Influence of UV Light Wavelength on Grafting of PVC

Abstract

PVC-(n-propyl xanthate) macroinitiators (PVC-nPX) with different fractions of xanthate groups were synthesized in THF/acetone solutions from PVC and potassium n-propyl xanthate (nPX). Methyl methacrylate (MMA) was grafted onto PVC-nPX macroinitiators using UV light of 254, 302, and 366 nm at 20 and 40°C. Reaction time was 1, 3, or 5 hours. Graft copolymerization and UV homopolymerization took place at the same time. Grafting was the most effective at a wavelength of 302 nm with a weight gain of copolymerization of up to 45%. The grafted copolymers were separated from the mixture by selective precipitation of THF solutions with hot ethanol and extraction with hot ethanol. The mechanism of grafting is discussed on the basis of the molecular weight of copolymers, on the quantity of homopolymers, on the structure of copolymers, and on the UV absorption of end groups.     

Binding Studies on the Control of the Conformation and Self-assembly of a Calix[4]arenedicarboxylic Acid through Hydrogen Bonding Interactions

A convenient method for measuring the dimerisation constant in solution of a calix[4]arenedicarboxylic acid is reported. This compound also co-crystallises with a bis(amidopyridyl)calix[4]arene as independent tubular calixarene stacks that are cross-linked via carboxyl–amidopyridyl hydrogen bonding and π-stacking of the amidopyridyl arms.     

Polyvinylpyrrolidone thin film pyrolysis as accessed by the real-time optical transmission measurements

Present results reveal basic features of the optical transmission thermo-analytical method in its employment to investigate the oxidative pyrolysis of supported thin polyvinylpyrrolidone films. The OT curves naturally vary in shapes and positions on the time/temperature scales, respective to the examined rate of sample heating, to the wavelengths of radiation as well as to the film thickness. Recorded OT curves exhibit characteristic shapes with well-expressed OT minima. The temperatures at which the OT minima appear are in a linear relationship with heating rates of samples, at a frequency of radiation as well as a film thickness kept constant. Similarly, the OT values at which the OT minima appear are in a linear relationship with film thickness, at a frequency of the radiation and sample heating rate unchanged.     

<Emphasis Type="BoldItalic">C</Emphasis>(<Emphasis Type="BoldItalic">X</Emphasis>)-objects in the Category of Semi-affine Lattices

In our previous paper (Hušek and Pulgarín, Topol Appl, doi:, 2009) we characterized the set C(X) of real-valued continuous functions on a topological space X as a real ℓ-group. The present paper weakens the situation to the level of semi-affine lattices.     

Dependence of aggregate strength, structure, and light scattering properties on primary particle size under turbulent conditions in stirred tank

The steady-state size and structure of aggregates produced under turbulent conditions in stirred tank, for primary particle diameter, d(p), equal to 420 nm and 120 nm, were studied experimentally for various values of the volume average shear rate, G, and solid volume fraction, phi, and compared with data for d(p) = 810 nm. To exclusively investigate the effect of dp, polystyrene latexes with same type and similar density of surface charge groups (sulfate) were used. The mass fractal dimension, d(f), obtained by image analysis, was found to be invariant of d(p) and G, with a value equal to 2.64 +/- 0.18. Small-angle static light scattering was used to characterize the cluster mass distributions by means of the root-mean-square radius of gyration, R(g), and the zero-angle intensity of scattered light, I(0), whose steady-state values proved to be fully reversible with respect to G. The absolute values of R(g) obtained for similar phi and G proved to be independent of d(p), and for all studied conditions, R(g) was proportional to G-1/2. At very low phi, a critical aggregate size for breakage was obtained and used to evaluate the aggregate cohesive force, as a characteristic for the aggregate strength. The aggregate cohesive force was found to be independent of aggregate size, with similar values for the investigated dp. Due to large d(p) and high d(f), the effect of multiple light scattering within the aggregates was found to be present, and by relating the scaling of R(g) with I(0) to d(f), the corresponding correction factors were evaluated. By combination of the independently measured aggregate size and structure, it is possible to experimentally determine the relation between the maximum stable aggregate mass and the hydrodynamic stresses independent of the multiple light scattering present for large d(p) and compact aggregates.     

Optimization of sol–gel/pyrolysis routes to silicon oxycarbide glasses

The optimization of the synthesis of silicon oxycarbide ceramics via the sol–gel/pyrolysis route is described, starting from several alkylalkoxysilanes and vinylalkoxysilanes. The main aim was to achieve low weight losses during cure and pyrolysis and also a compact ceramics morphology. The theoretical composition of the pyrolysates was changed between SiO_1.5C and SiO_1.2C_2.3, by varying monomer types and ratios. An assessment of the real composition was performed using energy-dispersive X-ray spectroscopy. The smallest weight losses were obtained for the resins based on vinyltriethoxysilane and dimethyldiethoxysilane which were additionally modified by the addition of a small amount of boric acid. Somewhat higher weight losses combined with the best toughness were found for resins based on non-vinylated silsesquioxane with a low content on linear dimethylsiloxane units. As an alternative, a precursor (SiO_0.9C_2.8) was prepared via hydrosilylation, based on cyclic dimethylsiloxane oligomers interconnected to a network, but its weight losses were higher than those of sol–gel silicon oxycarbide.     

Spark plasma-sintered Sn-based intermetallic alloys and their Li-storage studies

Journal of Solid State Electrochemistry - In the present study, SnSb, SnSb/Fe, SnSb/Co, and SnSb/Ni alloy powders processed by co-precipitation&nbsp;were subjected to spark plasma-sintering...