Fast and efficient single step liquid chromatography separation of parent homopolymers from block copolymers.

The modified layout of the barrier method called liquid chromatography under limiting conditions of enthalpic interactions is presented. It enables automated quantitative separation of blends of synthetic polymers, for example the single step discrimination of both parent homopolymers from the block copolymers. Moreover, this method enables the estimation of molar mass and molar mass distribution of the block copolymer precursor. Adjacent large sequences of mobile phase of different composition are applied as barriers. They are created by a computer controlled pair of pumping systems in the form of longitudinal profiles along the column. The home synthesized block copolymers polystyrene-block-poly(2-vinylpyridine) served as model examples of the method application. The adsorption retention mechanism was exploited using mesoporous bare silica gel column packing. Series of block copolymers of similar composition can be quickly handled with the method to optimize their synthesis.

Low-Temperature Meltable Elastomers Based on Linear Polydimethylsiloxane Chains Alpha, Omega-Terminated with Mesogenic Groups as Physical Crosslinkers: A Passive Smart Material with Potential as Viscoelastic Coupling. Part I: Synthesis and Phase Behavior.

Physically crosslinked low-temperature elastomers were prepared based on linear polydimethylsiloxane (PDMS) elastic chains terminated on both ends with mesogenic building blocks (LC) of azobenzene type. They are generally (and also structurally) highly different from the well-studied LC polymer networks (light-sensitive actuators). The LC units also make up only a small volume fraction in our materials and they do not generate elastic energy upon irradiation, but they act as physical crosslinkers with thermotropic properties. Our elastomers lack permanent chemical crosslinks-their structure is fully linear. The aggregation of the relatively rare, small, and spatially separated terminal LC units nevertheless proved to be a considerably strong crosslinking mechanism. The most attractive product displays a rubber plateau extending over 100 °C, melts near 8 °C, and is soluble in organic solvents. The self-assembly (via LC aggregation) of the copolymer molecules leads to a distinctly lamellar structure indicated by X-ray diffraction (XRD). This structure persists also in melt (polarized light microscopy, XRD), where 1-2 thermotropic transitions occur. The interesting effects of the properties of this lamellar structure on viscoelastic and rheological properties in the rubbery and in the melt state are discussed in a follow-up paper ("Part II"). The copolymers might be of interest as passive smart materials, especially as temperature-controlled elastic/viscoelastic mechanical coupling. Our study focuses on the comparison of physical properties and structure-property relationships in three systems with elastic PDMS segments of different length (8.6, 16.3, and 64.4 repeat units).

Retention Mechanism of Branched Macromolecules in Size Exclusion Chromatography.

The theory of Stockmayer in the modifications of Thurmond and Zimm has been used for the description of the size exclusion chromatography separation of randomly branched molecules with tetrafunctional branch points. It is assumed that free chain ends, created by the branching process, cause the molecules to be entrapped in the pores of the column packing with the time of their release given by the exponential law characteristic for the monomolecular reactions. Using this assumption, the anomalous elution behavior of such molecules can be modeled. With increasing elution volume, the average values of radius of gyration and, to a lesser degree, of molecular weight decrease and, after passing a minimum, again increase in the low-molecular weight region.

Toward ideal separation by size-exclusion chromatography.

In analyses of polystyrene standards by size-exclusion chromatography for polymers of molecular weight about thirty thousand and higher, the separation improved with decreasing flow-rate is in accord with Giddings observation of transversal diffusion as a factor decreasing the broadening of the band broadening function. The variance of the elution curves is larger than it corresponds to dispersity M¯w/M¯n and the shape of the elution curves depends on the experimental conditions which suggests that it reflects properties of the band broadening function. The skew and the excess kurtosis of the elution curves increase near the exclusion limit in accord with theoretical prediction for the band broadening function.

Fluorescent boronate-based polymer nanoparticles with reactive oxygen species (ROS)-triggered cargo release for drug-delivery applications.

A new drug-delivery system of polymer nanoparticles (NPs) bearing pinacol-type boronic ester and alkyne moieties displaying triggered self-immolative polymer degradation in the presence of reactive oxygen species (ROS) with the capability of cellular imaging is presented. The NPs specifically release their drug cargo under concentrations of ROS that are commonly found in the intracellular environment of certain tumors and of inflamed tissues and exhibit significant cytotoxicity to cancer cells compared to their non-ROS-responsive counterparts.

Decomposition of size-exclusion chromatography elution curves of complex branched polymers.

A new method for the decomposition of non-baseline-resolved multimodal elution curves of SEC with the concentration, light scattering and viscosity detection is presented. The method makes possible the characterization of the polymer-sample components, represented by the peaks forming multimodal elution curves, individually and reduces also the error in the calculation of molecular-weight averages. The procedure is demonstrated on narrow molecular-weight distribution polystyrene standards and their mixture as well as on a grafted polymer sample.

Hydrolysis of wheat B-starch and characterisation of acetylated maltodextrin.

Wheat B-starch was hydrolysed by α-amylase "Liquozyme supra" from Bacillus licheniformis at 90 °C and pH 7. After 2 h, the dextrose equivalent was 18; according to size exclusion chromatography, however, the hydrolysate contained not only dominant malto-oligosaccharides with the degree of polymerisation (DP)<10 but also more than 20% of components with DP higher than 40. The product was acetylated to a high degree as verified by FTIR and (1)H NMR (degree of substitution DS=3.1); nevertheless, detailed analysis of the MALDI-TOF mass spectra of the product showed that most of the malto-oligosaccharides molecules contained one or two residual hydroxyls. Size exclusion chromatography confirmed that the acetylated maltodextrin still contained a significant part with DP>40. This non-uniformity of acetylated maltodextrin, both with respect to DP and to DS, must be taken into account in the development of acetylated-maltodextrin applications such as use as plasticisers or compatibilisers in biodegradable composites.

Size-exclusion-chromatography separation of randomly branched polymers with tetrafunctional branch points and local dispersity.

The SEC separation of a randomly branched polymer, in particular local dispersity due to branching, are theoretically examined. A model of the SEC separation of randomly branched polymer with tetrafunctional branch points enabling the estimation of local dispersity was developed. Measurable quantities (branching indices) were compared with real data. Local dispersity due to branching is demonstrated to depend on elution volume and degree of branching and in the area of the beginning of the elution curve it can reach non-negligible values.

Self-assembly of poly(4-methylstyrene)-g-poly(methacrylic acid) graft copolymer in selective solvents for grafts: scattering and molecular dynamics simulation study.

Poly(4-methylstyrene)-g-poly(methacrylic acid) (P4MS-g-PMAA) graft copolymer was synthesized by the grafting-onto method from poly(4-methylstyrene), selectively brominated on methyl groups, and "living" poly(tert-butyl methacrylate). The average degree of polymerization of the backbone and the grafts and the average number of grafts per backbone were 251, 21, and 25, respectively. The self-assembly of P4MS-g-PMAA was studied in methanol and aqueous buffers (selective solvents for grafts). Micelles of P4MS-g-PMAA in methanol were studied by a combination of static and dynamic light scattering, TEM and SAXS. It was found that their spherical core/shell morphology resembles that of diblock copolymer micelles but they have a very low aggregation number (approximately 3) and a high cmc (approximately 0.8 mg/mL). The spherical core-shell structure revealed by SAXS was confirmed by the molecular dynamics study emulating an associate of comblike copolymers with structural parameters close to those of the experimentally studied system. Because P4MS-g-PMAA was not directly soluble in water, its aqueous solutions had to be prepared by dialysis of the methanolic solutions. In aqueous solutions, unlike in methanol, small P4MS-g-PMAA micelles (approximately 20 nm in diameter) form large secondary aggregates (approximately 100-400 nm).

Statistical properties of the band-broadening function.

Statistical properties of the band-broadening function calculated from the equilibrium and kinetic theories of Giddings and Eyring are compared with real liquid-chromatography elution curves of low-molecular-weight substances and with light-scattering elution curves of a high-molecular-weight polystyrene standard injected at several concentrations. The curves obtained by liquid chromatography agree in a large span of elution times with the theoretical ones and can be described by one value of the plate-height. The size exclusion chromatography (SEC) elution curves seem to approach the predicted statistical properties with decreasing concentration of injected polymer but, in general, a reliable prediction of band-broadening (BB) functions in SEC of polymers, especially of non-symmetric BB functions near the exclusion limit, seems not possible at this point. The relation of the theory with the characteristic-function approach developed by Dondi is also discussed.

Analysis of the influence of interdetector volume on local calibration in size exclusion chromatography with dual multiangle-light-scattering/concentration detection.

A comparison of the s- and w-detections of molecular weight, a necessary condition for precise determination of interdetector volume in size exclusion chromatography of polymers with the dual light scattering--concentration detection, is examined. From the theoretical analysis for a polymer with the log-normal molecular weight distribution it follows that the error in determination of the local calibration, i.e., of a logarithmic dependence of molecular weight on elution volume obtained by the s-detection, from the known dependence of radius of gyration on elution volume and of molecular weight on the radius of gyration, remains linear and is slightly shifted with respect to that obtained by the w-detection (dual detection giving the weight-average molecular weight) towards higher molecular weights, the difference being below the experimental error. It also follows that the error in the slope of local calibration found by the w-detection is given by the ratio of the error in interdetector volume and the variance of the elution curve. This is demonstrated on several polymer samples with symmetric elution curves of polymer samples differing in polydispersity indices. The range of this rule depends on the broadness and symmetry of elution curves. The precision of the interdetector volume determination depends therefore strongly on the Mw/Mn ratio of the sample.

Determination of the interdetector volume by s-detection in size-exclusion chromatography of polymers with on-line multiangle light-scattering detection.

The determination of the interdetector volume (IDV) in size-exclusion chromatography (SEC) of polymers with dual multiangle light-scattering/concentration detection based on the s-detection is demonstrated. By s-detection the determination is meant of local molecular mass from a known relation between molecular mass and radius of gyration, obtained from the angle dependence of the intensity of scattered light. IDV is found basing on the stipulation of equal slope of local calibrations found by the dual light-scattering/concentration detection, referred to as the w- and s-detection. As the s-detection uses just the light-scattering detector and, therefore, is independent of the value of IDV, this quantity can be found by searching for its value that gives the local calibration dependence obtained by the dual detection closest to that determined independently by the s-detection.

Relation between the kinetic and equilibrium quantities in size-exclusion chromatography.

Separation mechanisms in the adsorption and size-exclusion chromatography (SEC) modes are equivalent in the sense that both processes can be described in terms of a mean fraction of the analyte in mobile phase (MP) and the number of interactions of molecules of the analyte in MP and in pores of/on the solid phase (SP). This is derived by comparing a recent theory of SEC with the theory of Giddings and Eyring for the adsorption chromatography. The elution volume, i.e., the maximum of the elution curve of a species uniform in molecular weight and composition (i.e., the maximum of the spreading function) is the excluded volume divided by the mean fraction of the analyte in mobile phase. Relations between the probabilities of adsorption and desorption of the molecule and the fractions of the analyte in MP and SP were derived. This makes it possible to describe the SEC and adsorption separation mechanisms in the framework of a single unified theory, which is in accord with the Flodin model of separation.

Problems connected with band-broadening in size-exclusion chromatography with dual detection.

The sources of band-broadening (axial dispersion) in size-exclusion chromatography (SEC) of polymers and its influence on data obtained using dual detection of concentration and molecular weight are reviewed. Special attention is paid to the combination of a multiangle light-scattering photometer and a differential refractometer as detectors. The local polydispersity is discussed in the relation to the band-broadening as well as to heterogeneity of the polymer with respect to molecular weight and hydrodynamic volume.

Relations between the separation coefficient, longitudinal displacement and peak broadening in size exclusion chromatography of macromolecules.

The separation of a polymer by size exclusion chromatography is described as a series of interactions, i.e. consecutive establishments of equilibria between polymer fractions in the mobile and stationary phases followed by displacements of mobile phase containing the polymer. The elution curve is derived as the longitudinal concentration profile in the column observed in one position in space during the time of the analysis. The mean value of elution volume of a particular polymer species turns out to be the interstitial volume of the separation system divided by the mean fraction of polymer in the mobile phase. The number of the displacement-equilibrium steps can be estimated from the limiting values of the variance of the spreading function.