The performance of size-exclusion electrochromatography (SEEC) for the mass distribution analysis of synthetic polymers was studied and compared to conventional, pressure-driven size-exclusion chromatography (SEC). Electroosmotic flow control, within-day, day-to-day and column-to-column repeatability were determined for SEEC with respect to retention and separation efficiency. It was shown that by using the retention ratio instead of the migration time, the precision of the mass distribution calculations is sufficiently high, and that similar distributions were obtained for a sample analyzed by pressure-driven SEC and by SEEC. Furthermore, hexafluoroisopropanol was demonstrated to be a new and potent solvent for SEEC. It was used for the separation of narrow polymethylmethacrylate standards and several commercially important polymers such as polycarbonate, polycaprolactam and poly(ethylene terephthalate), using UV detection in the deep UV region (195-230 nm). 相似文献
A library of phosphoramidite monomers containing a main-chain cleavable alkoxyamine and a side-chain substituent of variable molar mass (i.e. mass tag) was prepared in this work. These monomers can be used in automated solid-phase phosphoramidite chemistry and therefore incorporated periodically as spacers inside digitally-encoded poly(phosphodiester) chains. Consequently, the formed polymers contain tagged cleavable sites that guide their fragmentation in mass spectrometry sequencing and enhance their digital readability. The spacers were all prepared via a seven steps synthetic procedure. They were afterwards tested for the synthesis and sequencing of model digital polymers. Uniform digitally-encoded polymers were obtained as major species in all cases, even though some minor defects were sometimes detected. Furthermore, the polymers were decoded in pseudo-MS3 conditions, thus confirming the reliability and versatility of the spacers library. 相似文献
A range of low molecular weight synthetic polymers has been characterised by means of desorption electrospray ionisation (DESI) combined with both mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Accurate mass experiments were used to aid the structural determination of some of the oligomeric materials. The polymers analysed were poly(ethylene glycol) (PEG), polypropylene glycol (PPG), poly(methyl methacrylate) (PMMA) and poly(alpha-methyl styrene). An application of the technique for characterisation of a polymer used as part of an active ingredient in a pharmaceutical tablet is described. The mass spectra and tandem mass spectra of all of the polymers were obtained in seconds, indicating the sensitivity of the technique. 相似文献
Recently, a new multiple-layer matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) sample spotting technique for poly(ethylene glycol), offering improved analysis possibilities, was described. In this contribution the application of ink-jet printing to automated, multiple-layer MALDI-TOFMS sample preparation of synthetic polymers is presented, allowing accurate deposition of matrix, additive and analyte solutions. The new sample preparation technique was evaluated for poly(ethylene glycol) as well as poly(methyl methacrylate) standards, and optimized settings for both synthetic polymers have been obtained. 相似文献
Advances in soft ionization techniques for mass spectrometry (MS) of polymeric materials make it possible to determine the masses of intact molecular ions exceeding megadaltons. Interfacing MS with separation and fragmentation methods has additionally led to impressive advances in the ability to structurally characterize polymers. Even if the gap to the megadalton range has been bridged by MS for polymers standards, the MS‐based analysis for more complex polymeric materials is still challenging. Charge detection mass spectrometry (CDMS) is a single‐molecule method where the mass and the charge of each ion are directly determined from individual measurements. The entire molecular mass distribution of a polymer sample can be thus accurately measured. Described in this perspective paper is how molecular weight distribution as well as charge distribution can provide new insights into the structural and compositional studies of synthetic polymers and polymeric nanomaterials in the megadalton to gigadalton range of molecular weight. The recent multidimensional CDMS studies involving couplings with separation and dissociation techniques will be presented. And, finally, an outlook for the future avenues of the CDMS technique in the field of synthetic polymers of ultra‐high molar mass and polymeric nanomaterials will be provided. 相似文献
MALDI-TOF mass spectrometry quantification is hampered by the poor reproducibility of the signal intensity and by molecular-mass and compositional discrimination. The addition of a suitable compound as an internal standard increases reproducibility and allows a calibration curve to be constructed. The concept was also verified with synthetic polymers but no instructions for practical implementation were given [H. Chen, M. He, J. Pei, H. He, Anal. Chem. 75 (2003) 6531-6535.], even though synthetic polymers are generally non-uniform with respect to molecular mass and composition and access to the polymer of the same molecular mass distribution and composition as that of the quantified one is thus the exception rather than rule. On the other hand, relative quantification of polymers e.g., the content of the precursor polymer in a batch of a modified polymer, is usually sought. In this particular case, the pure precursor is usually available and the modified polymer can serve as an internal standard. However, the calibration curve still cannot be constructed and the use of the internal standard has to be combined with the method of standard addition in which the precursor polymer is added directly to the analyzed sample. The experiments with simulated modified polymers, mixtures of poly(ethylene glycol) (PEG) and poly(ethylene glycol) monomethyl ether (MPEG) of similar molecular-mass distribution, revealed a power dependence of the PEG/MPEG signal-intensity ratio (MS ratio) on the PEG/MPEG concentrations ratio in the mixture (gravimetric ratio). The result was obtained using standard procedures and instrumentation, which means that the basic assumption of the standard-addition method, i.e., the proportionality of the MS and gravimetric ratios, generally cannot be taken for granted. Therefore, the multi-point combined internal-standard standard-addition method was developed and experimentally verified for the quantification of the precursor in modified polymers. In this method, the two parameters of the power-type calibration curve - the proportionality constant and the exponent-are assumed. If the exponent strongly deviates from unity the minority component can be significantly underrepresented in the spectrum. Therefore, the absence of the precursor polymer signals in the MALDI-TOF mass spectrum of a modified polymer sample does not prove the absence of the precursor in the sample. Such a conclusion has to be corroborated by the standard-addition method. 相似文献
The electrochemical preparation and molar mass characterization of conducting polymers, poly(thiophene-3-acetic acid) (poly(TPAA)), and poly(thiophene-co-thiophene-3-acetic acid) (poly(TP/TPAA)) are reported. RRDE results revealed that, unlike other conducting polymers, current efficiency during the deposition of poly(TPAA) is by far less than 1 due to significant solubility of the polymer. Up to 48% of the oxidation products of the disc electrode can dissipate into the bulk solution. These dissipated species are polymers in oxidized form and reactive towards reductant originally present in the coating solution. The low current efficiency necessitates the use of relatively high monomer concentration and high polymerization potential to obtain a conducting poly(TPAA) film. Characterization with gel permeation chromatography (GPC) of molar mass and its distribution has been carried out. The results show that up to 65% to 85% of the whole polymers are comprised of big molecules containing over 2000 monomer units, which indicates the possibility of cross-linking of polymer chains. The remaining parts of the polymers are relatively short chains containing several to dozens of monomers. Increase of TPAA content in the copolymers leads to better solubility and higher molar mass. The latter is accompanied by greater electronic conjugation in the polymer chains. 相似文献
A series of water-soluble polymers was synthesized by polycondensation of cyclodextrin with epichlorohydrin under basic conditions. We studied their molecular distribution as a function of molar ratios of reactants. NaOH concentration showed that very high molecular averages (Mw > 106) can be obtained. The substitution patterns were determined by 13C NMR analysis and standard methylation analysis of polysaccharides. The formation of side chains and bridges consisting of sequences of poly(2-hydroxypropyl)ether units were demonstrated by electrospray ionization mass spectrometry and gas liquid chromatography-mass spectrometry. The predominant position of substitution depends on the NaOH concentration. 相似文献
Polydispersity in polymers hinders fundamental understanding of their structure–property relationships and prevents them from being used in fields like medicine, where polydispersity affects biological activity. The polydispersity of relatively short‐chain poly(ethylene oxide) [(CH2CH2O2)n; PEO] affects its biological activity, for example, the toxicity and efficacy of PEOylated drugs. As a result, there have been intensive efforts to reduce the dispersity as much as possible (truly monodispersed materials are not possible). Here we report a synthetic procedure that leads to an unprecedented low level of dispersity. We also show for the first time that it is possible to discriminate between PEOs differing in only 1 ethylene oxide (EO) unit, essential in order to verify the exceptionally low levels of dispersity achieved here. It is anticipated that the synthesis of poly(ethylene oxide) approaching monodispersity will be of value in many fields where the applications are sensitive to the distribution of molar mass. 相似文献
Star polymers with different numbers and lengths of poly(tert-butyl acrylate) (PTBA) arms were obtained via atom transfer radical polymerization. Aliphatic alcohols with different number of hydroxyl groups varying from 3 to 6 and calix[4]arenes based on pyrogallol with 12 and 16 phenol groups were transformed to bromoester derivatives to prepare multifunctional ATRP initiators used as the cores of the stars. The star polymers were characterized by GPC with refractive index, multiangle laser light scattering and viscosimetric detectors. The molar masses of the stars reached 70,000 g/mol and the molar mass dispersities did not exceed 1.2. To elucidate the compact structure of the stars, their true molar masses were determined by GPC with triple detection (RI-MALLS-Visco) and compared with the apparent molar masses obtained from the calibration with linear poly(tert-butyl acrylate) standards. The intrinsic viscosities of the PTBA stars of the same molar mass decreased with the number of star arms but were always lower than the intrinsic viscosities of the analogue linear PTBA polymers. The values of the branching ratio g′ decreased with increasing number of arms indicating more compact structure of stars. The branching ratio g′ was correlated to the empirical predictions. 相似文献
The molar mass distribution (MMD) of synthetic polymers is frequently analyzed by size exclusion chromatography (SEC) coupled to multi angle light scattering (MALS) detection. For ultrahigh molar mass (UHM) or branched polymers this method is not sufficient, because shear degradation and abnormal elution effects falsify the calculated molar mass distribution and information on branching. High temperatures above 130 °C have to be applied for dissolution and separation of semi-crystalline materials like polyolefins which requires special hardware setups. Asymmetrical flow field-flow fractionation (AF4) offers the possibility to overcome some of the main problems of SEC due to the absence of an obstructing porous stationary phase. The SEC-separation mainly depends on the pore size distribution of the used column set. The analyte molecules can enter the pores of the stationary phase in dependence on their hydrodynamic volume. The archived separation is a result of the retention time of the analyte species inside SEC-column which depends on the accessibility of the pores, the residence time inside the pores and the diffusion ability of the analyte molecules. The elution order in SEC is typically from low to high hydrodynamic volume. On the contrary AF4 separates according to the diffusion coefficient of the analyte molecules as long as the chosen conditions support the normal FFF-separation mechanism. The separation takes place in an empty channel and is caused by a cross-flow field perpendicular to the solvent flow. The analyte molecules will arrange in different channel heights depending on the diffusion coefficients. The parabolic-shaped flow profile inside the channel leads to different elution velocities. The species with low hydrodynamic volume will elute first while the species with high hydrodynamic volume elute later. The AF4 can be performed at ambient or high temperature (AT-/HT-AF4). We have analyzed one low molar mass polyethylene sample and a number of narrow distributed polystyrene standards as reference materials with known structure by AT/HT-SEC and AT/HT-AF4. Low density polyethylenes as well as polypropylene and polybutadiene, containing high degrees of branching and high molar masses, have been analyzed with both methods. As in SEC the relationship between the radius of gyration (R(g)) or the molar mass and the elution volume is curved up towards high elution volumes, a correct calculation of the MMD and the molar mass average or branching ratio is not possible using the data from the SEC measurements. In contrast to SEC, AF4 allows the precise determination of the MMD, the molar mass averages as well as the degree of branching because the molar mass vs. elution volume curve and the conformation plot is not falsified in this technique. In addition, higher molar masses can be detected using HT-AF4 due to the absence of significant shear degradation in the channel. As a result the average molar masses obtained from AF4 are higher compared to SEC. The analysis time in AF4 is comparable to that of SEC but the adjustable cross-flow program allows the user to influence the separation efficiency which is not possible in SEC without a costly change of the whole column combination. 相似文献
Summary: Complex polymers are distributed in more than one direction of molecular heterogeneity. In addition to the molar mass distribution, they are frequently distributed with respect to chemical composition, functionality, and molecular heterogeneity. One approach for the analysis of the heterogeneity of complex polymers is their chromatographic separation by combining different separation mechanisms. A typical experimental protocol includes the separation of the sample according to composition to yield fractions that are chemically homogeneous. These fractions are transferred to a size‐selective separation method and analyzed with respect to molar mass. As a result of this two‐dimensional (2D) separation, information on both types of molecular heterogeneity is obtained. So far, 2D chromatography has been applied mostly to polymers that are soluble in organic solvents. There are several problems related to the use of aqueous mobile phases in polymer chromatography. These problems relate to the very polar or ionic character of the polymers and the experimental conditions, including the use of salt‐containing eluents. The present paper addresses the different parameters that influence the chromatographic experiments. For a model polymer system resulting from the grafting of methacrylic acid (MAA) onto poly(ethylene glycol) (PEG), i.e., PEG‐g‐PMAA, it will be shown that different chromatographic techniques including SEC, LC‐CC, and 2D chromatography, as well as coupled LC‐CC/FT‐IR can be used to analyze the molecular complexity of the copolymers.
LC‐CC/FT‐IR spectra of a PEG‐g‐PMAA sample as function of the elution volume. 相似文献
The significance of the analytical ultracentrifuge (AUC) for industrial research has not decreased during the last decades and seems to be growing. The AUC is used for the development and for controlling the production of emulsion polymers (via measurement of particle size distributions) as well as for the determination of molar masses and molar mass distributions of polymers which cause difficulties with conventional methods like light scattering or size exclusion chromatography. In order to speed up the principally very time-consuming AUC measurements, our machines were equipped with multiplexers for multiple place rotors and with video systems for digital recording and processing of the schlieren images. Furthermore for measurements with the UV scanner the optical system had to be considerably improved in order to assess wavelengths down to 210 nm because of the unfavourable UV absorption of the poly(methacrylates). The experimental methods and the data evaluation will be explained and discussed using a very high-molecular-weight poly(methylmethacrylate) and a cationic polyelectrolyte, viz. poly(trimethylammoniumethylmethacrylate hydrochloride), as examples. 相似文献
Solid-state Nuclear magnetic resonance (NMR) was used here to explore structural characteristics of samples to be subjected
to matrix-assisted laser desorption/ionization (MALDI) and prepared without the use of any solvent. The analytical systems
scrutinized in NMR were mixtures of a 2,5-dihydroxybenzoic acid (2,5-DHB) matrix and caesium fluoride (CsF), used as the cationization
agent in synthetic polymer MALDI mass analysis, at different molar ratios (1:1, 5:1, and 10:1). Complementary information
could be obtained from 13C, 133Cs, and 19F NMR spectra. Grinding the matrix together with the salt in the solid state was shown to induce a strong modification in
the molecular organization within the MALDI sample. The evidenced mechano-induced reactions allow strong interactions between
the matrix and the cation, up to the formation of a salt, and only occur in the presence of some water molecules. Addition
of a poly(ethylene oxide) polymer as the analyte did not further modify the observed molecular organizations. Although relative
matrix and salt concentrations in the scrutinized samples were unusual for MALDI analysis, mass spectra of good quality could
be obtained and revealed that cation attachment on polymers during the MALDI process is not a matrix-independent event since
a lower ionization efficiency was obtained from highly organized solid samples, mostly consisting of 2,5-DHB caesium salt
species. 相似文献