Influence Of Polymerization Research Articles

Influence of Polymerization with Argon Laser and LED on Shear Resistance of Adhesive Systems

objective: The aim of this work was to evaluate the shear strength of ceramic brackets as a function of two adhesive systems (kit TransbondTM XT; TransbondTM Plus Self Etching Primer/ 3M Unitek®) and two light sources (LED and Argon Laser). Method: 28 maxillary premolars were used, divided into two groups (n=14), according to the adhesive system and light source. The teeth were enclosed in ¾-inch PVC tubes, with special stone plaster, perpendicular to the ground and tubes. Brackets were fixed over the exposed crowns. The teeth were stored at 37ºC for 24 hours and then submitted to 1,000 thermal cycles with 30 seconds in each bath (5°C and 55°C). The shear test was performed on a Shimadzu® testing machine at a speed of 0.5mm/min. Enamel surfaces were qualified using the ARI (Adhesive Remaining Index). Data were submitted to statistical analyzes ANOVA, Tukey and Kruskal-Wallis (p<0.05). Results: the conventional TransbondTM XT kit adhesive system was superior to the self-etching system. LED and Argon Laser showed similar behaviors. Conclusion: Argon laser did not influence shear strength or ARI scores.

Influence of polymerization among Al- and Ga-containing molecules on growth rate and Al content in AlGaN

AlGaN metalorganic vapor-phase epitaxial growth simulation in a TMAl/TMGa/NH3/H2 system was studied to explain its growth rate and Al content. We proposed three kinds of Al- and Ga-containing polymers in this system. By using those polymers, we got good agreements in pressure, TMAl/(TMAl+TMGa) inlet ratio, and temperature dependences of AlGaN growth rate and its Al content between simulations and experiments, even at pressures higher than 40 kPa. Our results showed that the formation of these polymers is enhanced under higher pressures. The simulation considering those polymers could explain the linearity in the TMAl/(TMAl+TMGa) inlet ratio dependences of growth rate and Al content at lower pressure and their non-linearity at higher pressure.

Structure and Spectroscopic Properties of Gold(I) Diselenophosph(in)ate Complexes: A Joint Experimental and Theoretical Study

The structure and optical properties of several polynuclear gold(I) species, namely, diselenophosphate [Au{μ-Se(2)P(OR)(2)}](2) complexes (R = (i)Pr, Et, (n)Pr) respectively numbered 1, 2, and 3 and number 4 [Au{μ-Se(2)P(CH(2))(2)Ph)(2)}](2), exhibiting interesting structural, absorption, and emission properties have been studied. The synthesis, full characterization, and experimental spectroscopic study of 3 and 4 have first been carried out, 1 and 2 being previously studied. In the solid state, 3 gives polymers, like 1 and 2, whereas 4 exists under a dinuclear monomeric form. The absorption and phosphorescence properties of 4 have been rationalized using DFT and TDDFT computations. In particular, Au-Au bonding seems to appear in its first singlet and triplet states, whereas such a bond does not exist in the ground state. Then, the influence of polymerization through aurophilic bonding on the optical properties of 2 is investigated (1 and 3 behave as 2). It is shown using TDDFT computations that its observed UV-visible excitation spectrum in solution is due to high oligomers and not to monomers or low size oligomers. ESI-MS molecular weight measurements confirm the occurrence of such oligomers of 2 in solution. An assignment of the observed bands of 2 is proposed. The transition corresponding to the first excitation band, which is mainly a HOMO to LUMO one, exhibits metal-centered character, i.e., a gold 5d to 6p orbital transition, but concomitantly transfers significant electron density from gold to phosphorus atoms so that it is also a MLCT one.

Liquid injection in confined co-flow: Application to portal vein embolization by glue injection

Drop formation in liquid-liquid systems has received considerable attention over the last century owing to its many industrial applications. More recent applications may be found in the field of endovascular/percutaneous treatments. The present study focuses on portal vein embolization (PVE), which consists in the blockage of part of the portal trunk though the injection of surgical glue. The short-time injection is dominated by fluid dynamic effects: the influence of polymerization is secondary owing to the presence of ethiodized oil in the injected mixture. If the mechanism of liquid injection is well understood for injections in unconfined fluids at rest, fewer studies have so far considered the case of outer liquids flowing in confined environments. The objective is therefore to conduct a large range parametric study of liquid injections in confined co-flows. An experimental setup has been designed to simulate in vitro the injection in an immiscible liquid flowing in a cylindrical tube. The transition...

IN VITRO CHARACTERIZATION OF PORTAL VEIN EMBOLIZATION BY INJECTION OF SURGICAL GLUE

Glue embolization is a therapeutic treatment technique used to block the blood flow to specific targeted sites. It is achieved by injecting surgical glues that polymerize in contact with blood. One application concerns patients suffering from malignant liver tumors, who need to undergo partial liver ablation [deBaere 1996, Azoulay 1996]. When the volume of the remnant liver part is not sufficient, preoperative portal vein embolization is used to arrest blood flow in the liver part to be resected. This induces the hypertrophy of the remnant liver and enables the ablation procedure after a couple of weeks. Embolotherapy is currently based on empiric knowledge and therefore relies on the clinicians’ experience and competence. To reduce the risks associated with the medical procedure, there is a need for a better understanding of the mechanical and chemical processes that govern the behavior of glue once injected. Neglecting the polymerizing effects, we have recently shown that either drops or jets form at the tip of the catheter, each corresponding to a different regimes of ejection (dripping and jetting) [Sandulache 2011]; the dripping-to-jetting transition is governed by the Weber number of the disperse phase Wed, which is the ratio of its inertial to interfacial forces. The present objective is to have a more realistic in vitro simulation of the medical procedure and to study the influence of polymerization on the dynamics of glue ejection.

Structure−Activity Relationships of Polyphenols To Prevent Lipid Oxidation in Pelagic Fish Muscle

The influence of polymerization (number of monomers) and galloylation (content of esterified gallates) of oligomeric catechins (proanthocyanidins) on their effectiveness to prevent lipid oxidation in pelagic fish muscle was evaluated. Non-galloylated oligomers of catechin with diverse mean polymerization (1.9-3.4 monomeric units) were extracted from pine (Pinus pinaster) bark. Homologous fractions with galloylation ranging from 0.25 to <1 gallate group per molecule were obtained from grape (Vitis vinifera) and witch hazel (Hamamelis virginiana). The results showed the convenience of proanthocyanidins with medium size (2-3 monomeric units) and low galloylation degree (0.15-0.25 gallate group/molecule) to inhibit lipid oxidation in pelagic fish muscle. These optimal structural characteristics of proanthocyanidins were similar to those lately reported in fish oil-in-water emulsions using phosphatidylcholine as emulsifier. This finding suggests that the antioxidant behavior of polyphenols in muscle-based foods can be mimicked in emulsions prepared with phospholipids as emulsifier agents. The present data give relevant information to achieve an optimum use of polyphenols in pelagic fish muscle.

Dissipative particle dynamics simulation study on the binary mixture phase separation coupled with polymerization

The influence of polymerization on the phase separation of binary immiscible mixtures has been investigated by the dissipative particle dynamics simulations in two dimensions. During polymerization, the bulk viscosity increases, which consequently slows down the spinodal decomposition process. The domain size growth is monitored in the simulations. The absence of 23 exponent for inertial hydrodynamic mechanism clearly reflects the suppressing effect of polymerization on the phase separation. Due to the increasing viscosity, the individual phase may be trapped in a metastable stage instead of the lamellar morphology identified for symmetric mixtures. Moreover, the polymerization induced phase separation in the binary miscible mixture has been studied. The domain growth is strongly dependent on the polymerization probability, which is naturally related to the activation energy for polymerization. The observed complex phase separation behavior is attributed to the interplay between the increasing thermodynamic driving force for phase separation and the increasing viscosity that suppresses phase separation as the polymerization proceeds.

Effect of the Polymerization with Formaldehyde on the Thermal Reactivity of a Low-Temperature Coal Tar Pitch

The influence of polymerization with formaldehyde on the thermal reactivity of a low-temperature coal tar pitch has been investigated. The mechanism and extent of the polymerization depends on the catalyst used, the greatest extent of polymerization being achieved under basic catalytic conditions. After the polymerization treatment, samples were carbonized at 420 °C and the products were characterized by optical microscopy. According to the results, polymerization with formaldehyde increases the reactivity of the pitch, giving rise to increased carbonization yields and leading to the formation of the mesophase with milder conditions. The polymerization process also affects the morphology of the resultant anisotropic material, giving rise to the formation of irregularly shaped mesophase particles and reducing the optical texture size of the anisotropic domains, giving mosaic texture, especially when basic catalysis is used.

Influence of polymerization on the cholesteric structure in ethyl-cyanoethyl cellulose/acrylic acid solutions

Ethyl-cyanoethyl cellulose ((E-CE)C) forms cholesteric liquid crystals in acrylic acid (AA) and the cholesteric order in the solutions can be frozen when the AA is quickly polymerized but the cholesteric structure is changed after the polymerization though the property of the selective reflection is reserved. The maximum wavelength of the selective reflection of the cholesteric phase λ max is shifted to the shorter wavelength direction and the selectivity and the intensity of the reflection are decreased after the AA polymerization. It is found that the shift of the reflection wavelength results from the decrease of the cholesteric pitch after the polymerization and the variation of the cholesteric pitch is decreased with increasing the (E-CE)C concentration. The decrease of the pitch after the AA polymerization is due to the volume shrinkage of the solvent monomer during the polymerization and it depends on the polymerization temperature.

Polymerization of aqueous liquid-crystalline allyldimethyldodecylammonium bromide

Allyldimethyldodecylammonium bromide was polymerized by γ-ray irradiation in both hexagonal and cubic mesophases, and the conversion–time curves were obtained. The maximum conversion was about 35%, and the polymer remained in the liquid-crystalline structure formed by the nonpolymerized monomers. The influence of polymerization on the distribution of water in the different types related to the hydrophilic surfaces of microstructures was studied using Fourier transform infrared spectroscopy. The incomplete polymerization was explained by steric constraints in the liquid-crystalline structures.

Influence of surfactant vesicles and their polymerization on the complex formation between indoleacetate and methylviologen

The association constant K between methylviologen MV and indoleacetate IA was decreased by the addition of cationic vesicles, and the K increased at high vesicle concentrations. The influence of the polymerization of surfactants with different chain lengths on K was different. The concentration dependence of K was analyzed by a theory in terms of the partition coefficients of reactants between the bulk solvent phase and the local vesicle environment. The theoretical partition coefficients were determined graphically. The measured dependence of K on vesicle concentration was satisfactorily reproduced by the theory. When dimyrystyldiallylammonium bromide (DMAB) was added to the complex, the polymerization of the surfactant increased the partition coefficients of IA and the complex but decreased that of MV. However, the polymerization of dicetyldiallylammonium bromide (DCAB) showed the reverse tendency. The influence of polymerization on K or the partition coefficient was discussed in terms of the difference in the polymerization mechanism due to the differences in the distance between the neighboring nonpolymerized surfactant molecules and the polymerization induced change in that distance.

Influence of polymerization on the synthesis of SrTiO 3: Part I. Characteristics of the polymeric precursors and their thermal decomposition

The influence of polymerization on the thermal decomposition of polymeric precursors and phase formation was investigated during synthesis of SrTiO 3. The precipitation of polymeric precursor in acetone produced a more thermal stable precursor with lower weight loss during decomposition. This more stable precursor retarded the formation of the SrTiO 3 phase. From thermal analysis, XRD and FT-IR the presence of an intermediate phase during decomposition of the precursors was observed. This is a mixed (Sr,Ti) carbonate phase with the proposed composition of Sr 2Ti 2O 5.CO 3.

Terpolymérisation acrylonitrile‐styrène‐acrylate de méthyle, 5. Copolymérisation en emulsion styrène‐acrylate de méthyle en réacteur fermé en présence du styrène amorceur redox persulfate the potassium/hydrogénodisulfite de sodium

AbstractA series of emulsion copolymerizations of styrene (S) with methyl acrylate (MeA) initiated by the redox system potassium persulfate (KPS)/sodium hydrogen disulfite (SBS) was carried out at 50°C. The monomer feed composition and the monomer/water (M/W) ratios were widely varied. The polymerization rate was found to be higher than in the case when only KPS was applied. Initial (influence of polymerization in water phase) and final copolymer molecules (accumulation of MeA in the feed due to a lower reactivity) are richer in the more hydrophilic monomer (MeA). It could be shown that a high water solubility makes the emulsion reactivity ratios to be “apparent” kinetic parameters, which result in a higher number of azeotropic compositions, compared to bulk or solution, according to the M/W ratio. Particle sizes are smaller and the size distribution is larger than in polymerizations in the presence of KPS alone. Particle number (Np) tends to increase with conversion for monomer mixtures rich in MeA, contrary to S homopolymerizations in which Np remains constant. Comparison of Np and kinetic data suggests that only part of the particles in actually active in polymerization (N). N can be estimated assuming that the average number of radical per particle, ñ remains close to 0,5 – as found in a previous study – which gives also an estimate of very tiny particles generated at low conversion and undetectable by the usual QELS and MET techniques. The experimental data, to some extent, allow to quantify the competition between micellar and homogeneous nucleation mechanisms.

Polymerization in black lipid membranes

A variety of different lipids containing dienoyl groups in the side chains were tested for membrane formation using the planar lipid bilayer approach. One of these lipids formed stable bilayers which could be polymerized using UV-illumination. The influence of the polymerization was studied in monolayers, lipid vesicles and planar bilayers. The stability of the lipid bilayer membranes was increased by polymerization. Thus, the lifetime of the membranes increased from about 1 h to 4–5 h or longer. Furthermore, the specific conductance of unmodified membranes and of carrier-mediated transport is reduced. The transport of lipophilic ions was investigated as a function of polymerization using the charge-pulse method. The absorption of dipicrylamine (DPA-) is not affected. The translocation of this compound and of tetraphenylborate (B(Ph) 4 - ) showed a strong decrease with polymerization time. The influence of polymerization on the membrane structure may be explained on the basis of a strong viscosity increase in the lipid bilayer membrane.

Solid-state polymerization of a diacetylene studied by neutron scattering

The solid-state polymerization process of a diacetylene is investigated by neutron scattering. In contrast to x rays, neutrons do not induce polymerization and a detailed examination is possible in the autocatalytic region of the thermally activated polymerization process. In this region there appear diffuse sheets of diffracted intensity, split into doublets, which correspond to the one-dimensional propagation of the conversion. The Bragg reflections broaden, decrease, and also display multiple peaks. An Ising model for the limit of uncorrelated chains is compared to experiment. Above the 50%-conversion level the onset of chain interaction becomes visible. Preliminary data were obtained concerning the behavior of acoustic phonons and the structural phase transformation under the influence of polymerization.

The Influence of Polymerization for the Renal Handling of Light Chains

The Influence of Polymerization for the Renal Handling of Light Chains

Conformational changes in the antigenic determinant of tobacco mosaic virus protein resulting from polymerization of the subunits

The influence of polymerization on the antigenic specificity of tobacco mosaic virus protein was studied. Immunoelectrophoretic and Ouchterlony analyses performed at different temperatures revealed a number of distinct antigenic states correlated with different sized aggregates. Two alternative explanations were offered for the above observations. In one, the multideterminant hypothesis, it was assumed that each TMV subunit possessed a small number of unique antigenic sites. The number of such different sites available for combining with antibody changed as polymerization proceeded giving rise to an antigenically mixed population of aggregates. The second hypothesis assumed that a single determinant present on the surface of each subunit underwent a series of conformational changes as a result of polymerization. These conformational changes in the polypeptide chain were assumed to cause slight alterations in the antigenic configuration resulting in the generation of crossreactive antigens. The data presented were more compatible with the latter or single determinant hypothesis.

The mechanism of polymerization in the presence of the organic compounds of alkali metals

THE relationship of the structure of a polymeric chain and, oorrespondln~|y, of the properties of polymers, with ~he nature of the selectea catalyst and medium is an interesting characteristic of the polymerization of monomers under the action of organic components of lithium, sodium and-potaesium. Korotkov and others [1] have shown in the polymerization of butadiene that the fraction of 1,2-structures increases on t he replacement of li thium alkyl by sodium aikyl catadysta, and also on the transition from hydrocarbon to ethyl and dioxane. Tobohky and others [2] likewise established that in the polymerization of isoprene with alkyis and aryls of alkali metals, the poly-isoprene chain structure varies with the transformation of the nature of the metal and the solvent, and is not depend e n t on .the structure of the radical linked with the alb~li metal. They also found that ~he styrene content in copolymers obtained on polymerization with lithium organic compounds of the styrene-butauiiene [1] and styrene-isoprene ~ o m s [3] increases when the hydrocarbon solvent is replaced by ethyl. These authors show that the selective effect is determined by the polarity of the metal-carborL bond of the organo-metallic catalyst. I t is known that in the series LiR, Nal~, KR, the Li-R bond is the least polar. I t may be supposed that in the presence of LiR the interaction of the monomer with the catalyst ~11 be determined both by the electron-donor properties of group R and by the accepter properties of lithium. In the case of a typical anion. mechanism (e.g. NaR ill an ether medium), the growth of the chain is determined by the interaction of a monomer with a carbonian, and, correspondingly, the reactivity of a monomer is determined only by its electron-accepter properties. In such an examination it is to be expected that in a copolymer the content of monomers possessing the greater density of electrons in the binary bond will increase in the transition from sodium-to lithium-organic catalyst, and likewise on replacement of ethyl, amine and similar media by hydrocarbon solvents. To verify this supposition, it was essential to obtain certain quantitative data characterizing the simple sequences of these processes, and also to extend the invest,igation of the influence of polymerization on the composition of a copolymer