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Preferential solvation of polymer chains by molecules of the thermodynamically better component of the solvent mixture is a general phenomenon which affects properties of dissolved chains and has to be taken into account in the interpretation of results of methods for analysis and characterization of polymers. We have investigated (i) the effect of preferential solvation on vapor-pressure osmometry results in mixed solvents close to θ-conditions and (ii) the danger of formation of associates by coarse-grained computer simulations. The study shows that both effects are negligible and the measurements in mixed solvents can be safely performed. [ABSTRACT FROM AUTHOR]

Analytical temperature rising elution fractionation (TREF) of linear polyethylene (PE) samples with different densities was done in 1-chloronaphthalene using a gel permeation chromatograph (GPC) coupled with a gas chromatograph. The corrected peak elution temperatures completed the previously obtained data in trichlorobenzene, xylene, and dibutoxymethane. A mathematical correlation was found for diluted linear PE samples between the α parameter of the Mark-Houwink-Sakurada equation governing the retention time in GPC, the bulk melting temperature measured by differential scanning calorimetry (DSC), and the TREF peak elution temperature. The extrapolation to the melting temperature measured by DSC gives α = 0.5, thus confirming the hypothesis that polymer conformations in the melt are similar to those in a theta solvent. [ABSTRACT FROM AUTHOR]

Rotational Isomeric State (RIS) Metropolis Monte Carlo (RMMC) simulations of the conformational properties and chain dimensions of a series of chemically different poly(n-alkyl methacrylates) including poly(methyl methacrylate), poly(n-butyl methacrylate), poly(n-hexyl methacrylate), and poly(phenyl methacrylate), in the θ state were investigated, and (〈r2〉/M)1/2, (〈s2〉/M)1/2 and Cn were calculated and compared in order to obtain fundamental understanding of the influence of the chemical structure. Simulations were conducted for different molecular weights. Results obtained from the simulations are compared with experimentally obtained dimensions in the literature using the Mark-Houwink relationship as well as, in some cases, data available from direct determinations in θ solvents. Good agreement between simulation and experimental data was obtained. The backbone conformation is predominantly trans in these polymers. Increase in bulkiness and rigidity of the substituting acrylate side group results in an increase in trans and a decrease in gauche backbone conformer population. In the case of rotatable bonds in the side-group structure, increase in rigidity of the side group leads to a decrease in the trans population, although this effect is not uniformly observed. [ABSTRACT FROM AUTHOR]

Abstract: We report herein characteristic spreading behavior of amphiphilic block copolymer, polystyrene-block-poly(4-vinyl pyridine) (PS-P4VP) at the air–water interface. When the polymer was spread from cyclohexane, a theta solvent for PS and a poor solvent for P4VP, onto the air–water interface, an unexpected sharp temperature dependent change was observed in the surface pressure–area curves. In contrast, when non-theta solvents such as chloroform were used, only negligible temperature dependency was observed. In the cyclohexane solution, the aggregate size of the block copolymer strongly depends on the solution temperatures as revealed by dynamic light scattering measurements. The phenomena observed for cyclohexane should involve the coil-globule conformational transition taking place in the theta solvent. To our knowledge this work presents the first clear example that the aggregation state of polymers in solution is directly reflected to the two-dimensional spreading behavior at the air–water interface. [Copyright &y& Elsevier]

On-line two-angle (15° and 90°) light scattering measurements with a gel permeation chromatography for linear and branched polystyrene in tetrahydrofuran (a good solvent) and in trans-decalin (a theta solvent) were made and compared with data from a multi-angle light scattering detector and literature values. Theoretically, weight-average molecular weight and the radius of gyration Rg can be determined accurately in the range where Rg2k2 is less than 1.2 (rod)∼1.7 (random coil); here, k is the absolute value of the scattering vector for a right angle detector with the Berry square root method. Molecular weight dependence of the radius of gyration obtained from the two-angle light scattering detector for linear and branched polystyrenes under different thermodynamic conditions were measured and found to be almost the same as values measured with a multi-angle light scattering detector and literature values in the appropriate range of molecular weight. [Copyright &y& Elsevier]