extent of assembly occurred at pH 6.8 and optimal rate at pH 6.6. Inhibition of polymerization was half-maximal at added calcium concentrations of 1.0 mM and magnesium concentrations of 10.0 mM. EGTA (ethylene glycol bis(beta-aminoethyl ether)tetraacetic acid), which chelates Ca-2+, had no effect on polymerization over a concentration range of 0.01-10.0 mM. In contrast, EDTA (ethylenediaminetetraacetic acid), which chelates both Mg-2+ and Ca-2+, inhibited assemble half-maximally at 0.25 mM and totally at 2.0 mM. As determined from experiments using Mg-2+-EDTA buffers, magnesium was required for polymerization. Magnesium promoted the maximal extent of assembly at substoichiometric levels relative to tubulin, but was maximal for both rate and extent at stoichiometric concentrations. Elemental analyses indicated that approximately 1 mol of magnesium was tightly bound/mol of tubulin dimer. Viscosity development was dependent upon hydrolyzable nucleoside triphosphate, and stoichiometric levels of GTP were sufficient for maximal polymerization. The effect of magnesium in increasing the rate of GTP-dependent polymerization suggests that a Mg-2+-GTP complex is the substrate required for a step in assembly.

Alkanesulfonates↗

PubMed1999

Interaction between Hsc70 and DnaJ homologues: relationship between Hsc70 polymerization and ATPase activity.

We previously found that, in the presence of ATP, DnaJ homologues catalytically induce formation of a metastable Hsc70 polymer and, similarly, the DnaJ homologue auxilin catalytically induces formation of a metastable Hsc70-clathrin basket complex. Since this suggests that the induction of metastable complexes, which form in ATP but dissociate in ADP, may be a general property of DnaJ homologues, in the present study we investigated in more detail the ability of DnaJ homologues to induce polymerization of Hsc70. This study shows that DnaJ homologues induce polymerization of Hsc70 at the same rate as they induce an initial burst of Hsc70 ATPase activity, showing that polymerization is a specific effect of DnaJ homologue binding to Hsc70. However, polymerization does not always accompany the initial burst of ATPase activity. The dependence of the rates of ATPase activity and polymerization on DnaJ homologue concentration shows that DnaJ homologues bind very weakly to Hsc70 in the presence of ATP and do not bind at all in ADP. Surprisingly, however, under certain conditions the rate of polymerization appears to be independent of Hsc70 concentration, suggesting that polymerization is a first-order reaction, perhaps occurring when two Hsc70 molecules bind to a single DnaJ molecule and then shift their binding to each other. We propose that both the polymerization of Hsc70 by DnaJ homologues and the presentation of substrate by DnaJ homologues to Hsc70 involve the bringing of substrate into proximity with Hsc70 and then independently inducing rapid ATP hydrolysis to cause formation of a metastable Hsc70-substrate complex.

Adenosine Triphosphatases↗

PubMed2006

Enzyme-initiated miniemulsion polymerization.

Enzyme-catalyzed polymerization in vitro has gained considerable attention in the last two decades as an efficient tool in the polymerization of various monomers, such as saccharides, esters, phenols, and aromatic anilines; however, the polymerization of vinyl monomers using enzymes has been more limited, perhaps due to the hydrophobicity of most common vinyl monomers. Enzyme-initiated miniemulsion polymerization is demonstrated herein as a way to polymerize hydrophobic vinyl monomers such as styrene. By application of enzyme-initiated radical polymerization in miniemulsion, stable poly(styrene) latexes are prepared with a particle size near 50 nm. A very small amount of enzyme and surfactant is required to facilitate the miniemulsion polymerization, whereas a relatively high polymerization rate and conversion are achieved.

Catalysis↗

PubMed2003

Hydroxy- and silyloxy-substituted TEMPO derivatives for the living free-radical polymerization of styrene and n-butyl acrylate: synthesis, kinetics, and mechanistic studies.

The synthesis of new 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) styryl derivatives as mediators for the living free-radical polymerization is described. Two of the alpha-methyl groups at the 2- and 6-position of the parent TEMPO styryl alkoxyamine have been replaced by hydroxymethyl and silyloxymethyl groups. To further increase the steric hindrance around the alkoxyamine oxygen atom, the remaining two methyl groups have been substituted with larger ethyl groups. Styrene polymerizations using hydroxy-substituted TEMPO derivatives are fast, but are not well-controlled. As previously shown for other OH-substituted alkoxyamines, intramolecular H-bonding leads to an acceleration of the C-O bond homolysis and, hence, to an acceleration of the polymerization process. However, the OH groups also increase the alkoxyamine decomposition rate constant. The kinetics of the C-O bond homolysis have been determined using EPR spectroscopy. Decomposition studies have been conducted with the aid of 1H NMR spectroscopy. In contrast to the OH-substituted alkoxyamines, highly hindered silyloxy-substituted TEMPO alkoxyamines turned out to be excellent mediator/initiators for the controlled styrene polymerization. Polystyrene with M(n) of up to 80 000 g/mol and narrow polydispersities (PDI) has been prepared using the new alkoxyamines. Reactions have been conducted at 105 degrees C; however, even at 90 degrees C controlled but slow polymerizations can be achieved. Furthermore, and more importantly, poly(n-butyl acrylates) with narrow PDIs (<1.15) have been prepared at 105 degrees C with the new alkoxyamines. Controlled acrylate polymerization can be conducted at temperatures as low as 90 degrees C. The silylated alkoxyamines presented belong to the most efficient initiator/mediators for the controlled acrylate polymerization known to date. The effect of the addition of free nitroxide on the acrylate polymerization is discussed. Moreover, the synthesis of diblock copolymers with narrow PDIs is described.

Journal Article↗

PubMed2004

Synthesis of hydrophilic polymer-grafted ultrafine inorganic oxide particles in protic media at ambient temperature via atom transfer radical polymerization: use of an electrostatically adsorbed polyelectrolytic macroinitiator.

A new approach for the surface grafting of polymer chains to colloidal substrates is described. A cationic macroinitiator has been designed for the surface polymerization of a wide range ofhydrophilic methacrylates from ultrafine inorganic oxide sols by atom transfer radical polymerization in protic media at ambient temperature. One advantage of this approach is that it allows one-pot syntheses: the macroinitiator is adsorbed onto the sol, followed by an in situ polymerization. Nonionic, cationic, and betaine monomers can be polymerized directly by this protocol, with reasonably high conversions being obtained, as judged by 1H NMR spectroscopy. Anionic monomers such as sodium 4-styrenesulfonate cannot be polymerized directly due to incompatibility problems with the cationic macroinitiator-coated sol. However, hydroxylated monomers such as glycerol monomethacrylate can be surface-polymerized and then converted to anionic polyelectrolytes by reaction with succinic anhydride under mild conditions. This derivatization was confirmed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic analysis. Thermogravimetry was used to assess the degree of polymer grafting. Higher target degrees of polymerization led to increased grafted polymer loadings, as expected. Particle morphologies and relative degrees of dispersion in aqueous solution were assessed by transmission electron microscopy and dynamic light scattering, respectively. Surface characterization of the polymer-grafted sols was achieved by X-ray photoelectron spectroscopy and aqueous electrophoresis measurements. Most of the data reported in this study concern surface polymerizations from ultrafine silica sols, but some preliminary data for ultrafine tin(IV) oxide sols are also presented. Since most surfaces are negatively charged, this cationic macroinitiator approach can, in principle, be extended to include a wide range of sols, latexes, and planar substrates without requiring a separate surface functionalization step.

Journal Article↗

PubMed2005

Solvent-controlled organization of self-assembled polymeric monolayers on gold: an easy approach for the construction of protein resistant surfaces.

Protein resistant surfaces based on poly(ethylene glycol) (PEG) coatings are extensively applied in the fields of biosensors, tissue engineering, fundamental cell-surface interaction research, and drug delivery systems. The structural organization of the PEG film on the surface has a significant effect on the performance of the film to resist protein adsorption. In this paper, we report an approach using solvent to control the organization of the polymeric monolayer on gold. A water soluble copolymer with grafted PEG side chains and alkyl disulfide side chains was synthesized. A polymeric monolayer was fabricated on a gold surface from different solutions (water- and toluene-based) of the copolymer. The organization of the polymeric monolayers was characterized by means of ellipsometry, cyclic voltammetry, contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy. It was proven that the structural organization of the polymeric monolayer on a gold surface could be controlled by the solvent. A polymeric monolayer with PEG enriched at the outer level is obtained when water is used as the solvent. Various types of proteins, including fibrinogen, albumin, and normal human serum, were used to test the protein resistance of the gold surfaces modified by the polymeric monolayers. The polymeric monolayer formed from a water solution of the copolymer showed excellent protein resistance. In addition, by using water as the solvent, patterning of the polymeric monolayer could easily be achieved through a combination of lift-off and self-assembly. We believe that the approach reported here provides an easy, fast, and efficient way to fabricate a robust protein resistant surface.

Journal Article↗