Thermogravimetric analysis of thermal stability of poly(methyl methacrylate) films modified with photoinitiators

Films of poly (methyl methacrylate) (PMMA) were prepared by the addition of photoinitiator to the polymer. The influence of five organic photoinitiators on thermal stability of poly(methyl methacrylate) was studied by thermogravimetric analysis. Next, the PMMA films doped with these photoinitiators were UV irradiated and investigated in terms of changes in their thermal stability. It was found that the photoinitiators had accelerated thermal degradation of non-irradiated PMMA films due to the action of free radicals coming from the additives’ thermolysis. For UV-irradiated specimens, the effect of photoinitiator on PMMA thermal stability depended on the chemical structure of organic compound modifying the polymer. In general, thermal stability of irradiated samples was higher in the presence of additives. Thermal destruction of modified PMMA can be explained by the formation of resonance structures in aromatic photoinitiators and consumption of energy in dissipation processes.     

High‐Yield Synthesis of Amido‐Functionalized Polyoctahedral Oligomeric Silsesquioxanes by Using Acyl Chlorides

Homosubstituted amido‐functionalized polyoctahedral oligomeric silsesquioxanes (POSS) have been synthesized by using acyl chlorides in high yields (ca. 95 %). The method proved to be superior over “conventional” syntheses applying carboxylic acids or acid anhydrides, which are much less efficient (ca. 60 % yield). A palette of aryl and alkyl groups has been used as side‐chains. The structures of the resulting amide‐POSS are supported by multinuclear ¹H, ¹³C, ²⁹Si NMR and FTIR spectroscopy and their full conversion into octasubstituted derivatives was confirmed using mass spectrometry. We also demonstrate that the functionalized silsesquioxanes with bulky organic side‐chains attached to cubic siloxane core form spherical‐like, well‐separated nanoparticles with a size of approximately 5 nm.     

Influence of Surface-Active Compounds on Starch Dispersion in Water. Part I. Starch Pasting

The influence of native lipids and additives of surface-active compounds on starch paste rheology was investigated. The aim of the study was to gain better understanding of mechanisms involved in starch gelatinization and how these structure changes of granules later affect rheological properties of pastes and gels. Starches from three main sources—potato, maize, and wheat—were tested; sodium dodecylsulfate, oleate, and benzalkonium chloride were employed as additives. Starch pasting was examined by a rheometer to get a viscosity profile, also pastes were analyzed by differential scanning calorimetry, for particle size using a light scattering technique. Results revealed that there was a competition between native lipids and added surfactants for amylose complexation. Complexes formed during gelatinization were strongly affecting granule swelling and dissolution of starch polymers, and viscosity of pastes was mainly dependent on the particle size of a disperse phase in the paste. Addition of strong ionic surfactants to cereal starches resulted in smaller granular remnants and, therefore, decreased viscosity, while the weak anionic surfactant promoted an increase in the particle size and paste viscosity for both cereal and tuber starches. The mechanism of the effect of surfactants on the particle size in pastes is discussed.     

Study on the rate of plutonium vertical migration in various soil types of Lublin region (Eastern Poland)

Soil contamination level with ^239+240Pu of Lublin region was determined using the alpha spectrometric method. Results were compared with similar data from the study performed 15 year earlier. Decrease in total ^239+240Pu concentration and reducing quantity of Chernobyl fraction (up to almost negligible value of 1 %) has been observed in upper soil layer. Determination of ^239+240Pu concentration in soil profile layers allows calculating a vertical migration velocity of plutonium applying a compartment migration model. It was found that ^239+240Pu migration rate varies depending on soil type from 0.29 cm year^?1 in Podsols to 0.58 cm year^?1 in Fluvisols with mean value of 0.5 cm year^?1.     

Structure of Partially Ordered Cyclic Semigroups

This paper recalls some properties of a cyclic semigroup and examines cyclic subsemigroups in a finite ordered semigroup. We prove that a partially ordered cyclic semigroup has a spiral structure which leads to a separation of three classes of such semigroups. The cardinality of the order relation is also estimated. Some results concern semigroups with a lattice order.     

Bis(ethyl­ene­diaminium) bis­[oxalohydroxamato(3–)]nickelate(II) dihydrate

The title compound, (C₂H₁₀N₂)₂[Ni(C₂HN₂O₄)₂]·2H₂O, has an ionic structure containing a centrosymmetric complex 4− anion, charge‐balancing ethyl­ene­diaminium dications and solvent water mol­ecules. The oxalohydroxamate unit is triply deprotonated and forms five‐membered chelate rings with the central Ni ion; the Ni ion lies on an inversion centre. The two hydroxamate O atoms in the complex anion are linked by short intra­molecular hydrogen bonds.     

LC Separation of Fatty Acid Ceramides Using a Two Column System

Type II ceramides were separated according to the length of their fatty acid alkyl chain using two column system. The packing of the first column was non-polar adsorbent prepared by coating of macroporous spherical silica with cationized poly(vinyl alcohol) of low substitution degree. Commercial normal phase column Lichrosorb Si 60 was used as a second column in this system. Elution was performed in an isocratic mode using methanol:chloroform 50:50 (v/v) as an eluent.

     

Correlation between growth of high-index faces, relative growth rates and crystallographic structure of crystal

According to contemporary crystal growth theories, crystals are bound by low-index faces which are the most slowly growing. However, high-index faces are observed in crystal habits more and more often. In this paper the growth of high-index faces is analysed from a crystallographic perspective. It is shown that the crystallographic structure of a given crystal, expressed by the trigonometric function of appropriate interfacial angles, influences to great degree the crystallisation process and the morphology of crystals, in particular the behaviour of high-index faces. Additionally, it is concluded that at particular crystallographic structure of a crystal, a given high-index face may exist in the habit and develop its size, although it grows much faster than the neighbouring faces. Received 31 July 2001     

Small libraries of fused quinazolinone-sugars. Access to quinazolinedione nucleosides

Unprotected carbohydrates can readily be converted into base-modified nucleosides and deoxynucleosides through a short sequence involving the condensation of anthranilic acid derivatives with a suitably protected sugar-derived 2-alkylthio-1,3-oxazoline.     

Theoretical description of aggregation of cationic gemini surfactants in the bulk solution and on the silica surface

A theory of cationic dimeric (gemini) surfactant adsorption onto negatively charged surface is presented. In the proposed model it is assumed that the adsorbed phase is a mixture of singly dispersed molecules of surfactant and spherical, globular and cylindrical aggregates of different dimensions. Only the “excluded area” interactions between the adsorbed species are considered and the effects of surface heterogeneity on monomer adsorption are taken into account. The aggregation behavior of gemini surfactants is based on the additive free energy model proposed by Camesano and Nagarajan (2000). The calculated surfactant adsorption isotherms and the differential molar enthalpies of micellisation and adsorption are compared with the experimental results obtained for a series of gemini surfactants depending on the length of a spacer, temperature or the presence of electrolyte. On the basis of theoretical results the evolution of adsorbed phase of gemini surfactants with the increasing adsorption is discussed. It is shown that the evaluated cmc values and the dimensions of surfactant aggregates are in a good agreement with experiment. Unfortunately, the theoretical model does not describe properly the temperature dependence of micellisation process.