High resolution transmission electron microscopic (HRTEM) determination of the preferentially exposed faces onγ-Al2O3 andη-Al2O3

High resolution transmission electron microscopy has been used to examine the crystallites in -Al₂O₃ and -Al₂O₃. -Al₂O₃ has been found to be nearly hexagonally shaped crystallites whose identity distances and angles of fringe patterns indicate that (110) planes are preferentially exposed. -Al₂O₃ showed preferentially exposed surfaces of (100), (110) and super imposed (111)/(211). This information is valuable to the catalyst researcher trying to model the surfaces of these two supports.     

Conformational transition in (maleic anhydride mono-n-octyl itaconate) copolymer

Summary The dependence of intrinsic viscosity [] on temperature for fractions of poly(maleic anhydride-co-mono-n-octylitaconate) [p(MA-co-MOI)] was studied. A discontinuity in [] as function of temperature similar to that of poly(mono-n-octylitaconate) (PMOI) is found which has been attributed to a conformational transition of the polymer chain. This conformational transition can be removed by the addition of poly(dimethylsiloxane) (PDMS). The effect is interpreted in terms of interpolymer complexation.     

Rheological and mechanical performance of ethyl‐vinyl acetate/poly(vinyl chloride) formulations

A range of powdered ethyl‐vinyl acetate (EVA) copolymers and poly(vinyl chloride) (PVC) formulations were compounded at PVC:EVA ratios of 100:0, 60:40, 50:50, 40:60, and 0:100. Two grades of EVA with 20% and 27% of vinyl acetate (VAc) (EVA I and EVA II) and two grades of PVC with K values of 56 and 71 (PVC I and PVC II) were used in the investigation. Mechanical analysis was performed on injection molded samples of these blends, and the results showed that the tensile and flexural moduli decreased significantly with increasing EVA concentration. Rheological analysis was performed by using dual capillary rheometry, and the results showed only slight changes in shear viscosity with increasing EVA content, even at lower shear rates. Dynamic mechanical thermal analysis showed partial miscib lity of the PVC and EVA over the range of concentrations studied.     

Mark-Houwink-Sakurada coefficients for conventional poly(methyl methacrylate) in tetrahydrofuran

Summary Intrinsic viscosities [] in tetrahydrofuran (THF) at 30°C are reported for ten narrow molecular weight distribution poly(methyl methacrylate) (PMMA) samples covering nearly two orders of magnitude in molecular weight. By combining the viscosity results with absolute weight-average molecular weights determined via low-angle laser light scattering (LALLS) experiments, we have accurately determined the Mark-Houwink-Sakurada (MHS) parameters for this polymer-solvent pair (K=7.56x10⁵ and a=0.731, when [] is in dL g^-1).     

Gas permeation of polymer blends. I. PVC/ethylene–vinyl acetate copolymer (EVA)

The transport behavior of O₂ and N₂ were studied for series of physical blends of PVC with EVA having different vinyl acetate (VAc) contents in the EVA (45 and 65 wt-%) and using different milling temperatures (160° and 185°C). The polymer blends were further characterized by dynamic mechanical measurements, density measurements, and x-ray diffraction. At higher VAc content in EVA and with higher milling temperature, the rate of permeation (P) and the rate of diffusion (D) decrease, and the activation energy of D (from Arrhenius plots) increases. Furthermore, the experimental density values of PVC/EVA-45 blends agree well with calculated values, assuming volume additivity of the two components, while those of PVC/EVA-65 blends are higher than the calculated densities. These results are interpreted as due to denser packing of polymer molecules and increased PVC-EVA interaction at higher VAc content and with higher milling temperature, indicating better compatibility between the blend components. The x-ray diffraction data give no evidence of crystallinity. Sharp increases in P and D values at about 7.5% EVA (by weight) are found for PVC/EVA-45 blends (in agreement with our previous work) but not for PVC/EVA-65 blends. This is interpreted as due to a phase inversion at increasing EVA content in the former blends but not in the latter blends. The dynamic mechanical measurements show that the PVC/EVA-65 blends milled at 160°C behave largely as semicompatible systems with maximum interaction between the two polymers at compositions of about 50/50 by weight.     

Rheological properties of poly(ε-caprolactone) and poly(styrene-co-acrylonitrile) blends

Summary Rheological properties of poly(-caprolactone) (PCL) and Poly (styrene-co-acrylonitrile) (SAN) blends were examined as a function of the acrylonitrile (AN) content in SAN, to systematically understand the correlation between the interaction parameter and the theological properties of miscible polymer blends. When the plateau modulus (G _N ⁰) and zero shear viscosity ( ₀) of the PCL/SAN blends are plotted against the AN content in SAN, a minimum is observed. Qualitatively, the results obtained parallel the variation of the interchain interaction with the AN content. The negative deviation ofG _N ⁰ and ₀ from linearity seems to be attributed to the increase in the entanglement molecular weight between dissimilar chains which results from the chain extension caused by interchain interaction.     

Structure and thermal stability of zinc–nickel electrodeposits

ZnNi alloys were electrodeposited from a chloride bath on steel substrates. The effect of nickel bath concentration on chemical composition, structure and microstructure of the deposits is demonstrated. From 0 to 13 nickel, the phases obtained do not correspond to that reported on the thermodynamic phase diagram. It is shown that the substitution of zinc by nickel is responsible for the formation of distorted _d and _d phases corresponding to the supersaturated hexagonal phase of zinc and to the unsaturated cubic phase of Zn–Ni alloy, respectively. Differential scanning calorimetry indicates that the thermal instability of the alloys containing up to 13 wt of nickel, results from the crystallization of the phase from the _d and _d phases at around 200 °C and 250 °C, respectively.     

Head to head polymers

Blends of poly(-caprolactone) with either head-to-head or head-to-tail poly (vinyl chloride) were prepared by solvent casting in the form of films and their glass transition temperatures were determined by DSC analysis. The DSC scans of the blends of both poly(vinyl chloride) isomers were very similar. For blends containing 25% and 50% of poly(-caprolactone), a single transition step, a T_g, was observed, whereas for a blend containing 75% of poly (-caprolactone) three transition steps were observed, one glass transition and also a crystallization and a melting transition.Part 19: H. Kawaguchi, J. Muggee, Y. Sumida and O. Vogl, Polymer (London), in press     

Plastification of poly(vinyl chloride) by polymer blending

Blends of poly(vinyl chloride) (PVC) with different copolymers have been studied to obtain a plasticized PVC with improved properties and the absence of plasticizer migration. The copolymers used as plasticizers in the blends were acrylonitrile butadiene rubber, ethylene vinyl acetate (EVA), and ethylene-acrylic copolymer (E-Acry). Blends were studied with regard to their processing, miscibility, and mechanical properties, as a function of blend and copolymer composition. The results obtained were compared with those of equivalent compositions in the PVC/dioctyl phthalate (DOP) system. Better results than PVC/DOP were obtained for PVC/acrylonitrile butadiene rubber blends. The plasticizing effect on PVC of EVA and E-Acry copolymers was similar to that of DOP. It is shown that crosslinking PVC/E-Acry blends or increasing the vinyl acetate content in PVC/EVA blends, are alternatives that can increase the compatibility and mechanical properties of these blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1303–1312, 2000     

Effect of dehydrochlorination of PVC on miscibility and phase separation of binary and ternary blends of poly(vinyl chloride), poly(ethylene-co-vinyl acetate) and poly(styrene-co-acrylonitrile)

The enhancement of miscibility at the lower critical solution temperature (LCST) of the blends poly(vinyl chloride)/poly(ethylene-co-vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene-co-acrylonitrile) (PVC/SAN) and poly(vinyl chloride)/poly(ethylene-co-vinyl acetate)/poly(styrene-co-acrylonitrile) (PVC/EVA/SAN) was observed at the micron level. Such miscibility is attributed to the dehydrochlorination and formation of hydrogen bonds between blend components. However, macrolevel immiscibility of these blends heated to the LCST was observed. Such microdomain compatibility of these blends gives a synergistic character. Brittle-type failure observed for LCST samples testifies to the synergism in treated blends. ©1997 SCI     

Physico-chemical studies of polymeric carriers

Summary Fractionation procedure on copolymer of N-vinylpyrrolidone and maleic anhydride has been elaborated using water/acetone solvent/nonsolvent system. Viscosity and molecular weight measurements of the fractions were carried out in acidic aqueous medium at 25 °C. The relationship between the intrinsic viscosity and the molecular mass []_c = K·M was obtained at pH = 2.1.     

Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

Solvent/solvent/polymer ternary systems

Summary The paper investigates the agreement between experimental and theoretical data for the second virial coefficient A₂ and for the intrinsic viscosity [] for the acetonitrile/chlorobutane/poly(methyl methacrylate) ternary system.Dedicated to Prof. H.-J. Cantow on the occasion of his 70th anniversary     

[η]-M-relationship for polyacrylamide in aqueous 0.1 M Na2SO4 solution

Summary The intrinsic viscosity [] and the molecular weight M_W of 8 pure, unbranched polyacrylamide (PAAm) samples — prepared in our laboratory — were determined and lead to the following formula [] = 0,0194 · M_W ^0,70(cm³/g) Solvent: aqeous 0.1 M Na₂SO₄ solution; T=298K; M_W/M_n-2,5 . In addition a comparison to the []-M-relationships of PAAm in other solvents is given.     

Electron diffraction determination of an orientation-relationship for iridium-on-η-alumina

An iridium-on-alumina catalyst used for the spontaneous ignition of the decomposition of hydrazine in spacecraft position control thrusters exhibits nearly complete matching of the selected area electron diffraction patterns in the [110] orientation for iridium crystallites and for the support -alumina. The orientation-relationship is referred to the porous character of the -alumina skeleton favoring an oriented nucleation and growth of iridium crystallites in the pore mouths.     

Transparency of Hydrophobic Vinyl Polymers Containing Small Amounts of Inorganic Chloride Salts

Termination of n-BuLi-initiated anionic polymerizations of vinyl monomers (i.e. styrene or butadiene) by chlorotrimethylsilae (CTMS) or methoxytrimethylsilane (MTMS) resulted in an opaque or transparent polymer product. Small amounts of salt (i.e. LiCl from CTMS- or Li(OCH₃) from MTMS-terminated polymerization) generated during termination stage was presumably the cause of the transparency difference. To verify this, turbid solutions were prepared by mixing transparent polymers (prepared from a H₂O-terminated anionic polymerization) with controlled amounts of LiCl in mixed tetrahydrofuran/cyclohexane (THF/CHE) solvents. Reduced viscosity (_red) and particle size (determined from light scattering) of these turbid solutions were found to increase with polymer and LiCl content. On the contrary, both _red and particle size decrease with increasing THF content of the mixed solvent. These results suggest that interactions between the LiCl/THF complex and the polymer chains are responsible for particle formation and hence turbid appearance of the solutions. Solution ⁷Li NMR spectra of the salt/polymer solutions indicated that polystyrene (PSt) has stronger interactions with LiCl as compared to polybutadiene (PBu), which resulted in a more homogeneously salt distribution in PSt than PBu as evaluated from the TEM micrographs of the corresponding bulk samples after solvent removal. A model with the included LiCl/THF complexes surrounded by the polymer coils was proposed to account for the resulting turbidity in solutions and in the bulk state.     

Ternary Blends to Improve Heat Distortion Temperature and Rheological Properties of PVC

Summary: Binary and ternary blends of PVC mixed with α‐methylstyrene/acrylonitrile‐butadiene‐styrene copolymer (AMS‐ABS) and ethylene/vinyl acetate/carbon monoxide terpolymer (EVA‐CO) are investigated, with the aim to obtain a new PVC based material with an improved heat distortion temperature and good processability. Dynamic Mechanical Thermal Analysis (DMTA) reveals that ternary PVC/AMS‐ABS/EVA‐CO blends exhibit two glass transition temperatures: the lower T_g corresponds to a PVC/EVA‐CO phase and the higher one to a PVC/AMS‐ABS phase. An analysis of PVC respective interactions with AMS‐ABS and EVA‐CO leads to assert that the distribution of PVC in the ternary PVC/AMS‐ABS/EVA‐CO system is basically controlled by the binary immiscible blend composition, taken as Φ AMS‐ABS/Φ EVA‐CO ratio. The inclusion of AMS‐ABS and EVA‐CO to form ternary blends based on PVC, allows to improve heat distortion temperature (owed to the presence of AMS‐ABS), maintaining a low viscosity in the molten state, due to the plasticizing effect of EVA‐CO.

Viscosity function obtained at T = 170 °C from extrusion capillary measurements.     

Rigid backbone polymers

Summary It is shown that the inverse velocity of a fallingball in, or _m the apparent minimum viscosity of, anisotropic solutions of poly(n-hexylisocyanate) in toluene, are molecular weight dependent. The molecular weight dependence follows two linear branches. Below M_w=42600 the apparent minimum viscosity is very weakly dependent on M_w. Above M_w=42600 the apparent minimum viscosity of the anisotropic solution is strongly dependent on the molecular weight.     

Studies on miscibility of blends of poly (ethylene acrylic acid) and ethylene‐co‐vinyl acetate by melt rheology

Rheological behavior of blends of poly (ethylene‐acrylic acid) (EAA) and ethylene vinyl acetate (EVA) copolymer have been carried out at various temperatures, namely, 100, 110, and 120°C, and different shear rates from 61.33 to 613.30 s^?1 using a Monsanto Processability Tester. The melt viscosity of the blends shows synergism during processing. The activation energy of the blends is in the range 20.7–44.6 kJ/mol. Highest activation energy was observed for the blends containing 40–60% of EVA by weight. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1947–1954, 2005     

Palladium-Mediated Ring-Opening Reactions of Strained Cyclotetrasilanes

Room-temperature ring-opening polymerization of the strained monomer 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane mediated by palladium complexes was attempted. Examination of the reaction products between the cyclotetrasilane and the metal complex at high concentrations indicated that insertion of one cyclotetrasilane molecule between the ligand–palladium bond was followed by reductive elimination of the tetrasilane. Among the palladium complexes examined were (³-allyl)PdCp [Cp=⁵-cyclopentadienyl], [(³-allyl) PdCl]₂, (³-allyl)PdCl(PPh₃), (³-allyl)PdCl(PPh₃)₂, (³-allyl)Pd(PPh₃)₃ and PdCl₂(PPh₃)₂. Reaction of 1,1,2,3,4-pentamethyl-2,3,4-triphenylcyclotetrasilane with (³-allyl)PdCp provides similar products.