Structure of a styrene-butadiene-styrene block copolymer by light scattering..

The phase structure of a styrene-butadiene-styrene block copolymer (mol. wt. 21 000–98 0000– 21 000) film cast from tetrahydrofuran/methyl ethyl ketone is studied by light scattering. The scattered intensity I corresponding to V_v, H_v, V_h, and H_h polarization directions is measured as a function of scattering angle. From the In I vs sin² (θ/2) plots the domain sizes are found to be about 0.4 and 1.0 μ. The a values are independent of polarization directions. This proves that the domains are geometrically isotropic. The two sizes correspond to two correlation distances; the smaller value represents the extent of heterogeneity within a spherical domain and the larger valued the inter-domain separation distance.     

HPLC analysis of quaternary ammonium surfactants with the evaporative light scattering detector

A normal-phase high-pressure liquid chromatography technique has been elaborated for the separation of quaternary ammonium surfactants. The separation was achieved on a bonded polyphenol silica gel column with gradient elution and evaporative light-scattering (ELS) detection. The proposed method has been applied to the quantitative determination of low levels of monoalkyltrimethylammonium and trialkylmethylammonium chlorides in dialkyldimethylammonium chloride.     

Simultaneous multiple sample light scattering detection of LCST during copolymer synthesis

This work has two objectives in the investigation of polymer solution lower critical solution temperature (LCST): First, to develop a new instrument to monitor LCST onset during copolymer synthesis by coupling several thermostatted light scattering flow cells to the output stream of an ACOMP system (Automatic Continuous Online Monitoring of Polymerization reactions). Second, to use this to investigate effects on LCST when N-isopropylacrylamide (NIPAM) is copolymerized with a charged comonomer, styrene sulfonate (SS). This comonomer pair has widely separated reactivity ratios. SS is rapidly consumed, yielding composition drift toward NIPAM rich polymer. High content SS chains inhibited LCST, and SS was dramatically effective at suppressing LCST down to copolymers of 5% molar SS in 10 mM NaCl aqueous solvent. LCST for higher content SS chains was elevated and required significant additional ionic strength to occur. It was determined that the suppression of the LCST by SS is chiefly an intramolecular effect.     

Investigation of block copolymer micellization by high-performance size-exclusion chromatography

The formation and decomposition of micelles of the three-block copolymer polystyrene-block-poly(ethene-stat-butene)-block-polystyrene (Kraton G 1652, Shell) were investigated by high-performance size-exclusion chromatography in a mixed solvent dioxan–heptane. The association equilibrium may be shifted from the pure unimer to pure micelles by changing the composition of the mobile phase, and also (at constant composition) by a change in temperature. The shape of the chromatograms observed under conditions of comparable equilibrium concentrations of both species may be explained by the disturbance and reestablishment of the association equilibrium during separation in the chromatographic column. Experiments with changing flow rate show the dominating effect of degrading separation efficiency with increasing linear velocity of the mobile phase.     

Analysis of soybean lecithins and beef phospholipids by HPLC with an evaporative light scattering detector

Linear (r > 0.99) calibration curves were obtained for 10–150 μg of phosphatidylethanolamine (PE), 10–75 μg of phosphaditylinositol (PI), phosphaditylserine (PS) and lysophosphatidylethanolamine, 10–100 μg of phosphatidic acid (PA) and 10–250 μg of phosphatidylcholine (PC) by high-performance liquid chromatography analyses with an evaporative light scattering detector, a Zorbax 7-μm silica column and gradient elution with two solvents. One solvent (A) contained 415 mL isooctane (IOCT), 5 mL tetrahydrofuran (THF), 446 mL isopropanol (IPA), 104 mL CHCl₃ and 30 mL H₂O; and the other solvent (B) contained 216 mL IOCT, 4 mL THF, 546 mL IPA, 154 mL CHCl₃ and 80 mL H₂O. The gradient in which 100% A linearly changed to 100% B in 20 min followed by 12 min of 100% B and then a linear change to 100% A during 5 min separated PE, PS and PC in soybean lecithins and beef lipids, but failed to resolve PI and PA. In these same samples, less polar lipids were separated from phospholipids (PL) by elution from Bond-Elut silica columns with diethyl ether/hexane (20:80, vol/vol), and PL were recovered by elution with methanol. This procedure is useful for concentration of minor lipid components. Levels of PE, PI-PA, PS and PC were higher in granular than in liquid lecithin, and PC was the most abundant PL in soybean lecithins and beef lipids.     

Reversed‐phase analysis of triacylglycerols by ultra performance liquid chromatography‐evaporative light scattering detection (UPLC‐ELSD)

An improved reversed‐phase (RP) method has been developed for the analysis of triacylglycerols (TAG) in fats and oils. This method has shown superior performance over traditional reversed‐phase liquid chromatographic (LC) methods in speed and resolution, and equivalent to superior performance in quantitation accuracy (101%–109%) and reproducibility (1.3%–5.8% RSD). The method can easily be adjusted for use with different oils by simple modification of the gradient and run time. Additionally, a mobile phase is used that is compatible with liquid chromatography/mass spectrometry (LC/MS) that when required, can aid in identification of TAG, for which many standards do not exist. This method is suited to a broad number of applications including (but not limited to) research and development of new oils, quality control, production of industrial or edible oils, and seed strain selection.     

Rapid analysis of oxidized cholesterol derivatives by high-performance liquid chromatography combined with diode-array ultraviolet and evaporative laser light-scattering detection

Extensive evidence of the deleterious biological effects of oxidized 5-cholesten-3β-ol (cholesterol) derivatives has led to great interest in their detection. We observed that known oxidized cholesterol derivatives can be rapidly quantitated by combining reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) absorption and evaporative laser light-scattering (ELSD) detection. Using a 20 × 0.46 cm C18 HPLC column and methanol/acetonitrile (60:40, vol/vol) as the mobile phase at 1.0 mL/min, 10 species of oxidized cholesterol derivative were measured by UV (205, 234, and 280 nm) while 5-cholestan-5α,6α-epoxy-3β-ol (5α-epoxycholesterol), 5-cholestan-5β,6β-epoxy-3β-ol (5β-epoxycholesterol), and 5-cholestan-3β,5α,6β-triol (cholestanetriol) were detected by only ELSD. The minimal limits of detection ranged from 100 to 500 ng depending on sterol and detector. The response was linear in the range 0–1000 or 0–2000 ng depending on detector. These oxidized cholesterol derivatives were also identified by HPLC/mass spectrometry analysis combined with UV detector. Heated tallow contained cholestanetriol, 5-cholesten-3β,7α-diol (7α-hydroxycholesterol), 5-cholesten-3β,7β-diol (7β-hydroxycholesterol), 5-cholesten-3β-ol-7-one (7-ketocholesterol), 5α- and 5β-epoxycholesterols under the developed analysis condition. Photooxidized cholesterol had cholestanetriol, 7α- and 7β-hydroxycholesterols and 3,5-cholestadien-7-one. On the other hand, 7α- and 7β-hydroxycholesterols, 7-ketocholesterol, 5α- and 5β-epoxycholesterols and 3,5-cholestadien-7-one were observed in copper-oxidized low-density lipoprotein. Thus, this developed HPLC analysis method could be applied to identification of oxidized cholesterol derivatives in food and biological specimen.     

HPLC analysis of phospholipids by evaporative laser light-scattering detection

High-performance liquid chromatography (HPLC) for analysis of phospholipids has traditionally employed ultraviolet detection of the eluted compounds. The evaporative laser light-scattering detector (ELSD) offers new opportunities for quantitative analysis of lipids. Phospholipids were isolated from crude and degummed oils prepared from soybeans subjected to storage at high moisture content. Analytical and preparative separations of phospholipids by normal-phase HPLC were accomplished. Major class fractions were analyzed by transmethylation and capillary collumn chromatography for fatty acid composition, and by reverse-phase C-18 HPLC (RP-HPLC) for molecular species composition. The RP-HPLC-ELSD system was limited to the analysis of phosphatidylcholine and phosphatidylethanolamine.     

Small-angle neutron scattering measurement of block copolymer interphase structure

The notion of an interfacial layer at the domain boundary in block copolymers is reviewed and the possibility of its measurement by small-angle X-ray and small angle neutron scattering discussed. Values of the interfacial layer thickness and its volume fraction have been obtained for a range of styrene-isoprene copolymers. Interfacial layer thickness is not strongly dependent on molecular weight whilst the volume fraction shows a dependence more in line with the theory of Helfand.     

Analysis of oxylipins by high-performance liquid chromatography with evaporative light-scattering detection and particle beam-mass spectrometry

The metabolism of 13 S-hydroperoxy-9Z,11E,15Z-octadecatrienoic acid was investigated in a crude enzyme extract from mung bean seedlings (Phaseolus radiatus L.). Hydroperoxide-metabolizing activity was mainly due to a hydroperoxide lyase and, to a lesser extent, to an allene oxide synthase and a peroxygenase. Oxylipins originating from hydrolysis and cyclization of the allene oxide synthase product 12,13-epoxy-9Z,11,15Z-octadecatrienoic acid and from peroxygenase catalysis were identified by high-performance liquid chromatography (HPLC) particle beam-mass spectrometry (PB-MS) and quantified by normal-phase HPLC with an evaporative light-scattering detector (ELSD). An advantage of this methodology was the possibility to avoid extensive derivatization procedures commonly used for the gas chromatographic analysis of oxylipins. Owing to a comparable sample inlet system, the ELSD served an important analytical pilot function for the PB-MS: Qualitatively identical chromatographic patterns were obtained with both detection systems. The HPLC system enabled the separation of methyl 12-oxo-phytodienoate, methyl 11-hydroxy-12-oxo-9Z,15Z-octadecadienoate, methyl 12-oxo-13-hydroxy-9Z,15Z-octadecadienoate, methyl 9-hydroxy-12-oxo-10E,15Z-octadecadienoate, methyl 13-hydroxy-9Z,11E,15Z-octadecatrienoate, methyl 15,16-epoxy-13-hydroxy-9Z,11E,15Z-octadecatrienoate, and methyl 13-hydroperoxy-9Z,11E,15Z-octadecatrienoate on a Lichrospher DIOL column within 33 min. Compared with a diode array detector, the ELSD proved to be more sensitive, in the case of methyl 12-oxo-13-hydroxy-9Z, 15Z-octadecadienoate by a factor of about 15. In addition, volatile metabolites were analyzed by capillary gas chromatography. The yield of the hydroperoxide lyase product 2E-hexenal was 49%, whereas the sum of oxylipins reached about 15%.     

Separation and quantitation of cholesterol oxides by HPLC with an evaporative light scattering detector in a model system

A method to analyze cholesterol and 10 of its oxidation products, ranging from the weakly polar cholest-4-ene-3,6-dione to moderately polar cholest-5-ene-3β,7α-diol, in a single run is described. The separation was achieved by normal-phase gradient high-performance liquid chromatography with an evaporative light-scattering detector. This universal mass detector does not detect changes in solvent composition; this makes it possible to employ gradients, an essential technique whenever a wide range of compounds with diverse characteristics is to be separated. Standards at concentrations from 0.1–1.0 μg were separated within 37 min on an alumina/silica column with a gradient elution system that contained dichloromethane, acetonitrile, and water.     

Quantitative determination of monoglycerides and diglycerides by high-performance liquid chromatography and evaporative light-scattering detection

Neutral lipid classes were separated with normal-phase high-performance liquid chromatography, and mono- and diglycerides were determined with an evaporative light-scattering detector (ELSD). The 1,3-diacylglycerols were resolved from the 1,2-diacylglycerol positional isomers, although some 1,3-diacylglycerols of low molecular weight interfered with the 1,2-diacylglycerols of high molecular weight. For monoglycerides, the separations between 1-(and 3-)acyl and 2-acylglycerols were optimized only between those pairs with identical fatty acyl groups. Samples were dissolved in a solvent mixture and analyzed without derivatization. The results (monoglyceride) obtained from this method agreed well with those derived from gas chromatographic and supercritical fluid chromatographic methods. The universal nature of the ELSD makes this method applicable to oils and emulsifiers containing both saturated and unsaturated fatty acyl moieties.     

Small-angle neutron scattering study on block and gradient copolymer aqueous solutions

The small-angle neutron scattering investigation was carried out on semi-dilute aqueous solutions of block and gradient copolymers comprising pEOVE and pMOVE, pEOVE₃₀₀-block-pMOVE₃₀₀ (Block) and p(EOVE-grad-MOVE)₆₀₀ (Grad). Here, pEOVE and pMOVE denote poly(2-ethoxyethyl vinyl ether) and poly(2-methoxyethyl vinyl ether), respectively, and the numbers indicate the degrees of polymerization. The monomer composition in the Grad had a gradient along the polymer chain. For 20.0 wt% solutions, a microphase-separated structure and physical gelation were observed both in Block and in Grad systems. In the case of the Grad system, a gradual microphase separation took place as a function of temperature via a micellization with a small radius of core, characterized by the “reel-in” process, i.e., a winding of polymer chains to the core of a micelle because of the gradient composition. On the other hand, the Block system underwent a stepwise transition with respect to temperature. The relationship between microphase separation and the rheological behavior is explained from the viewpoint of microscopic structure.     

Characterization of styrene-ethylene oxide and methyl methacrylate-styrene block copolymers by light scattering

Several polystyrene-poly(ethylene oxide)-polystyrene (PS-PEO-PS) and poly(methyl methacrylate)-polystyrene-poly(methyl methacrylate) (PMMA-PS-PMMA) block copolymers, synthesized by free-radical polymerization, were studied in various solvents by using a light-scattering technique. The copolymers, which have different lengths of central blocks, had molecular weights within the range 3.0 × 10⁴ to 1.6 × 10⁶. It was found that almost all of them were confirmed as block copolymers from the variation of the product $\text{M}{}_{\mathrm{<mtext>app</mtext>}}\text{〈S}{}^2{}_{\mathrm{<mtext>app</mtext>}}\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ with $\text{W}{}_{\mathrm{<mtext>A</mtext><mtext>v</mtext><mtext>A</mtext>}}\text{v}$, although they were rather heterogeneous. The copolymer compositions determined either from the additivity of the refractive index increments of its constituent parts and the copolymer or from ultra-violet analysis were in excellent agreement with each other.     

Quantitative branching of linear and branched polysaccharide mixtures by size exclusion chromatography and on-line low-angle laser light scattering detection

The quantitative branching characterization of polysaccharide via size exclusion chromatography (SEC) and on-line low-angle laser light scattering (LALLS) detection is presented from both theoretical arguments as well as direct experimental evidence. The two measurable branching parameters g_v(m) [= (M_l/(M _n)_m)_v] and g′_v(m) [ = (M_l/(M _w)m)v] of a sample mixture have been related theoretically to the mixture's composition. There exists linear relationships between g_v(m) and W_b,v (the mass fraction of branched component in mixture) as well as between g′_v(m)^?1 and w_b,v. The latter correlation has been demonstrated experimentally employing a combined SEC/LALLS technique, and displays excellent agreement with the theoretical predictions. Furthermore, this polymer branching characterization method has been applied to study enzymatic starch hydrolysates products. The molecular weight distribution and branching distribution have been obtained.     

Enhanced light emission of nano-patterned GaN via block copolymer thin films

We demonstrate that the nanoscopic block copolymer patterns on GaN can enhance light extraction efficiency of GaN-based light emitting diodes. Nanoporous patterns were fabricated on a bare GaN substrate via self-assembly of poly(styrene-b-methyl methacrylate) block copolymers from which PMMA microdomains were selectively removed later on. A bare GaN surface was treated with a photo-crosslinkable thin layer of poly(styrene-r-methyl methacrylate) random copolymers to tune the cylindrical microdomain orientations. The nanoporous block copolymer thin film was controlled to be thicker than its typical repeat period in bulk by incorporating PMMA homopolymer into block copolymer. Consequently, the light extraction efficiency in photoluminescence spectra could be tuned with the thickness of nanopatterned thin film on GaN. This paper is dedicated to Professor Chul Soo Lee on the occasion of his retirement from Korea University.     

Light scattering evidence of selective protein fouling on biocompatible block copolymer micelles

Selective protein fouling on block copolymer micelles with well-known potential for tumour-targeting drug delivery was evidenced by using dynamic light scattering measurements. The stability and interaction of block copolymer micelles with model proteins (BSA, IgG, lysozyme and CytC) is reported for systems featuring a hydrophobic (poly[2-(diisopropylamino)-ethyl methacrylate]) (PDPA) core and hydrophilic coronas comprising poly(ethylene oxide)/poly(glycerol monomethacrylate) (PEO-b-PG2MA) or poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC). The results revealed that protein size and hydrophilic chain density play important roles in the observed interactions. The PEO(113)-b-PG2MA(30)-b-PDPA(50) nanoparticles are stable and protein adsorption is prevented at all investigated protein environments. The successful protein-repellent characteristic of these nanoparticles is attributed to a high hydrophilic surface chain density (>0.1 chains per nm(2)) and to the length of the hydrophilic chains. On the other hand, although PMPC also has protein-repellent characteristics, the low surface chain density of the hydrophilic shell is supposed to enable interactions with small proteins. The PMPC(40)-b-PDPA(70) micelles are stable in BSA and IgG environments due to weak repulsion forces between PMPC and the proteins, to the hydration layer, and particularly to a size-effect where the large BSA (R(H) = 4.2 nm) and IgG (R(H) = 7.0 nm) do not easily diffuse within the PMPC shell. Conversely, a clear interaction was observed with the 2.1 nm radius lysozyme. The lysozyme protein can diffuse within the PMPC micellar shell towards the PDPA hydrophobic core in a process favored by its smaller size and the low hydrophilic PMPC surface chain density (～0.049 chains per nm(2)) as compared to PEO-b-PG2MA (～0.110 chains per nm(2)). The same behavior was not evidenced with the 2.3 nm radius positively charged CytC, probably due to its higher surface hydrophilicity and the consequent chemical incompatibility with PDPA.     

Study of segmented ethylene terephthalate–caprolactone copolymer by differential refractometry and light scattering

A segmented ethylene terephthalate (ET)–caprolactone (CL) copolymer was characterized by light scattering in chloroform tetrahydrofuran and butanone. The flexibility of the copolymer chain is comparable with that of typical flexible chains, such as polystyrene. In the process of applying the Bushuk–Benoit light scattering theory to the segmented PET–PCL copolymer, we encountered not only the problem of finding three solvents with different refractive index but also the problem of determining the specific refractive index increments for the PET and PCL segments in the copolymer, i.e., ν_PET and ν_PCL . In principle, the approximate values of ν_PET and ν_PCL can be obtained from the PET and PCL homopolymers, respectively. In reality, it involves many practical problems, e.g., to find three solvents not only for copolymer but also for the PET and PCL homopolymers. In this study, a different method was used to find both ν_PET and ν_PCL , wherein the ν values of at least two segmented PET–PCL copolymers with different PET compositions were used. With ν_PET , ν_PCL , and ν, we characterized the absolute molecular weight. Further, we show that the composition of an unknown segmented PET–PCL copolymer can be estimated from ν_PET , ν_PCL , and ν. © 1994 John Wiley & Sons, Inc.     

Polymeric micelles formed by polypeptide graft copolymer and its mixtures with polypeptide block copolymer

Polymeric micelles based on poly(γ-benzyl-l-glutamate)-poly(ethylene glycol) graft copolymer (PBLG-g-PEG) with various degrees of grafting and the mixtures composed of PBLG-g-PEG and poly(γ-benzyl-l-glutamate)-poly(ethylene glycol) block copolymer (PBLG-b-PEG) were prepared by the dialysis method in deionized water. Fluorescence spectroscopy and transmission electron microscope (TEM) have been used to study the self-assembly behavior. The experimental results revealed that the degree of grafting exerts marked effect on the critical micelle concentration (CMC) and the morphology of the micelle formed by PBLG-g-PEG. With increasing the degree of grafting, the CMC value becomes larger and the morphology of formed micelle changes from irregular shape to spindle. It was also found that mixtures of PBLG-g-PEG/PBLG-b-PEG can associate into hybrid polymeric micelle with various shapes.