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The critical adsorption point (CAP) of linear and star-shaped polymers was investigated by normal phase and reversed phase liquid chromatography (NPLC and RPLC) and computer simulation. Three sets of polystyrenes (PS) differing in chain architecture and chemically distinct groups were prepared: linear PS (sec-butyl and hydrogen end group), 2-arm PS (linear, two sec-butyl end groups and one silyl group in the middle of the chain) and 4-arm star-shaped PS (four sec-butyl end groups and one silyl group in the center of the star). It was found that the column temperature at CAP, TCAP (linear PS) = TCAP (2-arm PS) > TCAP (4-arm PS) in both RPLC and NPLC which can be attributed to the variation in chain architecture. However, the elution times at CAP of three polymers are all different: In NPLC, tE,CAP (linear) > tE,CAP (2-arm PS) > tE,CAP (4-arm PS) while in RPLC, tE,CAP (4-arm PS) > tE,CAP (2-arm PS) > tE,CAP (linear). The variation of tE,CAP can be explained by the contribution of the chemically distinct groups. The computer simulation results are in good agreement with the chromatography experiments results and support the interpretation of experimental data. [ABSTRACT FROM AUTHOR]

Temperature programming has been used increasingly in liquid chromatography in recent years. In particular, temperature gradient elution has shown great potential in the analysis of complex polymers. In this study, the polymer retention behavior in temperature gradient interaction chromatography is investigated based on thermodynamic consideration of the retention factor. The polymer retention predicted by the model calculation is in good agreement with the experimental results, and the model allows devising a temperature program for designed retention behaviors such as a linear dependence of retention volume on log(molecular weight) of polymers. In addition, the migration behavior of polymeric solute along the separation column can be simulated, which shows strong molecular weight dependence. The migration behavior is also confirmed experimentally by employing different length columns or delayed injection. [ABSTRACT FROM AUTHOR]

Presents the characterization of poly(L-lactide)-block-poly-(ethylene oxide)-block-poly(L-lactide) triblock copolymers by liquid chromatography. Retention of liquid chromatography at the critical condition; Separation of mechanism of block copolymer.

Discusses the single-solvent liquid chromatographic critical condition for polyisoprene. Absence of the chromatographic invisibility of polystyrene-polyisoprene diblock copolymers under the critical condition; Effect of the length of the block copolymers on the chromatographic retention of the block.

The article offers information on a newly found epitaxial phase transition path between the hexagonally packed cylinder (HEX) and double gyroid (DG) structure, studied in block copolymers or in micelles. Thin film on a silicon wafer substrate was used, in which {121}dg planes orient parallel to the substrate plane after thermal annealing without applying any external field. A three dimensional transmission electron microphotography image of the transitional structure was obtained.

The small, well-characterized hammerhead ribozyme has served as a useful model for understanding the catalytic activity of RNA for the last two decades. A wealth of biochemical data was brought into focus by a series of X-ray crystallographic structures, and a full picture of this remarkable molecule is still evolving as new information is discovered. Because the exact location of metals in solution can be difficult to identify with certainty, particularly the biologically ubiquitous magnesium, the full scope of metal binding to RNA is not yet defined.

Temperature gradient interaction chromatography (TGIC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were applied for the characterization of highly branched polystyrenes (PS) prepared by linking living polystyryl anions using 4-chlorodimethylsilylstyrene. Reversed-phase (RP)-TGIC showed an unexpectedly high resolution according to the number of branches despite significant overlap of the molecular weight as confirmed by MALDI-TOF MS. The enhancement of the resolution is ascribed to the contribution of the nonpolar groups in the branched PS: the dimethylsilyl groups in the branching unit as well as the sec-butyl initiator groups. As the number of branches increases, the number of nonpolar groups increases, which in turn increases the RP-TGIC retention synergistically with increasing molecular weight. In contrast, a poorer resolution was found in normal-phase-TGIC, in which the nonpolar groups reduce the retention. The resolution in RP-TGIC appears superior to that of liquid chromatography at the chromatographic critical condition (LCCC) of PS. It is seemingly due to the synergistic contribution of the incremental PS molecular weight to the functionality in the branched PS in RP-TGIC while only the functionality contributes to the separation in LCCC. This type of resolution enhancement could be utilized efficiently for the analysis of highly branched polymers such as dendrimers or hyperbranched polymers. [ABSTRACT FROM AUTHOR]