Synthesis and characterization of novel curcumin based polyurethanes varying diisocyanates structure

In this research work, novel polyurethanes (PUs) based on blends of curcumin/1,4-butane diol (BDO) by varying the structure of diisocyanates were prepared following step growth polymerization. Structural study of blends and various diisocyanates based PU through Fourier Transform Infrared (FTIR) spectroscopy confirmed the incorporation of curcumin into the backbone of the PU. The scanning electron microscopic (SEM) study confirmed the well dispersion of incorporated curcumin and homogeneity of surface of synthesized samples. The SEM results also indicated that surface morphology of synthesized samples much dependent on diisocynates structure. Moreover SEM images inferred that phase separation is more pronounced in aromatic diisocyanate based PU. The anti-bacterial and anti-fungal tests were performed against different strains in order to determine the biocompatibility of the curcumin based PU. The antimicrobial activity results revealed that the material having aromatic diisocyanate are more biocompatible than the aliphatic diisocyanates in the PU structure. On the whole, this work is actually a step towards the generation of novel biocompatible materials preferably useful for biomedical applications.     

Synthesis and characterization of formal-group-containing diisocyanates and polyimides therefrom

Four new formal-group-containing diisocyanates, namely, bis(3-isocyanatophenoxy) methane, bis(4-isocyanatophenoxy)methane, bis[2-(3-isocyanatophenoxy)ethyl] formal, and bis[2-(4-isocyanatophenoxy)ethyl] formal, were synthesized by the Curtius rearrangement from the corresponding dicarboxylic acids. The diisocyanates were polycondensed with pyromellitic dianhydride (PMDA) and benzophenonetetracarboxylic dianhydride (BTDA) in dimethylacetamide (DMAc) to obtain formal-group-containing polyimides. These polyimides were characterized by viscosity measurements, IR spectroscopy, X-ray diffraction, and thermogravimetric analysis.     

Probing the degree of crosslinking of a cellulose based superabsorbing hydrogel through traditional and NMR techniques

The network structure of a cellulose-based superabsorbing material has been probed by using three different techniques: ¹³C solid state NMR, free swelling in water and uniaxial compression of water swollen samples. A good agreement between the three apporaches has been found in terms of concentration of crosslinks per unit volume.The results have been discussed taking into account that NMR technique is able to detect only chemically effective crosslinks while free swelling and compression are sensitive to elastically effective physical and chemical crosslinks.A depression of swelling capacity and an apparent increase of degree of crosslinking with time, promoted by ageing of the cellulosic material, has been experimentally evidenced and discussed in terms of development of intermolecular physical interactions.     

Adsorption of hexavalent chromium on cationic starches with different degree of crosslinking

The influence of the degree of crosslinking in the association with the degree of cationization on the adsorption of Cr(VI) by crosslinked cationic starches (CCS) was examined. The amount of adsorbed Cr(VI) depends on the preparation of CCS before adsorption experiments (dry or preswollen CCS) and has a higher value when dry CCS are used. The amount of crosslinks in CCS needed to reach the maximum effectiveness of the cationic groups of CCS in the binding of Cr(VI) depends also on the form in which CCS are used. The adsorption capacity for Cr(VI) decreases both with dry and preswollen CCS when the adsorption temperature increases. The thermodynamic parameters are calculated. The negative values of ΔG° and ΔH° indicated that the adsorption process in both cases was spontaneous and exothermic. If preswollen CCS is used, the entropy change has a positive value and indicates that the randomness of the system increases, whereas the negative value of entropy change when Cr(VI) species are adsorbed by dry CCS shows that in this case the order of the system increases like in the classical adsorption process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physicochemical and catalytic properties of Zr-pillared montmorillonite with varying pillar density

Preparation, characterization and catalytic activity of Zr-pillared clays with different pillar density, starting from Ni²⁺ exchanged clay, are described. The physicochemical characteristics of the pillared clays have been evaluated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared (IR), UV–visible diffuse reflectance spectroscopy (UV–VIS-DRS) and sorptometric studies. The decrease in the cation exchange capacity (CEC) of the Ni²⁺ exchanged clay depends upon the pretreatment temperature. The migration of the Ni²⁺ ions into vacant octahedral sites was observed in IR spectroscopy. The acidity of the pillared clays was calculated from TG analysis of the adsorbed n-butyl amine. Alkylation of phenol with methanol was carried out over these catalysts. Good correlation was observed between the alkylation activity and acidity of the pillared materials. Both O and C-alkylation was observed during the reaction. The pillared materials with lesser pillar density were found to be more selective towards anisole which can be attributed to the control in acidic properties of the materials.     

Effects of multifunctional crosslinking agents on the thermomechanical properties of polyimide Films

Four new poly functional amines were synthesized. Polyimide films containing varying amounts of the amine crosslinking agents were prepared. Their thermomechanical properties were compared with those of control film samples prepared from difunctional amines. The effect of crosslink density on isothermal weight loss, polymer softening, and glass transition temperature is discussed.     

聚酰亚胺微球掺杂纳米二氧化硅的制备及表征

以4,4’-二氨基二苯醚和均苯四甲酸二酐作为单体,采用非水乳液体系,加入纳米二氧化硅,制备聚酰亚胺微球.本文研究了纳米二氧化硅对聚酰亚胺热性能以及球形形貌、粒径大小的影响.通过红外分析(IR)、热重(TGA)、示差扫描(DSC)、电镜(SEM)、粒度等手段对其进行表征.表征结果显示当纳米SiO2的加入量为0.2g时,此时改性后的聚酰亚胺微球球形形貌良好,粒子表面光滑,呈单分散性,粒径为28.4μm,且失重率为5％时,其在氧气气氛下分解温度高达508℃,呈现高耐热性.     

交联度对交联羧甲基淀粉性能的影响

以玉米淀粉为原料,以环氧氯丙烷为交联剂,制备交联淀粉(CS),以高、中、低三种交联度的CS为原料,以氯乙酸为醚化剂,制备不同取代度的交联羧甲基淀粉(CCMS),分析其理化性能、吸附性能。结果表明,交联度相同时,随着取代度的增大,CCMS的透明度、溶解度和膨胀力均增大,吸附量提高;取代度相同时,CCMS的透明度、溶解度和膨胀力随着交联度的增加而减小,吸附量呈上升趋势可以改善其再生性能。     

Measurement of crosslinking degree for electron beam irradiated block copolymers

The molecular weight between crosslinking junctions (Mc) of styrene-butadiene-styrene (SBS) and that of styrene-isoprene-styrene (SIS) irradiated by electron beams (5 Mrad to 100 Mrad) was measured by dynamic modulus, glass transition temperature, static modulus, and swelling. The change in dynamic modulus at low temperature was smaller than that at high temperature in both SBS and SIS. The shift of Tg to higher temperature was observed in both SBS, and SIS systems except for 100 Mrad of SIS. Both dynamic and static moduli increased with irradiation doses, however, the change of static modulus was smaller than that of dynamic one. Those mechanical measurements were compared with the swelling measurements and discussed.     

Synthesis and characterization of magnetorheological polyimide gels

Magnetorheological polymer gels (MRPGs) are composite fluids containing ferrous particles suspended in a polymer gel. In addition to modification of the carrier fluid, the polymer gel, which includes crosslinked copolyimide (CCPI) and solvent N‐octylpyrrolidone, also changes the surface properties of the ferrous particles, thus reducing the particle settling and improving particle redispersion. The viscosity of MRPGs can be easily adjusted by controlling the concentration of CCPI in the carrier medium. High thermally resistant CCPI is synthesized from dianhydride, diamine, diaminobenzonic acid, and crosslinker and has a high glass transition temperature because the crosslinking ratio can be controlled by the molar ratio of diamine to diaminobenzonic acid. The redispersion and rheological properties are also investigated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2402–2413, 2005     

Synthesis,crosslinking, and characterization of energetic polymers through the azidification of glycidyl ether prepolymers

Low‐molecular‐weight atactic poly(propylene oxide) and poly(epichlorohydrin) (PECH) were chlorinated on average up to 4.42 chlorine atoms per repeat unit. A study of the products showed that chlorine substitution preferentially occurred on already chlorinated repeat units, yielding chlorine ‐rich and chlorine ‐poor sequences. As the extent of chlorine substitution increased, the glass‐transition temperature of the polymers markedly increased, and their solubility in most of the organic solvents drastically decreased. The chlorinated polymers were azidified with NaN₃ in dimethyl sulfoxide solutions. An analysis showed that azide groups replaced 99.8–99.9% of the initially present chlorine atoms. As the azide content of the samples increased, initially opaque polymers become dark brown, and their solubility increased in water but decreased in organic solvents. Samples with approximately four or more azide groups per repeat unit were only soluble in dimethyl sulfoxide and water. The standard enthalpy of formation of the polymers became increasingly positive as the azide content increased. The enthalpy of formation of a sample with 4.42 N₃/repeat unit was 6929 kJ/repeat unit, whereas this value was only 103 kJ/mol for classical GAP. An azidified sample from PECH (4.42 N₃/repeat unit) was crosslinked with a commercial triisocyanide into a rubbery product. The density and ultimate tensile strength of the rubbery product were 1.44 g/cm³ and 4.84 MPa, and it swelled about 10% at 20°C in water.© 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3785–3790, 2004     

含噁唑环支链的苯氧型共聚聚酰亚胺的合成与表征

以3,5-二硝基苯甲酰氯和邻氨基苯酚为原料合成了含苯并噁唑基团的二胺,然后将其与二氨基二苯醚(ODA)和二苯醚四甲酸二酐(ODPA)进行常温共聚合成聚酰胺酸,最后采用两步法合成了含苯并噁唑支链的可溶性聚酰亚胺(PI)。采用红外光谱(FT-IR)、差示扫描量热法(DSC)和热重分析(TGA)等测试手段分析了该PI的结构、热性能和在各溶剂中的溶解性能。实验结果表明,经300℃热处理1h后,聚酰胺酸转化为酰亚胺化比较完全;引入苯并噁唑支链基团可以提高PI的耐热性,其玻璃化转变温度(Tg)在300℃左右,初始热分解温度为552.5℃;该PI在强极性溶剂中溶解性能良好,但不溶于一般的极性溶剂中,说明其在提高加工性能的同时仍能保持耐一般溶剂的性能。     

Anomalous depression of rubbery modulus through crosslinking

Introduction of primary covalent crosslinks into linear, segmented elastomers was followed by observing their modulus–temperature behavior. The behavior of the linear segmented polymers is explained by association of glassy segments into regions which act as filler and quasi-crosslink. In several cases crosslinkage disrupts these regions and thereby lowers the “plateau” modulus.     

Structural characterization of vulcanizates. Part V. Determination of degree of chemical crosslinking of natural rubber gum vulcanizate networks

A general treatment is given of the methods to be used in other parts of this series for calculating the degree of chemical crosslinking in natural rubber vulcanizates from stress–strain measurements in extension and from equilibrium volume swelling measurements. Corrections are required for the presence in the vulcanizate of appreciable quantities of particulate solids or soluble diluents and for the introduction of foreign atoms into the rubber network. For this purpose distinction is made between the rubber vulcanizate, the rubber matrix, the rubber network, and the rubber hydrocarbon component of the network. Expressions are derived, in terms of these concepts, for the Money-Rivlin parameter, C₁, measured on vulcanizates which have undergone various treatments.     

Synthesis and characterization of new soluble and thermostable polyimides via novel diisocyanates

A facile synthesis of two novel diisocyanates containing methylene groups and preformed imide structure is described. Furthermore, six thermally stable and soluble polyimides were synthesized by polycondensation of these two diisocyanates with pyromellitic dianhydride (PMDA), 3, 3 ′,4, 4 ′‐benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene‐2,2‐bis‐(phthalic anhydride) (6FDA) in N,N ‐dimethyl acetamide. All monomers and polymers were characterized by conventional methods and their physical properties such as solution viscosity, solubility properties, thermal stability and thermal behaviour were studied. © 1999 Society of Chemical Industry     

Effect of the degree of crosslinking on penetrant transport in polystyrene

The effect of the degree of crosslinking of glassy polymers on the transport mechanism of penetrants was investigated using a series of divinyl benzene (DVB)-crosslinked polystyrenes of nominal crosslinking ratio X from 0.001 38 to 0.060 mol DVB/mol styrene. The number average molecular weight between crosslinks, $\text{M}\text{?}{}_{\mathrm{<mtext>c</mtext>}}$, was determined from equilibrium swelling experiments in cyclohexane. Dynamic swelling experiments with cyclohexane at 30°C showed that the mechanism of penetrant transport was anomalous. An overshoot in the penetrant uptake was observed, characteristic of macromolecular relaxations and of changing solubility of the cyclohexane in the continuously swelling polystyrene. Photographs of various samples during the swelling process showed that solvent crazing occurred predominantly in loosely crosslinked samples.     

Effect of degree of crosslinking on water transport in polymer microparticles

The water transport in microparticles of poly(2-hydroxyethyl methacrylate) crosslinked with small amounts of ethylene glycol dimethacrylate was investigated as a function of time. Dynamic swelling curves were obtained and analyzed with a simple, empirical, exponential expression, where the exponent n indicates the mechanism of water transport. It was determined that the mechanism changed from Fickian to non-Fickian transport as the nominal crosslinking ratio increased from X = 0.007 to X = 0.124 mol EGDMA/mol HEMA. Smaller particles attained their equilibrium swelling value faster. The velocity of the penetrant front was determined with optical microscopy, and it was found to decrease from 22.2 to 11.2 μm/min as the crosslinking ratio increased.     

Specific rebinding of protein imprinted polyethylene glycol grafted calcium alginate hydrogel with different crosslinking degree

Bovine serum albumin imprinted polyethylene glycol 600 (PEG600) grafted Calcium alginate (CaA) hydrogel microspheres were prepared and characterized. The adsorption and recognition properties of PEG600 grafted calcium alginate (CaA-g-PEG600) microspheres were evaluated and the results showed that the crosslinking structure of CaA-g-PEG600 microspheres exerted an obvious effect on the adsorption capacity and imprinting properties for bovine serum albumin. The adsorption isotherms and recognition properties indicated that the imprinted modified microspheres had excellent rebinding affinity toward target proteins and the imprinting efficiency varied according to PEG600 grafting degree. The adsorption capacity and the imprinting factor were 5.5 mg g^?1 and 3.6, respectively. Adsorption kinetics of CaA-g-PEG600 microspheres in accordance with the molecular weight between crosslinks (Mc) was investigated and the structural influence on protein selective rebinding was discussed. Furthermore, the binary solution separation performance of CaA-g-PEG600 microspheres with different Mc was investigated by selective binding bovine serum albumin from protein mixture solution.     

Synthesis and characterization of BDSDA/APB polyimide

A novel linear aromatic polyphenylene ethersulfideimide (BDSDA/APB) has been synthesized. Its physical, mechanical, thermal, and flow properties and its resistance to some of the more commonly used solvents were determined. The results of these property evaluations indicate this polymer system can be processed via conventional thermoplastic techniques. It has been molded, used as a resin, and cast into thin films and, accordingly, may have a wide variety of applications. Its molecular weight was varied by endcapping with phthalic anhydride. Over the M?_n range 14,000–45,000 the apparent viscosities and G_Ic values varied only slightly. However, a change in M?_n from 14,000 to 8700 resulted in a dramatic decrease in the apparent viscosity at both 250°C and 280°C. The G_Ic values for these same molecular weight materials decreased in a like manner as the M?_n decreased, indicating tradeoffs can be made between process optimization and final mechanical properties when polymer systems are developed.     

Synthesis and characterization of colorless polyimide nanocomposite films

A poly(amic acid) was prepared through the reaction of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride and 2,2′‐bis(trifluoromethyl) benzidine in N,N‐dimethylacetamide. Hybrid films were obtained from blend solutions of the precursor polymer and the organoclay dodecyltriphenylphosphonium–mica, with the organoclay content varying from 0 to 1.0 wt %. The cast films of poly(amic acid) were heat‐treated at different temperatures to create polyimide (PI) hybrid films. These PI hybrid films showed excellent optical transparency and were almost colorless. The intercalation of PI chains in the organoclay was examined with wide‐angle X‐ray diffraction and electron microscopy. In addition, the thermomechanical properties were tested with differential scanning calorimetry and thermogravimetric analysis, and the gas permeability was determined. The addition of only a small amount of the organoclay was sufficient to improve the thermal and mechanical properties of the PI, with the maximum enhancement being observed with 0.5 wt % organoclay. However, the water vapor permeability decreased with the clay loading increasing from 0 to 0.5 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007