Addition Of Cross-linking Agent Research Articles

Bioactivity and Mechanical Property of Starch-Based Organic-Inorganic Hybrids

So-called bioactive ceramics bond to living bone through the apatite layer formed on their surfaces in the body. The apatite deposition is triggered by dissolution of calcium ion (Ca2+) and by silanol (Si-OH) group formed on the surfaces of the ceramics. It is expected that organic modification of these components would produce bioactive materials with high flexibility. In this study, we examined bioactivity and mechanical properties of the organic-inorganic hybrids from starch by modification with silanol group and calcium ion. Effect of cross-linking agent was also investigated. The obtained hybrids showed bioactivity and mechanical properties analogous to those of human cancellous bone by appropriate control in their compositions. Addition of cross-linking agent to improve mechanical strength of the hybrids did not decrease their bioactivity.

Supersaturated lysozyme solution structure studied by chemical cross-linking

Glutaraldehyde cross-linking followed by separation has been used to detect aggregates of chicken egg-white lysozyme (CEWL) in supersaturated solutions. In solutions of varying NaCl content, the number of aggregates was found to be related to the ionic strength of the solution. Separation by SDS-PAGE showed that percentage of dimer in solution ranged from 25.3% for no NaCl to 27.1% at 15% NaCl, and the aggregates larger than dimer increased from 1.9% for no NaCl to 36.8% at 15% NaCl. Conversely, the percentage of monomers decreased from 72.8% without NaCl to 36.1% at 15% NaCl. Molecular weights by capillary electrophoresis (SDS-CE) were found to be multiples of the monomer molecular weights, with the exception of trimer, which indicates a very compact structure. Native separation was accomplished using size-exclusion chromatography (SEC) and gave a lower monomer concentration and higher aggregate concentration than SDS-CE, which is a denaturing separation method. Most noticeably, trimers were absent in the SEC separation. The number of aggregates did not change with increased time between addition of NaCl and addition of cross-linking agent when separated by gel electrophoresis (SDS-PAGE). The results suggest that high ionic strength CEWL solutions are highly aggregated and that denaturing separation methods disrupt cross-linked products.

Spherical MgCl 2-supported MAO pre-catalysts: preparation, characterization and activity in ethylene polymerization

The spherical magnesium chloride (MgCl 2)-supported methylaluminoxane (MAO) pre-catalysts were prepared using MgCl 2·2.6EtOH adduct as support material subjected to elimination of EtOH by thermal treatments. The pre-catalysts were characterized by X-ray diffraction (XRD), IR, 27Al solid-state NMR, scanning electron microscopy (SEM) and N 2 BET surface areas. Under the activation of triethylaluminum (TEA), polymerization of ethylene were carried out by contacting supported MAO with soluble dichloro(rac-ethylene-bis(1-indenyl))zirconium (rac-Et(Ind) 2ZrCl 2) prior to polymerization. As a result, the polymers with spherical form morphology and high bulk density (over 0.35 g/cm 3) were obtained. The addition of cross-linking agents (CAs) during the adsorption of MAO on the support (e.g. glycol, glycerol and triethanolamine) led to an increase in Al content from 3.8 to 9–12 wt.% and in the catalyst activity. The highest activity in ethylene polymerization (3.48×10 7 g polyethylene (PE)/(mol Zr h)) was achieved in the case of using glycerol as CA.

Chemically induced supramolecular reorganization of triblock copolymer assemblies: trapping of intermediate states via a shell-crosslinking methodology.

The mechanism of morphological phase transitions was studied for rod-shaped supramolecular assemblies comprised of a poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA(90)-b-PMA(80)-b-PS(100)) triblock copolymer in 33% tetrahydrofuran/water after perturbation by reaction with a positively charged water-soluble carbodiimide. Tetrahydrofuran solvation of the hydrophobic core domain provided the dynamic nature required for the rod-to-sphere phase transition to be complete within 30 min. The intermediate morphologies such as fragmenting rods and pearl-necklace structures were trapped kinetically by the subsequent addition of a diamino crosslinking agent, which underwent covalent crosslinking of the shell layer. Alternatively, shell-crosslinked rod-shaped nanostructures with preserved morphology were obtained by the addition of the crosslinking agent before the addition of the carbodiimide, which allowed for the shell crosslinking to be performed at a faster rate than the morphological reorganization. The formation of robust shell-crosslinked nanostructures provides a methodology by which the morphological evolution processes can be observed, and it allows access to otherwise thermodynamically unstable nanostructures.

Modified gas-permeable silicone rubber membranes for covalent immobilisation of enzymes and their use in biosensor development.

Novel enzyme membranes are introduced. Modified polymeric gas-permeable layers were developed enabling biological components which have available reactive groups (-NH2, -OH, -SH, -COOH) to couple covalently on to their surfaces. Therefore, gas-permeable two component room temperature vulcanizing (2K-RTV) silicone rubber was modified using additional cross-linking agents. Triethoxysilanes with functional groups on their side chains such as epoxy or amino groups were used. A special attribute of the resulting gas-permeable membranes is that their formation and modification occur simultaneously during one reaction step. IR spectroscopy was used to observe the changes in the polymeric structure due to the reaction with the additional cross-linking agents. Sensors equipped with these layers are suitable to measure dissolved gases such as O2, CO2 and NH3 consumed or produced by enzymes converting their substrates. Determination of glucose, a well investigated enzymatic detection process, was chosen to demonstrate the applicability of the enzyme immobilisation. Glucose oxidase was immobilised on the membranes and glucose was detected by amperometric measurement of oxygen consumption. It is expected that this immobilisation method will also be useful for miniaturised planar biosensors.

Anion-exchange resins from vinylbenzyl choride: control of hydrolysis during polymerization

Anion-exchange resins can be prepared by amination of vinylbenzyl chloride-divinylbenzene (VBC-DVB) copolymers. A limitation of the VBC route is that significant hydrolysis of benzyl chloride to benzyl alcohol occurs during copolymerization, which can reduce the ion-exchange capacity of the final resin. This article documents a novel technique to control hydrolysis with a staged polymerization process using a package of azo and peroxy initiators. The polymerization is initiated at low temperature to minimize hydrolysis, run to high conversion at moderate temperature and completed at high temperature to burn off residual monomer. The aqueous phase is buffered with bicarbonate salt to prevent low pH conditions. The technique effectively controls hydrolysis to less than 5%, producing a high capacity anion-exchange resin. The technique can be used to synthesize VBC-DVB resins that are equivalent to conventional styrene-DVB resins by incorporating additional crosslinking agent during polymerization to compensate for the lack of methylene bridging during functionalization

Effect of intermolecular cross links on drag reduction by polymer solutions

In this work we explore the effect of a cross-linking agent on the drag reduction capability of hydroxypropyl guar and guar gum solutions in turbulent flow through horizontal pipes. The results show that the addition of a cross-linking agent (borax) to solutions with concentrations below those required for gel formation enhances drag reduction due to the increased dimensions of the macromolecules in the presence of intermolecular cross links. The flow-induced degradation of the polymers is not appreciably affected by the addition of cross-linking agent.

Lifetime expectancy of polyurethane binder as magnetic recording media

The effects of the chemical structure and addition of cross-linking agent and polyvinyl chloride (PVC) on the tensile strength of polyurethanes (PU) binder have been investigated. An expectation of the lifetime of PU binder as magnetic recording media has been performed based on the tensile strength change in different environmental conditions. It was found that a small number of ester bonds which are directly responsible for the polymer degradation and suitable storage temperature are required to extend the lifetime of the recording media. In addition, the presence of PVC and polyisocyanate (CL) as cross linking agent extends the lifetime of PU binder. For example, poly(hexamethylene carbonate) diol-based polyurethane PU(PCD) in a mixture system such as PU(PCD)/CL/PVD can be expected to have a tensile half life of about 200 years at 20°C.

Characterization of Polyacryl Starch Microparticles as Carriers for Proteins and Drugs

Biodegradable microparticles of cross-linked starch (maltodextrin) have been designed as carriers of proteins and low molecular weight drugs in vivo. Methods are presented for the synthesis of acryloyl starch and its polymerization to microparticles. Macromolecules were immobilized in the microparticles in high yields, i.e., up to 40% of the dry weight consisted of the immobilized protein. The optimal conditions of immobilization were investigated by varying the concentration of starch (D), the concentration of acryloyl groups (T), and the amount of additional cross-linking agent (C). Exclusion of the cross-linking agent gave maximal immobilization of the macromolecules. Enzyme kinetics, release profiles, surface localization, and heat stability of the immobilized macromolecules are also presented. Microparticles based on starch with small amounts of acryloyl groups were completely degraded after incubation with amyloglucosidase. The degradation of microparticles in serum and in the target organelle, the lysosome, was investigated in vitro. The polyacrylic starch microspheres (mean diameter, 0.5 μm) constitute an attractive alternative to other drug and enzyme carriers.