1,721,112 research outputs found
Recent advances in liquid chromatography analysis of synthetic polymers
No full textSynthetic polymers are rarely homogeneous chemical species but have multivariate distributions in molecular weight, chemical composition, chain architecture, functionality, and so on. For a precise characterization of synthetic polymers, all the distributions need to be determined, which is a difficult task, if not impossible. Fortunately in most of the cases it is sufficient to analyze a limited number of molecular characteristics in order to obtain the information required for a given purpose. Nonetheless, it is still nontrivial if there exists distributions for more than one molecular characteristic. There have been continuing efforts to solve the problem. One approach is to find chromatographic methods sensitive to one molecular characteristic only. In favorable cases, the effect of all but one molecular characteristic can be suppressed to a negligible level. Various interaction chromatographic techniques as well as size exclusion chromatography are employed for the purpose. Also the multiple detection methods each sensitive to a specific molecular characteristic can provide additional information. Various detection methods developed recently such as FT-IR, FT-NMR, and mass spectrometry brought about significant progress in the characterization of complex polymers. This review presents the recent developments in the analysis of various heterogeneities in synthetic polymers by a variety of liquid chromatographic separation as well as detection methods.X11116sciescopu
Polymer molecular weight characterization by temperature gradient high performance liquid chromatography
No full textWe report a novel method of temperature gradient interaction h.p.l.c. for the characterization of molecular weight distribution of macromolecules. A very fine and reproducible control of interaction between polymer chains and the packing material can be achieved by altering the column temperature. A mixture of 10 polystyrene standard samples (molecular weight range: 1700-2890 000) of narrow molecular weight distribution are analysed by this method. Near complete separation down to the baseline is achieved with the use of a single C18 bonded silica column. This method is thus proven to provide a much superior resolution to the conventional size exclusion chromatography. Copyright (C) 1996 Elsevier Science Ltd.X1174sciescopu
Thermodynamic prediction of polymer retention in temperature-programmed HPLC
No full textTemperature programming has been used increasingly in liquid chromatography in recent years. In particular, temperature gradient elution has shown great potential in the analysis of complex polymers. In this study, the polymer retention behavior in temperature gradient interaction chromatography is investigated based on thermodynamic consideration of the retention factor. The polymer retention predicted by the model calculation is in good agreement with the experimental results, and the model allows devising a temperature program for designed retention behaviors such as a linear dependence of retention volume on log(molecular weight) of polymers. In addition, the migration behavior of polymeric solute along the separation column can be simulated, which shows strong molecular weight dependence. The migration behavior is also confirmed experimentally by employing different length columns or delayed injection.X112930sciescopu
Viscosity and diffusion constants calculation of n-alkanes by molecular dynamics simulations
No full textIn this paper we have presented the results for viscosity and self-diffusion constants of model systems for four liquid n-alkanes (C-12, C-20, C-32, and C-44) in a canonical ensemble at several temperatures using molecular dynamics (MD) simulations. The small chains of these n-alkanes are clearly /6 >(1), which leads to the conclusion that the liquid n-alkanes over the whole temperatures considered are far away from the Rouse regime. Calculated viscosity eta and self-diffusion constants D are comparable with experimental results and the temperature dependence of both 17 and D is suitably described by the Arrhenius plot. The behavior of both activation energies, E-eta and E-D, with increasing chain length indicates that the activation energies approach asymptotic values-as n increases to the higher value, which is experimentally observed. Two calculated monomeric friction constants zeta and zeta(D) give a correct qualitative trend: decrease with increasing temperature and increase with increasing chain length n. Comparison of the time auto-correlation functions of the end-to-end vector calculated from the Rouse model for n-dodecane (C-12) at 273 K and for n-tetratetracontane (C-44) at 473 K with those extracted directly from our MD simulations confirms that the short chain n-alkanes considered in this study are far away from the Rouse regime.X1120sciescopuskc
TEMPERATURE-DEPENDENCE OF PROBE DIFFUSION IN POLYMER MATRIX
No full textThe temperature dependence of diffusion of methyl red derivatives through semidilute toluene solutions of poly(vinyl acetate) was studied by forced Rayleigh scattering. The magnitude of the hydrogen bonding effect on probe diffusion was estimated from the activation energy of the diffusion process.X119sciescopu
Rapid molecular weight analysis of polymers by temperature gradient interaction chromatography
No full textTemperature gradient interaction chromatography (TGIC) has been established as a high-resolution technique for the characterization of synthetic polymers. So far, most of the TGIC investigations focused on the high-resolution analysis and little effort has been made on the reduction of the analysis time. In this study, we examined the effect of the column heating rate, the eluent flow rate, and the column length on the TGIC analysis time. We found that the heating rate is the most important experimental parameter to control the TGlC retention time. With a C18 silica column (50 mm x 4.6 rum I.D.), a set of PS standards of wide molecular weight range (5-648 kg/mol) could be separated within 4 min at a heating rate of 8 degrees C/min. (c) 2005 Elsevier B.V. All rights reserved.X1111sciescopu
CHARACTERIZATION OF SPHERICAL-PARTICLES BY LIGHT-SCATTERING
No full textWe have studied a characterization method of accurate size of spherical particles by fitting experimental light scattering profile to the rigorous theoretical scattering function. An efficient software has been developed for computation of the theoretical scattering function and regression analysis. A light scattering instrument has been built and the necessary data acquisition and analysis are carried out by use of a personal computer with an emphasis on the reduction of analysis and time aiming that this study will be extended toward a development of a practical particle sizing apparatus. The performance of the instrument and the software has been evaluated with latex spheres and found to be satisfactory.X116sci
A NEW ANALYSIS SCHEME FOR COMPLEX FORCED RAYLEIGH-SCATTERING PROFILES
No full textA recently proposed mechanism for complex signal profiles of forced Rayleigh scattering (Park et al. J. Phys. Chem. 1991, 95, 7121) is tested with a system of globular protein-surfactant complexes. The mechanism starts with a hypothesis of double grating of pure phase complementarity which is shown to produce extreme departures, such as decay-growth-decay type, from single exponential decay. A new analysis scheme for such a complex signal type is proposed, and it has been validated here experimentally with the dynamic light scattering results in conjunction with the FRS measurements.X1111sciescopu
Spatial control of cellular adhesion using photo-crosslinked micropatterned polyelectrolyte multilayer films
No full textCHARACTERIZATION OF BINARY POLYMER MIXTURES BY SIZE-EXCLUSION CHROMATOGRAPHY WITH MULTIPLE DETECTION
No full textWe demonstrated that both components of binary polymer mixtures of polystyrene and poly(methyl methacrylate) can be characterized simultaneously by size exclusion chromatography equipped with multiple detectors. In this analysis scheme, the individual peaks of the two components are separated from the overlapped chromatogram by simultaneously solving the response signal intensities from two concentration detectors, i.e. a refractive-index detector and an ultra-violet/visible absorption detector. Then the absolute molecular-weight distribution of each component is obtained from the response of a light-scattering detector in conjunction with universal calibration. This method can be applied to binary mixture systems the two components of which have a distinguishable difference in refractive index as well as in absorptivity.X1116sciescopu
- …
