1992 рік

A statistical thermodynamics theory of a polydisperse polymer based on a lattice model of a fluid is formulated. The pure polydisperse polymer is completely characterized by three scale factors and the distribution law of the system. The equation of state does not satisfy a simple corresponding state principle, except for the polymer fluid with sufficiently high molecular weight.

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This paper describes the use of specific thermoplastic polyurethane elastomers (TPU) in blends with poly(vinyl butyral) (PVB). This work was directed towards the development of an interlayer having improved impact resistance and less sensitivity to variations in impact resistance over the useful temperature range. A family of commercially available cycloaliphatic polyether TPUs was found which produced optically clear, mechanically and thermodynamically miscible blends with PVB. The concept of a miscibility parameter was used to rationalize the compatibility of these blends. Support for compatibility is given by Tg, d.s.c, and d.m.a, data. The Gordon-Taylor relationship has been extended from use as a predictive tool for estimating the Tg of blends to estimating the physical properties of blends. Good agreement between tensile, tear and the measured values was obtained. Impact data on laminates using PVB/TPU (60/40) lightly plasticized (7%) with a glycol ether show almost complete lack of temperature sensitivity.

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The influence of initial deformation defects (localized prestrain) on the subsequent tensile behaviour of cylindrical bars of high-density polyethylene was investigated experimentally and theoretically. It was observed that neck nucleation occurs at the defect for moderate prestrains and outside the defect for larger prestrains. In the former case, the growth of the neck is limited and a secondary neck forms on the border of the predeformed zone. In all instances after the rod is fully drawn, a hard nodule remains at the defect location, the diameter of which increases with the prestrain. A simplified long-wavelength analysis proves that the above phenomena are controlled by the effect of the prestrain on the constitutive behaviour of the material. It is shown in particular that (i) prestraining softens the anelastic response of the polyethylene and (ii) prestraining hardens the material in the steady-state plastic regime. The complete stretching evolution of defect-containing samples can be modelled precisely by means of a finite-difference computer analysis.

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The protonation of polyaniline (PAN) by a non-volatile acid, H2SO4, has been studied by X-ray photoelectron spectroscopy. The amount of acid incorporated can be effectively varied by varying the synthesis conditions. At a sulphate/monomer ratio of > 0.5, both the HSO~ anion and adsorbed molecular H2SO 4 can be quantitatively differentiated in the S2p core-level spectrum. The Nls core-level spectrum indicates that the amine units of the emeraldine oxidation state of PAN are also susceptible to protonation in the presence of excess H2SO4.

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I.r. dichroism measurements were used to study the orientation in stretched networks of cis-1,4-polyisoprene (PIP) containing atactic poly(vinylethylene) (PVE). When both components are part of a network, their relaxation behaviour and equilibrium orientation are essentially identical. In blends of crosslinked PIP with linear PVE, the orientation of the latter is reduced relative to that of the former; however, the PVE retains an equilibrium orientation by virtue of its presence in the strained network. Consistent with earlier results on isotropic crystallization of PIP in this blend, strain induced crystallization evidently entraps some of the amorphous PVE when it is high in molecular weight, thus enhancing the extent of orientational coupling. In amorphous networks, the coupling is dependent on the degree to which the PVE chains can be accommodated within the network mesh; hence, coupling is enhanced for lower molecular weight PVE in less crosslinked PIP. The addition of diluent weakens the coupling in a manner consistent with the excluded volume origin of the interchain interactions.

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The viscoelasticity of a series of monodisperse molten polystyrenes was investigated over a wide molecular weight range (9200 to 756 300). The plateau modulus was determined as the value of G' at the minimum of tan 6 in the rubbery zone, because this point defines a gel-like viscoelastic behaviour. A possible dependence of the entanglement density on chain length was explored, as a recent model predicts such an effect. The experimental indication is that the onset of the entanglement network occurs rather abruptly around M e and that the entanglement density is constant for M > M e.

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In order to achieve new biocompatible materials, graft copolymerization of mixtures of hydroxyethyl methacrylate/ethyl acrylate (HEMA/EA) and hydroxypropyl methacrylate/ethyl acrylate (HPMA/EA) onto amylopectin by ceric ammonium nitrate initiation was carried out. The influence of feed composition was studied with respect to the characteristic grafting reaction yields. Homopolymer formation decreases as the per cent of HEMA monomer increases in the feed and increases as the per cent of HPMA monomer increases in the feed. The values obtained for the percentage grafting were quite high for all the feed compositions

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The fracture behaviour of isotropic and oriented polyethylene has been combined with studies of the internal microstructure using optical and electron microscopic observations of permanganic etched samples. Very considerable differences in fracture toughness were obtained for oriented polymers of different molecular weight or degree of branching, and it has been found that there are corresponding differences in morphology

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The fracture resistance of a range of polyethylenes was examined. The tearing modulus, T, was used as a measure of the resistance of the polymer to crack propagation. The values of the tearing modulus were calculated from the gradient of the J-integral versus crack extension lines, J(Aa). Strain rates in the range from 10 7 s 1 to 0.1 s- 1 were tested. The strain rate dependency of crack initiation and crack propagation have been correlated with the composition and morphology of the polymers. The thickness of the lamellae, side chain concentration and degree of order in the crystalline regions have been shown to influence the resistance of the polymer to crack initiation, Jc(~). The tearing modulus appears to be influenced mainly by changes to the morphology that are due to short side chain branches.

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The photoinitiated polymerization of the liquid crystalline (LC) diacrylate monomer 1,4-(-2-methyl phenylene)-bis[4-(6-acryloyloxy-hexamethyleneoxy)benzoate] with Tk. n = 85°C and T i = 118°C, was studied by d.s.c, at various temperatures under different conditions. In the crystalline state there is a low polymerization rate which increases on approaching Tk.,. In the LC state the initial rate is temperature independent up to 10-20°C above T~ signifying that a better monomer ordering in the LC state does not appear to affect the rate. Rate invariance on elevation of temperature may be the consequence of a compensation of propagation rate increase by termination rate increase. At still higher temperatures the rate drops probably due to depropagation. The 0.65 order in photoinitiator (= 2,2-dimethoxy-2- phenylacetophenone) points to the presence of a first-order termination mode besides the usual second-order mode. The results on temperature dependence were compared with those of a LC monoacrylate monomer, 4-acryloyloxybexamethyleneoxybenzoic acid

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