The segmental relaxation properties of a low molecular weight (4.6 kg/mol), cyclic polystyrene (PS) were characterized. The sample was obtained by fractionation using HPLC at the chromatographic critical condition, which yields a ring uncontaminated by its linear precursor. Both the glass temperature and the temperature dependence of the segmental relaxation times for the ring PS were equivalent to the high molecular weight limiting values for the linear polymer. These results are interpreted by considering the configurational mobility of a polymer lacking chain ends.

In the chromatographic separation of macromolecules with a porous stationary phase, the retention is determined by both size exclusion and interaction mechanisms. At the chromatographic critical condition, the effects due to the two separation mechanisms compensate each other, and the retention of homopolymer molecules becomes independent of molecular weight. Liquid chromatography at the critical condition has attracted much interest for the characterization of block copolymers since it might permit the characterization of individual blocks of a block copolymer by making one block chromatographically "invisible". In this study, we critically examine this method using two sets of styrene-isoprene block copolymers designed to have one block length constant while varying the other block length. For these block copolymer systems we found that a block cannot be made completely "invisible" at the critical condition of its homopolymer, and the retention of block copolymers is affected to some extent by the length of the "invisible" block under its chromatographic critical condition.

A two-component multiblock copolymer with undecablockstwo of them on both chain ends are long and nine of them are shortswas successfully prepared by anionic polymerization using the sixstep sequential monomer addition technique. Polymer components are polystyrene (S) and polyisoprene (I), its total molecular weight is 275K, and the overall S/I volume ratio is 0.70/0.30. Microphase-separated structure of the copolymer was observed by transmission electron microscopy and small-angle X-ray scattering, and it was confirmed that the copolymer forms a complex lamellar structure; its long period is 45 nm, which is composed of one thick lamellar domain formed by long polystyrene chains and I-S-I three thin lamellar domains, the length of the short period for I-S lamellae being about one-third of the longer period. This fact shows short block chains at the center favorably adopt a loop conformation over a bridge one. This unique lamellar structure having two length scales must be the first experimentally observed simple hierarchical structure for the block copolymer where the component polymers are connected by covalent bonds.

The synthesis of an H-shaped polybutadiene homopolymer as well as its detailed structural characterization is investigated. Anionic polymerization techniques together with chlorosilane linking agents were used for the production of the material. After each reaction step samples were taken and analyzed by size exclusion chromatography (SEC), membrane osmometry (MO), NMR, and temperature gradient interaction chromatography (TGIC). According to the characterization by SEC, MO, and NMR, the H-polymer showed a high degree of structural uniformity after purification by fractionation, and no significant amounts of differently branched byproducts could be detected. The TGIC analysis however revealed the presence of large amounts of structures, mainly with lower branching degree.We also found that a significant isotope effect exists in the TGIC retention between deuterated and hydrogenous polymers. In our case, where the H-polymer is partially deuterated, the TGIC analysis enabled us to resolve all the side products. Comparison of the different analysis methods indicates that the precise structural analysis of branched model polymers such as the H-polymer requires more sophisticated methods than used in the past.

The effect of molecular weight distribution on microphase-separated structures for both AB diblock and BAB triblock copolymers was investigated in comparison with that of composition distribution. Monodisperse poly(styrene-b-2-vinylpyridine) (SP) and poly(2-vinylpyridine-b-styrene-b-2vinylpyridine) (PSP) parent block copolymers were synthesized by living anionic polymerizations whose volume ratios were all designed to be 0.5/0.5. Three parent copolymers were blended variously with both number-average molecular weight and composition kept constant but having different molecular weight distribution. Microphase-separated structures of sample films obtained by solvent-casting followed by annealing were observed by transmission electron microscopy and small-angle X-ray scattering. It has been found that both SP and PSP block copolymers show simple lamellar structures even when the molecular weight distribution is relatively wide and that lamellar domain spacing increases with increase in polydispersity index of the blend system. Furthermore, the increment for PSP triblock is larger than that for SP diblock as was the result for the study on composition distribution. The microdomain expansion can be caused by the localization of polydisperse block chains in both phases, which was commonly observed for both the composition distribution system and the molecular weight distribution system.

ABSTRACT:Macrocyclic polystyrenes with various molecular weight were prepared by the reaction of linear polystyrene having two end vinyl groups and potassium naphthalenide as a coupling agent. Intermolecular side reactions produced higher molecular weight polycondensates and undesirable chain termination reactions also produced linear precursors in addition to the designed molecules. In order to isolate cyclic polymers from the ring closure reaction mixtures, preparative size exclusion chromatography (SEC) method was employed. The purity of SEC-fractionated cyclic polystyrenes was rigorously examined by liquid chromatography at the critical condition (LCCC) and interaction chromatography (IC). After SEC-fractionation, we obtained large amount of highly pure cyclic polymers, though high molecular weight cyclic polymers contain very small amount of linear precursor (< 5%). The purity and isotope effect on reversed-phase liquid chromatography (RPLC) were also rigorously investigated by preparing a deuterated cyclic polystyrene. [DOI 10.1295/polymj.37.506] KEY WORDS Cyclic Polystyrene / GPC Fractionation / LCCC / Isotope Effect / Cyclic macromolecules are of great interest in the investigation of the influence of cyclization on their solution, melt, and solid-state properties. Various physical properties of cyclic polymers have been predicted not only by theoretical methods 1-4 but also by computer simulation studies, 5-7 while they have also been examined experimentally. [8][9][10][11][12][13][14] Cyclic polymers were usually synthesized by the coupling reaction between living precursor polymers with functional groups on both ends and bifunctional linking agents. For example, polystyrenes 9,15-19 and poly(2-vinylpyridine)s 20,21 have been synthesized by this method. Furthermore, , !-heterobifunctional polymers have been used for the synthesis of cyclic polymers.22-24 However, side reactions produce linear precursor polymers, and intermolecular reactions simultaneously produce dimeric and higher molecular weight linear polycondensates. Therefore, it is very difficult to obtain pure cyclic polymers directly, and fractionation is necessary in order to obtain cyclic polymers with high purity. For the isolation of cyclic polymers from the ring closure reaction mixtures, two major fractionation methods have been employed: fractional precipitation method 9,14,[16][17][18] and preparative size exclusion chromatography (SEC). 25,26 Furthermore, liquid chromatography at the critical condition method (LCCC) has been successfully applied for the characterization of cyclic polymers.27-30 Throughout these experimental studies, however, the direct evidence of cyclic structure was not shown, in addition to the fact that the purity of the cyclic molecules has not been determined quantitatively in most of the works. Only for the low molecular weight cyclic polymers, the detailed cyclic structures were directly confirmed by NMR analysis of linking points, 22,23 pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 31 and matri...

Obesity is caused by an imbalance between caloric intake and energy expenditure and accumulation of excess lipids in adipose tissues. Recent studies have demonstrated that green tea and its processed products (e.g., oolong and black tea) are introduced to exert beneficial effects on lipid metabolism. Here, we propose that fermented green tea (FGT) extract, as a novel processed green tea, exhibits antiobesity effects. FGT reduced body weight gain and fat mass without modifying food intake. mRNA expression levels of lipogenic and inflammatory genes were downregulated in white adipose tissue of FGT-administered mice. FGT treatment alleviated glucose intolerance and fatty liver symptoms, common complications of obesity. Notably, FGT restored the changes in gut microbiota composition (e.g., the Firmicutes/Bacteroidetes and Bacteroides/Prevotella ratios), which is reported to be closely related with the development of obesity and insulin resistance, induced by high-fat diets. Collectively, FGT improves obesity and its associated symptoms and modulates composition of gut microbiota; thus, it could be used as a novel dietary component to control obesity and related symptoms.

In this study we fractionated polystyrene-block-polyisoprene diblock copolymers (PS-b-PI) prepared by anionic polymerization into fractions which have a narrower distribution in molecular weight as well as in chemical composition. The strategy was to use two-dimensional HPLC:  reversed phase HPLC to fractionate PI block and normal phase HPLC to fractionate PS block with a minimal effect of the other block. The working principle of the separation method was confirmed for a low molecular weight PS-b-PI (2.4 kg/mol). With the aid of matrix assisted laser desorption/ionization mass spectrometry, we found that the separation method could resolve each mer of the PS-b-PI. We extended the application to a high molecular weight diblock copolymer (24 kg/mol) and established the method as a promising tool to further fractionate block copolymers into molecular species better defined in molecular weight as well as in composition. We observed a significant variation in average molecular weight as well as in composition of the fractionated samples. These variations were large enough to show different morphologies for the fractions taken from the same mother block copolymer.