The effect of densification on the mechanical properties of amorphous glassy polymers

Four polymers, viz. polystyrene, polycarbonate, poly(methyl methacrylate), and poly-(vinyl chloride), were cooled from the melt to room temperature under hydrostatic pressures of 30 and 1000 atm. Cooling under high pressure increased the density by 0.4–0.6%, and the effect of this has been examined for the torsional creep properties, the dynamic properties at 1 Hz, the Charpy impact strength, the thermal expansivity, and the torsional yield stress. It turned out that, in general, densification affects the thermomechanical properties only slightly.     

The effect of hydrostatic pressure on the flow properties of various polymers

A novel device to fit on the exit of the ACER capillary extrusion rheometer has been designed to allow the controlled application of hydrostatic pressure to the body of the fluid under test. The rheological properties of the fluid can be examined over a wide range, ambient to 200MPa. This paper will describe the equipment and the effect of hydrostatic pressure and temperature on the flow properties to the various polymer melts, PC, ABS, PP and HDPE.     

The effect of crosslinking on thermal and mechanical properties of perfluorocyclobutane aromatic ether polymers

As the minimum features in semiconductor devices decrease, it is a new trend to incorporate copper and polymers with dielectric constant less than 3.0 to enhance the performance of the devices. Two fluorinated polymers, poly(biphenyl perfluorocyclobutyl ether) (BPFCB) and poly(1,1,1-triphenyl ethane perfluorocyclobutyl ether) (PFCB), are newly developed polymers with dielectric constants below 3.0. These two polymers have a similar backbone structure, but PFCB has the capability of crosslinking. To know the implications of these two polymers in the semiconductor industry, properties that are important for the integral reliability of Integral Circuits (IC), such as thermal and mechanical properties, should be understood. This comparative study shows that the crosslinking in perfluorocyclobutane aromatic ether polymer can reduce vertical thermal expansion and increase glass transition temperature (T_g) while water absorption, crystalline-like phase, and dielectric constant are slightly increased. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1383–1392, 1998     

Structure and properties of non-classical polymers. IV. Magnetic properties of polymers with superexchange interaction

It is shown that, for a new class of polymers, ferromagnetic superexchange may arise. The model polymers of the new class have specific electronic structure. In addition to the delocalized system of coupled π electrons, these polymers have singly occupied molecular orbitals localized within each monomer unit. The localized electrons are indirectly exchange coupled, mediated via delocalized orbitals. The resultant exchange interaction is ferromagnetically signed. It depends strongly on the energy gap of the delocalized π-electron system. The suggested model is close to the superexchange of some rare earth magnetics where magnetic f electrons interact indirectly due to delocalized s electron system. The theory of Ruderman, Kittel, Kasuya and Yosida is used in the quantitative treatment of the exchange interaction.     

The effect of hydrogen bonding on the physical and mechanical properties of rigid‐rod polymers

The idea of competing effects between intramolecular and intermolecular hydrogen bonding was investigated. Results indicate that the formation of one type of hydrogen bond does not preclude the formation of the other. The strength of the intermolecular association was measured by ab initio calculations for several polymer systems, including methyl pendant poly(p‐phenylene benzobisimidazole) and poly‐{2,6‐diimidazo[4,5‐b:4′5′‐e]pyridinylene‐1,4(2,5‐dihydroxy)phenylene} (PIPD). Fibers with strong intermolecular association have high compressive strength and torsional modulus. The influence of intermolecular hydrogen bonding on torsional modulus is discussed in light of the transverse texture present in poly(p‐phenylene terephthalamide) and some other high‐performance fibers. Enhanced intermolecular interaction not only influences the aforementioned properties but also results in higher fiber density. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3053–3061, 2000     

The influence of network structure on the macroscopic mechanical properties of crosslinked polymers

Neat and rubber-toughened epoxy resin systems EPN/BA and EPN/DDS with significantly different crosslink densities and glass transition temperatures were tested under widely different experimental conditions ranging from impact to long-term loading. The resulting deformation mechanisms were examined in order to ascertain the effects of network structure and toughening modifiers. Different toughening mechanisms were observed in low- and high-crosslink-density epoxy systems, modified with the same core-shell rubber particles.     

Thermodynamics of crystalline linear high polymers. IV. The effect of ethyl,acetate, and hydroxyl side groups on the properties of polyethylene

Copolymers of ethylene with vinyl acetate, vinyl alcohol, and butene-1 have been investigated by differential thermal analysis. The method of fast heating is used to approximate a zero entropy production heating path. The activity of crystallizable units in the melt, the crystallinity, and the a-axis spacings are determined and compared with previous results for copolymers of ethylene and propylene and carbon monoxide. Carbonyl and hydroxyl groups form point defects, forming solutions in both the crystalline and amorphous regions. Methyl, ethyl, and acetate groups form large amorphous defects. The maximum melting point of polyethylene is calculated to be 142.6°C.     

The mechanical properties of MoN under high pressure and effect of metallic bonding on its hardness

Using first-principles calculations, the structural, electronic and thermodynamic properties of MoN under high pressure are investigated, as well as the effect of metallic bonding on its hardness. Five structures are considered, i.e., δ-MoN, WC-MoN, NiAs-MoN, NaCl-MoN and CsCl-MoN. The obtained lattice constant, elastic constants are in good agreement with the available experimental data and other theoretical results. δ-MoN phase is found to be energetically the most stable phase closely followed by NiAs-MoN phase at ambient conditions. On the basis of the third-order Birch–Murnaghan equation of states, a pressure-induced structural phase transition from δ-MoN to NiAs-MoN is observed. Elastic properties, Poisson's ratio, Debye temperature, and thermal expansion coefficient of MoN under high pressure are derived. Furthermore, the bonding nature of MoN can be described as covalent-like due to hybridization of N and Mo states, together with ionic and metallic characters. Based on Mulliken population analysis, hardness of MoN is evaluated and the obtained results, namely, NiAs-MoN (26.6 GPa) and δ-MoN (24.7 GPa), are consistent with experimental data excellently. Moreover, the hardness of MoN increases with the pressure. This is a first-principles investigation on the structural and thermodynamic properties of MoN, and it still awaits experimental confirmation.     

Capillary and slit-die flow of two liquid-crystalline polymers. The effect of pressure on viscosity

Viscosity measurements on two commercial thermotropic liquid crystalline polymers (LCPs) (a copolyester and a polyesteramide) were performed using both capillary and slit die methods. The results are in agreement with those presented in the literature for the same LCPs, when the measurements are carried out with a L/D = 30 die; these results are affected more by Bagley corrections for the polyesteramide than for the copolyester. For both LCPs, viscosities measured in the slit die are lower than those obtained by capillary rheometry. Nevertheless, the difference is much bigger in the case of the polyesteramide, for which a reduction by a factor of 3 is observed. This is not due to the preshear or thermal history, since the same piston-barrel system and thermal treatment were applied in both types of measurements. Depending on the polymer sample and temperature, concave and convex curvatures were observed in the pressure profiles during the slit flow. From these curvatures, the pressure coefficient α of viscosity was evaluated. However, in the case of the polyesteramide the convex curvature leads to a negative coefficient (the viscosity decreases with pressure, instead of increasing). This result may be explained by envisaging a change in the structure of the melt along the slit length. © 1993 John Wiley & Sons, Inc.     

Dilatometric measurements on some polymers: The pressure dependence of thermal properties

Summary For linear polyethylene, polyethyleneoxide and isotactic polypropylene we report measurements of the specific volume as a function of temperature and pressure, up to 1 kbar (for PE up to 10 kbar) obtained by slow cooling from the melt (6 K/h). Expansivity and compressibility of the melt and the temperature of crystallization are evaluated. By means of the volume of fusion and the Clausius-Clapeyron equation — the applicability of which is discussed briefly — one gets the enthalpy and the entropy of fusion. For polyethylene and polyethyleneoxide these data are shown to decrease with increasing pressure.

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Zusammenfassung Messungen des spezifischen Volumens als Funktion der Temperatur und des Drucks wurden an linearem Polyäthylen, an Polyäthylenoxid und an isotaktischem Polypropylen durch langsames Abkühlen aus der Schmelze (6 K/h) in einem Bereich bis 1 kbar (PE bis 10 kbar) durchgeführt. Daraus ausgewertet wurden die Ausdehnung und die Kompressibilität der Schmelze, sowie die Kristallisationstemperatur. Der Volumensprung sowie die Schmelzenthalpie und die Schmelzentropie wurden berechnet — die beiden letzteren mit Hilfe der Clausius-Clapeyronschen Gleichung, deren Anwendbarkeit diskutiert wird. Für Polyäthylen und Polyäthylenoxid nehmen diese Werte mit steigendem Druck ab.

     

The effect of sugars on the mechanical properties of processed cereals

Breakfast wheat-flake materials of different composition have been reconstituted as barshaped test pieces to reduce geometry and structure effects and allow better comparison of the matrix mechanical properties. The ground flakes comprised a control formulation and others in which components had been subtracted or substituted. The aim was to compare the mechanical properties of pressed specimens of multiple-component systems with those published for simpler one- and two-component materials. Sucrose or fructose, present in the ratio sugarwheat 15.9–6.1, lowered the modulus of wheat-flake material, but by progressively lesser extent with decreasing water content below 22% (wet-weight basis, w.w.b), the difference becoming negligible at water contents of 7 to 10% (w.w.b). However, the energy to break wheat-flake samples and their fracture toughness were reduced more by fructose than sucrose addition to a control formulation sample at these water contents. The energy to break and fracture toughness increased markedly with increasing water content for all formulations.This work was supported by a MAFF-DTI LINK grant under the Food Processing Sciences Programme involving Weetabix Ltd, APV Baker, Campden Food and Drink Research Association, University of Nottingham and Novo Nordisk (UK) Ltd. The authors acknowledge the scientific and financial support of the MAFF and LINK participants. They would also like to thank Dr. Simon Livings (University of Cambridge, Cavendish Laboratory) for his advice on preparation of hot pressed-samples and Mr. David Steer for the design of the hot press.     

The mechanical and optical properties of oriented fibres of semicrystalline polymers

The mechanical properties of semicrystalline polymers are very much dependent on the molecular orientation. The orientation function to deal with the elastic moduli data of Hadley et al. (1969) are treated under new aspects. To determine the nature of orientation function from empirical data a relation of the form Sinθ=f (n) Sinθ′ is assumed to describe the change in the orientation angle of a unit from θ′ to θ for the draw ration. Birefringence experimental data are used to find the orientation functionf (n) which is then used to calculate elastic properties. The agreement of the experimental values ofE ₀ andE ₉₀ over the entire draw ratio range is found to be satisfactory for Nylon, low density polyethylene and polyethylene terephthalate. This furnishes strong empirical evidence for the validity of the orientational model for the above substances.     

The effect of pressure on the discotic nematic-isotropic transition properties

We study the influence of pressure on the stability, ordering and thermo-dynamic properties of the discotic nematic-isotropic transition. In the present calculation we include both the second and fourth Legendre polynomial order parameters in the evaluation of the angle-dependent term in the expression of the excluded volume and the perturbation term.     

Organometallic polymers. IV. Organometallic modifications of halogen-containing polymers

The synthesis of ferrocene-containing polymers by chemical modification of chlorinated polyethylenes, polyvinyl chloride (PVC), and other halogenated polymers, under Friedel-Crafts conditions, is described. The effect of reaction conditions on the structure and composition of the products obtained with various substrates was investigated. Soluble polymers of up to 62% ferrocene content were obtained. In most cases, substitution was accompanied by dehydrohalogenation. The ferrocene-to-vinylene ratio was higher in the reaction products of chlorinated polyethylenes than in those of PVC.     

Heterogeneity of structure and mechanical properties of polymers

Specific features of development of micro- and macrofibrils as well as the structure of their interfaces are considered for oriented filaments of high-density polyethylene with different initial supermolecular structures. As evidenced by SAXS, WAXS, EPR, Raman spectroscopy and electron microscopy, the melt-crystallized samples contain a greater amount of tie molecules connecting macro- and microfibrils than the samples crystallized from solution. This hampers slippage of fibrils past each other and does not allow high draw ratios to be achieved. It was found that the density of macrofibrillar ends in the drawn melt-crystallized samples is nearly an order of magnitude greater than that in the drawn samples crystallized from solution. This leads to generation of kink bands (dangerous large-scale defects) and, as a result, the sample, being oriented, fractures long before high draw ratios and a perfect fibrillar structure are reached. The ultraoriented samples produced from solution have a more perfect intrafibrillar structure, and the density of intrabrillar disordered regions is close to that of crystalline ones. Nevertheless, they do contain clusters of defects which limit their mechanical properties. The analysis of the Raman and X-ray data shows that these defects are localized at crystallite boundaries in the long periods. Possible routes for improvement of the parameters of the fibrillar structure and their relation with mechanical properties are discussed.     

Temperature dependence of the dynamic mechanical properties of filled polymers

A theory has been developed to explain the jump in the relative modulus of filled polymers near the glass transition temperature T_g and the subsequent decrease in relative modulus at temperatures above the glass transition temperature. The theory is based upon the concept that there are some particle–particle contacts in doublets and in agglomerates containing a larger number of particles. Below T_g motion of particles at the contact points is possible because of the high modulus of the polymer. At T_g particle–particle motion mostly ceases because of the low modulus of the polymer. At higher temperatures, the mismatch in the coefficients of expansion allows some motion to occur at points of contact and slippage may occur at the polymer–particle interfaces, so the modulus decreases. It is shown theoretically and experimentally that both the elastic modulus and the mechanical damping depend upon the nature of the surface of the particles.     

Sulfur-containing polymers. IV. Preparation and properties of poly(sulfenyl thiocarbonates)

Poly(sulfenyl thiocarbonates) have been prepared for the first time by the stepwise condensation of chlorocarbonylsulfenyl chloride with diols and dithiols. The polymers were obtained in high yield. Generally they were crystalline solids and were soluble in chlorinated hydrocarbons. On treatment with benzyl mercaptan in the presence of triethylamine, the polymers afforded a diol, carbonyl sulfide, and a disulfide compound. This reaction was extended to the preparation of alternating copolydisulfides.