Polymer aqyeous solutions as quenching media. I. Polyvinylpyrrolidone

The cooling power of aqueous solutions of polyvinylpyrrolidone are studied with a silver standard sample by using two apparatuses quench with injection and quench with agitation. The dependences of the cooling rates at each temperature on polymer concentration and solution viscosity are established and empirical laws of variation are given.     

The determination of adjacent oxypropylene–oxyethylene units in propylene oxide–ethylene oxide adducts by infrared spectroscopy

A study of several base-catalyzed propylene oxide—ethylene oxide adducts of glycerin and certain model compounds has shown that an infrared absorption band at 10.30 μ can be associated with a structural entity represented by an oxyethylene unit attached to an oxypropylene unit at the secondary position. Coupled with other information such as total oxyethylene content and primary hydroxyl content, this finding has proved most useful in differentiating average molecular structure for commercial polyether polyols used in the manufacture of polyurethanes.     

Fractionation of ethylene–propylene copolymers

Ethylene–propylene (EP) copolymers were fractionated according to chemical composition, molecular weight, or monomer sequence length, which are fundamental distribution factors. Cloud points of polyethylene (PE), polypropylene (PP), and EP copolymer were determined prior to the fractionation. From the results, it was estimated that xylene–butyl cellosolve and tetralin–ethyl carbitol systems were suitable for the fractionations according to chemical composition and molecular weight, respectively. EP random-type copolymers were fractionated using a xylene–butyl cellosolve system. Separations according to chemical composition were obtained as expected. Then, the above polymer fractions were further fractionated in a tetralin–ethyl carbitol system. and the dependence on molecular weight was observed fairly well. Furthermore, fractionation according to monomer sequence length was satisfactorily achieved by solvent extraction using ethyl ether, n-hexane, cyclohexane, and n-heptane. Therefore, it is concluded that the more detailed characterizations of EP copolymers are made possible by a combination of these techniques.     

Photoluminescence quenching of graphene oxide by metal ions in aqueous media

The photoluminescence (PL) quenching of water-soluble graphene oxide (GO) solution was systematically investigated in the presence of transition metal ions. Their PL spectra were analyzed by the Stern–Volmer equation, and the trend of the quenching efficiency was Fe²⁺ > Co²⁺ > Ni²⁺ > Cd²⁺ > Hg²⁺. The results of the steady-state and time-resolved PL spectra of the GO solution suggested that the PL quenching was related to the new non-radiative optical transitions from the bridging states due to the hybridization of the sp³ orbitals of GO and the 3d orbitals of metal ions, proven by density functional theory calculations. The overall results indicated that the bridging states from the hybridization of GO sp³ and unfilled 3d orbitals (Fe²⁺) in comparison with filled 3d orbitals (Hg²⁺) were highly localized, and their energy levels were more suitable for being non-radiative transition states.     

Viscosity characteristics of aqueous solutions of block copolymers of propylene and ethylene oxides

Brookfield viscosity measurements were made on aqueous solutions of surface-active agents composed of block copolymers of propylene and ethylene oxides in which the molecular weights of the polymers varied from 1100 to over 15,000. The hydrophobia bases were polyoxypropylene glycols varying in molecular weight from 940 to 4000. To these were added varying amounts of ethylene oxide so that the polyoxyethylene hydrophil comprised from 15 to 80% of the surfactant total weight. This work has materially expanded previous viscosity studies of aqueous solutions of nonionic surfactants by using a unique type of hydrophobe, two ethylene oxide chains, and far higher molecular weights of hydrophobe and of hydrophil, up to 280 moles of ethylene oxide. The surface-active agents with hydrophobe base molecular weights from 940 to 1100, and in which the polyoxyethylene sections comprised from 15 to 80% of the total weight, did not form gels in aqueous solution. Some surfactants with a hydrophobe base molecular weight of 1750 to 2750, to which varying amounts of polyoxyethylene were added, formed gels in water at a surfactant concentration range of 40% to 80%. With a hydrophobe molecular weight of 3250, gels formed at from 30% to 90% surfactant concentration, while with one nonionic derived from a 4000 molecular weight hydrophobe, a gel formed at only 20% polyol concentration. Two viscosity maxima were found in some cases, as reported occasionally for other systems. An increase in temperature from 0C to 50C generally reduced the viscosity of systems based on hydrophobes of 1175 and lower molecular weights, and increased it in systems based on hydrophobes of 1750 and higher molecular weights. The behavior of these surfactants in forminggels is explained on the basis of hydrogen bonding, micellar aggregation and water entrapment. The moles of water per ethylene oxide group in the adduct varied with the hydrophobe base weight and with the polyoxyethylene hydrophil, and within systems showing maximum viscosities, ranged from 0.3 to 17.1, at 25C, which is much higher than observed in other nonionics.     

Study of elastic and thermoelastic properties of ethylene–propylene and ethylene–vinyl acetate copolymers. II. Thermoelastic properties

The thermoelastic properties of ethylene–propylene and ethylene–vinyl acetate copolymers crosslinked to different degrees were studied. An equation was proposed for calculating the relative contribution of the internal energy, f_U/f, from the temperature dependence of shear modulus G. Analysis of a relation for calculating f_U/f derived on the basis of the Mooney-Rivlin equation was made.     

Morphology of photodegraded heterophasic ethylene–propylene copolymers

The morphology of photooxidative degraded films of heterophasic ethylene–propylene copolymer (EPQ‐30R) was investigated and compared with isotactic polypropylene and linear low‐density polyethylene by scanning electron microscopy. Surface damage caused by polychromatic ultraviolet irradiation (λ ≥ 290 nm) at 55°C in air is presented in different micrographs. Changes occurring due to the formation of polar groups during photooxidative degradation are discussed. Morphological study of these photodegraded polymer samples show very good correlation with the photodegradation results. The rate of photooxidation is very fast in case of isotactic polypropylene, compared with polyethylene and ethylene–propylene copolymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 215–225, 1999     

Vinylpyridine oxide copolymers: viscosity/pH relationship of aqueous solutions

Complex variations with pH in the viscosity of poly(2-vinylpyridine 1-oxide) in aqueous solution have been observed and large changes in viscosity with small changes in pH at certain pH values have been related to conformational changes. A viscometer is described that allows the viscosity changes to be followed with greater accuracy. The new observations indicate that at some pH values the viscosity readings are not reproducible, probably because the change in viscosity is large over a pH range that is too small to measure accurately. This suggests that in passing from one extreme conformation to another the polymer passes through a highly unstable conformation. The variation of viscosity with pH has been studied for certain vinylpyridine oxide copolymers, namely poly(2-vinylpyridine 1-oxide-co-4-vinylpyridine 1-oxide), poly(2-vinylpyridine 1-oxide-co-2-methyl-5-vinylpyridine 1-oxide) and poly(4-vinylpyridine 1-oxide-co-2-methyl-5-vinylpyridine 1-oxide). The shapes of the viscosity/pH curves are interpreted in terms of the curves of the polymers formed from each comonomer.     

Molecular weight enhancement of vinyl chloride–propylene copolymers

The chain transfer activity of propylene leads to the formation of vinyl chloride–propylene copolymers with molecular weights lower than those of PVC homopolymers produced under similar conditions. It has been found that the addition of specified quantities of monomers with two or more active double bonds can increase the molecular weight of these copolymers without causing crosslinking.     

Elastic and viscoelastic behavior of ethylene–propylene copolymers

The viscoelastic behavior of an ethylene–propylene copolymer is analyzed. Two different vulcanization procedures were followed; in the first a binary mixture of initiator-polymer was used, while in the second the polymer was diluted by a solvent. The networks thus obtained show a different viscoelastic behavior depending on the different vulcanization procedure used. Results, analyzed in terms of supramolecular organization being present in the amorphous material, give some important information about the molecular nature of the C₂ coefficient of the Mooney-Rivlin equation, and therefore about the well-known deviations from the Gaussian theory shown by all rubber-like networks.     

Reversible sol–gel transitions in aqueous solutions of N‐isopropylacrylamide ionic copolymers

Ionic copolymers of N‐isopropylacrylamide (NIPA) exhibiting sol–gel transitions in aqueous solutions were investigated. The studies were aimed at understanding of the structure–property relationship in the design of injectable, in situ forming gels for potential biomedical applications in delivery of therapeutics and tissue engineering. Aqueous solutions of NIPA ionic copolymers were found to flow freely at ambient temperatures and formed soft gels with controlled syneresis above 32 °C, the lower critical solution temperature of NIPA. The sol–gel transitions and temperature‐dependent properties of the resulting gels were analyzed using dynamic rheometry and ultraviolet and infrared spectrometry, and were found to be controlled by the molecular weight and composition of copolymers, ionization state of comonomers and composition of aqueous solvent. Copyright © 2008 Society of Chemical Industry     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 1. Type PE copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(propylene oxide)/poly(ethylene oxide) type PE block copolymers with E-block length 40 chain units and P-block lengths 0 to 11 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. The crystalline lamella thickness is found to be about 25 E chain units, i.e. the crystals are predominantly of extended-chain type. The specific volume of the polymer in the amorphous lamellae is found to be lower than that of polymer of corresponding composition in the supercooled melt. The melting points are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 47 to 51°C compared with T⁰_m = 76°C. This is due to the positive free energy of formation from the melt of the amorphous layer (σ₅ 3.5 kJ/mol) and the crystalline/amorphous) interface (σ_o 3 kJ/mol).     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 2. Type PEP copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(ethylene oxide)/poly(propylene oxide) type PEP block copolymers with E-block length 48 chain units and P-block lengths 0 to 7 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. Both extended-chain and once-folded-chain crystalline lamellae are found, the former with thickness about 32 E chain units and the latter with thickness about 21 E chain units. Compared with the specific volume of supercooled melt of the same composition the specific volume of the polymer in the amorphous lamellae is lower in the extended-chain polycrystals and higher in the once-folded-chain polycrystals. The melting points of the copolymers are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 37 to 55°C compared with T⁰_m = 76°C. This is due to the large positive free energy of formation from the melt of the crystalline/amorphous end interface (σ_o) and the amorphous layer (σ_a). For extended-chain polycrystals we find σ_o 3 kJ/mol and σ_a 3.5 kJ/mol; for once-folded-chain polycrystals we find σ_o 6 kJ/mol and σ_a 2 kJ/mol. We also find σ_o,x = 2.5 kJ/mol for a completely extended-chain end interface and σ_o,f = 10 kJ/mol for a completely folded-chain end interface.     

Catalytic oxidation of methanol over molybdenum oxide–tungsten oxide

The vapour phase oxidation of methanol to formaldehyde over molybdenum oxide, tungsten oxide and their mixtures has been investigated in an integral flow reactor at atmospheric pressure. The effect of several process variables on the conversion and yield were determined. A high conversion of 95.6% methanol with nearly 95% selectivity was obtained at 430°C. A rate expression has been derived from the kinetics of the reaction.     

Stress–strain optical study of styrene–butadiene and ethylene–propylene rubbery copolymers

Birefringence–temperature behavior at constant stress during cooling and heating of styrene–butadiene and ethylene–propylene copolymers between ?120°C and +60°C was investigated. Copolymer composition, thermal treatment, and stress levels were shown to have a pronounced effect on the photoelastic properties.     

Fracture behaviour of controlled‐rheology ethylene–propylene block copolymers

The evolution of the molecular weight distribution and the thermal, mechanical and fracture behaviour of controlled‐rheology ethylene‐propylene block copolymers (ca 8 wt% ethylene content) has been analysed. Various concentrations of di‐tert‐butylperoxide were utilized. The melt flow index increased with the peroxide content due to the reduction of the molecular weight and the narrowing of the molecular weight distribution. However, the thermal behaviour and degree of crystallinity were not improved and some mechanical properties, such as the tensile strength and elongation at break, presented an anomalous behaviour. This trend can be explained by the presence of the elastomeric phase. The addition of peroxide influenced strongly the J–R curves obtained via the elastic–plastic fracture mechanics approach. The slope of these curves was markedly reduced with addition of peroxide to almost being flat for the highest concentration. This loss of ductility and the sudden decrease of the fracture toughness values with an increasing amount of peroxide were mainly due to the reduction in the molecular weight. Copyright © 2011 Society of Chemical Industry     

Photoinitiated oxidation of heterophasic ethylene–propylene copolymers. I. Comparison of oxidation products

Detailed photoproducts from photoirradiation of heterophasic ethylene-propylene copolymers and their fractions have been compared by infrared spectroscopy combined with chemical derivatization. The oxidized films were treated with gaseous NH₃, SF₄, and NO for the rapid identification and resolution of the various carbonyl species, alcohols, and hydroperoxides. The photoproduct formation depends upon the composition of the sample. The heterogeneities in thin films were also determined by micro FTIR spectroscopy. © 1993 John Wiley & Sons, Inc.     

Polymer–solvent interaction parameters and efficiency of crosslinking of ethylene–propylene copolymers

A study has been carried out of the vulcanization of ethylene–propylene copolymers having different propylene contents, by use of an organic peroxide. The polymersolvent interaction parameter μ, calculated by the Flory-Rehner equation from values of ν_e and v_r, was found to be a linear function of v_r with benzene as the swelling agent. Values of μ and their dependence upon v_r were independent of copolymer composition, at least within the limits of experimental error, for samples having a propylene content of 30–60 mole-%. The crosslinking efficiency of the peroxide used was found to depend considerably on copolymer composition, in agreement with the results found for dicumyl peroxide. Finally, sulfur as a crosslinking coagent was found to exert a large effect on the value of ν_e, calculated from the equilibrium retractive force of benzene-swollen specimens.     

Bulk functionalization of ethylene–propylene copolymers. III. Structural and superreticular order investigations

An ethylene-propylene copolymer (EPR) has been functionalized with dibutyl maleate (DBM) by means of a radical-initiated bulk process. Different degrees of grafting have been obtained by varying the overall composition of the reaction mixture as well as the processing procedures. The influence of the grafting degree on the structural and superreticular (or “long range”) order has been investigated by differential scanning calorimetry (DSC), Fourier transform infrared analysis (FTIR), and wide (WAXS) and small angle X-ray scattering (SAXS) techniques. The functionalization leads to a decrease of the “residual crystallinity” present in the parent copolymer. Linear relationships between the grafting degree and the crystallinity degree X_c evaluated by both DSC and WAXS have been obtained. The results of the structural investigations, in agreement with previously reported ones, suggest that the grafting preferentially occurs onto the longer or more perfect methylene sequences. SAXS investigations showed that the significant degree of structuration, i.e., crystalline and paracrystalline order, present in the parent elastomer, gradually disappears by increasing the degree of grafting.