Differences in structure growth in amine curing of diglycidyl ether of bisphenol a and N,N-diglycidylaniline epoxy resins: Bifunctional models

The reaction of diepoxides, diglycidylaniline (DGA), or diglycidyl ether of Bisphenol A (DGEBA) with aniline was followed using HPLC and SEC. The effect of molar ratio of reagents, dilution of the system, reaction temperature, and the difference between the reaction mechanisms for DGA and DGEBA systems on the reaction kinetics and molecular weight evolution is discussed. Molecular weights of the DGA-aniline polymers were by an order of magnitude lower than those of the DGEBA-aniline polymers due to the formation of small cyclic products in the former case. Also, a reduction in M_n with increasing temperature, dilution, and diluent polarity is brought about by a greater tendency toward cyclization under these conditions. Theoretically calculated molecular weight evolution during the reaction is in satisfactory agreement with the experiment. © 1995 John Wiley & Sons, Inc.     

A review of the application of HPLC and GPC to the analysis of synthetic resins

Summary The article gives a brief survey of the use of liquid chromatography in characterizing different kinds of synthetic resins and presents several examples of the application of this technique for analysis of such materials.     

The distribution of cerium (III) cations between aqueous and nitrobenzene phases in the presence of dicarbolide anions

Extraction of micro- and macroquantities of Ce³⁺ (C°_Ce = 10^6??10^?1 mole/dm³) with a nitrobenzene solution of dicarbolide (C°_H⁺B^? = 0.04?0.5 mole/dm³) from a nitric acid solution (C°_HNO3 = 0.1?0.3 mole/dm³) was investigated. Coextraction of water and simultaneous extraction of Ce³⁺ and Ba²⁺ ($\text{C}$_Ce⁺ + C_Ba = 0.3 mole/dm³) from 0.3 and 0.5 M HNO₃ was also studied. It was found that the reaction Ce³⁺ + 3H?Ce?³⁺ + 3H (K_Ce/3H) takes place in all cases. The dependence of the apparent exchange extraction constant K_Ce/3H on the initial composition of both phases was determined and the effect of the composition of the aqueous phase on the values of K_Ce/3H and K_Ba/2H was discussed. The stability constant of the CeNO²⁺₃ complex and the hydration number of the Ce³⁺ cation in the organic phase (h³⁺_Ce = 16.2 ± 2) was determined and a linear correlation between individual extraction constants of mono-, bi- and trivalent cations and the hydration numbers in the nitrobenzene phase was found using data from the present paper and values given in literature.     

Structure analysis of group I plant nucleases

Anticancer drugs attacking nucleic acids of the target cells have so far been based on animal or fungal ribonucleases. Plant nucleases have been proved to exhibit decreased cytotoxic side effects. Tomato bifunctional nuclease 1 with activity against both single-stranded and double-stranded RNA and DNA was produced in tobacco leaves as recombinant protein. The enzyme crystallizes under several different crystallization conditions. The presence of Zn(2+) ions was confirmed by X-ray fluorescence. First crystallographic data were obtained.     

Model reactions of amine curing of glycidylamine epoxy resins: Homopolymerization of N-methylglycidylaniline

The kinetics of homopolymerization of the monofunctional epoxide N-methylglycidylaniline in the presence of a tertiary amine or an amino alcohol has been followed by reversed phase high performance liquid chromatography and size exclusion chromatography. The reaction products were identified by mass spectrometry using potassium ionization of desorbed species (K⁺IDS). 1,3-Di-N-methylanilino-2-propanol (P) was the main reaction product and low molecular weight oligomers with M_n > 600 were also formed. The molecular weight and fraction of oligomers decrease with increasing concentration of the initiator. The suggested complex reaction mechanism involves formation of four stable oligomeric series initiated by reaction of the epoxide with either an OH group of (a) the amino alcohol, (b) product P, (c) traces of water, or (d) the tertiary amine to form ionic species resulting in the ionic propagation. Regeneration of the initiator and formation of new initiating centers during the polymerization are the causes of low molecular weights of oligomers. © 1992 John Wiley & Sons, Inc.     

Asymmetric Flow Field-Flow Fractionation: Current Status,Possibilities, Analytical Limitations and Future Trends

Chromatographia - The development and applications of asymmetric flow field-flow fractionation (AF4) are outlined in comparison with the older and better-known size exclusion chromatography. Recent...     

Non-seeded semi-continuous emulsion polymerization

Semi-continuous emulsion polymerization of acrylic monomers was investigated from the point of view of the particle growth. In the process no seed latex was used and the monomers were fed in an emulsion form. Oscillations of surface tension and particle number indicated a periodical generation and flocculation of particles during the polymerization. Investigation of particle size and molecular weight changes in the first tens of seconds of polymerization has shown that the coagulation process proceeds even in the earliest stage of the polymerization. Initial emulsifier concentration in the reactor strongly affects the particle growth and the final particle number.