Molecular weight characterization of soluble high performance polyimides. 1. Polymer-solvent-stationary phase interactions in size exclusion chromatography

Soluble, fully cyclized m-amino phenyl acetylene terminated polyimides based on several anhydride/diamine monomers were prepared in N-methylpyrrolidine (NMP) and cyclized by solution imidization to controlled molecular weight. The polyimides and a polyamic acid precursor were successfully analyzed by size exclusion chromatography (SEC) utilizing online parallel coupled refractive index and differential viscometer detectors. The calculated M _nvalues were varied from 3,000 to 20,000 daltons. N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and chloroform served as mobile phases for the cross-linked polystyrene gel packings. Normal retention behavior of the polyimides was observed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over P₂O₅ before use. Values of Mark-Houwink-Sakurada exponents for narrow distribution linear polystyrene indicate that pure NMP and NMP with 0.06 M LiBr are good solvents for polystyrene standards at 60°C. In contrast, SEC behavior of polyimides in pure NMP leads to splitting of the peaks with the major portion observed to pass through the columns at the exclusion limit. In contrast to strong polymeric chain expansion of the polyamic acid in dilute solution, presumably due to a polyelectrolyte effect, no increase of intrinsic viscosity of polyimide samples in pure NMP was observed. This exclusion effect of polyimides analyzed in NMP is discussed in terms of possible ion-exclusion from pores of the stationary phase. Differences in polystyrene calibration in NMP with or without additives and the temperature dependence of calibration curves in these mobile phases is discussed as well. ©1995 John Wiley & Sons, Inc.     

The size exclusion chromatography calibration of ‘Mixed-A’ and ‘Mixed-D’ columns using various polymers and compounds: An application to coal-derived materials

This work attempts to obtain the calibration curves of two different size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent by using various standards. Polystyrene (PS) and polymethylmethacrylate (PMMA) standards were used for obtaining calibration curves, and checked against polysaccharide (PSAC) standards, some small aromatic polycyclic standards and miscellaneous polymers. Polystyrenes and polymethylmethacrylates gave identical calibrations while polysaccharides and miscellaneous polymers lay within 1 or 2 min of the polystyrene calibration. Small molecules of mass less than 1000 units lay on or near to the polystyrene calibration lines, with a shift to late elution for the smallest molecules. This shift may be caused by the interaction with the column packing. A sample has been examined by analytical size exclusion chromatography, which was calibrated using polystyrene and polymethylmethacrylate standards. Molecular mass (MM) distributions of the sample have been examined in terms of these calibrations.     

Novel polystyryl resins for size exclusion chromatography

New size exclusion chromatography (SEC) resins based on a crosslinker having independent vinyl groups have been produced and compared with SEC resins based on divinylbenzene-55 (DVB). 1,2-Bis(p-vinylphenyl)ethane (p,p-BVPE) and its meta-isomers were suspension-copolymerized with p-methylstyrene in the presence of different porogens to give particles of about 5 μm average diameter. The porous particles were slurry-packed into stainless steel columns for SEC evaluation. Calibration curves were obtained using narrow disperse polystyrene standards with molecular weights ranging from 580 to 3,040,000. The calibration curves for the new BVPE resins covered wider useful molecular weight ranges than those for comparable divinylbenzene resins. Particle size, surface morphology and the properties of pores were studied using a Coulter Multisizer II, scanning electron microscopy, nitrogen adsorption, and mercury porosimetry. © 1994 John Wiley & Sons, Inc.     

Structural characterisation of Baltic amber and its solvent extracts by several mass spectrometric methods

A sample of Baltic amber ( approximately 40 million yrs old) has been extracted using pentane, toluene and 1-methyl-2-pyrrolidinone (NMP). The relationship between solubility characteristics of the extracts in relation to molecular mass and chemical makeup has been investigated. The extracts were first characterised by (13)C-NMR spectrometry, size exclusion chromatography (SEC) and UV-fluorescence spectroscopy. The fractions differed less in terms of chemical structural features than they did in terms of molecular mass. This contrasts markedly with data on fractions of coal-derived liquids, but parallels results from petroleum-derived vacuum residues. In SEC, the toluene soluble/pentane insoluble fraction gave a peak for high mass material at about 67 000 u. Material excluded from the column porosity in this fraction and in NMP solubles eluted between 8 and 11 min, corresponding to polystyrene masses between 200 000 and several million u. A column with a larger pore size distribution was calibrated using polystyrene and polymethylmethacrylate standards with detection by a light-scattering evaporative analyser. The largest polystyrene standard (15.4 million u) eluted at 13.4 min, similar to that of the earliest eluting amber-derived material in the NMP solubles fraction. Results from probe-MS and pyrolysis-GC/MS have been used to confirm the similarity of chemical structures of the three solubility fractions. Broadly, low mass ions appear to correspond to the various monomeric units of structures present in the amber, the higher mass ions to dimer units and the molecular ions to the different combinations of three or more monomeric units. The main monomer groups have been identified in detail, showing a situation very different from that of coal-derived materials, where the sizes of aromatic ring systems increase with molecular size.     

Fast molecular mass and size characterization of polysaccharides using asymmetrical flow field-flow fractionation-multiangle light scattering

Asymmetrical flow field-flow fractionation (asymmetrical flow FFF), connected on-line to multi-angle light scattering detection (MALS) was shown here to be an efficient method for size characterization of pullulan standards and dextrans ranging from 20 000 up to 2 000 000 in molecular mass. The characterization of molecular mass and the molecular mass distribution of these polysaccharides is often complex and may require different methods. Using asymmetrical flow FFF-MALS, information was obtained not only about molecular mass and molecular mass distribution but also about hydrodynamic size as well as radius of gyration and conformation. The analysis time was very short, often below 5 min. It was shown that the pullulan standards have a narrow molecular mass distribution compared to the more polydisperse dextrans. Obtained molecular masses and distributions were in good agreement with data from the manufacturer. The dextrans, especially at high molecular mass, were found to have a more compact structure than the pullulans in both water and 0.1 M NaCl.     

Determination of thickness, aspect ratio and size distributions for platey particles using sedimentation field-flow fractionation and electron microscopy

Sedimentation field-flow fractionation (SdFFF) can be used to prepare fractions of very narrow mass range for electron microscopic (EM) analysis. Assuming the particle density is the same for all particles within that fraction the equivalent spherical diameter for the particles can be calculated from SdFFF theory. Integration of the micrograph image of each particle yields an area measurement which, when used in conjunction with the equivalent spherical particle diameter (from SdFFF), provides information about the particle thickness and aspect ratio. Thus SdFFF-SEM can be used to provide detailed information about clay morphology across the particle size distribution of the sample. Three clay minerals have been studied using the methodologies outlined in this paper. The aspect ratio for the Purvis School Mine kaolinite ranged from 2.8–5.9, for RM30 illite from 11.3–24.3, and for Muloorina illite from 3.1–4.3.     

Electrokinetic behaviour of polymer colloids with adsorbed Triton X-100

An experimental study on the electrophoretic mobility (µ_e) of polystyrene particles after adsorption of Triton X-100 (TX100) is described. Three polystyrene particles with different functionality (sulphate, carboxyl and amidine) were used as solid substrate for the adsorption of the surfactant. The electrophoretic mobility of the polystyrene-TX100 complexes at different electrolyte concentrations has been studied versus the amount of adsorbed surfactant. The presence of TX100 onto the colloidal particles seems to produce a slight shifting of the slipping plane. This is observed for electrolyte concentrations above ~10^-3 M. On the other hand, the electrophoretic mobilities of the latex-surfactant complexes with maximum surface coverage were measured versus pH and salt concentration. Specific ion interactions between H⁺/carboxyl groups and OH^-/amidine groups appeared at extreme pH which explain the anomalous electrophoretic behaviour encountered in the region where surface charge change.     

Structure,thermodynamics and diffusion in asymmetric binary mixtures: a molecular dynamics simulation study

Structural and thermodynamic properties as well as diffusion coefficients of binary fluid mixtures with asymmetry in mass, size, charge and their combinations have been studied using classical molecular dynamics simulations. The fluid mixture is modelled as spherical particles interacting via the Weeks–Chandler–Andersen and Coulomb potential. The diameter, charge and mass of the fluid particles are in the range 6–60 Å, 1–10e and 1—500 amu, respectively. Systematic variations in pair-correlation functions, thermodynamic properties as well as the self-diffusion coefficient are found with the size, charge and mass ratio of the particles. The self-diffusion coefficient for systems having more than one type of asymmetry is calculated and expressed in terms of diffusion coefficients of systems with only one type of asymmetry.     

A versatile method for tuning the chemistry and size of nanoscopic features by living free radical polymerization

A novel approach is presented for manipulating the size and chemistry of nanoscopic features using a combination of contact molding and living free radical polymerization. In this approach a highly cross-linked photopolymer, based on a methacrylate/acrylate mixture, was patterned into submicrometer-sized features on a silicon wafer using a contact-molding technique. A critical component of the monomer mixture was the incorporation of an initiator containing monomer into the network structure, which provides sites for functional group amplification. Features ranging in size from 5 microm to <60 nm were accurately replicated by this process and living free radical polymerizations, both atom transfer radical and nitroxide-mediated polymerization (NMP), could be conducted from these initiating sites to yield polymer brushes which represent a grafted layer of linear chains attached to the original network polymer. Grafts consisting of polystyrene, poly(methyl methacrylate), and poly(2-hydroxyethyl)methacrylate were grown with controlled thicknesses ranging from 10 to 143 nm and graft molecular weights of between 18 000 to 290 000 amu. As a result of this secondary graft process, feature sizes could be tuned from the original 100 nm down to 20 nm, and the surface chemistry varied from hydrophilic to hydrophobic starting from the same initial master pattern. The thin films and patterned features were characterized by contact angle, ellipsometry, optical, and atomic force microscopies.     

Remarks on the Calibration of Steric Exclusion Liquid Chromatography by Polymolecular Standards

Abstract

The relation of polymer molecular characteristics versus chromatographic parameters in steric exlusion liquid chromatography (GPC) was considered as a typical black box problem. Practical problems were discussed for cases of the GPC black box calibration with polymolecular polystyrene standards and of using an improper calibration model. It was concluded that checking the reliability of the GPC black box calibration is of utmost importance especially when narrow calibration standards are not available.     

Direct determination of band broadening in size exclusion chromatography

A simple method to correct the measured extent of band broadening in size exclusion chromatography for the contribution of narrow (polydisperse) standards is presented. It is based on the assumptions that commercial polymer standards can be described by a Poisson distribution and the additivity of peak variances. Two sets of standards (polystyrene from two suppliers) were investigated under normal working conditions, i.e. a combination of four columns with different porosities and a flow rate of 1 ml/min. Furthermore, the polystyrene standards were used to determine the extent of band broadening for four additional combinations of columns (varying in their separation range and porosities) as a function of the elution volume. The assumption of a constant peak variance for band broadening turned out to be a (very) rough approximation for some combinations of columns, but all results taken together demonstrate that this assumption is not generally applicable. Qualitative agreement between theory and experiment was found with a rearranged van Deemter equation.     

On the determination of molecular weight distributions of asphaltenes and their aggregates in laser desorption ionization experiments

Molecular weight distributions (MWD) of asphaltenes and their aggregates have been investigated in laser desorption ionization (LDI) mass spectrometric experiments. A systematic investigation of the dependence of the measured MWD on the asphaltene sample density and on the laser pulse energy allows the assignment of most probable molecular weights within 300-500 amu and average molecular weights of 800-1000 amu for the monomeric asphaltenes, as well as for the estimation of the contribution from asphaltene clusters in typical LDI measurements. The results serve to reconcile the existing controversy between earlier mass spectrometric characterizations of asphaltenes based on laser desorption techniques by different groups. Furthermore, the MWD measurements performed on particularly dense samples yield an additional differentiated broad band peaking around 9000-10,000 amu and extending over 20,000 amu, not observed previously in LDI experiments, thereby revealing a strong propensity of the asphaltenes to form clusters with specific aggregation numbers, which is in qualitative agreement with previous theoretical predictions and with the interpretation of measurements performed with other techniques.     

Charging and stability of anionic latex particles in the presence of linear poly(ethylene imine)

Charging properties and colloidal stability of negatively charged polystyrene latex particles were investigated in the presence of linear poly(ethylene imine) (LPEI) of different molecular masses by electrophoresis and dynamic light scattering (DLS). Electrophoretic mobility measurements illustrate that LPEI strongly adsorbs on these particles leading to charge neutralization at isoelectric point (IEP) and charge reversal. Time-resolved DLS experiments indicate that the aggregation of the latex particles is rapid near the IEP and slows down away from this point. Surprisingly, the colloidal stability does not depend on the molecular mass, which indicates that the adsorbed LPEI layer is rather homogeneous.     

"Depth-profiling" and quantitative characterization of the size, composition, shape, density, and morphology of fine particles with SPLAT, a single-particle mass spectrometer

A significant fraction of atmospheric particles are composed of inorganic substances that are mixed or coated with organic compounds. The properties and behavior of these particles depend on the internal composition and arrangement of the specific constituents in each particle. It is important to know which constituent is on the surface and whether it covers the particle surface partially or entirely. We demonstrate here an instrument consisting of an ultrasensitive single-particle mass spectrometer coupled with a differential mobility analyzer to quantitatively measure in real time individual particle composition, size, density, and shape and to determine which substance is on the surface and whether it entirely covers the particle. For this study, we use NaCl particles completely coated with liquid dioctyl phthalate to generate spherical particles, and NaCl particles partially coated with pyrene, a solid poly aromatic hydrocarbon, to produce aspherical particles with pyrene nodules and an exposed NaCl core. We show that the behavior of the mass spectral intensities as a function of laser fluence yields information that can be used to determine the morphological distribution of individual particle constituents.     

Studies on Simultaneous Molecular Weight and Spreading Calibration in Steric Exclusion Liquid Chromatography

Abstract

Two improved methods of molecular weight calibration are described where simultaneously parameters of a symmetrical spreading function are obtained through the use of polymolecular molecular weight standards and of average retention volumes. In the first method a linear molecular weight calibration is assumed and the second method is based on a universal molecular weight calibration curve obtained with narrow MWD polystyrene standards.

The proposed methods have been tested using two polymolecular polystyrene standards confirming good convergence of the applied iteration procedures and giving very promising results.     

Sizing large proteins and protein complexes by electrospray ionization mass spectrometry and ion mobility

Mass spectrometry (MS) and ion mobility with electrospray ionization (ESI) have the capability to measure and detect large noncovalent protein-ligand and protein-protein complexes. Using an ion mobility method of gas-phase electrophoretic mobility molecular analysis (GEMMA), protein particles representing a range of sizes can be separated by their electrophoretic mobility in air. Highly charged particles produced from a protein complex solution using electrospray can be manipulated to produce singly charged ions, which can be separated and quantified by their electrophoretic mobility. Results from ESI-GEMMA analysis from our laboratory and others were compared with other experimental and theoretically determined parameters, such as molecular mass and cryoelectron microscopy and X-ray crystal structure dimensions. There is a strong correlation between the electrophoretic mobility diameter determined from GEMMA analysis and the molecular mass for protein complexes up to 12 MDa, including the 93 kDa enolase dimer, the 480 kDa ferritin 24-mer complex, the 4.6 MDa cowpea chlorotic mottle virus (CCMV), and the 9 MDa MVP-vault assembly. ESI-GEMMA is used to differentiate a number of similarly sized vault complexes that are composed of different N-terminal protein tags on the MVP subunit. The average effective density of the proteins and protein complexes studied was 0.6 g/cm(3). Moreover, there is evidence that proteins and protein complexes collapse or become more compact in the gas phase in the absence of water.     

Molecular weight characterization of soluble high performance polyimides. 2. Validity of universal SEC calibration and absolute molecular weight calculation

Six different soluble high-performance aromatic polyimides, each prepared by solution imidization to three controlled average molecular weights, were analyzed by size exclusion chromatography (SEC) using on-line parallel coupled refractometric and viscometric detectors. N-methylpyrrolidone (NMP) with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phase for four of the polyimides; NMP with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phases for four of the polyimides; NMP with 0.06 M LiBr tetrahydrofuran (THF) and chloroform served as mobile phases for the other two polyimides. For all the samples the stationary phase in the SEC columns was cross-linked polystyrene beads. Molecular weight averages of the polyimides were calculated using universal SEC calibration with polystyrene standards in each solvent. The agreement of the calculated molecular weight averages in the different solvents confirms that the universal SEC calibrations are valid for these semiflexible polymers. There was good agreement with weightaverage molecular weights obtained by low-angle laser light scattering (LALLS) performed in pure NMP. Intrinsic viscosity and molecular weight data for a series of nine samples of one polyimide covering a M_w = 20,000–70,000 g mol^–1 interval were treated to obtain Mark-Houwink-Sakurada constants. Unperturbed chain dimensions of this polyimide were obtained by application of the Stockmayer-Fixman extrapolation procedure to these data. ©1995 John Wiley & Sons, Inc.     

Photochemical interaction of polystyrene nanospheres with 193 nm pulsed laser light

The photochemical interaction of 193 nm light with polystyrene nanospheres is used to produce particles with a controlled size and morphology. Laser fluences from 0 to 0.14 J/cm2 at 10 and 50 Hz photofragment nearly monodisperse 110 nm spherical polystyrene particles. The size distributions before and after irradiation are measured with a scanning mobility particle sizer (SMPS), and the morphology of the irradiated particles is examined with a transmission electron microscope (TEM). The results show that the irradiated particles have a smaller mean diameter ( approximately 25 nm) and a number concentration more than an order of magnitude higher than nonirradiated particles. The particles are formed by nucleation of gas-phase species produced by photolytic decomposition of nanospheres. A nondimensional parameter, the photon-to-atom ratio (PAR), is used to interpret the laser-particle interaction energetics.     

Synthesis and characterization of magnetic and non-magnetic core-shell polyepoxide micrometer-sized particles of narrow size distribution

Core polystyrene microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Uniform polyglycidyl methacrylate/polystyrene core-shell micrometer-sized particles were prepared by emulsion polymerization at 73 degrees C of glycidyl methacrylate in the presence of the core polystyrene microspheres. Core-shell particles with different properties (size, surface morphology and composition) have been prepared by changing various parameters belonging to the above seeded emulsion polymerization process, e.g., volumes of the monomer glycidyl methacrylate and the crosslinker monomer ethylene glycol dimethacrylate. Magnetic Fe(3)O(4)/polyglycidyl methacrylate/polystyrene micrometer-sized particles were prepared by coating the former core-shell particles with magnetite nanoparticles via a nucleation and growth mechanism. Characterization of the various particles has been accomplished by routine methods such as light microscopy, SEM, FTIR, BET and magnetic measurements.     

Electrophoretic mobility of latex particles: effect of particle size and surface structure

The influence of particle size on the electrophoretic mobility of negatively charged latex particles was examined by a comparison between theory and experiment. Theoretical values for the dependence of the mobility on electrolyte concentration were calculated by a modified White–O’Brian model (Hidalgo-Alvarez et al., Adv. Coll. Interf. Sci. 67 (1996) 1) which enables the consistent calculation of the zeta (ζ) potential. For three polystyrene latexes of different size but similar surface charge density the measured mobilities increased with increasing radius for the electrolyte range under consideration. The theoretical calcalations resulted in a qualitatively correct prediction of the experimental data. The experimental comparison of the mobilities of hydrophobic and hydrophilic particles of similar size and surface charge density lead to the conclusion that hydrophilic surfaces lower the electrophoretic mobility. The same theoretical model was able to describe correctly this observed behavior by assuming a greater distance of the plane of shear. The effect of a spatial distribution of the charges was examined by characterizing an electrosterically stabilized latex. Contrary to all standard latices with surface charges this latex didn't show any mobility maximum as a function of electrolyte concentration.