1993 рік

Poly (2-acrylamido-2-methyl propane sulfonamide) (PASAM) is a new, neutral polymer which is soluble in water and formamide. Fundamental parameters obtained previously by light scattering, osmometry and viscometry in these good solvents have been analysed by extrapolation procedures to yield the unperturbed dimensions ((r 2 )o/Mw)1/2, steric factor a and characteristic ratio C~o. 0-Conditions were established as water/dioxane (81.5/ 18.5 v/v ) at 298 K and verified by osmometry and viscometry. There was good accord between the values of ((r 2 >o/M,)1/2, tr and C~ thereby obtained directly and those derived indirectly, the mean values being 8.73 x 10 -9 cm gl/2 mo11/2, 4.07 and 32 respectively. The temperature coefficient of the unperturbed dimensions was - 5.5 x 10- 4 K- 1. The high rigidity of the PASAM chain is discussed.

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In this paper time-of-flight secondary ion mass spectrometry is used to study the chemical modification, upon exposure to u.v. light of 185 and 254 nm in an Ar atmosphere, of the surfaces of polycarbonate derived from bisphenol-A (PC-A) and from the bisphenol of acetophenone (PC-B). On irradiation with u.v. light, the polycarbonates show main chain scissions and photo-oxidative reactions. By this treatment hydroxyl groups are introduced on the polycarbonate surface, which is confirmed by chemical derivatization reactions. In addition, evidence is presented for the occurrence of a Photo-Fries rearrangement.

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An epoxy based on the diglycidyl ether of bisphenol A (DGEBA) has been modified with poly(phenylene oxide) (PPO) and cured with piperidine. A two-phase alloy resulted, in which the DGEBA epoxy was the continuous phase. Several PPO loadings were investigated. The tensile yield strengths of these PPO-modified epoxies were found to be independent of PPO content. In contrast, the fracture toughness improved with PPO content in a linear fashion. The micromechanical mechanism responsible for the improvement in toughness was found to consist of crack bifurcation and microcracking. Some evidence of particle bridging was also observed, and it is thought that particle bridging may play an important role in the formation of a microcracked damage zone.

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In part 1 of this series the phenomenon of a critical ligament thickness (ID?) below which brittle polymers become ductile was investigated for polystyrene (PS). Using the thermoplastic polystyrene-poly(2,6- dimethyl-l,4-phenylene ether) (PS-PPE) model system, it was demonstrated in part 2 of this series that the absolute value of ID? as well as the maximum toughness (i.e. maximum strain to break) was dependent on the network density of the polymer used. In this study the toughness and IDc of crosslinked thermosetting polymers were investigated using epoxides based on the diglycidyl ether of bisphenol A as a model system. The crosslink density (re) is varied between values comparable with (v? = 9 x 1025 chains m-3), up to values much higher than (v?=235 x 102s chains m-3), the entanglement density in the thermoplastic PS-PPE system. The maximum macroscopic toughness proportional to the strain to break (2re,c,) or given by the slow-speed fracture toughness (Gl?) and the notched high-speed tensile toughness (Gh) of core-shell rubber-modified epoxides uniquely increases with an increasing molecular weight between crosslinks (Me). Only by using extreme testing conditions (notched high-speed impact testing), could the ID, of a limited range of epoxides be" determined: 0.21/tm (v? = 9 x 1025 chains m- 3) ~< ID~ <~ 0.29/am (v?= 14 x 102~ chains m-3). Both the experimentally determined values of ID? and the toughness of the epoxides compare well with the values determined for the entangled thermoplastic PS-PPE model system in the same range of network densities, elucidating the principal similarity of the influence of entanglements and crosslinks on the deformation processes. Good agreement was observed between the experimentally determined values of ID? of the epoxides and the values predicted by the simple model introduced in part 2 of this series.

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Differential scanning calorimetry (d.s.c.) of blends of polystyrene ionomers and polyamide-66 shows that lithium sulfonate groups are more effective than lithium or sodium carboxylate groups in enhancing the miscibility between this polyamide and polystyrene. The miscibility between aliphatic polyamides and the polystyrene ionomer containing 9.8 mol% lithium sulfonate groups decreases as the amide content of the polyamide decreases. Thus, while blends of this ionomer with polyamide-66 and polyamide-610 (PA-610) appear miscible by d.s.c., the blends with polyamide-ll (PA-11) show evidence of some phase separation. Dynamic mechanical measurements of the 50:50 blends of this ionomer with PA-610 and PA-11 confirm the one-phase and two-phase behaviour of these blends, respectively.

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The influence of controlled purification and thermal treatment on the nuclear magnetic relaxation of poly(p-phenylene sulfide) (PPS) has been studied. The temperature dependence of spin-lattice relaxation times at 30 and 90 MHz in modified samples has been measured. High temperature annealing leads to an increase in the number of paramagnetic centres, which are most probably radical cations, and to the observed increase in molecular weight of PPS. Sustained purification and degassing of PPS causes the removal of low molecular weight oligomers and paramagnetic oxygen. This effect leads to non-exponential magnetization recovery

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Isotactic polypropylene (iPP) based blends containing as second component ethylene-propylene co__Eolymers (EPR) having, for constant propylene (C3) content (wt/wt), different average molecular masses (M w and/or Mn) and, for constant average molecular mass, different molecular mass distributions (MMD) were investigated. The study was undertaken to establish the influence of the melt phase viscosity ratio p in determining the average particle size of the EPR phase in the vicinity of the minimum expected according to the Taylor-Tomotika theory for the average particle size versus log/~ function, when ~ is about equal to unity (in previous studies we have in fact reached/~ values far above 1). Moreoever, we also report the effects of molecular mass and molecular mass distribution of the EPR phase on the melt rheological behaviour of iPP/EPR blends, on the mode and state of dispersion of the EPR phase in the melt, as well as, in the solid state after iPP crystallization in injection moulded samples, on the crystalline lamellar thickness and the thickness of the amorphous interlayer of iPP phase, and finally on the impact properties of blend materials. It should be pointed out that the apparent viscosity of all the iPP/EPR blends investigated is expected to obey the logarithm additivity rule that applies at constant temperature and shear rate. The application of the Cross-Bueche equation revealed that the zero-shear viscosity t/o of these iPP/EPR blends deviates positively from the logarithm additivity rule. Assuming that the crystallization of the iPP phase freezes the morphology of the EPR phase, a strict correlation is confirmed to exist between the values of EPR particle size and EPR particle size range, as measured by scanning electron microscopy on samples in the solid state, and/~ value. The number average particle diameter (D,) and the particle size range of the EPR phase (D) are found to increase with increasing /~ value as expected according to the Taylor-Tomotika theory. Finally, when the iPP phase crystallizes from its blends with EPR under non-isothermal conditions, the phase structure developed in the blends is characterized by lamellar thickness and interlamellar amorphous layer thickness, respectively, lower and higher than that shown by plain iPP

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Mechanical tensile tests and morphological analyses were carried out on samples of isotactic polypropylene/hydrogenated oligo(cyclopentadiene) (iPP/HOCP) blends. The blends were obtained by melt mixing in a Brabender-like apparatus. Sheets of such blends were prepared by moulding the material under pressure, quenching in iced water and then annealing them in an oven at 140°C under vacuum for 24 h. Stress-strain tensile tests, previously obtained at room temperature, were performed at higher temperatures (80°C and 100°C). Morphology observations were performed by scanning electron microscopy after treatment of the blends with two different etching solvents (n-heptane and chloroform) at their boiling temperatures for various times in order to dissolve the HOCP component. An acid solution with a strong oxidizing action was used as well. In all' the investigated blends (from pure iPP to up to 80% HOCP in the blend) the iPP molecules provide the material interconnection, as evidenced by fibre formation. The transition from ductile to brittle in the mechanical behaviour depends on temperature and composition.

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Interactions in dilute aqueous solution at 25°C between atactic polyl-diethyl-(2-methacryloyloxyethoxy- 2-ethyl)-l-(3-sulfopropyl)ammonium betaine] (lateral group -N+--(CH2)3-SO~ with dipole moment /~ = 22.7 D) and a series of low and high molecular weight dipolar or ionic species were studied by viscometry and fluorescence. For constant additive concentrations (

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The effect of a blending sequence in acrylonitrile-butadiene-styrene terpolymer(ABS)/nylon-6 blend modified by poly(styrene-co-maleic anhydride) (SMA) on the dynamic mechanical and rheological properties, and morphology was studied. When nylon-6 was blended with the preblended ABS/SMA(90/10) blend, the SMA-g-nylon-6 formed during the blending process seemed to lie at the interfacial region and act as an effective compatibilizer. However, when ABS was blended with the preblended SMA/nylon-6(10/90) blend, the SMA-g-nylon-6 formed during the preblending process seemed to lie preferentially at the nylon-6 domain and improve the thermal resistance and modulus of the nylon-6 rich domain.

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