Influence of degree of N-butyrylation on critical concentration of N-butyrylated chitosan/dichloroacetic acid liquid crystalline solution

Summary N-butyrylated chitosan with various degree of N-butyrylation (DB) were prepared by mixing completely deacetylated chitosan and butyric anhydride in mild condition without serious degradation and O-substitution. A standard curve to measure DB was obtained by plotting the infrared absorbance ratio of A₁₅₆₀/A₂₈₈₀ against the known DB (from 0%∼99%) of eight specimens. The influence of DB on the critical concentration C^* of N-butyrylated chitosan/dichloroacetic acid solutions required to form mesophase was investigated by optical method. A maximum C^* value appeared at medium DB. The effect was explained by the disordering of chain with medium composition ratio of the copolymer of glucosamine and N-butyryl glucosamine. Received: 13 September 2000/Revised version: 20 November 2000/Accepted: 22 November 2000     

Effect of degree of deacetylation of chitosan on the kinetics of ultrasonic degradation of chitosan

The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003     

紫外测定壳聚糖脱乙酰度方法的探讨

分别采用直接、一阶导数、多波长和双内标等4种紫外分光光度法测定壳聚糖的脱乙酰度,评价4种紫外测定方法,并与胶体滴定、电位滴定和氢核磁3种测定方法进行了比较。结果表明,采取上述紫外法测定壳聚糖脱乙酰度值均高于胶体滴定和氢核磁测定值。故准确测定高脱乙酰度壳聚糖的脱乙酰度,紫外法非首选方法。     

红外光谱法测定壳聚糖脱乙酰度

以碱量法为对比方法,考察了基于A1655／A3450和A1320／A1420的2种红外光谱计算壳聚糖脱乙酰度方法的准确性。结果表明,红外光谱法虽精密度低于碱量法,但基于A1655／A3450的红外测试结果与碱量法基本相吻合;基于A1320／A1420加的红外光谱计算结果略高于碱量法,与商家标注值相吻合,且不受样品含少量水、残酸或残碱的影响。红外光谱法是一种较为理想的壳聚糖脱乙酰度测定方法,同时采用A1655／A3450和A1320／A1420计算更利于得到准确的测定结果。     

Liquid‐crystalline behavior of chitosan in malic acid

This report describes how the degree of deacetylation and molecular weight of chitosan and the concentrations of sodium chloride and malic acid affect the formation of lyotropic chitosan liquid crystals. Chitosan samples of various degrees of deacetylation were prepared from β‐chitin that was isolated from squid pens. They were degraded by ultrasonic irradiation to various molecular weights. The critical concentrations forming chitosan liquid crystals were determined with a polarized microscope. A chitosan sample with a degree of deacetylation of 67.2–83.6% formed cholesteric lyotropic liquid crystals when it was dissolved in 0.37–2.59M malic acid. The critical concentrations increased with increasing degrees of deacetylation of chitosan. They decreased with increasing molecular weights or increasing concentrations of sodium chloride and malic acid. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mesomomorphism enhancement of modified side‐chain liquid‐crystalline polysiloxanes by copolymerization

The liquid‐crystalline (LC) monomer 4‐allyoxybenzoyloxy‐4′‐buthylbenzoyloxy‐p‐phenyl (M₁), whose LC phase appeared at lower temperatures, from 137 to 227°C, and the modified mesogenic monomer 4‐allyoxybenzoyloxy‐4′‐methyloxybenzoyloxy‐p‐biphenyl (M₂), whose LC phase appeared at higher temperatures, from 185 to 312°C, were prepared. A series of side‐chain LC polysiloxanes containing M₁ and M₂ were prepared by graft copolymerization. Their LC properties were characterized by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. The results show that the introduction of the modified mesogenic monomer M₂ into the polymeric structure caused an additional increase in the clearing point (isotropic transition temperature) of the corresponding polysiloxanes, compared with unmodified polysiloxanes, but did not significantly affect the glass‐transition temperature. Moreover, the modified polysiloxanes exhibited nematic phases as the unmodified polymer did. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1196–1201, 2005     

Studies on the effect of substitution degree on the liquid crystalline behavior of cyanoethyl chitosan

An alkali–chitosan method was employed to prepare cyanoethyl chitosan (CNCS) with different degrees of substitution (DS) from chitosan by controlling the reaction time. The effect of the DS (from 0.36 to 1.21) on the liquid crystalline behaviors of CNCS was investigated. The critical concentration and texture of CNCS liquid crystalline in dichloroacetic acid and formic acid showed no obvious dependence on the DS. However, increase of the DS could enhance the birefringence of liquid crystalline solutions under a polarized microscope, which implied improved liquid crystallinity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2057–2061, 2000     

壳聚糖脱乙酰度测定方法的总结与比较

测定壳聚糖脱乙酰度(DD)的方法主要分为三类:①光谱法:紫外、红外光谱和核磁法;②破坏样品法:色谱法、差示扫描量热和元素分析法;③滴定法:酸碱、电位和胶体滴定等方法。对壳聚糖脱乙酰度测定方法进行总结与比较,为研究者选择最佳的壳聚糖脱乙酰度测定方法提供理论依据。     

Thermal and morphological properties of thermotropic liquid‐crystalline copolyesters containing poly(ethylene terephthalate), 4‐hydroxyphenylacetic acid and main‐chain rigid aromatic units

Thermotropic liquid‐crystalline polymers (TLCPs) have aroused considerable interest due to their attractive properties as high‐performance materials. Significant research attention has been devoted to investigating the relationship among monomer structures, syntheses and end‐use properties of TLCPs. The study reported here concerns the preparation, characterization and melt spinning of novel copolyesters containing two different flexible units together with two different aromatic units in the polymer chains. A range of copolyesters based on p‐hydroxybenzoic acid (p‐HBA), m‐hydroxybenzoic acid, p‐hydroxyphenylacetic acid and poly(ethylene terephthalate) were synthesized. The liquid crystallinity, thermal properties and degrees of crystallinity of these copolyesters were investigated using hot‐stage polarized light microscopy, differential scanning calorimetry, thermogravimetry and wide‐angle X‐ray diffraction. Copolyester fibres were characterized using scanning electron microscopy. The copolyesters were melt‐processable, thermally stable and could be processed above their melting temperatures without degradation. The degree of crystal structure was found to depend upon the content of p‐HBA. The fibres prepared showed that polymer chains had a well‐developed fibrillar structure. Novel TLCPs containing flexible units in the main chain were synthesized and characterized. Copolyesters containing p‐HBA units ranging from 55 to 70 mol% exhibited phase‐separated liquid‐crystalline morphology, appropriate melting temperatures and high thermal stability for melt processing. Copyright © 2010 Society of Chemical Industry     

Main‐chain liquid‐crystalline ionomers bearing potassium sulfonate groups

A series of thermotropic main‐chain liquid‐crystalline (LC) ionomers were prepared, which contained potassium sulfonate groups pendent to the chains. The polymers were prepared in an esterifying reaction with potassium ion contents ranging between 0 and 3.9 wt %. The content of potassium ion was characterized by spectrophotometric analysis with sodium tetraphenylboron as the titrant. Chemical structures were determined by various experimental techniques including Fourier transform IR spectroscopy and ¹H‐NMR. LC properties were characterized by differential scanning calorimetry, polarizing optical microscopy, and X‐rays. All of the polymers displayed nematic or smectic mesophases. With increasing potassium sulfonate ionic concentration in the polymers, the melting temperatures and isotropic transition temperatures changed little, whereas the temperature of the smectic A–nematic phase transition increased. The ionic aggregation was tangled with the rigid mesogenic groups of LC segments to form multiple block domains, leading the soft main chains to fold and form a lamellar structure due to their electrostatic interactions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2021–2026, 2005     

Thermotropic liquid‐crystalline polyphosphate esters containing phenolphthalein moiety

A new series of thermotropic liquid‐crystalline (LC) polyphosphate esters containing phenolphthalein as a part of their mesogen has been synthesized by a solution polycondensation method. The even‐numbered methylene spacers were varied from 2–10, and ethyl phosphate was used as a phosphorus heterogeneity. Thermal analysis showed that these polymers are stable up to 275–342°C with high char yield. All of the polymers exhibited liquid‐crystalline properties except for Polymers I and VI. Differential scanning calorimetry (DSC) confirmed the mesophase formation of the polymers. The glass transition temperature (T_g) and melting temperature (T_m) of the polymers were considerably low. A polymer containing phenolphthalein alone as a rigid segment with decamethylene spacers was also synthesized, but it did not show birefringent melt properties. These results reveal that phenolphthalein alone cannot act as a mesogen, whereas phenolphthalein phenylester can. Molecular modeling studies and conformational analysis confirmed that the steric hindrance of phenylester and the conjugation effect could explain the promotion of mesogenic behavior by phenolphthalein phenylester. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 194–200, 2004     

Influence of fillers on the mechanical response of an amorphous liquid‐crystalline polymer

A semirigid and amorphous commercial liquid‐crystalline copolyester (Rodrun) was filled with mica and calcium carbonate (up to 25 wt %) by direct injection molding. The fillers led to decreases in the processability, as observed by torque increases, but maintained the thermal resistance of Rodrun. The effects of the two fillers on the modulus of elasticity, ductility, and tensile strength were the same or very similar. The decrease in the tensile strength (20% for a 10% filler content) was compensated by a generally slight increase in the modulus of elasticity, whatever the filler content was. This balance of properties found in these new liquid‐crystalline‐polymer‐based materials and the important savings that the fillers bring may spread the applications of these materials' matrices. © 2003 Wley Periodicals, Inc. J Appl Polym Sci 88: 998–1003, 2003     

Electrical conductivity modeling of carbon‐filled liquid‐crystalline polymer composites

Electrically conductive resins are needed for bipolar plates used in fuel cells. Currently, the materials for these bipolar plates often contain a single type of graphite powder in a thermosetting resin. In this study, various amounts of two different types of carbon, carbon black and synthetic graphite, were added to a thermoplastic matrix. The resulting single‐filler composites were tested for electrical conductivity, and electrical conductivity models were developed. Two different models, the Mamunya and additive electrical conductivity models, were used for both material systems. It was determined how to modify these models to reduce the number of adjustable parameters. The models agreed very well with experimental data covering a large range of filler volume fractions (from 0 to 12 vol % for the carbon black filled composites and from 0 to 65 vol % for the synthetic graphite filled composites) and electrical conductivities (from 4.6 × 10^?17 S/cm for the pure polymer to 0.5 S/cm for the carbon black filled composites and to 12 S/cm for the synthetic graphite filled composites). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3293–3300, 2006     

Synthesis and thermotropic liquid‐crystalline behavior of novel main‐chain poly(aryl ether ketones)

Novel aromatic poly(ether ketones) containing bulky lateral groups were synthesized via nucleophilic substitution reactions of 4,4′‐biphenol and (4‐chloro‐3‐trifluoromethyl)phenylhydroquinone (CF‐PH) with 1,4‐bis(p‐fluorobenzoyl)benzene. The copolymers were characterized by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, and polarized light microscopy observation. Thermotropic liquid‐crystalline behavior was observed in the copolymers containing 40, 50, 60, and 70 mol % CF‐PH. The crystalline–liquid‐crystalline transition [melting temperature (T_m)] and the liquid‐crystalline–isotropic phase transition appeared in the DSC thermograms, whereas the biphenol‐based homopolymer had only a melting transition. The novel poly(aryl ether ketones) had glass‐transition temperatures that ranged from 143 to 151°C and lower T_m's that ranged from 279 to 291°C, due to the copolymerization. The polymers showed high thermal stability, and some exhibited a large range in mesophase stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1347–1350, 2003     

Synthesis and characterization of side‐chain liquid‐crystalline polyacrylates containing azobenzene moieties

Syntheses of novel liquid‐crystalline polymers containing azobenzene moieties were performed by a convenient route with an acrylate backbone. The azobenzenes were key intermediates of the monomers, and side‐chain liquid‐crystalline polymers were prepared, that is, poly[α‐{4‐[(4‐acetylphenyl)azo]phenoxy}alkyloxy]acrylates, for which the spacer length was 3 or 11 methylene units. In addition, poly[3‐{4‐[(3,5‐dimethylphenyl)azo]phenoxy}propyloxy]acrylate was prepared with a spacer length of 3 methylene units. The structures of the precursors, monomers, and polymers were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR techniques. The polymers were obtained by conventional free‐radical polymerization with 2,2′‐azobisisobutyronitrile as an initiator. The phase‐transition temperatures of the polymers were studied with differential scanning calorimetry, and the phase structures were evaluated with a polarizing optical microscopy technique. The results showed that two of the monomers and their corresponding polymers exhibited nematic liquid‐crystalline behavior, and one of the monomers and its corresponding polymer showed smectic liquid‐crystalline behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2653–2661, 2002     

The effect of reaction time and temperature during heterogenous alkali deacetylation on degree of deacetylation and molecular weight of resulting chitosan

The objective of the study is to elucidate the effect of reaction time and temperature during heterogenous alkali reaction on degree of deacetylation (DD) and molecular weight (MW) of the resulting chitosans, and to establish the reaction conditions to obtain desired DD and MW chitosan products. Chitin was extracted from red shrimp process waste. DDs and MWs were determined by infrared spectroscopy (IR) and static light scattering, respectively. The results are as follow: The DD and MW of chitin obtained were 31.9% and 5637 kDa, respectively. The DD of the resulting chitosan increased along with reaction time and/or reaction temperature. The DDs of the resulting chitosan that were obtained from 140°C were higher than those reacted at 99°C. The highest DD of the resulting chitosans after alkali deacetylation at 99 and 140°C were 92.2 and 95.1%, respectively. The DDs of chitosans increased fast at the beginning of reaction process then slowed over time. The reaction rate and rate constant of the deacetylation reaction decreased with increasing DD of the reactant. The MWs of chitosans decreased along with the deacetylation time. MW of those chitosans reacted at 140°C are smaller than those at 99°C. The rate of chitosan degradation was above 43.6%/h in the initial stage, then decreased to about 20%/h. The degradation rate constants raised substantially in the late stage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2917–2923, 2003     

Synthesis and characterization of side‐chain cholesteric liquid‐crystalline polysiloxanes containing different space groups

A series of liquid‐crystalline (LC) polysiloxanes were synthesized by two different cholesteric monomers, cholest‐5‐en‐3‐ol(3β)‐10‐undecenoate and cholesteryloxycarbonylmethyl 4‐allyloxybenzoate. The chemical structures and LC properties of the monomers and polymers were characterized by various experimental techniques, including Fourier transform infrared spectroscopy, ¹H‐NMR, elemental analysis, differential scanning calorimetry, and polarized optical microscopy. The specific rotation absolute values increased with increasing rigid spacers between the main chain and the mesogens. All of the polymers exhibited thermotropic LC properties and revealed cholesteric phases with very wide mesophase temperature ranges. With a reduction in the soft‐space groups in the series of polymers, the glass‐transition temperature and the isotropic temperature increased slightly on heating cycles. Reflection spectra of the cholesteric mesophase of the series of polymers showed that the reflected wavelength shifted to short wavelengths with decreasing soft‐space groups in the polymers systems, which suggested that the helical pitch became shorter with increasing rigid‐space groups. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Toughening liquid‐crystalline polymers with polyethylenes containing epoxy functionality

To improve toughness, a liquid‐crystalline polymer (LCPs) was blended with polyethylenes containing epoxy functionality in concentrations of 2, 6, and 15 wt %. The blends were prepared with a corotating twin‐screw extruder and were injection‐molded into specimens for mechanical testing. The effect of the amount of the epoxy‐functionalized polyethylenes on the morphology and mechanical and thermal properties was studied. The toughness improved with increasing amount of functionalized polyethylene, and the blend containing 15 wt % epoxy‐functionalized polyethylene had the best toughness properties. Impact strength values up to three times higher than those of the neat LCP were achieved. However, the stiffness of the LCP concurrently decreased substantially. The morphology became much more uniform, and the melting behavior changed. The results show that considerable improvements in the toughness properties of LCPs can be achieved with epoxy‐functionalized polyethylenes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1886–1891, 2002     

Effects of the molecular weight and the degree of deacetylation of chitosan oligosaccharides on antitumor activity

Effects of the degree of deacetylation (DDA) and the molecular mass of chitosan oligosaccharides (CTS-OS), obtained from the enzymatic hydrolysis of high molecular weight chitosan (HMWC), on antitumor activity was explored. The DDA and molecular weights of CTS-OS were determined by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-TOF MS) analysis. The CTS-OS were found to be a mixture of mainly dimers (18.8%), trimers (24.8%), tetramers (24.9%), pentamers (17.7%), hexamers (7.1%), heptamers (3.3%), and octamers (3.4%). The CTS-OS were further fractionated by gel-filtration chromatography into two major fractions: (1) COS, consisting of glucosamine (GlcN)(n), n = 3-5 with DDA 100%; and (2) HOS, consisting of (GlcN)(5) as the minimum residues and varying number of N-acetylglucosamine (GlcNAc)(n), n = 1-2 with DDA about 87.5% in random order. The cytotoxicities, expressed as the concentration needed for 50% cell death (CC(50)), of CTS-OS, COS, and HOS against PC3 (prostate cancer cell), A549 (lung cancer cell), and HepG2 (hepatoma cell), were determined to be 25 μg·mL(-1), 25 μg·mL(-1), and 50 μg·mL(-1), respectively. The HMWC was approximately 50% less effective than both CTS-OS and COS. These results demonstrate that the molecular weight and DDA of chitosan oligosaccharides are important factors for suppressing cancer cell growth.     

Investigation of different natural sources of chitin: influence of the source and deacetylation process on the physicochemical characteristics of chitosan

Several sea sources for chitin have been investigated, and the chitin content and crystallographic polymorph of the extracted chitin determined. Deacetylation of the chitin was carried out and the physicochemical characteristics of the resulting chitosan studied. The influence of the reaction parameters (reaction duration, temperature, nature of alkaline reagent, etc) was followed. Thus it became possible to determine adequate reaction conditions for obtaining chitosans with the required properties. The physicochemical characteristics of the obtained chitosan are closely related to the taxonomy of the source. New sea sources for chitin have been investigated and considered for industrial purposes. © 2000 Society of Chemical Industry