Stability of a model alkali-soluble associative polymer in the presence of a weak and a strong base

 Hydrophobically modified alkali-soluble emulsion (HASE) polymer is solubilized by the addition of a base. When the pH is increased to greater than 6.5, methacrylic acids on the polymer backbone are neutralized and the carboxylated latex polymer goes into solution causing a large increase in the viscosity due to inter-molecular associations of the hydrophobes. The stability of the viscosity of the polymer solution at pH in the range 9–10 was studied in the presence of a strong (NaOH) and a weak [1-amino-1-methylpropanol (AMP)] base. No change in the viscosity or the moduli was observed for the polymer in AMP. Reduction in the viscous and elastic properties of the polymer solution in NaOH was observed after 4 weeks. Such small changes are detectable using the superposition of oscillation on the steady shear technique. The decrease in the viscoelastic properties is attributed to the hydrolysis reaction of the urethane groups of the macromonomer, which resulted in a decrease in the number of hydrophobes per polymer chain. It is recommended that a weak base be used to neutralise the HASE polymer in order to avoid the possibility of compositional changes in the polymer after neutralisation for more than 6 weeks. Received: 19 May 1998 Accepted in revised form: 26 October 1998     

Functional polymers. XXVII: 2[2-hydroxy-4-acryloxy(methacryloxy)phenyl]2H-benzotriazole: Monomers,polymers, and copolymers

2(2,4-Dihydroxyphenyl)2H-benzotriazole has been prepared in about 50% yield by condensation ofo-nitrobenzenediazonium chloride with resorcinol followed by reductive cyclization of the initially obtained azo compound with zinc and sodium hydroxide. The condensation of the diazonium salt had to be carried out under carefully controlled conditions and in acidic medium, otherwise bis-condensation occurred which, after reductive cyclization, yielded 2(2,4-dihydroxyphenyl)1,3-2H-dibenzotriazole. 2(2,4-Dihydroxyphenyl)2H-benzotriazole was allowed to react with acryloyl or methacryloyl chloride. Monoacylation in the 4-position occurred by interfacial acylation technique and 2[2-hydroxy-4-acryloxy (or 4-methacryloxy)]2H-benzotriazole was obtained in over 60% yield. The two monomers were homopolymerized and copolymerized with styrene, methyl methacrylate, andn-butyl acrylate to polymers of high molecular weight. Incorporation of 2[2-hydroxy-4-acryloxy (or 4-methacryloxy)]2H-benzotriazole into the copolymer was from 1 to 10 mol% of the comonomer mixture. The ultraviolet spectra of monomers, homo- and copolymers were also determined.This paper is dedicated to Professor Dr.Karl Schlögl on the occasion of his 60th birthday with our warmest wishes.     

Microhardness studies of chain-extended PE. I. Correlations to microstructure

The hardness–microstructure correlation of various polyethylene (PE) samples crystallized at high pressure from the melt (chain-extended), with different molecular weights, has been investigated and compared to melt crystallized samples at atmospheric pressure (chain-folded). The hardness, H, of melt crystallized PE is confirmed to increase linearly with the logarithm of the annealing time, t_a, at a constant annealing temperature. The H increase with t_a is discussed in terms of the crystallinity and crystalline lamellar thickness variation. Unusually high hardness values are obtained for samples crystallized or annealed at high pressure as a consequence of the resulting high degree of crystallinity and large crystalline lamellar thickness values. However, it is shown that the high surface free energy value of the chain-extended crystals considerably lowers the hardness values from that of an ideal infinitely thick PE crystal. Analysis of the crystal hardness and the melting temperature data of different polymeric materials emphasizes the close existing relationship between both quantities. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3151–3158, 1999     

Rheological properties of hydrophobically modified alkali-soluble polymers—effects of ethylene–oxide chain length

The rheological properties of hydrophobic alkali-soluble associative polymers (HASE) were studied using controlled rate (Mettler LS40) and controlled stress (TA CSL 500) rheometers. The effects of pH and polymer concentrations on the rheological properties of three HASE model polymer systems (i.e., HASE 5141, 5134, and 5142, with a degree of ethoxylation of 2.5, 10, and 40 mol, respectively) and a reference polymer without associative hydrophobes (MAAEA) were examined. As the pH is increased by addition of ammonia to greater than 5–6, the carboxyl groups ionize to carboxylate ions and the polymers become water soluble. The HASE polymers thicken mainly by hydrophobic association. Viscosity can increase by two to three orders of magnitude as pH is raised to 9. The degree of ethoxylation in the macromonomer controls the nature of the hydrophobic association junctions by altering the flexibility and hydrophobicity of the macromonomer. Optimum thickening efficiency is observed in the system with approximately 10 mol of an ethylene–oxide spacer between the polymer backbone and the macromonomer. Viscoelastic study shows that the maximum thickening efficiency also corresponds to the dominant elastic property observed in the system with 10 mol of EO. All the model systems except the control system without hydrophobe exhibit strain thickening of the viscous and elastic components. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2275–2290, 1998     

A permanganic etchant for polyolefines

A permanganic etchant has been developed which reveals lamellar and other fine detail in surfaces of at least three crystalline polyolefines, viz., polyethylene (of both high and low density), isotactic polypropylene, and isotactic poly(4-methylpentene-1). In typical treatments of high-density polyethylene ca. 2 μm of material is removed with defective regions suffering preferential attack. The etchant also discriminates between lamellar orientations, eating deeper where side surfaces of laminae are exposed than on fold surfaces, and between different polymers, attacking isotactic polypropylene more strongly than polyethylene. Comparison with other techniques authenticates the detail exposed and samples appear to be otherwise unaltered by their treatment. Besides normal imaging, it is also possible to use etched samples for transmission diffraction studies in the electron microscope. The method has very considerable application for revealing lamellar details in crystalline polyolefines (which can be chosen to be representative or selective according to the nature of the surface used). Examples are given of a wide variety of melt-crystallized morphologies for the three polymers cited and also of lamellae in a drawn polyethylene sample. It is pointed out that permanganic etching is complementary to the technique of chlorosulfonation used to stain polyethylene in a similar way as bright field microscopy is to dark field.     

Controlled assembly of luminescent racks based on heteroleptic dinuclear lanthanide complexes

Luminescent lanthanide racks are formed in solution through supramolecular assembly of lanthanide ions with a rigid bis-didentate sensitiser ligand and octadentate aminopolycarboxylate ligands.     

The reaction of C2F5 radicals with H2S

The reaction of C₂F₅ radicals with H₂S was studied over the range 1°?123°C using C₂F₅ radicals generated by photolysis of perfluoropropionic anhydride. The rate constant k_H for reaction (2) is given by where θ = 2.303RT/cal mole^?1. The relevance of this result to conflicting published data on the analogous reaction between CF₃ radicals and H₂S is discussed. It is concluded that there is little difference in the Arrhenius parameters for reaction of CF₃ and C₂F₅ radicals with H₂S.     

The photochemistry of hexafluoroacetylacetone in the vapour phase. Occurrence of a novel HF elimination reaction

Photolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of HF giving 2,2-difluoro-2,3-dihydro-5-trifluoromethylfuran-3-one: The HF is not vibrationally excited. Photolysis of the cyclic product of reaction (5) yields CF₂ radicals which, if HFAA is present, undergo an insertion into the enolic OH bond, (9) The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and (5) have been obtained. Both ?₁ and ?₅ depend on pressure and the ratio ?₁/?₅ increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio ?₁/?₅ increases as the vibrational energy of electronically excited HFAA increases.     

A general test of the Copernican principle

To date, there has been no general way of determining if the Copernican principle--that we live at a typical position in the Universe--is in fact a valid assumption, significantly weakening the foundations of cosmology as a scientific endeavor. Here we present an observational test for the Copernican assumption which can be automatically implemented while we search for dark energy in the coming decade. Our test is entirely independent of any model for dark energy or theory of gravity and thereby represents a model-independent test of the Copernican principle.