kpilogo shields

cpsm@kpi.ua
+38 044 204 8430

The phase behaviour of blends of poly(1-vinyl-2-pyrrolidone) and poly(vinyl formal) was studied by means of differential thermal analysis and differential mechanical thermal analysis. Both techniques showed that the blend studied exhibits a single glass transition, which is intermediate between the glass transitions associated with each constituent polymer and depends on polymer concentration. Discussion of this phase behaviour in terms of various common equations is also carried out. The blend preparation method as well as the blend thermal history are found to exert a relevant influence on the phase behaviour associated with the polymer alloy studied here. This behaviour is explained as the consequence of hydrogen-bonding interactions between both polymers as demonstrated by infra-red spectroscopy. An additional study on the mechanism of complex formation associated with poly(1-vinyl-2-pyrrolidone) and poly(vinyl butyral) is also carried out.

Детальніше...  

The concentration and temperature dependences on micelle formation by a polystyrene-blockpoly( ethylene/propylene) copolymer in several ketones (methyl ethyl ketone, methyl propyl ketone, diethyl ketone, methyl isobutyl ketone, dipropyl ketone, 5-methyl-2-hexanone and 5-methyl-3-heptanone) are studied by laser light scattering and viscometry. No micelles were detected in solutions of 5-methyl-3- heptanone. The standard Gibbs energy, AG °, the standard enthalpy, AH °, and the standard entropy, AS °, of micellization were estimated from the dependence of the critical micelle temperature on concentration. The values of AG °, AH ° and AS ° were negative for all ketones studied. AG ° and AH ° depend on the polar character of the ketone. The weight average molar mass, second virial coefficient and apparent radius of gyration have been calculated from the standard Zimm plots obtained. Huggins and Kraemer equations have been employed to determine the limiting viscosity number of the micelles. The micelles formed in ketone solutions show larger association numbers and densities than those formed in n-alkane solutions.

Детальніше...  

Inverse gas chromatography has been used to investigate the thermodynamic compatibility of blends of poly(vinyl chloride) (PVC) and nitrile rubber (NBR) as a function of blend composition and acrylonitrile (AN) content of NBR. The values of the polymer-polymer thermodynamic interaction parameters (Z~3 and B23 ) and the solubility parameter (6) of the polymers and their blends were determined with the help of the measured retention data for various polar and non-polar probes in the pure and mixed stationary phases of these polymers. Out of all the probes studied only dioxane and cyclohexanone have similar values to those of the blends. The B23 values for the PVC/NBR blends were ~-0.i and -1.1 cal m1-1 depending on the AN content of NBR. Thus, the two polymers are fairly compatible and show increased compatibility with increase in AN content of NBR.

Детальніше...  

Various crosslinked poly (4-vinylpyridines) (CP4VP) with different degrees of crosslinking were prepared by radical copolymerization of 4-vinylpyridine with N,N'-tetramethylenebisacrylamide as crosslinker. The binding abilities of these crosslinked polymers were investigated at various temperatures in a buffer solution of pH 7. The first binding constant (K1) and thermodynamic parameters were evaluated from the equilibrium amounts of binding. The first binding constants showed bell-shaped curves when plotted against both the binding temperature and the degree of crosslinking. Lower temperature and higher degree of crosslinking at maximum binding in these bell-shaped curves were observed for this binding system when compared with those of the previously reported binding system (CP4VP/methyl orange) containing CP4VP prepared using N,N'-methylenebisacrylamide as crosslinker. The values of the enthalpy and entropy change increased on increasing the degree of crosslinking and decreasing the binding temperature, whereas the absolute magnitude of the free-energy change was not increased. These results could be accounted for in terms of the temperature dependence of the hole size of CP4VP in addition to the hydrophobic interactions in the binding process.

Детальніше...  

The effect of temperature on the kinetics of methanol transport in PMMA has been investigated for the first time in spherical sample geometry over the temperature range of 25-50°C. The observed penetration of methanol in PMMA beads of 1.045 +_0.03 mm diameter exhibits a geometry-dependent Case II transport behaviour up to 50°C. This is characterized by an induction period followed by an extended region of linear front penetration before an acceleration of front movement towards the centre. This front acceleration, being absent in sheet samples, was shown to be characteristic of the solvent penetration behaviour in spheres. The induction period has been observed to decrease, whereas the front velocity to increase, with increasing temperature, consistent with their known dependencies on the solvent diffusivity and the viscosity of the polymer glass. Both the induction time and the velocity of the methanol front are thermally activated, with apparent activation energies of 27.8 kcal mol- 1 and 26.4 kcal tool- 1, respectively. No further increase in the PMMA bead diameter has been observed after the penetrating methanol fronts have met at the centre, suggesting a negligible concentration gradient behind the Case II swelling front. In addition, the continuous increase of PMMA bead diameter during the induction period for methanol front penetration provides new supporting evidence for the existence of a Fickian precursor penetrating ahead of the sharp Case II front in the PMMA methanol system.

Детальніше...  

Two novel 2-substituted derivatives of thioxanthone-containing cinnamate (ethyl ester of 2-propenoic acid) and cinnamamide (N,N-dimethylacrylamide) groups are synthesized and characterized. The spectroscopic properties of these two new photoinitiators are examined and related to their photocuring behaviour in an epoxy acrylate resin and compared with those of commercial 2-isopropylthioxanthone. Despite an increase in the longest wavelength absorption maximum and corresponding extinction coefficient, most of the derivatives showed little improvement in photocuring activity when compared with 2-isopropylthioxanthone. Their lower activities were reflected in reduced fluorescence quantum yields and reduced phosphorescence quantum yields. Photolysis quantum yields of the cinnamate esters, however, were found to be increased compared with those of 2-isopropylthioxanthone. In this case photoreaction was observed in both nitrogen-saturated and oxygen-saturated 2-propanol. Using FTi.r. and FTh.m.r. analysis, the cinnamate groups were found to undergo a primary reaction involving (2 + 2) cycloaddition via the lowest excited singlet excited state. The cycloaddition reaction is found to compete effectively with hydrogen atom abstraction. This is confirmed on microsecond flash photolysis by the absence of any ketyl radical formation in nitrogen-saturated 2-propanol. The role of the cycloaddition reaction in controlling the photochemical activity of the thioxanthone chromophore is discussed

Детальніше...  

A new series of aromatic polyesters was prepared from bis(4-carboxy-2-methoxyphenoxy)alkanes and various aromatic diols such as hydroquinone, 4,4'-biphenol and bis(4-hydroxyphenyl)terephthalate; they were characterized especially for liquid crystalline properties. When the diol employed is hydroquinone and the alkylene spacer is hexa- or decamethylene, the polymer is not liquid crystalline. In contrast, the longer diols resulted in thermotropic compositions. Introduction of methoxy groups into the mesogenic units appeared to reduce the axial ratio of mesogenic groups, which caused depression in glass transition temperature, melting point and isotropization temperature of the polymers. Methoxy groups were also found to reduce the crystallizing tendency of polymers, probably due to their hindrance of chain and molecular packing in the solid.

Детальніше...  

Poly(1,4-butylene isophthalate)s containing sodium sulfonate groups were prepared from dimethyl isophthalate, 3,5-bis(carbomethoxycarbonyl) benzenesulfonate (5SIPNa) and 1,4-butanediol. Polymers of fairly high molecular weight were obtained with a content of ionic comonomeric units up to 16.7 mol%; however, increasing amounts of 5SIPNa led to a decrease in the molecular weight and to an increase in the COOH/OH terminal-group ratio. The ionomer samples were characterized for chemical structure, terminal groups, the concentration of sulfonate groups, solubility and their thermal properties. Results from different methods of terminal-group and sulfonate-group analysis were compared. Solubility was found to be strongly affected by the introduction of sulfonate groups, and samples containing 16.7 mol% of SO3Na groups were water dispersible. D.s.c. studies on samples containing sulfonate groups, either in the free acid or sodium salt form, suggested that the effects on glass transition temperature and crystallization were due to the introduction of bulky sulfonate groups into the polymer backbone rather than to ionic interactions. Thermogravimetry showed that SO3H groups decreased the thermal stability significantly, while SO3Na groups had only a limited effect with respect to pure poly(1,4-butylene isophthalate).

Детальніше...  

A series of aliphatic polyesters of 3,3'-thiodipropionic acid and linear glycols containing a different number of ethylene oxide groups has been prepared and characterized. These polymers show low values of glass transition temperature and appear, at room temperature, as highly viscous liquids, in which LiC104 can be dissolved easily. The resulting transparent semi-solid solutions behave as polymer electrolytes with high ionic conductivity, which has been investigated as a function of LiC104 concentration, temperature and chemical structure, i.e. the number of thioether sulfur and ether oxygen atoms in the backbone. The main factors that affect conductivity are the glass transition temperature and the solvating capacity for the lithium ions. It was found that both the oxygen and sulfur atoms contribute to solvating lithium ions.

Детальніше...  

An improved method for obtaining cross-sectional images of thin polymer films by transmission electron microscopy is described. Two examples are described in order to demonstrate the simplicity and flexibility of the technique, In the first example, the structure of a highly ordered block copolymer on a solid surface is examined. In the second example, the behaviour of colloidal gold particles at the interface between immiscible polymers is considered.

Детальніше...