Jürgen Pionteck

Electrical properties and stability of polypyrrole containing conducting polymer composites

Abstract Conducting polymer composites of polyethylene and polypyrrole (PE/PPy), polypropylene and polypyrrole (PP/PPy), and poly (methyl methacrylate) and polypyrrole (PMMA/PPy) were prepared by means of a chemical modification method, resulting in a network-like structure of polypyrrole embedded in the insulating polymer matrix. The content of polypyrrole determined by elemental analysis varied from 0.25 to 17 wt.%. Electrical conductivity of compression-moulded samples depends on the concentration of polypyrrole and reached values from 1 × 10 −11 to 1 S/cm. The morphology of the composites was investigated by low-voltage scanning electron microscopy (LVSEM). Potential contrast measurements as a function of the acceleration voltage were used to prove the perfection of the PPy network structure. The electrical transport mechanism in PP/PPy composite was studied. The data of the temperature dependence of conductivity were fitted following the function for a charge-energy-limited tunnelling (CELT) model. There is only a small drop in conductivity caused by annealing of PP/ PPy composites in air at temperatures up to 80 °C. A stabilizing effect of PPy on thermal stability of polypropylene is shown by thermogravimetric analysis. The antistatic properties of PE/PPy and PMMA/PPy composites were demonstrated.

Influence of processing conditions on the multiphase structure of segmented polyurethane

Abstract The multiphase structure of thermoplastic polyurethane elastomers is not only influenced by the chemical structure, but also by the processing conditions. The polymorphism of hard segment (HS) crystallites of a commercial polyurethane was investigated in dependence on the melt processing conditions using WAXS and d.s.c. The observed crystalline morphology types are strongly influenced by the processing temperature. Analysis of the results permits the assignment of HS crystallites of so-called ‘type II’ with high WAXS intensity to those melting above 220°C. Additionally, the tensile strength was determined. These results related to the d.s.c. data allow to establish a processing-structure-property relation.

Study of molecular dynamics of pharmaceutically important protic ionic liquid-verapamil hydrochloride. I. Test of thermodynamic scaling

Relaxation dynamics of verapamil hydrochloride (VH), which is a representative of ionic liquids, was studied under isobaric and isothermal conditions by using dielectric spectroscopy. In addition we also carried out pressure-temperature-volume (PVT) measurements. The obtained data enable us to examine the structural α-relaxation time τα as a function of temperature, pressure, and volume. Since the examined sample is a typical ionically conducting material, we employed the dielectric modulus formalism to gain information about α-relaxation process. It was found that application of pressure changes the shape of the modulus spectrum. The α-peak becomes narrower with compression. Consequently, it was also shown that the stretching parameter βKWW increases with pressure. Based on experimental data both the isobaric fragility (mp) at various pressures and isothermal fragility (mT) at various temperatures were calculated. Analyzing the effect of pressure on the dependences τα(T) as well as on the shape parameter...

Temperature Dependence of the Free Volume in Fluoroelastomers from Positron Lifetime and PVT Experiments

The microstructure of the free volume and its temperature dependence in fluoroelastomeric copolymers of tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether) (PMVE), PFE, as well as vinylidene fluoride (VDF) and hexafluoropropylene (HFP), VDF78/HFP22, were studied by pressure- volume-temperature experiments (PVT, T ) 300-485 K, P ) 0-200 MPa) and positron annihilation lifetime spectroscopy (PALS, T ) 100-473 K, P ) 0 MPa). Employing the Simha-Somcynsky equation of state (S-S eos), the excess free (hole) volume fraction h and the specific free and occupied volumes, Vf ) hV and Vocc ) (1 - h)V, were estimated from the specific total volume V. The temperature and pressure variation of these volumes and their expansivity and compressibility will be discussed. The PALS spectra were analyzed using the routine LT9.0 assuming a dispersion in both the positron (U2) and ortho- positronium (o-Ps) lifetime (U3). From the lifetime parameters the hole size distribution, its mean value 〈vh〉 and dispersion Uh were calculated. From a comparison of 〈vh〉 with V and Vf the specific hole number Nhwas estimated. Nhwas determined to be independent of the temperature. Indications were found that o-Ps may prefer larger holes with a weight approximately proportional to the hole volume. Apparent discrepancies between S-S modeling and the conclusions from PALS are discussed. From the comparison of the hole size distribution with the theory of thermal fluctuation a fluctuation volume 〈V〉 is estimated which decreases above Tg with increasing temperature. Attempts are made to interpret the PALS results in terms of the theory of structural and dynamic heterogeneity of glass-forming liquids.

Preparation and characterization of electrically conductive polypropylene/polypyrrole composites

Abstract Polypropylene particles 35 μm in diameter were chemically coated with polypyrrole. The content of polypyrrole varied from 1.1 to 10.4 wt%. Polypropylene/polypyrrole (PP/PPy) composite films about 0.2 mm thick were prepared by compression moulding of modified powders. The electrical conductivity of compression moulded samples depends on the concentration of polypyrrole, and reached values from 4 × 10 −10 to 5 × 10 −3 S cm −1 , which is about seven orders of magnitude higher than the conductivity in the blends prepared by mechanical mixing of PP and PPy in the same PPy concentration range. The PP/PPy composites were characterized by elemental analysis, infrared spectroscopy, light microscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). SEM pictures showed significant different in coverage of the surface of the PP particles, while the concentration change was within the range from 1.1 wt% to 8.9 wt% PPy.

Electrical and mechanical properties of conducting polymer composites

The method of chemically initiated oxidative modification of polypropylene particles in suspension by pyrrole was used for preparation of conductive polypropylene/polypyrrole composites. Their properties were compared with either polypropylene/polypyrrole composites prepared by melt mixing of virgin polypropylene with chemically synthesized polypyrrole or with polypropylene/carbon black composites prepared also by melt mixing. The composites were characterized by elemental analysis and by mechanical testing. The influence of the processing conditions on the properties of composites is shown. The antistatic properties of prepared composites were demonstrated.

Free volume in two differently plasticized poly(vinyl chloride)s: a positron lifetime and PVT study

The temperature dependence of the specific volume, V; and of the mean size of local free volumes (holes), vh; of poly(vinyl chloride) containing 10 wt% (PVC-h) and 30 wt% (PVC-s) of the plasticizer di-n-butyl phthalate (DBP) were studied by pressure ‐ volume ‐ temperature (PVT) and positron annihilation lifetime spectroscopy (PALS) experiments. Using the Simha ‐ Somcynsky equation-of-state, the hole fraction h was calculated from the PVT data. It was found that the thermal expansivity of the specific volume V; the specific free volume Vf ¼ hV; and vh increase with the content of plasticizer. From the comparison of V and Vf with vh the hole number per gram N 0 is estimated. Other than vh; N 0 does not depend on the temperature nor on the content of plasticizer.

Synthesis, electrical properties and stability of polypyrrole-containing Conducting polymer composites

Conducting polymer composites of polyethylene and polypyrrole (PE/ PPy), polypropylene and polypyrrole (PP/PPy) and poly(methyl methacrylate) and polypyrrole (PPMA/PPy) were prepared by means of a chemical modification method resulting in a network-like structure of polypyrrole embedded in the insulating polymer matrix. The content of polypyrrole determined by elemental analysis varied from 0.25 to 17wt%. Electrical conductivity of compression-moulded samples depended on the concentration of polypyrrole and reached values from 1 x 10 -11 to 1Scm -1 . The morphology of the composites and blends was studied by low-voltage scanning electron microscopy. The stability of PP/PPy composites was investigated by thermogravimetric analysis and by conductivity measurements during heating-cooling cycles. There was only a small drop in conductivity caused by the annealing of PP/PPy composites in air at temperatures up to 80°C. The results of thermogravimetric analysis showed a stabilizing effect of PPy on PMMA/PPy composites against thermal degradation. The antistatic properties of PMMA/PPy composites were demonstrated.

Synthesis of functional polymers by atom transfer radical polymerization

The preparation of monochelic polystyrene by atom transfer radical polymerization (ATRP) was investigated. The polymer analogous pathway by substitution of the bromide by an alcoholate resulted in significant elimination of the bromide and the degree of functionalization was low. Better results were achieved by the use of functional initiators. Carboxylic acid- and anhydride-bearing initiators were prepared by bromination of the commercially available 4-ethylbenzoic acid and the 4-methylphthalic anhydride, respectively. With these two products monochelic polystyrenes were synthesized. Further modification of the 4-(1-bromoethyl)benzoic acid led to initiators with a hydroxy or an oxazoline moiety. Again, the respective functional polystyrenes were obtained.

Degradation of interpenetrating polymer networks based on PE and polymethacrylates by electron beam irradiation

This paper describes the synthesis of interpenetrating polymer networks (IPN) materials based on polyethylene (PE) and polymethacrylates and the effect of ionising irradiation on degradation and grafting reactions in these materials. Two IPN systems, polyethylene/poly(butyl methacrylate-co-methyl methacrylate) and polyethylene/poly(dodecyl methacrylate-co-ethyl methacrylate), were synthesized by the in situ method using a peroxidic initiator and a divinyl crosslinker. During the synthesis the PE crosslinks and grafting reactions between PE and polymethacrylates occur. By electron beam irradiation the methacrylate phase partially degrades. After extraction with xylene a porous structure in the material is observed. The effect of the IPN composition, the synthesis conditions, and the electron beam irradiation on the amount of extractable material and the morphology of the IPN has been studied.