Determination of composition distribution of acrylonitrile-styrene copolymers by thin-layer chromatography

Determination of chemical composition distribution of acrylonitrile-styrene copolymers was carried out by thin-layer chromatography (TLC). A mixture of benzene and methyl ethyl ketone gave the most suitable calibration curve of R_f values versus acrylonitrile (AN) contents, where a concentration gradient technique was applied for development. Average AN contents obtained by TLC are coincident with those found by elemental analysis. The copolymers extracted from ABS resins are sufficiently arranged in the order of breadth of composition distribution by using the data from TLC. The agreement between the composition distribution curve and that from the theory of copolymerization is good.     

Thermal fractionation of vinyl acetate-vinyl alcohol copolymers

Thermal fractionation via the method of successive self-nucleation and annealing was used for the first time to study the crystallinity of vinyl acetate-vinyl alcohol copolymers with different random distributions of chain units. The lamella-thickness distribution was calculated through the Gibbs-Thomson equation. It was shown that, for all samples, the minimum lamella thickness is the same and corresponds to a block of no less than 15 vinyl alcohol units. On the basis of these data and with the use of the computer simulation of the polymer-analogous reaction via the Monte Carlo method, the block-length distribution in the crystalline phase was found. It was shown through a comparison of the lamella-thickness and block-length distributions that the maximum lamella thickness increases with the block length and vinyl alcohol content in the copolymer. In crystallites, blocks with lengths exceeding the maximum lamella thickness comprise a significant fraction. Thus, it is probable that these blocks form folds. The dependences of melting temperatures of crystalline lamellas on their thicknesses, as well as the dependences of the melting temperatures of copolymers not subjected to thermal fractionation on the chain-structure parameters, are adequately described by the Flory crystallization theory.     

Characterization of impact polypropylene copolymers by solvent fractionation

The compositional heterogeneity of two impact polypropylene copolymers(IPCs) was studied by a combinatory investigation of temperature rising elution fractionation(TREF) and solvent fractionation.The chain structures and composition of fractions obtained from solvent fractionation were examined in detail.The TREF results shows that there are much more E-P segmented copolymer and more uniform distribution of ethylene sequence in IPC-1,which is responsible for its better comprehensive mechanical performance.The fractions from hexane and heptane are ethylene-propylene rubber phase and E-P block copolymers respectively.The result of solvent fractionation method also shows that custom hexane or heptane extractions can not extract the E-P copolymer completely.     

Analysis of fractionation of ethylene–propylene copolymers

Analysis of the solution fractionation of ethylene–propylene copolymers was carried out by assuming a bivariate normal distribution function for the distribution of molecular weight and chemical composition. It was found that the variation of the molecular weight and composition distributions in fractions was complicated, because two distribution characteristics of the original copolymer affect fractionation to differing extents. The hypothetical cumulative weight distribution curves thus obtained agreed essentially with those obtained experimentally.     

Sorption isotherms of acrylonitrile on an acrylonitrile-styrene copolymer

Inverse Gas Chromatography (IGC) was used to construct sorption isotherms of acrylonitrile (ACN) on an acrylonitrile-styrene copolymer. The absolute value of the isosteric heat of adsorption (at constant uptake) increased with decrease in the amount of ACN adsorbed, indicating a stronger monomer-polymer interaction at the lower monomer concentrations. The Gibbs free energy obtained from the partition coefficients, as calculated from the ratio of monomer concentrations in the stationary and moving phases, was of the same order of magnitude as the values obtained from the specific retention volumes. The absolute value of this energy increased with decrease in monomer concentration and temperature, indicating a more favourable monomer-polymer interaction at the low temperatures and monomer concentrations.     

Thermal field-flow fractionation of colloidal materials: Methylmethacrylate-styrene linear di-block copolymers

Summary Model methylmethacrylate-styrene, linear di-block, copolymers were used to investigate the respective influnnces of temperature, of molar mass and of chemical composition on their Soret coefficient, s_T, by means of thermal field-flow fractionation (thermal FFF) in toluene and in THF. A recently developed thermal FFF retention model, which takes into account the variation of the basic FFF parameter λ with temperature, is applied to investigate the dependence of the Soret coefficient on temperature. It is found that the coefficient decreases approximately linearly with increasing temperature. At constant chemical composition and temperature, s_T exhibits a power law dependence on molar mass with an exponent é ? 0.55. At constant molar mass and temperature, s_T decreases monotonously with increasing weight percent styrene in the copolymer composition. At 300 K, s_T values are slightly larger in THF than in toluene. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

Separation and composition distribution determination of triblock copolymers by thermal field-flow fractionation

Thermal field-flow fractionation (ThFFF) is used to separate a linear triblock copolymer of polystyrene, poly(tert-butyl acrylate), and poly(methyl methacrylate) by composition. Fractions were collected and subjected to off-line NMR analysis. The resultant mole fraction versus retention time plots for each of the three polymer components confirmed the success of the separation and yielded the composition distribution of the copolymer. The composition distribution was also obtained using a second approach that involved solving a series of equations comprised of polymer thermal diffusion coefficients and quasi-elastic light scattering, differential refractometry, and UV detector responses. Both sets of data showed similar trends of composition variations in each polymer component as a function of retention time. However, discrepancies were observed in the mole fraction values. The ability to compositionally separate and to determine composition distribution of copolymers is important as demonstrated by the presence of diblock impurities in the ThFFF with off-line NMR results.     

Composition and molecular weight analysis of styrene-acrylic copolymers using thermal field-flow fractionation

Thermal field-flow fractionation coupled with online multiangle light scattering, differential refractive index and quasielastic light scattering (ThFFF-MALS/dRI/QELS) was used to simultaneously determine the molecular weight (MW) and composition of polystyrene-poly(n-butyl acrylate) (PS-PBA) and polystyrene-poly(methyl acrylate) (PS-PMA) copolymers. The online measurement of the normal diffusion coefficient (D) by QELS allowed calculation of the copolymer thermal diffusion coefficient (D(T)) of sample components as they eluted from the ThFFF channel. DT was found to be independent of MW for copolymers with similar compositions and dependent on composition for copolymers with similar MW in a non-selective solvent. By using a solvent that is non-selective to both blocks of the copolymer, it was possible to establish a universal calibration plot of DT versus mole fraction of one of the monomer chemistries comprising the copolymer. PS-PBA and PS-PMA linear diblock polymers were determined to vary in composition from 100/0 to 20/80 wt% PS/acrylate and ranged in MWs between 30 and 360 kDa. The analysis of a PS-PBA miktoarm star copolymer revealed a polydisperse material with a weight percent PBA of 50-75% and MW ranging from 100 to 900 kDa. The presented ThFFF-MALS/dRI/QELS method allowed rapid characterization of polymers with MW and chemical distributions in a single analysis.     

Continuous spin fractionation and characterization by size-exclusion chromatography for styrene-butadiene block copolymers

Linear and star-shaped styrene-butadiene block copolymers synthesized by anionic polymerization of butadiene and styrene were fractionated by applying a newly developed large-scale fractionation technique, named continuous spin fractionation (CSF). Their molecular weight and polydispersity index (d=M(w)/M(n)) were measured with size-exclusion chromatography and static light scattering. For the linear triblock copolymer a fractionation via temperature variation turned out to be better suited than the usual isothermal procedure. The star-shaped polymer with the d value of 1.33 was fractionated in two CSF steps to get the targeted sample, which has a considerably more uniform structure and a narrower molecular weight distribution (d=1.11). The corresponding starting linear diblock copolymer was fractionated in one step reducing d from 1.68 to 1.17. With one set of simple laboratory equipment, 1kg polymer can be fractionated per day. Utilizing CSF, for the first time, we fractionated successfully the block copolymers.     

Preparative solution crystallization fractionation: a simple and rapid fractionation method for the chemical composition separation of complex ethylene-propylene copolymers

The molecular structure elucidation of complex ethylene-propylene copolymers (EPCs) has benefited tremendously from the ability to combine preparative temperature rising elution fractionation (prep TREF) with various conventional analytical techniques. Recently reported, prep TREF-high-temperature solvent gradient interaction chromatography (HT-SGIC) (Cheruthazhekatt et. al, Macromolecules 45:2025–2034, 2012) is one of the most effective and highly useful coupled methods that allow for the exact measurement of the chemical composition distribution (CCD) present in various components of EPCs. The major drawback of prep TREF involving slow crystallization and elution steps is the long time per experiment. Here, we present a new and by far the simplest and fastest preparative fractionation method for complex polyolefins—preparative solution crystallization fractionation (prep SCF). The scope of the present study was to achieve a fast fractionation of complex bulk samples into an amorphous, semicrystalline and highly crystalline fraction, in sufficient amounts for the subsequent detailed compositional analysis. The effects of two different solvents, xylene and trichlorobenzene (TCB), and their influence on the solution crystallization of chemically different components of EPC were systematically investigated by combining prep SCF with crystallization analysis fractionation (CRYSTAF), FTIR, differential scanning calorimetry (DSC) and HT-SGIC analyses. Significant differences in the chemical composition of similar SCF fractions obtained from xylene and TCB were observed indicating the strong influence of the solvent on solution crystallization. Prep SCF-HT-SGIC results showed that, under similar experimental conditions, TCB as the fractionation solvent provides superior separation of complex semicrystalline ethylene-propylene (EP) components. Very interestingly, for the first time, separation of soluble fractions (30 °C) of iPP, EPC and PE homopolymer components in complex EPC was achieved by prep SCF in TCB. On the other hand, SCF fractionation in xylene provides a soluble fraction that is perfectly amorphous as has been shown by DSC and CRYSTAF. Based on these results, the present SCF approach and an updated method of the combination of prep SCF-HT-SGIC hold significant promise for the fractionation and characterization of similar complex EPCs in a simple way within a short analysis time, by using significantly smaller amounts of solvent compared to the previously reported, rather time-consuming, prep TREF-HT-SGIC combination. No similarly selective solution crystallization fractionations in preparative scale have been reported before.

Asymmetrical flow field-flow fractionation as a novel technique for the analysis of PS-b-PI copolymers

Asymmetrical flow field-flow fractionation (AF4) was used as a fractionation technique to investigate the molecular heterogeneity of poly(styrene-b-isoprene) diblock copolymers synthesized by either sequential living anionic polymerization or coupling of living precursor blocks. AF4 coupled to multi-angle laser light scattering (MALLS), refractive index (RI), and ultraviolet (UV) detectors was used to separate the diblock copolymers from the homopolymers and coupling products, and the molar masses of the different components were analyzed. In order to get more information about the separated block copolymers, homopolymers, and coupling products, fractions were collected directly after the AF4 channel. The collected fractions were analyzed offline by ¹H NMR to provide identification of the different species and additional information on the true chemical composition, and the microstructure of the diblock copolymer was obtained.

Mathematical modeling of crystallization analysis fractionation of ethylene/1‐hexene copolymers

Crystallization analysis fractionation (Crystaf) is a polymer characterization technique for estimating the chemical composition distributions of semicrystalline copolymers. Although Crystaf has been widely used during the recent years, it is still a relatively new polymer characterization technique. More quantitative understanding of its fractionation mechanism is essential for further developments. In this work, three ethylene/1‐hexene copolymers with different 1‐hexene fractions, but similar number‐average molecular weights, were analyzed by Crystaf at several cooling rates. A mathematical model was proposed to describe the effect of comonomer fraction and cooling rate on Crystaf fractionation from a fundamental point of view. The model describes the experimental Crystaf profiles of ethylene/1‐hexene copolymers with different 1‐hexene fractions measured at distinct cooling rates very well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1010–1017, 2007     

Rapid detection of compositional drift of polydisperse copolymers using thermal field-flow fractionation and multi-angle light scattering

Summary The use of thermal field-flow fractionation (ThFFF) with multi-angle light scattering (MALS) for the rapid detection of compositional heterogeneity in random copolymers is demonstrated. Soret coefficients were directly calculated from the ThFFF retention times while the MALS detector provided the polymer's radius of gyration (R _g) distribution. FromR _g, the diffusion coefficient (D) could be calculated and this allowed, in combination with the Soret coefficient, the calculation of the thermal diffusion coefficient (D _T). It was shown that theD _T distribution can serve as a measure for the chemical composition distribution of random styrene acrylonitrile copolymers. Comparison of ThFFF-MALS results with literature data from ThFFF-hydrodynamic chromatography (HDC) cross-fractionation experiments showed a fair agreement.     

Column chromatography fractionation of complex waste water sample extracts for measurement of ppt levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The novel application of azulene as a visual monitor of column chromatography performance during fractionation of complex waste water extracts for measurement of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at part-per-trillion concentrations is described. TCDD elutes directly behind azulene, the blue visual aid, in the 6% ethyl ether/hexane fraction during Florisil column chromatography.     

Study of the compositional heterogeneity of ethylene-1-hexene copolymers via thermal fractionation with the use of differential scanning calorimetry

The compositional heterogeneity of ethylene-1-hexene copolymers synthesized with various types of supported catalysts, namely, the titanium-magnesium catalyst TiCl₄/MgCl₂ and the zirconocene catalyst SiO₂(MAO)/Me₂Si(Ind)₂ZrCl₂, is studied via the method of successive self-nucleation-annealing (SSA) with the use of differential scanning calorimetry. On the basis of the data on the temperatures of individual peaks on SSA curves, the thickness of lamellas composed of macromolecules with a certain degree of short-chain branching is estimated. The copolymer synthesized with the zirconocene catalyst has a narrower range of fusion and does not contain large lamellas composed of molecules with a low degree of short-chain branching. With the use of the broadness index, it is shown that the copolymer synthesized with the zirconocene catalyst has a more uniform distribution of the comonomer than does the copolymer synthesized with the titanium-magnesium catalyst. For the copolymers synthesized with the titanium-magnesium catalyst, the compositional heterogeneity increases with an increase in the content of 1-hexene.     

The use of SSA fractionation to detect changes in the molecular structure of model ethylene-butene copolymers modified by peroxide crosslinking

Four model ethylene-butene copolymers of different molecular weights modified with various concentrations of peroxide were analyzed by a DSC based successive self annealing method. The original copolymers had the same intra and intermolecular homogeneous branching distribution along the linear chains with approximately 2.4% mol of ethyl branches. The copolymers with average molecular weights of 29,000, 45,000, 81,000 and 125,000 g/mol were modified with different amounts of 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane (DBPH) as a crosslinking initiator. The molecular changes induced by the reaction with the peroxide affect the semicrystalline structure of the material. Variations in the crystal thickness distributions of the material as a consequence of the modification are related to the peroxide induced free radical reactions.     

Preparation,fractionation, and dilute-solution behavior of ABA poly(methyl methacrylate-b-α-methylstyrene) block copolymers

The preparation by anionic polymerization of six ABA poly(methyl methacrylate-b-α-methylstyrene) block copolymers and of sixteen poly(α-methylstyrene)s is described. The block copolymers, of similar molecular weight but with different chemical compositions, were fractionated by preparative gel permeation chromatography and their behavior in dilute solution was investigated using viscometry. The results obtained indicate that the intramolecular phase separation does not occur under the conditions utilized, the block copolymers assuming randomcoil configurations in all of the copolymer/solvent systems studied. Consequently the block copolymer molecules are more expanded than homopolymers of the same molecular weight. The series of poly(α-methylstyrene)s covered the molecular weight range 2.7 × 10³–1.3 × 10⁶ and enabled the determination of Mark–Houwink–Sakurada constants for poly(α-methylstyrene) in the solvents chosen for the block copolymer studies.