			Home About us Contact

Polymer Fraction (polymer + fraction)

Distribution by Scientific Domains

Polymers and Materials Science	66%

Selected Abstracts

Physically crosslinked composite hydrogels of PVA with natural macromolecules: Structure, mechanical properties, and endothelial cell compatibility

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009
Y. Liu
Abstract Polyvinyl alcohol (PVA) hydrogels have been considered potentially suitable for applications as engineered blood vessels because of their structure and mechanical properties. However, PVA's hydrophilicity hinders its capacity to act as a substrate for cell attachment. As a remedy, PVA was blended with chitosan, gelatin, or starch, and hydrogels were formed by subjecting the solutions to freeze-thaw cycles followed by coagulation bath immersion. The structure-property relationships for these hydrogels were examined by measurement of their swelling, rehydration, degradation, and mechanical properties. For the case of pure PVA hydrogels, the equilibrium swelling ratio was used to predict the effect of freeze thaw cycles and coagulation bath on average molecular weights between crosslinks and on mesh size. For all hydrogels, trends for the reswelling ratio, which is indicative of the crosslinked polymer fraction, were consistent with relative tensile properties. The coagulation bath treatment increased the degradation resistance of the hydrogels significantly. The suitability of each hydrogel for cell attachment and proliferation was examined by protein adsorption and bovine vascular endothelial cell culture experiments. Protein adsorption and cell proliferation was highest on the PVA/gelatin hydrogels. This study demonstrates that the potential of PVA hydrogels for artificial blood vessel applications can be improved by the addition of natural polymers, and that freeze-thawing and coagulation bath treatment can be utilized for fine adjustment of the physical characteristics. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source]

Multi-walled carbon nanotubes encapsulated with polyurethane and its nanocomposites

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008
Xiao Wang
Abstract Poly(acryloyl chloride) (PACl) was employed to enhance the surface of multi-walled carbon nanotubes (MWCNTs). MWCNTs were first acid treated to generate hydroxyl groups on the surface, which was reacted with PACl to obtain an encapsulation. The numerous acryloyl chloride groups on the out layer were esterified with a proper amount of ethylene glycol (EG). Subsequently, 4,4,-methylenebis (phenylisocyanate) (MDI) and 1,4-butanediol (BDO) were introduced into the system, and a polyurethane (PU) layer was formed in situ. The formation of PU layers on MWCNTs was confirmed by Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscope (XPS). The morphology of encapsulated MWCNTs was observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). Thermo gravimetric analysis (TGA) showed the grafted polymer fraction was up to 90%. On introducing the modified MWCNTs into a PU matrix, an increase in tensile strength by 60.6% and improvement in modulus by 6.3% over neat PU was observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4857,4865, 2008 [source]

Synthesis and polymerization of (E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene with Ziegler,Natta, rhodium, and palladium complexes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005
J. Gonzalo Rodríguez
Abstract The synthesis and polymerization of (E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene was carried out with a homogeneous vanadium acetylacetonate/aluminum triethyl catalyst system, a bis(rhodium chloride cycloocta-1,5-diene) complex, and a palladium/trimethylsilyl complex. In all cases, the main fraction was a polymer with a stereoregular structure. The polymerization with the vanadium catalyst gave a polymer fraction in a low yield. The polymerization of (E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene with the soluble rhodium complex gave a polymer in a high yield. The soluble palladium/chlorotrimethylsilane complex gave a polymer in a good yield. On the basis of the spectroscopic data, the poly{(E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene)} obtained, in all cases, showed a cis,transoidal stereoregular structure. The molecular mass of poly{(E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene)} was determined by the matrix-assisted laser desorption/ionization time-of-flight technique. The kinetics of the reaction were analyzed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6438,6444, 2005 [source]

Isolation and Characterisation of Procyanidins from Rumex obtusifolius

PHYTOCHEMICAL ANALYSIS, Issue 3 2007
Paul Spencer
Abstract An acetone:water (7:3) extract obtained from the leaves of Rumex obtusifolius was fractionated into procyanidin oligomer and polymer fractions using a linear gradient and a simple step method on Sephadex LH-20. The chemical characteristics of the procyanidin fractions were studied by 13C-NMR spectroscopy, acid-catalysed degradation in the presence of benzyl mercaptan, matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS and electrospray ionisation (ESI) MS. The 13C-NMR showed that the polymer fraction consisted predominantly of procyanidin polymers, some with galloyl groups attached. The thiolysis reaction products indicated a mean degree of polymerisation (DP) of 4.3 for the step method, and a range of 2.3,8.2 mean DP for the gradient fractionation, with epicatechin as the most abundant flavan-3-ol extension unit, while the terminal units consisted of equal proportions of catechin, epicatechin and epicatechin gallate. Singly charged ions observed in MALDI-TOF/MS showed a range of oligomeric procyanidins and their polygalloyl derivatives. These species (in the range DP 2,7) were also observed by ESI/MS but the spectra were more complex due to overlapping multiply charged ions. Isolation of oligomers from the Sephadex LH-20 fraction by chromatography on polyamide and C18 yielded B1, B2, B3 and B7 dimers, an A-type trimer and a B2 3,3,- O -digallate. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye Polymer

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2006
Mikhail Kozlovsky
Abstract Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non-fractionated polymer. The ,nind value decreases by increasing the degree of polymerization () within the oligomeric range but becomes independent of molecular weight starting from a of ,70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording. Birefringence induced after 10 min, ,nind(600) and its growth rate at the same moment versus molecular weight. [source]