Degradation mechanism of poly(lactic-co-glycolic) acid block copolymer cast films in phosphate buffer solution

We have investigated the degradation of poly(lactic-co-glycolic) acid copolymer with a lactic to glycolic ratio of 50:50. Solvent-cast films were incubated at 37 °C in phosphate buffered saline solution and their degradation was followed using potentiometry, light microscopy, gravimetry, size exclusion chromatography, differential scanning calorimetry and infrared spectroscopy. The degradation process was found to have two main steps. The first step was observed from 0 to 7 days of degradation. During the first few days a soft layer formed at the surface of the film. As degradation time increased this soft surface layer was found to swell and wrinkle. The polymer molecular weight in the bulk was found to decrease as soon as the film was placed in the medium while the polymer present in the surface layer was found to degrade at a much slower rate. The second step of degradation was found to occur after 8 days. At this stage of the degradation process the molecular weight of the polymer in the bulk of the films was so low that the materials became liquid resulting in the detachment of the film from the glass slide. At this stage the mass loss and amount of acid released in the media were found to increase significantly.     

Measurement of Hydrodynamic Sizes of Ultralairge Water-Soluble Polymers by Nucleopore Filtration and Multicell Equilibrium Dialysis

Membrane filtration and equilibrium dialysis using Nucleopore membranes have been carried out to determine the hydrodynamic sizes of large water-soluble polymers. The macromolecules were found to have been significantly deformed even under very low stress. Multicell equilibrium was somewhat long. The hydro-dynamic radius obtained from this method was found to be in reasonable agreement with that found by ultracentrifugation and size exclusion chromatography.     

低共熔溶剂用于高效可逆捕集二氧化碳的研究

本文通过一步合成法合成了四种不同摩尔比的四乙基氯化胺-乙醇胺低共熔溶剂（TEAC-MEA DES）。红外光谱表征分析表明该DES是依靠氢键作用而形成的;DES的热稳定性高于MEA,且随着MEA的比例的增加而降低;对不同比例的DES进行了四次循环CO₂吸收-解吸实验,发现其吸收容量几乎不变,重复使用性能较好。在不同温度下计算了化学平衡常数,lnK对1/T线性拟合结果表明DES吸收CO₂的反应焓是负值,即吸收CO₂的反应是放热过程。该DES在吸收CO₂方面具有很大的潜力。     

Green Synthesis of 2‐Substituted Imidazolines using Hydrogen Peroxide Catalyzed by Tungstophosphoric Acid and Tetrabutylammonium Bromide in Water

Various 2‐substituted imidazolines were constructed from aromatic aldehydes with ethylenediamine using hydrogen peroxide as an oxidant in water. Tungstophosphoric acid (HPW) was found to be active for this transformation due to its ubiquitous catalytic and oxidative nature, and further combination of tetrabutylammonium bromide (TBAB) made this transformation more efficient and attractive. It was found that the yields of the corresponding 2‐substituted imidazolines were markedly influenced by the position and nature of the substituents on the phenyl ring. A plausible mechanism was also proposed to clarify this catalytic oxidative system.     

Gas-chromatographic identification of fluorine-containing organic compounds

The gas-chromatographic retention of a series of fluoroalkylarenes on the standard nonpolar polydimethylsiloxane stationary phase OV-101 was characterized, and the retention indices of these compounds were determined. It was found that large negative values of the homological increments of these constants can serve as a sign of fluorine derivatives that contain no less than three fluorine atoms per molecule. The retention indices on polar inorganic sorbents, the silica gels Silipor 75 and Silipor 600, were chosen as the second chromatographic parameter. On these sorbents (unlike partition separation), the nonadditivity effect of the retention indices of polyfunctional organic compounds with respect to their simpler structural analogs was found for the first time. It was found that a mutual correlation between indices for this combination of a phase and a sorbent was lower than that for the combinations of phases with different polarities; this fact is responsible for the higher information content of this combination for the identification of compounds from this class.     

Vinyl acetate emulsion polymerization. I. Effect of ionic strength and temperature on monomer solubility in the ionically stabilized polymer particle

Solubility of monomer in the polymer was strongly affected by ionic strength; with increasing ionic strength, solubility was found to increase. At constant temperature, this was entirely due to the decrease in interfacial tension, as the condensation of surfactant proceeded at the interface. The temperature affected both the polymer–solvent interaction parameter as well as the interfacial tension. These are the two parameters on which solubility depends. The variations of interfacial tension with temperature was found to be complex, but entirely dependent on the entropic consideration of adsorption. The polymer–solvent interaction parameter–inverse temperature dependence was found to be linear, as expected.     

Antimony(III) Sulfate Catalyzed Condensation Reaction of Indoles with Carbonyl Compounds

Summary. Antimony sulfate was found to be on effective catalyst for the condensation reaction of indoles with carbonyl compounds at room temperature. This catalyst is inexpensive, easily available and it was also found that this catalyst could be recovered quantitatively and reused without much loss of catalytic activity.     

A study on the thermodynamic properties of polyimide BTDA-ODA by adiabatic calorimetry and thermal analysis

Polyimide BTDA-ODA sample was prepared by polycondensation or step-growth polymerization method. Its low temperature heat capacities were measured by an adiabatic calorimeter in the temperature range between 80 and 400 K. No thermal anomaly was found in this temperature range. A DSC experiment was conducted in the temperature region from 373 to 673 K. There was not phase change or decomposition phenomena in this temperature range. However two glass transitions were found at 420.16 and 564.38 K. Corresponding heat capacity increments were 0.068 and 0.824 J g^–1 K^–1, respectively. To study the decomposition characteristics of BTDA-ODA, a TG experiment was carried out and it was found that this polyimide started to decompose at ca 673 K.This revised version was published online in November 2005 with corrections to the Cover Date.     

Multi-scale study of the mineral porosity of veined gneiss and pegmatitic granite from Olkiluoto,Western Finland

The purpose of this work was to support the long-term experiments for investigation of rock matrix retention properties at the spent nuclear fuel repository site ONKALO, in Olkiluoto, Western Finland. Towards this end, rock samples were characterised in terms of porosity connected to mineralogy, with emphasis on pore sizes, and fillings. Both filled and unfilled pores were found with unfilled pores being majority in the pegmatitic granite veins of the mostly veined gneiss samples. It was found that the fillings were often connected to local alteration and the alteration caused variation in the range of pore sizes.     

Adsorption of bovine serum albumin to acrylamide–itaconic acid hydrogels

In this study, acrylamide–itaconic acid hydrogels containing different amounts of itaconic acid prepared by irradiating with γ radiation are discussed. They have been used in experiments of swelling, diffusion and bovine serum albumin (BSA) adsorption. Maximum and minimum swellings were observed with water (1520%) and BSA (890%), respectively. Diffusion of water, NaCl and BSA within hydrogels were found to be non-Fickian in character. In the experiments of BSA adsorption, type III adsorption was found. The hydrogel prepared with 60 mg itaconic acid and irradiated at 2.00 kGy was found to be the best adsorption system for BSA. The adsorption capacity of acrylamide–itaconic acid hydrogel was found to exceed that of acrylamide hydrogel by more than 80–100%.     

Kinetic study of preirradiation grafting of acrylic acid onto poly(tetrafluoroethylene–perfluorovinyl ether) copolymer

A kinetic study has been made on the preirradiation grafting of acrylic acid (AAc) onto poly(tetrafluoroethylene–perfluorovinyl ether) (PFA) film. The effect of grafting conditions was investigated. The dependences of the grafting rate on preirradiation dose and monomer concentration was found to be of the order of 0.5 and 1.3, respectively. The final degree of grafting was found to increase with dose and monomer concentration. However, it decreases as the grafting temperature increase. The overall activation energy for the graft polymerization was calculated from Arrhenius plots to be 5.6 kcal/mol. The activation energy for this grafting system was found to be independent of preirradiation dose used in the range from 10 to 100 kGy. The relationship between the grafting rate and film thickness gave a negative first-order dependence. The results suggest that the grafting proceeds by radical mechanism with bimolecular termination of growing chain radicals. It was reasonable concluded that this grafting proceeds from the surface to the center of film with progressive monomer diffusion through the grafted layer which swells in the monomer solution.     

Adsorption of Nitrogen,Oxygen, and Argon Vapors on Supermicroporous Oxides

The adsorption of N₂, O₂, and Ar vapors on a number of supermicroporous tin dioxide and zirconia xerogels at 77.4 K was studied. The micropore volumes calculated with the use of sorbate densities at the corresponding temperature were found to be in satisfactory agreement for all of the sorbates. At the same time, the volumes of larger pores measured using nitrogen were greater than the values found with other sorbates. The previously found behavior of oxygen and nitrogen molecules in the geometrically restricted space of supermicropores was substantiated. In particular, this behavior manifests itself in a change in the adsorption properties of a unit surface area of supermicropores as compared with the surface of mesopores. However, the effects of this kind were not found for the argon–nitrogen sorbate pair.     

Synthesis and some reactions of bis(triphenylstannyl)carbodiimide, N′-(triphenylstannyl)-N′-tritylcarbodiimide,and (triphenylstannyl)cyanamide

Some methods for preparing bis(triphenylstannyl)carbodiimide (I), N-(triphenylstannyl)-N′-tritylcarbodiimide (II), and (triphenylstannyl)cyanamide are described. (I) was found to react with 1,3-disubstituted thioureas in refluxing acetonitrile or toluene to give bis(triphenyltin) sulfide and the corresponding N,N′-disubstituted-N″-cyanoguanidine. Some evidence for a diorganocarbodiimide intermediate in this reaction was found. The reaction of(I) with thiourea in refluxing acetonitrile was found to give bis(triphenyltin) sulfide,(triphenylstannyl)cyanamide and unchanged thiourea. The reaction of (I) with cyanamide gave (triphenylstannyl)cyanamide. (Triphenylstannyl)cyanamide was found to react with bis(triphenyltin) oxide in refluxing acetonitrile to give (I). (Triphenylstannyl)cyanamide was found to disproportionate in refluxing benzene to give (I) and dicyandiamide. (II) was found to be more hydrolytically stable than (I). The SnN bonds in both (I) and (II) were found to be readily cleaved by acetic acid. It was found that triphenyltin iodide and triphenyltin chloride can be conveniently prepared in good yield by the reaction of bis(triphenyltin) oxide with either calcium iodide or calcium chloride in refiuxing acetonitrile.     

Mitotic factors from mammalian cells: a preliminary characterization.

The objective of this study was the preliminary characterization of the factors from mitotic HeLa cells that can induce meiotic maturation in Xenopus laevis oocytes. We found that this factor is a heat-labile, Ca2+-sensitive, nondialyzable protein with a sedimentation value of 4-5S. Furthermore, no new protein synthesis was found to be required for this mitotic factor to induce maturation in the amphibian oocytes. These data suggest that the factors involved in the breakdown of nuclear membrane and the condensation of chromosomes that are associated with three different phenomena, mitosis, meiosis, and premature chromosome condensation, are very similar in different animal species.     

Optimization of Enzyme Co-Immobilization with Sodium Alginate and Glutaraldehyde-Activated Chitosan Beads

In this study, two different materials—alginate and glutaraldehyde-activated chitosan beads—were used for the co-immobilization of α-amylase, protease, and pectinase. Firstly, optimization of multienzyme immobilization with Na alginate beads was carried out. Optimum Na alginate and CaCl₂ concentration were found to be 2.5% and 0.1 M, respectively, and optimal enzyme loading ratio was determined as 2:1:0.02 for pectinase, protease, and α-amylase, respectively. Next, the immobilization of multiple enzymes on glutaraldehyde-activated chitosan beads was optimized (3% chitosan concentration, 0.25% glutaraldehyde with 3 h of activation and 3 h of coupling time). While co-immobilization was successfully performed with both materials, the specific activities of enzymes were found to be higher for the enzymes co-immobilized with glutaraldehyde-activated chitosan beads. In this process, glutaraldehyde was acting as a spacer arm. SEM and FTIR were used for the characterization of activated chitosan beads. Moreover, pectinase and α-amylase enzymes immobilized with chitosan beads were also found to have higher activity than their free forms. Three different enzymes were co-immobilized with these two materials for the first time in this study.     

Oxidation of organic substances with compounds of trivalent manganese: XIII. Oxidation of pyruvic acid with manganese(III) sulfate in a medium of sulfuric acid and with hexaquomanganese(III) ions in noncomplexing medium of perchloric acid

The oxidation of pyruvic acid with manganese(III) sulfate in a medium of sulfuric acid and with hexaquomanganese(III) ions in noncomplexing perchloric acid medium was studied. It was found that pyruvic acid is oxidized by both reagents to give acetic acid and carbon dioxide and the optimal conditions for the analytical application of this reaction on both a semimicro and micro level were found.     

Bromamine-T mediated aziridination of olefins with a new polymer supported Manganese(II) complex as catalyst

Chloromethylated styrene-divinyl benzene of 8% cross-link was functionalized using o-phenylene diamine and finally it was treated with Mn(II) for the formation of metal complex on the surface. The metal content was estimated using atomic absorption spectroscopy. The thermal stability of the catalyst was seen by the use of DTA-TG analyses and the catalyst was found to be stable up to ˜125°C. The modern spectroscopic methods such as FT-IR, ESR were used in order to confirm the probable structure of the catalyst. The catalytic activity of this supported Mn(II)-complex was investigated for aziridination of olefins with bromamine-T as the source of nitrogen. The catalyst was found to be effective in this reaction and could be reused with no substantial loss of activity for up to three cycles.     

Pyranine-induced self-assembly of colloidal structures using poly(allylamine-hydrochloride)

Complexes of dyes and polyelectrolytes have found widespread use in a variety of functional materials and interfaces. Here it is found that upon mixing the anionic dye pyranine and a cationic polyelectrolyte, poly(allylamine-hydrochloride), two different colloidal structures may form. Above a certain concentration of anionic dye, crosslinking of the polyelectrolyte is initiated, and the formation of sheet-like colloidal structures was observed. Addition of hydroxyl ions resulted in the formation of micron-sized spherical colloids. It was also found that the colloidal shape transition was accompanied by a significant red-shift in the fluorescence emission. Combining fluorescence measurements with studies of the particle size with time, it was found that red-shift was related to the crosslinking of the dye and the polyelectrolyte, and was not influenced significantly by the aggregation and particle growth. Further information about the colloidal behavior and stability was obtained by letting droplets dry and follow the kinetics of this process. It was found that the particles collapsed near the contact line and formed a ring deposit, in agreement with previous studies. However, unlike previous studies, the thickness of the ring deposit did not grow significantly with time, due to the peculiar process of formation found here.     

A novel crosslinker for UV copolymerization of N-vinyl pyrrolidone and methacrylates to give hydrogels

Methacryloxyethyl vinyl carbonate, a novel crosslinker containing a vinyl carbonate and a methacrylate group which is capable of copolymerizing N-vinyl pyrrolidone and methacrylates, was prepared. With this crosslinker, N-vinyl pyrrolidone (NVP) and methacrylates can copolymerize efficiently under strictly UV conditions. It was found that this crosslinker was able to give hydrogels with higher water content, higher tear strength, and lower modulus, compared to a traditional dimethacrylate crosslinker. In addition, hydrogel lenses fabricated by UV curing of formulations using this crosslinker were found to be superior to those fabricated with established process in terms of optical quality. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1039–1046, 1997     

Graft Copolymerization of Methyl Methacrylate onto Nylon 6 Using Thallium(III) Ions as Initiator

Abstract

Graft copolymerization of methyl methacrylate onto nylon 6 was investigated in aqueous perchloric acid medium using thallium(III) ions as initiator. The rate of grafting was evaluated by varying the concentrations of monomer, initiator, acid, and temperature. The rate of grafting was found to increase with an increase of both monomer and initiator concentrations. The graft yield was found to increase with an increase in the acid concentration up to 0.49 mL^?1, and beyond this concentration of perchloric acid the graft yield was found to decrease. It also increased with an increase of temperature. From the Arrhenius plot the overall activation energy was found to be 3.9 kcal/mol. The effects of inhibitors, various solvents, inorganic salts, and swelling agents on graft yield were studied. A suitable kinetic scheme has been proposed and a rate equation has been derived.