Polymer
A new test, known as antistress relaxation, allows us to study, exclusively, the anelastic deformation, i.e. one which is recoverable with time, of various polymers over a wide range of stresses and temperatures until the yield flow point is reached. In the linear regime, this test is linked with certain viscoelastic properties, such as the loss tangent, tan φ and the loss dynamic compliance, J″,...
Changes in the mechanical properties of amorphous polycarbonate during the fatigue failure initiation stage lead to overall embrittlement of the polymer. The results indicate that the fracture toughness of the material can be reduced by ∼ 35% without visible damage. The ‘static’ mechanical characteristics, such as yield stress and strain and absorbed energy, are influenced very modestly by the cyclic...
High-molecular-weight copolymers of -caprolactone (CL) and 1,5-dioxepan-2-one (DXO) over the complete range of compositions have been synthesized and studied. Stannous 2-ethylhexanoate was used as a catalyst and the polymerization was carried out in bulk. Reactivity ratios were r C L = 0.6 and r D X O = 1.6, which giver 1 r 2 = 1, thus leading to an...
A model is proposed for the complex conductivity σ * of a conducting polymer composite as a function of frequency ω, based on an equivalent electrical network of series and parallel circuits containing resistors and capacitors. The results are similar to the power laws derived from percolation theory, i.e. σ * ∞ ω α . The effect of frequency and volume fraction of polypyrrole...
Acrylonitrile was polymerized using a redox system. The polyacrylonitrile was modified by heating with aqueous 50% H 2 SO 4 or with aqueous 50% NaOH. Acrylonitrile was also copolymerized with acrylic acid or acrylamide or methylenebisacrylamide using a redox system. The sorption abilities of the modified acrylics and copolymers were determined from aqueous solutions of two dyes,...
The influence of constitutional defects (those resulting from variations of the comonomer molar ratio from5050 and those due to the introduction of termonomer units) and thermal history on the polymorphic behaviour of ethylene-tetrafluoroethylene (ETFE) copolymer is investigated. At low temperatures, while well developed orthorhombic structures are obtained for copolymers with a C 2 F ...
Large voids of about 100 μm are often found in rigid-rod polymer thin films coagulated from isotropic solutions. To understand the mechanism of this void formation so as to improve the optical quality of coagulated rigid-rod polymer thin films, surface and internal structures of various coagulated poly(p-phenylene benzobisthiazole) solutions were investigated on freeze-dried films by high resolution...
Poly(di-n-hexylsilane)(PDHS) films cast at various conditions from toluene solutions were studied by X-ray diffraction, d.s.c., u.v.-vis. spectroscopy and fluorescence spectroscopy. The higher-order structure of cast films is discussed in relation to their phase transitions. Films dried slowly at 2°C (film a), quickly at room temperature (film b) and slowly at 36°C (films c and d) have low, moderate...
Optimal molecular geometry and the barrier to internal phenyl rotation were obtained from ab initio molecular orbital calculations of model compounds of poly(p-phenylene benzobisthiazole). Bond lengths and angles are in good agreement with those found from a previous X-ray crystallographic study of a similar model compound. Based on the calculated torsional potential, the discrepancy between theoretical...
A systematic study of char formation in blends of two thermoplastic polymers, poly(vinyl chloride) and acrylonitrile-butadiene-styrene, containing a char-forming/smoke-suppressing iron compound, suggests that the active species which promotes char-forming reactions in these polymer systems is iron(iii) oxychloride (FeOCl).
Optically active N-(l-menthoxycarbonylmethyl)maleimide (MGMI; M 1 ) was radically and anionically copolymerized with N-phenylmaleimide (PhMI; M 2 ) or N-benzylmaleimide (BZMI; M 2 ), in benzene at 60°C and toluene at 0°C, respectively. The monomer reactivity ratios (r 1 , r 2 ) were calculated. In both the radical and anionic copolymerization systems, relationships...
In attempting to melt blend polymethylphenylsilane (PMPS) and polystyrene, an unusual morphology was observed which led to a more detailed examination of the thermal and physical properties of PMPS. Thermogravimetric analysis shows that PMPS is stable under the conditions used for the melt mixing. For apparently the first time, the results of differential scanning calorimetry, dynamic mechanical...
The comonomer unit sequence distributions and stereoregularity of copolymers of p-methoxystyrene (p-MST) with maleic anhydride (MA), prepared in CHCl 3 at 50 ± 0.1°C, have been determined over a wide range of comonomer feed mole fractions using 1 3 C n.m.r. spectroscopy. The results were compared with those obtained from p-MST/MA copolymers prepared in methyl ethyl ketone (MEK)...
Solvent transport into Santoprene thermoplastic rubber samples exposed to n-alkanes (C 5 to C 1 6 ), 2,2,4-trimethylpentane, cyclohexane and 1,2,3,4-tetrahydronaphthalene in the temperature interval 25-70°C has been studied. For all liquids, equilibrium penetrant uptake and degree of penetrant overshoot have been influenced by factors such as penetrant size, shape, polymer morphology...
In the seeded semicontinuous emulsion copolymerization of methyl methacrylate and n-butyl acrylate, the use of mixed surfactant systems (anionic sodium lauryl sulfate and non-ionic Brij 35 and Glytanox 1001) leads to a decrease in the total particle number in the reactor during the reaction. Moreover, the decrease in the particle number is higher when the emulsifier used is non-ionic. The kinetic...
Optically active poly(γ-ketosulfide)s having the asymmetric centres in the main chain have been prepared by polyaddition of 1,3-dimercaptobenzene to trans,trans-dibenzylidene acetone in the presence of catalytic amounts of chiral amines. The extent of asymmetric induction on the polymeric product is found to be dependent on the type of amine, cinchona and ephedra alkaloids giving the highest optical...
A series of polyisophthalamides (PIPAs) containing pendent isonicotinamido groups has been prepared from six aromatic diamines and a novel monomer, 5-(isonicotinoylamino)isophthalic acid. These polymers, which should be considered as modified PIPAs, have high inherent viscosities (about 1.0 dl g - 1 ) and are synthesized in high yields by the phosphorylation polycondensation method. ...
The effect of shear flow on the miscibility behaviour of the model polymer blend polystyrene/poly(vinyl methyl ether) has been investigated in real time by two-dimensional light scattering and optical microscopy. Under certain shear and dynamic temperature conditions large waves have been observed which are aligned either in the direction parallel to the applied shear flow or just off it. Two-dimensional...
Rubber-modified polyamides were probed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering and various mechanical tests. TEM studies showed that in tough samples the crystalline orientation in the interparticle region is of a distinctly different character. The lamellae are organized perpendicular to the rubber-matrix interface, while the...
Stress-relaxation functions in bending and in tension were obtained for several polymer films with widely different microstructures and relaxation characteristics. For all the films tested, non-linear viscoelastic response is observed at strains exceeding 0.8%, with the relaxation time being generally lower the higher the strain. It is also observed that, within the linear viscoelastic range, the...