1999 рік

Studies of ethylene/1-octene copolymers prepared by a metallocene catalyst were carried out through dynamic-mechanical experiments (DMTA), differential scanning calorimetry (DSC), Raman spectroscopy and gel permeation chromatography (GPC). The influence of comonomer content on the ethylene/1-octene properties, specially those related to the dynamic-mechanical behaviour were studied. It was observed that the intensity of the b -transition increases as the comonomer content increases and decreases crystallinity.

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The influence of the interfacial tension on the composition range within which fully co-continuous polymer blend structures can exist is studied for different blends with selected matrix viscosities and viscosity ratios. The critical composition for full co-continuity is found to increase with increasing interfacial tension, narrowing the composition range. The effect of the interfacial tension on the critical composition is composed of two counteracting effects, i.e. the stability of the co-continuous morphology and the phase dimensions. The latter effect is smaller than the former. The experimental results can quantitatively be predicted by a model published earlier, provided the phase dimensions are measured separately.

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Direct polymerization of bisphenol A with CO was carried out using a Pd–Cu-based redox catalyst system. A base for activating the hydroxy group of bisphenol A and a dehydrating agent for removing the water produced during the reaction were other important components of the catalyst system. Synthesized polycarbonate was characterized using IR, NMR, and GPC. MALDI-TOF mass spectroscopy was used for understanding the structure of polymer chain end groups.

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In this work we describe the conditions of preparation and the electrical, mechanical, thermal and morphological characteristics of a conductive blend prepared by combining the elastomer poly(ethylene-co-propylene-co-diene-monomer) and polyaniline doped with ptoluene sulfonic acid. Polymer mixtures were prepared in a mixer chamber (cam rotors) coupled to a rheometer. A higher mixing temperature improves the homogeneity of the mixtures, as seen by an increase in conductivity and in crosslinking efficiency. In spite of the good homogeneity, the mixtures are imiscible. Therefore, the formation of bonds between the high molar mass chains of polyaniline and the oligomers explain the increase of the conductivity with an increase in polyaniline content. The modulus values also increase by adding polyaniline to the rubber suggesting a reinforcement effect.

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In this work the influence of the chemical structure and of the morphology on the gamma-radiation effects on polypropylene based polymers is studied on the basis of a previously discussed kinetic model [1]. For this aim an isotactic polypropylene and a random ethylene– propylene copolymer were irradiated under vacuum at one dose rate and several absorbed doses after well defined solidification conditions. We show that the model is reliable varying both the chemical structure and the morphology of the polypropylene based polymer. An inversion of the response of the material to gamma radiation under vacuum is always observed, and the inversion conditions depend on the irradiation parameters. In particular at a fixed dose rate we check an absorbed dose, depending on the ethylene and mesomorphic phase content in the polymer, in correspondence of which a significant change in the molecular response to gamma irradiation occurs.

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A range of per-deuterated cyclic poly(dimethylsiloxanes) (PDMS) have been conveniently prepared in a high dilution reaction from bis(trideuteriomethyl)diphenylsilane using a catalytic amount of trifluoromethanesulphonic (triflic) acid in the presence of water as proposed. The cyclic and linear per-deuterated polymers produced have been separated and the cyclics fractionated by preparative gel permeation chromatography (GPC). The resulting sharp fractions of per-deuterated cyclic PDMS have been obtained in up to 0.6 gram quantities ranging in size from 45 to 605 number–average number of skeletal bonds, all with dispersities less than 1.2. The purity of the samples obtained has been verified by various analytical techniques and these materials will allow the first studies of the conformations and properties of cyclic polymers in chemically identical blends using neutron scattering.

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This study assesses the nature of sorbed water and the related hygrothermal effects in epoxy resins. This paper is the first of a two-paper series. Three epoxy systems, DGEBA 1 mPDA, TGDDM 1 DDS, and Fiberite 934, were used in the investigation. Water sorption was achieved by immersing the materials in distilled water at constant temperature of 458C, 608C, 758C and 908C for 1530 h. Water absorption and desorption profiles were analyzed to determine the diffusion parameters. Solid state nuclear magnetic resonance (NMR) was conducted to determine the mobility of water in epoxy. The study shows that water molecules bind with epoxy resins through hydrogen bonding. Two types of bound water were found in epoxy resins. The binding types are classified as Type I or Type II bonding, depending on difference in the bond complex and activation energy. The activation energy of Type I and Type II bound water is , 10 and , 15 kcal/mol, respectively. Type I bonding corresponds to a water molecule which forms a single hydrogen bond with the epoxy resin network. This water molecule possesses a lower activation energy and is easier to remove from the resin. Type II bonding is as a result of a water molecule forming multiple hydrogen bonds with the resin network. This water molecule, therefore, possesses a higher activation energy and is correspondingly harder to remove. Type I bound water is the dominant form of the total amount sorbed water. The amount of Type II bound water depends strongly on the exposure temperature and time. Higher immersion temperature and longer exposure time result in a greater amount of Type II bound water.

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The crystallisation behaviour and morphology of polyethylene-based single polymer composites has been investigated by light microscopy and low voltage scanning electron microscopy techniques. The surface crystals on ultra high molecular weight polyethylene fibres act as nucleation centres for the high density polyethylene matrix, which may result from epitaxial crystallisation. After crystallisation from the melt and independent of air-cooled or isothermal crystallisation conditions, a transcrystalline layer was found having lamellar crystals grown perpendicular to the fibre axis.

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The photopolymerization of acrylamide in aqueous medium initiated by redox system consisting of 4-carboxybenzophenone and sulfurcontaining amino acids was studied. The rate of polymerization depends on the quenching rate of the 4-carboxybenzophenone triplet by the sulfur-containing amino acid and on the kind of radicals obtained.

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Three epoxy systems (DGEBA 1 mPDA, TGDDM 1 DDS, and Fiberite 934 TM) were used to investigate glass transition temperature (Tg) variation of epoxy under hygrothermal environment exposure. Materials were immersed in distilled water at constant temperatures of 45 oC, 60 oC, 75 oC, and 90 oC for water absorption and then desorbed at different temperatures. Thermomechanical analysis (TMA) and differential scanning calorimetry (DSC) were employed to determine Tg changes at different hygrothermal stages. The investigations revealed the following results: i) the change of Tg does not depend solely on the water content absorbed in epoxy resins, ii) Tg depends on the hygrothermal history of the materials, iii) for a given epoxy system, higher values of Tg resulted for longer immersion time and higher exposure temperature, and iv) the water/resin interaction characteristics (Type I and Type II bound water) have quite different influence on Tg variation. A sorption model and collateral evidence introduced in Part I of the series were used to interpret and explain Tg variation in epoxy resin systems. Both Type I and Type II bound water influence Tg variations, albeit in different ways. Type I bound water disrupts the initial interchain Van der Waals force and hydrogen bonds resulting in increased chain segment mobility. So Type I bound water acts as a plasticizer and decreases Tg. In contrast, Type II bound water contributes, comparatively, to an increase in Tg in water saturated epoxy resin by forming a secondary crosslink network. The experimental Tg values encompass the combined effect of the two water-resin interaction mechanisms described briefly in the preceding text and in detail in Part I of this paper series. The often-cited polymer-diluent model used to predict Tg variation of polymers exposed diluent media is lacking when a dual sorption mechanism is involved during hygrothermal exposure process.

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