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Acylated derivatives of chitosan oligomers with a relatively high degree of polymerization (DP=4, 5, or 6) were synthesized and their mesophase properties were studied in comparison with those of the lower-DP homologues (DP=2 and 3) previously reported. By differential scanning calorimetry (DSC), all the compounds were found to show thermotropic mesomorphism in a temperature region below 150°C. The isotropization temperatures decreased with increasing DP, while the melting point remained at around 65°C, independent of DP. In addition to the narrowing of the mesomorphic region, the optical anisotropy as observed under a polarizing microscope remarkably decreased with increasing DP, indicating that the mesophase becomes less stable and ordered with an increase in DP. An X-ray diffraction analysis revealed that the tetramer as well as the dimer and trimer form a hexagonal ordered columnar phase (Dho), while the pentamer forms a disordered one (Dhd). On the other hand, the phase formed by the hexamer was not a columnar but a discotic nematic phase (ND). This is attributable to the highly anisotropic shape of the oligosaccharide core in the hexamer.

Mono- and Multilayer Langmuir-Blodgett Films of Cellulose Tri- n -alkyl Esters Studied by Transmission Electron Microscopy

The feasibilities of thin-layer chromatography as a tool to identify the chain architecture of given copolymer samples have been investigated. To this end, styrene—butadiene (SB) block copolymers with known chain architecture were prepared and used as reference samples. Preliminary TLC experiments on these samples indicated that the random, tapered, diblock and triblock SB-samples could be chromatographically distinguished from one another under suitable development conditions. By applying the procedures thus established, the chain architecture of various commercial SB-products could be identified without appreciable interference from the molecular weight and composition.

The copolymer of 1-chloro-1,3-butadiene (CB) and styrene (St) was synthesized and its composition and distribution in poly(CB-co-St) were investigated by thin-layer chromatography (TLC). The concentration gradient development method of a tetrahydrofuran–cyclohexane mixture was useful for separating the copolymer into its components. Resolution by molecular weight was not significant under the present conditions. The experimental results on the compositional distribution of poly(CB-co-St)s obtained at high conversion were in close agreement with the values calculated from the monomer reactivity ratios and conversion. Also, the composition of the copolymers having a CB content too small for ordinary elemental analysis to be applicable could be assayed by TLC. The observed CB content was below 1 mol%, and agreed well with that calculated.

Aqueous Gel-Permeation Chromatography of Electrolytes and Polyelectrolytes I. Effect of Electrolytic Nature of Gel

The binding of Cu(II) by keratin proteins extracted from wool in aqueous solution has been investigated by gel filtration and equilibrium dialysis in order to compare the binding data obtained by different methods. The gel filtration binding experiments were carried out on a Sephadex G-25 gel column using 0.05 M acetate buffer as eluent in a pH range of 4.5—6.5. The elution profiles of the Cu(II)–keratin complexes were classical at equilibrium Cu(II)–concentrations from 1 to 25 ppm in the range of pH from 4.5 to 5.5. It was found that if the elution profile is classical, reliable binding data can be obtained by gel filtration with a simple technique. On the other hand, at a higher pH of 6.5, anomalous elution profiles were observed; in addition to the classical peaks, a ghost peak with respect to the Cu(II)–concentration appeared. Different mechanisms proposed for the appearance of the ghost peak by other authors were tested but failed to explain the present data. However, it was experimentally proved that the gel filtration data agreed with those of equilibrium dialysis if the Cu(II) exhibiting the ghost peak was independent of the binding by protein.

The hypochromic effect in the UV spectra of polystyrene and styrene copolymers in solution was investigated in detail. For this purpose, isotactic and syndiotactic-rich polystyrenes as well as their dimer model compounds, 2,4-diphenylpentanes, and styrene-methyl methacrylate copolymers were prepared. UV absorption measurements were carried out in dioxane and tetrahydrofuran at various temperatures. The extinction coefficients of phenyl rings depended not only on the solvent and the temperature but also on the microstructure of the polymers. A discontinuous temperature dependence of the extinction coefficients was observed between 40 and 50°C for homopolystyrenes as well as their dimer model compounds. It was suggested that this might be explained in terms of the rotation of phenyl rings. On the other hand, the hypochromicity in binary copolymers appeared to depend strongly on the sequential arrangement of monomers (the chain architecture and the chemical composition of copolymers). The measured average extinction coefficients were well interpreted by a simple treatment by using triad probability proposed by Harwood. The results were discussed in relation to the UV spectrometer which is being used as an auxiliary detector in gel-permeation chromatography and microcolumn chromatography.

The Stereocomplex Formation in Poly(methyl methacrylate) and the Stereospecific Polymerization of Its Monomer