Zlatka Grubišić-Gallot

Characterization of block copolymers by size exclusion chromatography

SummaryPoly(ethyl methacrylate-b-deuterated methyl methacrylate), poly(styrene-b-methyl methacrylate), and poly(styrene-b-dimethylsiloxane)diblock copolymers have been characterized by means of size exclusion chromatography (GPC) apparatus fitted with four detectors in series, viz continuous viscometer, UV spectrophotometer, low angle light scattering photometer, and differential refractometer. The continuous measurements of the scattered light intensity, the limiting viscosity number, the concentration, and the chemical composition permits complete determination of the molecular characteristics of block copolymers.

Characterization of star-shaped polystyrene samples by size exclusion chromatography

Abstract Well defined star-shaped polystyrene samples have been studied by means of size exclusion chromatography (GPC) apparatus fitted with three detectors in series, viz. low angle light scattering photometer, continuous viscometer, and differential refractometer. Thus, the light scattering intensity, the limiting viscosity number and the concentration are measured continuously on the eluate of the chromatographic column. The agreement between the molecular weight averages computed from these GPC data and those measured by standard techniques on the overall sample has been found quite satisfactory. The viscometric data arising from the GPC set-up are somewhat less accurate, but they clearly indicate the highly branched character of the samples studied. Access to the actual molecular weight distribution for a sample of star polymer is rendered possible by this method. Even the presence of linear contaminants does not interfere provided the elution curves for stars and for the linear constituents do not overlap.

Study of polystyrene-block-poly(methyl methacrylate) micelles by size exclusion chromatography/low angle laser light scattering. Influence of copolymer composition and molecular weight

Abstract Results of size exclusion chromatography study of the micellar systems polystyrene-block-poly(methyl methacrylate) in the mixed solvent 1,4-dioxane/cyclohexane are reported and the behaviour of copolymers with different overall molecular weight and chemical composition is compared. At higher content of cyclohexane, the effect of the solute trapping in the column due to the adsorption of the unimer on the packing was observed. This effect was more pronounced for the lower molecular-weight copolymers as compared with the higher molecular-weight ones and was found to depend significantly on the thermodynamic quality of solvent (eluent). Experiments in 1,4-dioxane/70 vol.% cyclohexane showed strong influence of unimer—micelles re-equilibration in the column on the resulting chromatograms, especially for the micellar systems of the lower molecular-weight copolymers. For the copolymers of higher molecular-weight, the micelles dissociation in the column was reduced probably due to the more entangled and...

Study Of Polystyrene-block-poly(methyl methacrylate) Micelles by Size Exclusion Chromatography/Low Angle Laser Light Scattering Anomalous Micellization

Anomalous micellization behaviour consisting in the simultaneous presence of two kinds of micelles was observed in the micellar system polystyrene-block-poly(methyl methacrylate) in 1,4-dioxane/cyclohexane. This anomaly already known, particularly from static light scattering studies of various micellar systems, was now observed by size exclusion chromatography/low-angle laser light scattering technique. For the solvent mixture 1,4-dioxane/70 vol. % cyclohexane, this method enabled a partial size exclusion chromatography separation of the regular and anomalous micelles and allowed to estimate the weight-average molecular weight of both. Anomalous micellization was reliably detected by size exclusion chromatography although the static light scattering data provided only weak confirmation of this phenomenon.

Study of irradiated polymers using double-modulation electron spin resonance and size exclusion chromatography

Abstract Irradiated polymers such as polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(α-methylstyrene) (PαMS) have been studied using size exclusion chromatography and double-modulation electron spin resonance (d.m.e.s.r.). Size exclusion chromatography coupled on-line with low-angle laser light scattering and viscometry have demonstrated that PS irradiated in the solid state gives only slight increases of molecular weight and viscosity with increasing dose. When irradiated in solution, the results confirm the existence of a highly crosslinked and heterogeneous PS matrix. PMMA and PαMS undergo degradation at the same doses. The d.m.e.s.r. spectra of a spin probe in the slow-motion region have been used to investigate the heterogeneity of the polymer matrix introduced by changes in crosslinking or by degradation. Discrete molecular motions of a spin probe above the internal probe transition (≈ 190 K) are very sensitive to local matrix density and to side-chain relaxation modes. The d.m.e.s.r. spectra indicate clearly a bimodal motion of spin probes located in regions of two considerably different crosslink densities of the PS matrix irradiated in solution.

STUDY OF POLYSTYRENE-BLOCK-POLY(METHYLMETHACRYLATE) MICELLES BY SEC/MALS. DETERMINATION OF MOLECULAR WEIGHTS AND SIZE DISTRIBUTION

Polystyrene-block-poly(methyl methacrylate) micelles in 1,4-dioxane/cyclohexane were studied by size exclusion chromatography coupled with multi angle light scattering (SEC/MALS). A sufficient unimer — micelles resolution achieved by SEC made it possible to use MALS detector for the direct determination of distributions and corresponding averages of molecular weights and gyration radii of micelles. Contrary to the standard static light scattering approach,the SEC/MALS technique provided these averages in one analytic run with a minimum amount of copolymer sample. In most systems, very narrow molecular weights and size distributions of micelles were obtained. For a given copolymer, the micellar association number increased with decreasing thermodynamic quality of solvent. Under given thermodynamic conditions, it increased with increasing length of insoluble poly(methyl methacrylate) block and with decreasing length of soluble polystyrene block. The micellar radius of gyration was predominantly controlled b...

Slow molecular motion in uniaxially stretched poly(ethyl methacrylate) as observed by double modulation electron spin resonance

SummaryThe double modulation ESR (DMESR) technique has been applied to investigate the change of very slow molecular dynamics ({ei235-1} >10-7 s) of nitroxide spin probe in amorphous poly(ethyl methacrylate) (PEMA) at low drawing ratios. The polymer has been characterized by means of size exclusion chromatography (SEC) apparatus fitted with three detectors in series with continuous viscometer, low angle light scattering photometer and differential refractometer. The side chain group motion and segmental motion well below the glass transition temperature are discussed in terms of local density changes induced by orientational anisotropy of the chain segments.