No abstract

Four amphiphilic block copolymers polyisobutylene-block-poly(methacrylic acid) (IB m -MAA n ; m = 70−134, n = 52−228) were synthesized and transferred into aqueous medium at pH 10−12. Their structure in solution was characterized by fluorescence correlation spectroscopy (FCS), static and dynamic light scattering (SLS, DLS), analytical ultracentrifuge (AUC), and by transmission electron microscopy (TEM) with freeze-fracturing and staining techniques. DLS data, AUC sedimentation traces, and TEM images indicate at least two different kinds of particles. TEM shows spherical micelles; however, especially for polymers with larger hydrophobic blocks, additional particles are observed. FCS shows extremely low critical micelle concentrations (cmc < 0.3 mg/L). The main part of the particles consists of micelles with diameters from 15 to 50 nm, built by 130−200 block copolymer molecules. Aggregation numbers and diameters are consistent with a model recently proposed by Förster et al. (J. Chem. Phys. 1996, 104, 9956−9970). The packing densities are determined from the hydrodynamic diameters and the aggregation numbers; they vary between 6 and 32%. For large hydrophobic block lengths additional structures are found, in most cases with a narrow size distribution. The origin of these structures is discussed.

No abstract

Laser light scattering (LLS) was employed to monitor the microemulsion-like polymerization processes by using poly(methyl methacrylate)-b-poly(methacrylic acid) (P(MMA-b-MAA)) block copolymers with different block lengths (MMA58-b-MAA57, MMA67-b-MAA217, and MMA32-b-MAA69) or sodium dodecyl sulfate (SDS) surfactant as dispersants. A combination of static and dynamic light scattering techniques (SLS and DLS) was used to monitor the microemulsion-like systems before, during, and after polymerization. The polymerization of MMA (methyl methacrylate) was found to occur first in the dispersing aqueous medium, and then it was transferred inside the micellar cores to continue the polymerization process, which is similar to the homogeneous nucleation mechanism found when using small-molecule surfactants as dispersants. Depending on the hydrophobicity of the micellar cores, a rearrangement of micellar chains was found to take place during the different stages of the polymerization process. The similarities and differences of the dispersants between SDS surfactant micelles and P(MMA-b-MAA) block copolymer micelles are discussed. The polymerization of n-BA in micellar solution was also studied and compared with that of MMA.

No abstract

A new FFF method is presented which combines asymmetrical flow-FFF (AF4) and electrical FFF (ElFFF) in one channel to electrical asymmetrical flow-FFF (EAF4) to overcome the restrictions of pure ElFFF. It allows for measuring electrophoretic mobility (μ) as a function of size. The method provides an absolute value and does not require calibration. Results of μ for two particle standards are in good agreement with values determined by phase analysis light scattering (PALS). There is no requirement for low ionic strength carriers with EAF4. This overcomes one of the main limitations of ElFFF, making it feasible to measure proteins under physiological conditions. EAF4 has the capability to determine μ for individual populations which are resolved into separate peaks. This is demonstrated for a mixture of three polystyrene latex particles with different sizes as well as for the monomer and dimer of BSA and an antibody. The experimental setup consists of an AF4 channel with added electrodes; one is placed beneath the frit at the bottom wall and the other covers the inside of the upper channel plate. This design minimizes contamination from the electrolysis reactions by keeping the particles distant from the electrodes. In addition the applied voltage range is low (1.5-5 V), which reduces the quantity of gaseous electrolysis products below a threshold that interferes with the laminar flow profile or detector signals. Besides measuring μ, the method can be useful to improve the separation between sample components compared to pure flow-FFF. For two proteins (BSA and a monoclonal antibody), enhanced resolution of the monomer and dimer is achieved by applying an electric field.

No abstract

A semi-empirical blending rule for the components of the complex shear viscosity of homopolymer melts is shown to be valid over a broad range for unbranched polymers. The experimental results from the literature and the authors own data for PS, HDPE and polybutadiene agree reasonably with the results of the blending rule; this holds at least as long as the molecular weight ratio of the components does not exceed ten. The application of the blending rule totally fails for the extreme case of a star branched component at small frequencies of oscillation. The rule allows a convenient quantitative description of phenomena known from experience, e.g., (1) the admixture of high molecular weight components may drastically enhance elastic properties of the melt; (2) the admixture of low molecular weight polymer components eases processing without lowering the zero-shear viscosity too much, as e.g. plasticizers would do.