The solvent-free synthesis of allyl-substituted chitosan derivatives through reactive co-extrusion of chitosan powder with allyl bromide at shear deformation was performed. For the structural characterization, FTIR and NMR methods were employed. The results were confirmed by chemical analysis. The total content of allyl substituents from 5 to 50 per 100 chitosan units as a function of the component ratio in the reactive mixtures was revealed. Carrying out the reaction without any additives leads to the selective formation of N-alkylated derivatives, whereas in the presence of alkali the ethers of chitosan were preferentially formed. The results suggest that the proposed approach allows significantly higher yield of products to be obtained at high process speeds and significantly lower reagent consumption as compared with the liquid-phase synthesis in organic medium. The synthesized unsaturated derivatives are promising photosensitive components for use in laser stereolithography for fabrication of three-dimensional biocompatible structures with well-defined architectonics.

The blends of ground rubber tires (>50 wt%) and thermoplastics have been obtained under conditions of high temperature shear deformation and characterized. The elongation at break of the blends is higher than 100%.

Chitosan-g-oligolactide copolymers with relatively long oligolactide grafted chains of various stereochemical compositions have been synthetized via a solvent-free mechanochemical technique and tailored to fabricate three-dimensional hydrogels using two-photon induced microstereolithography. An effect of the characteristics of chitosan and oligolactide used for the synthesis on the grafting yield and copolymer’s behavior were evaluated using fractional analysis, FTIR-spectroscopy, dynamic light scattering, and UV-spectrophotometry. The lowest copolymer yield was found for the system based on chitosan with higher molecular weight, while the samples consisting of low-molecular weight chitosan showed higher grafting degrees, which were comparable in both the cases of l,l- or l,d-oligolactide grafting. The copolymer processability in the course of two-photon stereolithography was evaluated as a function of the copolymer’s characteristics and stereolithography conditions. The structure and mechanical properties of the model film samples and fabricated 3D hydrogels were studied using optical and scanning electron microscopy, as well as by using tensile and nanoindenter devices. The application of copolymer with oligo(l,d-lactide) side chains led to higher processability during two-photon stereolithography in terms of the response to the laser beam, reproduction of the digital model, and the mechanical properties of the fabricated hydrogels.

Biodegradable composites based on polylactide (PLA) and starch are obtained via solid‐phase mixing under conditions of shear deformation. The mechanical properties and biodegradability of composites under action of mold fungi as well as during exposure in soil are investigated. Using the scanning electron microscopy, the comparative study of the morphology of the initial samples and samples after biodegradation is carried out and the formation of structural defects resulting in sample destruction followed by fragmentation is revealed. The influence of PEG on mechanical properties and biodegradation process of the composites is shown. The analysis of composites by FTIR spectroscopy allows the estimation of the change in the PLA crystallinity and morphology of the film composites during the biodegradation in soil. The appearance of starch on the surface of films after exposure in soil enables a mechanism of biodegradation to be proposed.

Biodegradable composites of polysaccharides (cellulose, starch, and ethylcellulose) with low-density polyethylene (LDPE) and poly(ethylene oxide) (PEO) as well as composites of two polysaccharides (cellulose–chitin, cellulose–chitosan, starch–chitin, starch–chitosan) with LDPE were produced in a rotor disperser under conditions of shear deformation. Using various physicochemical (mechanical tests, FTIR-spectroscopy) and structural (SEM) methods, the properties and structure of obtained composites were studied. The investigation of the change in the fractional composition depending on the nature of third component has shown that the introduction of PEO leads to appearance of fraction with coarse particles, while the addition of second polysaccharides results in production of finely-dispersed powders. The comparison of the mechanical properties of binary and ternary composites has showed that the presence of third component leads to change in their characteristics. The investigation of sample biodegradability by three independent methods showed that the introduction of third component leads to a significant increase in the biodegradation as compared to the binary polysaccharide–LDPE composites studied earlier.

In medical and pharmaceutical applications, chitosan is used as a component of hydrogels-macromolecular networks swollen in water. Chemical hydrogels are formed by covalent links between the crosslinking reagents and amino functionalities of chitosan. To date, the most commonly used chitosan crosslinkers are dialdehydes, such as glutaraldehyde (GA). We have developed novel GA like crosslinkers with additional functional groups-dialdehyde derivatives of uridine (oUrd) and nucleotides (oUMP and oAMP)-leading to chitosan-based biomaterials with new properties. The process of chitosan crosslinking was investigated in details and compared to crosslinking with GA. The rates of crosslinking with oUMP, oAMP, and GA were essentially the same, though much higher than in the case of oUrd. The remarkable difference in the crosslinking properties of nucleoside and nucleotide dialdehydes can be clearly attributed to the presence of the phosphate group in nucleotides that participates in the gelation process through ionic interactions with the amino groups of chitosan. Using NMR spectroscopy, we have not observed the formation of aldimine bonds. It can be concluded that the real number of crosslinks needed to cause gelation of chitosan chains may be less than 1%.

Solvent-free N-allylation of chitosan with allyl bromide was performed under shear deformation in an extruder and the obtained chitosan derivatives were successfully used for the microfabrication of 3D structures by laser stereolithography.

In this study, two novel chitosan-graft-poly(vinyl alcohol) copolymers are synthesized and used as water-soluble at physiological conditions polycations for preparation of smart microcapsules. The microcapsules provide growth and proliferation of eight mammalian cell lines, including hybridoma and tumor cells, at long-term cell cultivation in vitro. The microcapsules are stable in cell culture medium but can be dissolved by changing pH value of the medium (up to 8.08.2), thus making possible a simple release of the entrapped cells. Monoclonal antibody production by encapsulated hybridoma cells is demonstrated. Cultivation of tumor cells within the microcapsules allows the formation of 3D multicellular spheroids, which can be proposed as an in vitro model for anticancer drug screening.

The mechanism of negative coefficient of thermal expansion (CUE) generation for non-stretched polyimide (PI) films is proposed in this work Negative CTE behavior was observed in some miscible binary blend films composed of a major fraction of a rod-like semi-crystalline PI derived from pyromellitic dianhydride (PMDA) with p-phenylenediamine (PDA) and flexible Pls based on 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) whereas homo PMDA/PDA PI film shows a considerably low but a positive CTE value. The results suggest that the negative CTE generation is related to not only a considerably high extent of in-plane orientation of the PMDA/PDA chains but also to the crystallinity of the blends. The present work revealed that some other Pls, a poly(ester imide), and a polybenzoxazole system also display negative CTE and these systems also possess extremely high extents of in-plane chain orientation without exception. In addition to CTE, the morphologies were monitored as a function of imidization temperature for two PI systems, PMDA/2,2'-bis(trifluoromethyl)benzidine and PMDA/m-tolidine by wide-angle X-ray diffraction, FT-IR spectroscopy, birefringence, and film density measurements. The results suggested that the negative CTE phenomenon occurs when PI films possess very high extents of in-plane orientation and a less crystalline morphology simultaneously, thereby significant thermal expansion can be allowed to the thickness direction. (C) 2010 Elsevier Ltd. All rights reserved.

Six poly(amic acid) (PAA) systems based on pyromellitic dianhydride (PMDA) formed some ordered structures with optical anisotropies clearly detectable on an optical polarizing microscope (POM) in N-methyl-2-pyrrolidone (NMP) at room temperature at high solute concentrations (15-25 wt.%) with complete sol-gel transition reversibility, whereas PAA systems based on 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) with a variety of diamine components showed no optical anisotropy in solution. However, a fluorescence probe technique combined with solution viscosity measurements suggested that a PAA derived s-BPDA with 1,4-phenylenediamine (PDA), i.e., PAA(s-BPDA/PDA) forms some ordered structure with a POM-undetectable very local scale during prolonged storage in NMP at room temperature. The introduction of the biphenyldiimide (BPDI) units at 33% into the PAA(s-BPDA/PDA) main chains by copolymerization allowed the formation of optically anisotropic gels with a smectic liquid crystal-like ordered structure by cooling the NMP solution at -20 degrees C. PI films derived from s-BPDA with PDA, i.e., PI(s-BPDA/PDA) were prepared upon thermal imidization of the BPDI-containing PAA films dried at 40 degrees C for 2.5 h. An increase in the BPDI content caused a gradual decrease in the linear coefficient of thermal expansion (CTE) of the PI films. This can be interpreted as a result of an intensified preorientation at the stage of the PAA cast films by incorporation of the BPDI units. When the BPDI-containing PAA solutions were heated at 70 degrees C for 4 min prior to the drying process at 40 degrees C, the ordered structures can be cancelled without imidization, and the CTE values of the resulting PI films appreciably increased compared to the case without heating at 70 degrees C. A similar effect was observed even in the BPDI-free original s-BPDA/PDA system. The results suggest the presence of a POM-undetectable very locally ordered structure in the PAA cast films, which promotes the pre-orientation of the PAA chains in the cast films and consequently can contribute to a further decrease in the CTE of the PI(s-BPDA/PDA) films. (C) 2009 Elsevier Ltd. All rights reserved.

Polyimide (PI) derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) with trans-1,4-cyclohexanediamine (CHDA), i.e., s-BPDA/CHDA was investigated from the viewpoint of ordered structure and intermolecular interaction. Thermodynamic parameters of the model compounds for melting behavior suggested significantly restricted conformational changes in the trans-1,4-cyclohexylene unit and the presence of strong BPDI—BPDI interaction in s-BPDA/CHDA. The effect of diamine structure on the fluorescence yield also supported the presence of the BPDI—BPDI interaction or the BPDI dimer in s-BPDA-based semi-cycloaliphatic PIs. The results of the fluorescence depolarization measurements can be rationalized by a proposed mechanism assuming the presence of the BPDI dimer sites, where the fluorescence of s-BPDA/CHDA occurs by excitation of the lower energy trap sites consisting of the BPDI dimer via excitation energy migration or direct excitation of the dimer. The structure-sensitive infrared band around 550 cm-1 gradually shifted toward higher frequency with simultaneous narrowing with increasing cure temperature, suggesting gradual ordered structure formation in s-BPDA/CHDA. Thermal imidization at 400 °C caused splitting of the C—H stretching band around 2940 cm-1, corresponding to the disappearance of distinct glass transition for the s-BPDA/CHDA system.

Polybenzoxazoles (PBO) are also expected as low-K & low-CTE dielectric materials as well as polyimides. High molecular weight PBO precursors, polyhydroxyamides (PHAs), were prepared from silylated bis(3-hydroxy4-amino)biphenyl(p-HAB) and dichlorides of terephthalic acid (TPA) or trans-1,4-cyclohexanedicarboxylic acid in DMAc/ITMPA in the presence of pyridine and LiCl. After precipitation of the PHA solution into water to remove the salts, it was difficult to re-dissolve into salt-free aprotic solvents. Therefore, the salt-containing PHA solution was cast on a glass plate and washed with water to remove salt, then the dried films fixed in a frame were heated at 400degreesC/1h to ensure complete transformation to PBO. The obtained PBO films showed a much lower K, a lower CTE and a higher Tg than the corresponding PIs. The use of a fluorine-containing bis(o-aminophenol) as a comonomer for the homo p-HAB/TPA system improved significantly the solubility into salt-free solvents. Another PHA derived from an isomer of p-HAB, bis(4-hydroxy-3-amino)biphenyl (m-HAB) and TPA also showed a high solubility. These new PBO systems made possible the convenient film formation process (cast-drying-thermal treatment like PI systems) for microelectronic applications. Simultaneously, these PBO films maintained comparatively low K values, considerable low CTEs, and high Tg's as in the homo p-HAB/TPA systems.

Complete N-acylation of chitosan has been achieved by treating with cyclic acid anhydrides in aqueous homogeneous media at pH 4 to 8. Some of the resulting N-(carboxy)acyl chitosans were successfully converted into the corresponding imido forms by thermal dehydration.