Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Studies on the glass transition temperature (Tg) of chitosan are difficult to pursue because of the difficulty in sample preparation and the hydroscopicity of samples. There are a few works concerning this principal relaxation of chitosan. Among them, several quite different values (150℃, 161℃, and 203℃) have been reported. In this paper, the Tg of chitosan (140～150℃) was determined by means of four techniques, namely, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermally simulated current spectroscopy (TSC), and dilatometry (DIL). DSC measurement has been assumed not to be sensitive enough to detect the relaxation temperature of polysaccharides. We propose a new method to improve the sensitivity of the DSC measurement. After a physical aging treatment of samples, the transition in DSC traces became much more distinct because of the enthalpy relaxation. This technique was also used to distinguish the Tg from other relaxations. The Tg of chitosan with different degree of deacetylation (D.D.) was examined by DSC. No influence of D.D. on Tg was found.

Two chitooligosaccharide samples (COS1 and COS2) were prepared by enzymatic degradation of chitosan. The molecular weight of the main component was determined by mass spectrometry to be 2340 and 4303, respectively. They showed cholesteric liquid crystal structures in concentrated solutions. The critical concentrations to form a lyotropic liquid crystalline phase in formic acid were measured by means of polarized optical microscopy, refractometry and Fourier transform infrared spectroscopy. The results from the three methods agreed with each other. The experimental value of COS2 was quantitatively consistent with that calculated according to Khokhlov and Semenov theory. But the experimental value of COS1 diverged from the theoretical one, which is explained by the inaccuracy at higher concentrations of the second virial approximation underlying this theory.

合成了氮上完全取代的邻苯二甲酰化壳聚糖（PhthCS）。用DSC研究了PhthCSPDMSO液晶溶液的热致相转变。偏光显微镜和DSC测定都表明临界浓度为43wt%。在浓度高于43wt%的溶液的DSC曲线中观察到了除了液晶-各向同性液体转变（清亮点）外还有一个明显的凝胶-溶胶转变，凝胶-溶胶转变温度和转变焓均比文献报道的不规则取代的N-邻苯二甲酰化-O-乙酰化壳聚糖大得多，可见取代的规整性对凝胶-溶较转变有很大的影响。根据DSC研究结果绘制了PhthCSPDMSO体系的相图。

The influence of concentration on the helicoidal change of N-phthaloylchitosan (PhCh) solutions in Me2SO, DMAc and DMF was investigated by means of circular dichroism (CD). The critical concentrations to form liquid crystal phase in these three solvents were 43, 45 and 48wt%, respectively as measured with polarized optical microscope. There were two kinds of CD peaks, sharp peaks with absorption maximum at about 330nm induced by the helical conformation of molecular chain, and very broad peaks covering almost whole visible region induced by the cholesteric helix of mesophase. The later only appeared in concentrated solutions with the concentration higher than the critical concentration. The handedness of both levels of helicoidal structures changed from left-to right-handed with the increase of concentration for PhCh/Me2SO solutions. The chirality transfer occurred between these two chiral levels. For PhCh/DMAc and PhCh/DMF systems, only the handedness of helical conformation reversed, but the cholesteric helix did not change. As a method to measure critical concentration, CD is more sensitive than polarized optical microscopy (POM).

ia evaporation procss. The crystalline morphology of these films was investigated by means of ploarized optical microscopy and scanning electron microscopy. Normal spherulites with a low growth rate formed in the casting films. The different morphologies of spherulite appeared in the filims cast from the solutins with diiferent concentration. After further crystallizing for a few days, the spherulites were decorated by thousands of needlelike extended-chain crystals, which had a typical size of ～50μm(length)×2～5μm(lenght)×1～2μm(width)×1～2μm(height) in the fringe part of the spherulite. The real concentration for crystallization was dedtermined solution.

A selectively side-modified chitosan derivative, N-phthaloyl chitosan (PhthCs), was prepared. Five techniques, including circular dichroism (CD) spectropolarimetry, ultraviolet-visible (UV-vis) spectroscopy, small-angle light scattering (SALS), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), were simultaneously applied to investigate the order-disorder phase transition for the lyotropic PhthCs/dimethyl sulfoxide system. POM observations suggested that the critical concentration was 48w%, which agreed well with the DSC measurements. A four-leaf SALS picture was recorded in biphasic solutions. The four-leaf type became a circular symmetric scattering picture with a further increase in the concentration. A sharp peak at 330 nm was recorded in dilute isotropic solutions with CD measurements. The sharp peak turned into a broad tailed peak from 330 to 800nm after the phase transition occurred. The sharp peak was induced by a chromophore (phthoyl group). The broad peak was attributed to the formation of short-range-ordered organization in the concentrated solutions. In UV-vis studies, when the system varied from isotropic to anisotropic, the absorption band turned into platform. These five techniques were proven to be feasible methods for measuring the phase transition of cholesteric liquid crystals.

Hydroxypropyl chitosan (HPCS) with different degree of molar etherification (DME, from 0.6 to 6.0) were synthesized and characterized by FTIR, 1H-NMR and elemental analysis. The effect of DME on critical concentration forming lyotropic liquid crystal (C*) was investigated in three solvents (formic acid, dichloroacetic acid and water). C* increased as DME raised but presented a platform at low DME (less than about 2.6), which was explained based on both the amount and the size of flexible substituents. HPCS with DME ≥3.2 were water soluble. C* of HPCS aqueous solutions were evidently lower than those of formic acid or dichloroacetic acid solutions. Typical cholesteric texture appeared in HPCS solutions of all three solvents at proper concentrations.