Leyla Aras

The glass transition behaviour and thermodynamic properties of amorphous polystyrene

Abstract The effect of molecular weight (MW) and thermal history on the heat capacity ( c p ) of amorphous polystyrene over the temperature range from 200–440 K has been measured using differential scanning calorimetry (d.s.c.) General equations are given that show the influence of MW on c p in both the glassy and liquid states. An enthalpic definition of the glass temperature reflects changes in the glass structure, due to thermal history, that are not found using conventional d.s.c. constructions. Thermodynamic and statistical mechanical theories give reasonable approximations to the observed T g -MW curve but small systematic deviations are found. The effect of thermal history on T g can be reproduced using a MW-dependent activation enthalpy.

Synthesis and characterization of waterborne and phosphorus-containing flame retardant polyurethane coatings

Phosphorus-containing flame retardant water-dispersed polyurethane coatings were produced by incorporating different amounts of a phosphorus compound onto the polyurethane main chain. The novel phosphorus containing compound (phosphorus phenyl dihydroxy) was synthesized in three steps using benzaldehyde, pentaerythritol, phenyl phosphonic dichloride, and acetic acid.The addition of phosphorus phenyl dihydroxy to the main chain of polyurethane, in which NCO/OH ratio was kept constant at 1.5 and the amount of dimethylolpropionic acid (DMPA) at 3.5 wt%, increased the hardness and abrasion resistance, but only slightly decreased the gloss values of the polyurethane paints. All the samples showed superior impact resistance and flexibility. Moreover, increasing the phosphorus content increased the char yield, and the maximum fire retardancy was reached at 1.5% P content with a limiting oxygen index (LOI) value of 29.

Synthesis of mainly linear poly(dichlorophenylene oxide) based on the electro-oxidation of bis(pyridine)bis(4-bromo-2,6-dichlorophenoxo)copper(spii) complex in dimethylformamide

Anodic oxidation of bis(pyridine)bis(4-bromo-2,6-dichlorophenoxo)copper(spii) complex leads mainly to linear poly(2,6-dichlorophenylene oxide) under constant-potential electrolysis in the dimethylformamide-tetrabutylammonium tetrafluoroborate solvent-electrolyte couple at room temperature under air or nitrogen. Polymerization conditions were based on the peak potentials measured by cyclic voltammetry. Characterization of the polymer was performed by 13C and 1H nuclear magnetic resonance, Fourier-transform infra-red spectroscopy, differential scanning calorimetry, molecular-weight and dipole moment measurements.

Polymerization of bis(2-bromo-4,6-dichlorophenoxo)bis(pyridine) copper (II) complex in DMF by electroinitiation

Abstract Polymerization of bis(2-bromo-4,6-dichlorophenoxo)bis(pyridine) copper (II) complex was achieved in dimethylformamide by electrooxidation. A cyclic voltammogram (CV) of the complex was obtained in dimethylformamide in advance. Constant potential yielded polymers in anode compartment only under nitrogen atmosphere and air. In the final polymer product, incorporation of neither the ligand nor the copper was observed and the post-polymerization proceeded in the absence of current. The structural analyses of the polymers were done by 13C n.m.r., 1H n.m.r., FTi.r. spectroscopy, differential scanning calorimetry (d.s.c.) and dipole moment measurements. The molecular weight of the polymer was determined by cryoscopic method. The poly(dihalophenylene oxides) obtained at different potentials were found to be similar in structure and both 1,2 and 1,4 catenations took place at roughly equal rates.

Graph theoretical approach to the mechanical strength of polymers

In this research work, a graph theoretical approach has been introduced to find a mathematical model for the change of hardness of weakly cross-linked polymer network systems with the change of configurations. The polymers studied are (i) poly(methyl methacrylate), (ii) styrene–acrylonitrile copolymer and (iii) polystyrene. In very weakly cross-linked polymer network systems, both the chain entanglement and the network rigidity competitively contribute to the hardness of polymer network. The average length (i.e. molecular weight), and length distribution of chains between the cross-linking sites both play important roles in network rigidity. The former can be changed by the mole fraction of the cross-linker, and the latter by the molecular weight of the prepolymer formed, which can be controlled by the late addition of the cross-linker. Graph theoretical approach introduces simplifications to the dynamics of polymer chains and polymer network, and thus can explain the change of hardness with the change of chain statistics. It was shown that there was a very good agreement between the theoretical equations and the experimental hardness values of polymer network systems studied. It was also found that there were scaling relations between the parameters used in the theoretical equation.

Effect of ion association on the properties of ionomers obtained from methyl methacrylate-methacrylic acid copolymer

Abstract The solution behaviour of Na, Ba, Zn and Al ionomers of methyl methacrylate-methacrylic acid copolymer (P(MMA-MAA)) with different ion contents has been studied by viscosity and dipole moment measurements. Two solvents with different character are chosen for viscosity measurements: dioxane ( e = 2.22) and acetone ( e = 20.7). The expected polyelectrolyte behaviour of the ionomers in acetone is reflected by the viscometric measurements. Mean squared dipole moment 〈 μ 2 〉 values are calculated over a temperature range of 20–100°C in dioxane. Effects of neutralization, cation size and cation charge are discussed for each ionomer.

Synthesis and Characterization of Surface Sulfonated Polypropylene Films

The basic reseach on the surface sulfonation of polypropylene (PP) is very important for design of surfaces for higher functionalization. For this purpose, liquid-phase sulfonation of polypropylene surfaces at various temperatures and different time periods was performed using concentrated sulphuric acid. The physical and chemical changes produced by the sulfonation on the polypropylene surfaces were determined by contact angle measurements, mechanical analysis, UV-Vis spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Both surface polarity and wettability of PP films were improved by sulfonation at low temperatures for short time periods; however, sulfonation at longer times, or higher temperatures, caused degradation of PP films. All sulfonated film samples had lower yield stress and stress at break.

The compatibilization of methyl methacrylate-methacrylic acid copolymer and polystyrene through the functionalization of polystyrene

Abstract The compatibility of ionomer/polymeric acid blends has been studied for polymer pairs consisting of sodium salts of sulfonated polystyrene and methyl methacrylate-methacrylic acid copolymer using dilute solution viscometry. The intrinsic viscosities of the blends, prepared in three different weight fractions (25, 50 and 75%) using the solution-blending technique, were measured in two solvents with different polarities: dioxane ( ϵ = 2.24) and tetrahydrofuran ( ϵ = 7.26). The degree of compatibility of the blends was characterized using the Δb parameter. Results show that the percentage sulfonation, temperature and polarity of the solvent all affect the miscibility.

Conductivity and Thermally Stimulated Processes in Ionomers Based on SIS Block Copolymers

The relaxation and conductivity properties of ionomers based on styrene-isoprene-styrene triblock copolymers modified by maleic anhydride were investigated from 100 to 400 K by means of thermally stimulated depolarization and polarization methods, stressing the comparison of materials containing alkaline and alkaline-earth cations. It was shown that the behavior is largely determined by the thermal stability of ionic associations and their ability to trap charge carriers. With alkaline-earth cations, the associations are thermally stable at least up to 400 K, which gives rise to a conductivity level smaller than that of the starting material by several orders of magnitude. An opposite result is observed with alkaline cations as a consequence of the thermal breaking of ionic associations, which occurs in the glass transition range and results in a rapidly growing number of mobile ions.

Synthesis and characterization of 1,4-diazophenylenebridged Cu-phthalocyanine polymer

Abstract A novel type of phthalocyanine polymer, 1,4-diazophenylene-bridged Cuphthalocyanine, was prepared from the diazonium salt of diaminobenzene and Cu(II) 1,8,15,22-tetraaminophthalocyanine. The polymer is partially soluble in tetrahydrofuran, dichloromethane, and dimethylformamide. Characterization of the polymer was performed by IR and UV-visible spectroscopy, X-ray diffraction, ash analysis, viscometry, differential scanning calorimetry and thermogravimetric analysis. The molecular weight of the soluble part of the polymer was determined by ebullioscopy. Electrical conductivity of the polymer and its doped samples were determined by the 4-probe technique. It was found that the electrical conductivity increased up to 10-4 S/cm after doping. The redox behaviour of the polymer was investigated utilizing cyclic voltammetry.