PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Polymers”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed2005

Preferential interactions in pigmented, polymer blends - C.I. Pigment Blue 15:4 and C.I. Pigment Red 122 - as used in a poly(carbonate)-poly(butylene terephthalate) polymer blend.

Some important characteristics of selected pigments have been evaluated, using the inverse gas chromatography (IGC) technique, that indicate the occurrence of preferential interactions in pigmented polymer blends. Attention has been given to copper phthalocyanine pigments and to quinacridone pigments incorporated in polycarbonate-poly(butylene terephthalate) blends. Selected supporting techniques were used to provide supplementary information concerning the pigments of interest, C.I. Pigment Blue 15:4 and C.I. Pigment Red 122. For C.I. Pigment Red 122 and for C.I. Pigment Blue, the dispersive component of the surface free energy decreases as the temperature increases, indicating the relative ease with which the molecules can be removed from the surface.

Azo Compounds↗
PubMed2004

The transition of polymers into a network of polymers alters per se the water activity.

We have found that polyacrylamide gels cross-linked with bisacrylamide induce a larger macromolecular osmotic pressure than the non cross-linked gels. This means also that in the cross-linked gels hydration water is held more tightly to the polymer, i.e., more work is needed to remove water, than in the non cross-linked gel. Since the chemical nature of the two gels is extremely similar, we propose that the formation of the network alters per se the water activity.

Acrylamide↗
PubMed2005

Controlled release from bioerodible polymers: effect of drug type and polymer composition.

The effect of the chemical nature of the drug on matrix degradation and drug release behavior of degradable polymers was studied, using lidocaine as a model drug in base and salt forms. We show in this study that the drug in the base form has a substantial effect on the release characteristics, through an accelerating effect on matrix degradation. Study of drug release from PdlLGA shows that lidocaine salt follows a three-phase release pattern, in contrast to the biphasic release of the lidobase. However, PlLA shows a different drug release pattern, with only a single diffusion phase exhibited for both lidobase and lidosalt. We also demonstrate that the crystallinity of matrix plays an important role on drug release profiles: a crystalline matrix (PlLA IV=2.04) releases the drug at a much slower rate compared to its amorphous counterpart of similar molecular weight (PdlLA IV=2.4). The details of the study of different factors influencing the drug release may have important implications for the control of delivery of potent drugs in various therapeutic windows.

Algorithms↗
PubMed2006

The use of soluble polymers and polymer microparticles to provide improved vaccine responses after parenteral and mucosal delivery.

It is important when developing new vaccine systems to give proper attention to the question of delivery. In some cases the judicious choice of a delivery system can provide a greatly enhanced immune response and avoid the need to use a vaccine adjuvant. Delivery systems that have been developed originally for the administration of challenging drug can be used with success for vaccines. Polymer microspheres and lamellar particle based on the biodegradable materials polylactide and polylactide co-glycolide can be employed for the improved parenteral and mucosal administration of antigens. Likewise soluble biopolymers such as chitosan can be used for the improved nasal delivery of various antigens as well as DNA. Results from animal studies and recent clinical trials are provided.

Absorbable Implants↗
PubMed2002

Molecular modelling of chain end effects in separating oligomers by reversed-phase gradient polymer elution chromatography; adsorption transition as revealed by a self-consistent-field theory for polymer adsorption.

HPLC experiments to separate butyl-terminated polystyrene (B-PS) oligomers have been mimicked by equilibrium self-consistent-field calculations based upon the Scheutjens Fleer formalism for polymers at interfaces. The adsorption-desorption transition as a function of the fraction of good solvent in a non-solvent (water)-solvent (tetrahydrofuran) mixture has been analysed and correlated to corresponding experiments. Much attention is paid to keeping the modelling as realistic as possible; for example, the effects of the solvent mixture on the C18-alkyl tails that are grafted on the silica surface are retained in the calculations. It is shown that the butyl end groups affect the elution properties up to chains with approximately 30 styrene units. Excellent semi-quantitative comparison is found with experiments for a realistic set of interaction parameters. Molecular-level information is available for the adsorption layer as a function of the solvent quality. Going from poor to good solvent, it is typical to find that the B-PS is fully absorbed inside the alkyl brush, then adsorbed on top of it, and finally depleted from it. The depletion effect in good solvents increases with increasing molecular mass.

Adsorption↗
PubMedDate not supplied

Hydrophilic polymer supports for solid-phase synthesis: preparation of poly(ethylene glycol) methacrylate polymer beads using "classical" suspension polymerization in aqueous medium and their application in the solid-phase synthesis of hydantoins.

Lightly cross-linked hydrophilic polymer beads representing new types of supports for solid-phase synthesis have been prepared from commercial oligoethylene glycol monomethacrylates using an aqueous suspension polymerization process and specifically designed polymerization mixtures. These beads swell extensively in solvents with a wide range of polarities from dichloromethane, tetrahydrofuran, and water to dimethylformamide, and they enable high functional loadings of 1.2-1.8 mmol g(-1). Their ability to serve as supports was demonstrated in the model solid-phase synthesis of a small library of hydantoins. This four-step synthesis using primary amines readily affords yields of over 70%.

Amines↗
PubMed2006

Beyond the metal-insulator transition in polymer electrolyte gated polymer field-effect transistors.

We have studied the carrier transport in poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) field-effect transistors (FETs) at very high field-induced carrier densities (10(15) cm(-2)) using a polymer electrolyte as gate and gate dielectric. At room temperature, we find high current densities, 2 x 10(6) A/cm(2), and high metallic conductivities, 10(4) S/cm, in the FET channel; at 4.2 K, the current density is sustained at 10(7) A/cm(2). Thus, metallic conductivity persists to low temperatures. The carrier mobility in these devices is approximately 3.5 cm(2).V(-1).s(-1) at 297 K, comparable with that found in fully crystalline organic devices.

Electric Conductivity↗
PubMed2002

Migration of additives from polymers into food simulants: numerical solution of a mathematical model taking into account food and polymer interactions.

The principle of a computing program describing precisely the migration of additives from a polymer into a food simulant is presented. As six parameters are used to fit the simulnnt sorption and additive extraction kinetics, the parameters have been determined by independent experiments. Owing to the complicated coupling between the liquid and additive diffusion processes, migration kinetics cannot be obtained by a mathematical resolution of kinetic equations, but they must be calculated by numerical analysis. The method is applied to a UV absorber in polypropylene migrating into glyceryl tripelargonate, a pure triglyceride, of which behaviour and average molecular weight are similar to official fatty food simulants. Properly designed experiments validate the model used to fit the migration kinetics. The possibility of erasing any parameters is also discussed.

Computer Simulation↗
PubMed2006

Glass transition of miscible binary polymer-polymer thin films.

The average glass transition temperatures, Tg, of thin homopolymer films exhibit a thickness dependence, Tg(h), associated with a confinement effect and with polymer-segment-interface interactions. The Tg's of completely miscible thin film blends of tetramethyl bisphenol-A polycarbonate (TMPC) and deuterated polystyrene (dPS), supported by SiO(x)/Si, decrease with decreasing h for PS weight fractions phi >0.1. This dependence is similar to that of PS and opposite to that of TMPC thin films. Based on an assessment of Tg(h, phi), we suggest that the Tg(h, phi) of miscible blends should be rationalized, additionally, in terms of the notion of a self-concentration and associated heterogeneous component dynamics.

Elasticity↗
PubMed1999

Novel polymer-polymer conjugates for recovery of lactic acid by aqueous two-phase extraction.

A new family of polymer conjugates is proposed to overcome constraints in the applicability of aqueous two-phase systems for the recovery of lactic acid. Polyethylene glycol-polyethylenimine (PEI) conjugates and ethylene oxide propylene oxide-PEI (EOPO-PEI) conjugates were synthesized. Aqueous two-phase systems were generated when the conjugates were mixed with fractionated dextran or crude hydrolyzed starch. With 2% phosphate buffer in the systems, phase diagrams with critical points of 3.9% EOPO-PEI-3.8% dextran (DEX) and 3.5% EOPO-PEI-7.9% crude starch were obtained. The phase separation temperature of 10% EOPO-PEI solutions titrated with lactic acid to pH 6 was 35 degrees C at 5% phosphate, and increased linearly to 63 degrees C at 2% phosphate. Lactic acid partitioned to the top conjugate-rich phase of the new aqueous two-phase systems. In particular, the lactic acid partition coefficient was 2.1 in 10% EOPO-PEI-8% DEX systems containing 2% phosphate. In the same systems, the partitioning of the lactic acid bacterium, Lactococcus lactis subsp. lactis, was 0.45. The partitioning of propionic, succinic, and citric acids was also determined in the new aqueous two-phase systems.

Biotechnology↗
PubMedDate not supplied

[Biodegradable co-polymers of amino acids and synthetic polymers].

The methods of synthesis and properties of copolymers of natural amino acids and of oligopeptides with synthetic polymers are considered as well as their liability to biodestruction processes both under the effect of proteolytic enzymes in vitro and under conditions of the implantation to animals. Such copolymers may be successfully used in biology and medicine as a material for manufacturing temporal endoprostheses, carriers of medicinal preparations, immobilization of biologically active compounds as well as in studies of the mechanism of their action.

Amino Acids↗
PubMed1996

Enzyme purification with aqueous two-phase systems: comparison between systems composed of pure polymers and systems composed of crude polymers.

The main drawback when using aqueous two-phase systems for macromolecule purification is the high cost of most polymers used. The purification of an enzyme, alcohol dehydrogenase, from a crude extract of Saccharomyces cerevisiae was tested in systems composed of poly(ethylene glycol) and a crude hydroxypropyl starch or Reppal PES 100, a purified fraction of hydroxypropyl starch. Purification factors measured for the enzyme were very similar in both systems (between 0.8 and 1.4 for both systems in the upper phase). However, systems composed of Reppal PES present a greater recovery of enzyme, between 77% and 100% versus 60% and 100%, while systems composed of crude hydroxypropyl starch exhibit a larger delta log K for the tested ligand, 1.26 versus 0.81.

Alcohol Dehydrogenase↗
PubMed2003

Application of the SAXS method and viscometry for determination of the thickness of adsorbed polymer layers at the ZrO2-polymer solution interface.

The authors studied the influence of the molecular weight of polyacrylic acid (PAA) and polyacrylamide (PAM), solution pH and ionic strength, and the background electrolyte type on adsorption and the thickness of polyelectrolyte adsorption layers formed on ZrO(2) surface. Carboxyl groups distributed along PAA and PAM chains were shown to be responsible for their interface conformation, which directly influences the thickness of the adsorbed polyelectrolyte layers. Bonding of macromolecules with solid surface occurs through the hydrogen bridges of these groups. Two methods were applied to determine the PAA and PAM adsorption layer thickness on ZrO(2), i.e., SAXS (small angle X-ray scattering) and viscometry. Despite some limitations of the SAXS method resulting from the relationship between the size of solid pores, polymer molecular weight, and conformation of the adsorbed macromolecule, all obtained SAXS results were very close to those calculated from viscometry data.

Journal Article↗
PubMed1998

Use of compatible polymer blends to fabricate arrays of carbon black-polymer composite vapor detectors.

Compatible blends of poly(vinyl acetate) and poly(methyl methacrylate) have been used to produce a series of electrically conducting carbon black composites whose resistance is sensitive to the nature and concentration of an analyte in the vapor phase. The dc electrical resistance response of the composites was found to be a nonlinear function of the mole fraction of poly(vinyl acetate) in the blend. These compatible blend composite detectors provided additional analyte discrimination information relative to a reference detector array that only contained composites formed using the pure polymer phases. The added discrimination power provided by the compatible blend detectors, and thus the added diversity of the enhanced detector array, was quantified through use of a statistical metric to assess the performance of detector arrays in various vapor classification tasks.

Carbon↗
PubMedDate not supplied

Chemically optimized antimyosin Fab conjugates with chelating polymers: importance of the nature of the protein-polymer single site covalent bond for biodistribution and infarction localization.

Murine antimyosin Fab fragment was conjugated with 111In-labeled N-terminal-modified DTPA-polylysine using three bifunctional reagents: N-hydroxysuccinimide esters of 3-(2-pyridyldithio)propionic acid (SPDP conjugate), 4-(maleimidomethyl)cyclohexanecarboxylic acid (SMCC conjugate) and bromoacetic acid (BrAc conjugate) for potential localization of experimental myocardial infarction. Using various antibody preparations and a rabbit acute myocardial infarction model the following parameters were observed: (1) an in vitro antigen binding activity of SPDP conjugate = SMCC conjugate > BrAc conjugate, (2) a blood clearance rate of SPDP conjugate > BrAc conjugate > SMCC conjugate, (3) a liver and splenic accumulation of SPDP conjugate > BrAc conjugate > SMCC conjugate, and (4) the infarcted tissue activity showed an accumulation of SMCC conjugate > SPDP conjugate > BrAc conjugate. This study exemplifies the importance of rational chemical design of antimyosin Fab-chelating polymer conjugate for improved target tissue localization in vivo.

Animals↗
PubMedDate not supplied

Polymer fractionation in aqueous two-phase polymer systems.

We consider the effects of the addition of poly(ethylene glycol) (PEG) of different molecular weights to aqueous two-phase system of PEG 8000 and dextran 500. The first purpose of this study was to determine the molecular weight partitioning of the polymers themselves so that, for example, aqueous two-phase separations using affinity ligands can be improved. The second purpose was to examine whether this molecular weight partitioning could be predicted by using solution thermodynamic models so that it would be possible to optimize affinity partitioning without extensive laboratory work. Experimentally, we find that, by increasing the PEG concentration of any molecular weight in the feed, the high molecular weight PEG concentration in the dextran-rich phase is reduced. This observation can be used to reduce the loss of expensive ligated PEG used in affinity partitioning. Further, there is generally good agreement between our experimental data and the predictions of a solution thermodynamic model.

Dextrans↗