Juraj Pavlinec

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.

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.

Thermal degradation of free radically prepared poly(methyl methacrylate). A nonisothermal weight loss study

Abstract The effect of initial molecular mass on the nonisothermal degradation of free radically prepared poly(methyl methacrylate) has been re-examined at a rate of heating of 10 K/min and in a dynamic nitrogen atmosphere. Apparent activation energies and pre-exponential factors have been ascribed to both the unsaturated end initiation and random chain initiation, taking into account the formal isokinetic temperatures. The corresponding values of isothermal rate constants were compared with literature data. It was found that cross-linking of poly(methyl methacrylate) leads to an increase in the thermal stability of the polymer fraction which undergoes initiation by random chain scission, the effect being particularly obvious for samples cross-linked with diamines.

Photocured polymer networks based on multifunctional β-ketoesters and acrylates

The objects of this study are highly crosslinked networks. The base-catalyzed Michael reaction of β-ketoesters with vinyl groups of the pentaerythritol tetra-acrylate (PETA) was used for a step grow formation of the crosslinked polymer in dark. The nonreacted vinyl groups and vinyl monomer were built up to the network structure by photopolymerization in the second step of synthesis. An analysis of crosslinked polymers shows that the long spacer between β-ketoester groups in propylenglycol-425-diacetoacetate (PGDAA) favors an extent of reaction compared to pentaerythritol tetrakis (acetoacetate) (PETAA). The excess of vinyl monomers added to polymerization batch functions in the first step of the synthesis as a reactive solvent [triethylene glycol dimethacrylate (TEGDMA); PETA]. The dissolution of reactants has a positive effect on homogeneity, conversion, and crosslink density of prepared networks. The consumption of reactive groups in a course of the network formation, the crosslink density, and dynamic mechanical properties of the prepared networks were determined from Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), sol-gel analysis, dynamic testing, and stress-strain dependencies. The dynamic testing indicates that the networks synthesized in two steps from batches containing an excess of vinyl monomer consist from two highly crosslinked phases interpenetrating each other.

Thermal degradation of multilayer methacrylate-acrylate particle-bead polymer powders and melts

Abstract The effect of the composition and form of polymer sample on a nonisothermal weight loss study of submicrometric multilayer polymer particles has been examined. Polymer beads consist of a poly(methyl methacrylate) (PMMA) core, poly(butyl acrylate) copolymer (BAC-co) network shell and a further layer of poly (methyl methacrylate) copolymer with butyl acrylate (MMA-co). Dynamic thermogravimetric curves show two stages for multilayer polymer powders and for particle polymer mixtures prepared by mixing emulsions before the freeze-thaw isolation of polymer. The first degradation step, due to PMMA depolymerization starts at a temperature 45 °C lower compared with degradation of the PMMA particle polymer powder alone. The polymer samples which were processed by melt stirring, press molded or even isolated from emulsions as transparent films before thermogravimetry analysis are more stable than polymer powders from emulsion. The weight loss of bulk samples proceeds smoothly in one stage like a one type polymer; nevertheless the PMMA is more sensitive to thermal degradation than the BAC-co network. The stabilization of PMMA in a blend with BAC-co in a bulk polymer sample is possibly due to the BAC-co compressed network which prevents PMMA depolymerization.

The Stability of Free Radicals in Densely Crosslinked Acrylate Polymer Networks

The four types of crosslinked polymer samples based on pentaerythritol tetraacrylate (PETA) and propylene glycol-425-diacetoacetate (PGDAA) were prepared in two steps. At first the Michael dark addition of vinyl groups of PETA to PGDAA results in polymer network (cf. Scheme 1). The higher conversion of residual vinyl monomer and pendant double bonds built up in the Michael network was achieved by a photo-initiated free radical polymerization in the second step of polymer network synthesis. The lifetime of trapped radicals was estimated by following the decay of radicals in the dark period of intermittent illumination directly in the resonator cavity of ESR spectrometer. The determined values of bimolecular termination rate constants k t are of order 10 -1 to 10 2 kg/mol . s in dependence on composition, structure of network, and environment. It was observed that oxygen facilitates the decay of free radicals. The k t values are of about 1 to 2 decimal orders higher than that determined in nitrogen. Moreover, as in each subsequent light-dark cycle the k t was increased, we believe that it is a consequence of enhancement the diffusion of free radicals by assisted oxygen chain reaction with formation of hydroperoxides. The exception is the sample B with the highest final crosslinks density and conversion of monomers to network. More tightly trapped free radicals were present in polymer networks photo-cured in nitrogen. The k t values in all four types of networks decreased in each consecutive light-dark cycle.

Molecular characterization of statistical copolymers: 1. Potential and limitations of full adsorption–desorption procedure in separation of statistical copolymers

Dynamic integral desorption isotherms for a series of poly(methyl methacrylate) homopolymers and poly(methyl methacrylate)–polystyrene statistical copolymers were measured. Nonporous silica was the full adsorption–desorption (FAD) column packing and various adsorption-promoting and desorption-promoting liquids were used. The aim of this study was to evaluate the applicability of the FAD approach for separation of statistical copolymers. The effects of the adsorbing liquid and desorbing liquid nature were demonstrated on the positions and shapes of desorption isotherms. The desorption isotherms also strongly depended on both (co)polymer molar mass and copolymer chemical composition. This indicates large fractionation potential of the FAD procedure. Simultaneously, the interference of both above parameters prevents the direct use of FAD for fractionation of the copolymers. It is anticipated that the fractionation and/or reconcentration potential of the FAD procedure can be very effectively utilized in combination of FAD with size-exclusion chromatography and/or with gradient elution liquid adsorption chromatography.

The oxidative decomposition of poly(methyl methacrylate)-crosslinked poly(butyl acrylate) core-shell polymers

Abstract The thermo-oxidative stability of polymer samples based on submicrometric three-layer bead particles was evaluated by dynamic thermogravimetry (TG). Polymer particles synthesized in emulsion consist of a poly(methyl methacrylate) core, a butyl acrylate crosslinked copolymer interlayer and a methyl methacrylate butyl acrylate copolymer shell. The comparative mass loss study in oxygen and nitrogen leads to the following conclusions. Oxygen retards the decomposition to volatiles of the polymer sample isolated from the emulsion in powder form at lower temperatures at the beginning of the process. The second stage of the TG record which is relevant to the mass loss of the butyl acrylate copolymer shows a higher rate of formation of volatiles. In oxygen, the densified polymer samples prepared by melting the particle polymer powder do not show a substantial difference compared to the TG curves observed for powder samples. However, the thermodegradation in nitrogen is shifted by more than 60 °C to higher temperatures. We explain the different course of the TG curves by a denser packing of core-shell particles in the processed samples. The diffusion of reaction products from the reaction cage is slowed down with a positive effect on thermostability. Oxygen acts in the opposite way through the oxidative polymer chain scission of macromolecules and increases the rate of initiation of depolymerization. Increasing the rate of heating of the sample in oxygen only has a small effect on shifting the volatilization to higher temperatures. This is less evident than in nitrogen.

Influence of shear stress treatment on stress-strain properties of methyl methacrylate-crosslinked butyl acrylate core-shell polymers

The incorporation of multilayer toughness modifiers to glassy polymers proceeds frequently by kneading the polymers in a molten state. This process influences the primary structure of the modifier and the properties of the blend in dependence on a shear stress intensity. In this article, we compare the properties of polymer materials prepared from a multilayer poly(methyl methacrylate) core, butyl acrylate copolymer interlayer, and methyl methacrylate copolymer shell particles {P[MMA-(BAC-co)-(MMA-co)]} by press-molding from powder and from polymer obtained by stirring a melt of this powder in the chamber of a Brabender mixer (200°C, 60 rpm, 10 min). The powder is obtained from a latex by coagulation after polymer synthesis in emulsion. Tensile testing shows different responses of the particle polymers when crosslinked in the middle layer by diallylphthalate (DAP) or by triallylcyanurate (TAC). Although many of the properties of the samples with DAP are improved by kneading, the presence of TAC in polymer particles led mostly to less desirable properties. The maximum percent strain in the polymer with 4.2 wt % of DAP upon shearing increases from 27% to 50%. In the samples with 4.5% TAC the maximum percent strain falls from 39% to 7%. Comparison of Youngs modulus E for identical samples shows an analogous effect: a shift from 429 MPa to 638 MPa and from 624 MPa to 548 MPa. The design of the polymer particles used in this work leads to the conclusion that stress during kneading induces a partial desintegration of the crosslinked cage around the particle core. Thus, the varied behaviors of polymers used in this study are connected with the BAC-co network structure and its transformations during the shear stress treatment of the initial polymer material.