bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of optically active 2,4‐disubstituted‐2‐oxazolines and their polymerization
Authors: Guo Xin Qui , Schulz Rolf C.
Published: April 2003

Four different optically active 2,4‐disubstituted‐2‐oxazolines were synthesized and characterized. Cationic polymerization of these oxazolines were studied. Three of the oxazolines could be polymerized using methyl trifluoromethanesulfonate as initiator. S‐(–)‐2‐Phenyl‐4‐isopropyl‐2‐oxazoline could not be polymerized under the conditions used.
On the low frequency dielectric behavior of carboxymethyl cellulose and its sodium salt
Authors: Moteleb M. M. Abdel
Published: April 2003

A dielectric dispersion and frequency loss peak within the low frequency range 0.05–1 kc/s and at temperatures of 283–333 K was observed in the case of the sodium salt of carboxymethyl cellulose and absent in the case of its acid form. The critical frequency of the dielectric absorption was independent of molecular weight and of the presence of low moisture content. The results obtained show that the variation with temperature of the dielectric constant is exponential at low frequency only in the case of the sodium salt of carboxymethyl cellulose. The significance of the results is discussed.
Optical activity measurements in solids 7. Polylactides and poly(β‐hydroxybutyrates)
Authors: Bartus Jan , Weng Dexi , Vogl Otto
Published: April 2003

The optical activities of poly‐(R)‐lactide, poly‐(S)‐lactide, poly(β‐hydroxybutyrate) and two β‐hydroxyvalerate copolymers were measured in solution, as solid powders in suspension, and where possible, as films. Poly‐(+)‐3‐methyl‐1‐pentene was also reinvestigated. In some cases the specific rotation values of powder samples showed significant differences from the values of the solution measurements. The discrepancies of the data observed seem to reflect the local environment of the polymer chains in supermolecular assemblies and consequently the solid state structure(morphology)of the polymers.

The circular dichroism (CD) spectra of the polymers were also measured in solution and in the form of their films. For comparison, the CD spectra of the naturally occurring protein casein and of the synthetic polypeptide poly‐(L)‐proline were also measured.
Use of inverse gas chromatography to quantify interactions in amine cured epoxy resins
Authors: Jackson Paul L. , Huglin Malcolm B. , Cervenka Antonin
Published: April 2003

Flory–Huggins interaction parameters, λ, were determined for a series of probes in an amine cured epoxy resin matrix (433–493 K) and its precursors (324–363 K) by inverse gas chromatography (IGC). Hildebrand–Scatchard theory was combined with Flory–Huggins theory in order to estimate infinte dilution solubility parameters (δ2) for the matrix and its precursors at 298 K. It was shown that the value of the solubility parameter for the cured resin matrix lies between those of its precursors. Compared to the majority of published work, an unusual aspect of this application of IGC is that solubility parameters have been determined when the stationery phases are (i) small molecules and (ii) a highly crosslinked polymer. Moreover, all possible attempts have been made to ensure equilibrium conditions between probe and stationary phase, and compensation for asymmetry of peak profile has been applied in determining δ2. The solubility parameters estimated by IGC are in good agreement with those calculated by other methods.
Use of inverse gas chromatography to quantify interactions in anhydride cured epoxy resins
Authors: Jackson Paul L. , Huglin Malcolm B. , Cervenka Antonin
Published: April 2003

Previous work has shown that the inverse gas chromatography (IGC) method combined with Flory–Huggins and solubility parameter theories could be used to quantify interactions in an amine cured epoxy resin matrix. In the present communication the same procedures have been adopted for an anhydride cured epoxy resin matrix. The solubility parameter at 298 K thereby obtained for the cured resin was 20–6 (MPa)1/2, which lies between the corresponding values of 18.8(MPa)1/2 and 22.5 (MPa)1/2 for the precursors, viz. Epikote 828 (an epoxide resin) and phthalic anhydride, respectively. It was noted that great care must be exercised regarding choice of solvent used for deposition of phthalic anhydride on a glass bead support because of reaction to phthaclic acid. Similar consderations apply to the choice of probes used.
Investigations by inverse gas chromatography relevant to coated glass fibre/epoxy composites
Authors: Jackson Paul L. , Huglin Malcolm B. , Cervenka Antonin
Published: April 2003

Inverse gas chromatography has been used on two types of coated glass fibre over a range of temperatures. Interaction parameters, χ, extrapolated to 298K yielded values for the solubility parameter, δ, of 20.1 (MPa)1/2 and 23.5(MPa)1/2. After removal by combustion of the coatings, a higher value was yielded for the δ of glass. The findings, in conjunction with values of 19.8(MPa)1/2 and 20–6(MPa)1/2 for an amine cured epoxy resin and phthalic anhydride cured epoxy resin, respectively, provide a useful guide to the appropriate combination of cured resin matrix with coating with respect to optimum interfacial interaction.
Spontaneous current emission in metal‐ferrocene‐doped ethyl cellulose‐metal systems
Authors: Khare P. K. , Chandok R. S. , Dubey Neeraj , Srivastava A. P.
Published: April 2003

Spontaneous current emission (SCE) has been studied in sandwiched different electrode configurations [metal(1)–undoped/doped ethyl cellulose (EC)–metal (1)/(2)] as a function of heating rate, film thickness and dopant concentration in the temperature range 40–200°C. The magnitude and direction of current depend on the combination of electrode metals. SCE thermograms for the Al undoped/doped EC–AI system exhibit two well resolved transition at 110 and 160°C in opposite directions to each other. The phenomena related to these transitions are explained in terms of creation of field at the interfaces and field produced in the bulk of the material. No negative direction transition was observed for electrode systems like Ag–Ag, Pb–Pb, Sn–Sn and Au–Au except for a shoulder of a peak around 100°C. When dissimilar electrode systems (i.e. Al–undoped/doped EC–Ag/Pb/Sn) are used, the current rises and then saturates beyond around 160°C.
Morphology and crystallization of poly(ethylene terephthalate)
Authors: Al Raheil Ismail Ahmad M.
Published: April 2003

The melting behaviour and the morphology of poly(ethylene terephthalate) crystallized from the melt are reported. In general, dual or triple melting endotherms are seen, and single endotherms are seen when the samples are crystallized above 215°C for long times. The location of the uppermost endotherm was found to be constant below Tc = 230°C, and above that temperature the location depends on Tc. Therefore, we have shown that samples of PET which are crystallized above Tc = 230°C contain perfect crystals only; below Tc = 230°C, they contain perfect and imperfect crystals. Scanning electron microscopy showed that the perfect crystals are the dominant lamellae in the spherulitic structure, while the imperfect crystals are the subsidiary lamellae in the spherulitic structure, The amorphous regions are located between individual lamellae.
Light scattering study of the swelling process of poly(acrylonitrile‐co‐butene)‐graft‐poly(acrylonitrile‐co‐methylacrylate) film
Authors: Goto A. , Kuwahara N. , Sato H. , Kubota K.
Published: April 2003

The time evolution of the size and density of the swollen domains during the swelling of poly(acrylonitrile‐co‐butene)‐graft‐poly(acrylonitrile‐co‐methylacrylate) film in methanol was studied by light scattering measurements. The observed scattered light intensity was analyzed by the Guinier plot. The time evolution of the mean radius R(t) and number density N(t) of the swollen domains was given by R(t)3 ∼ t0.12 and N(t) ∼ t1.42.
Synthesis and characterisation of two novel cyanosilicones
Authors: Cameron G. G. , Derouiche Y. , Hirabayashi T. , Lazare P. , Reid J. , White I. M.
Published: April 2003

Two new cyanosilicones, poly[(dicyanopropyl)dimethylsiloxane] A and poly[(dicyanopentyl)dimethylsiloxane] B, have been synthesised by reaction of the corresponding disilanols with phosgene generated in situ from triphosgene. Both polymers show glass‐to‐rubber transitions at about 250K and crystalline melting points at about 310K. Polymers A and B undergo thermal decomposition at 410 and 550K respectively.
Some of the dielectric properties of starch
Authors: Moteleb M. M. Abdel
Published: April 2003

The dielectric constant and dielectric loss were determined for solid starch free of and contaminated with sodium chloride over a frequency range of 0.1–10 000 kc/s at temeperatures from 10 to 60°C. The results are compared with those of cellulosic fibers. At high frequency both starch and cellulosic fibres exhibit a dielectric dispersion and loss peak. The chain flexibility of starch has a decided effect on the locationof the peak. The low frequency absorption appears only when starch is contaminated with sodium chloride, which modifies the dielectric properties of the starch sample.
Dynamic mechanical properties of isotactic PMMA
Authors: Katime Issa , Calleja Ricardo Diaz
Published: April 2003

The aim of this paper is a comparison of the dynamic mechanical behaviour of amorphous and partially crystallised isotactic PMMA. Parameters are proposed that affect the different relaxations that appear in the dynamic mechanical isochronal spectra. It has been found that the temperature of the maximum of the loss tangent, as well as the activation energy, is higher for the totally amorphous polymer. The beta‐relaxation appears clearly in the case of the completely amorphous polymer, with an activation energy of 105kJ/mol; this relaxation cannot be found for the semicrystalline polymer.
Polymerization of methyl methacrylate with metal acetylacetonates and triethylaluminum catalysts
Authors: Endo Kiyoshi , Inukai Akihiro , Otsu Takayuki
Published: April 2003

Polymerization of methyl methacrylate (MMA) with metal acetylacetonates, especially vanadium (III) acetylacetonate [V(acac)3], in combination with AIEt3 was studied. V(acac)3–AIEt3 catalyst could initiate the polymerization of MMA, although other Mt(acac)xs are also effective. It was found that the polymerization of MMA with V(acac)3–AIEt3 catalyst proceeded through a coordination mechanism, from the results of copolymerization with styrene and polymerization in the presence of radical inhibitors. The resulting polymers were found to form stereocomplexes in acetone. Based on these results, it is concluded that multi‐active sites in the polymerization of MMA with V(acac)3–AIEt3 catalyst were produced.
Polymerization of allylthiourea by constant current electrolysis
Authors: Özkan Hülya , Usanmaz Ali , Önal M. Ahmet
Published: April 2003

Allylthiourea was polymerized by constant current electroinitiation in acetonitrile using tetrabutylammonium fluoroborate as supporting electrolyte. The polymer obtained was insoluble in common organic solvents. FTIR studies showed that polymerization propagates by addition through the C=C double bond. The cyclic voltammogram of the monomer gave two irreversible oxidation peaks at + 1.3V and + 2.4V versus Ag°/Ag+ reference electrode at 25°C. Polymerization at room temperature gave a limiting conversion of about 10% for 2mA current and 30% for 5mA current, in acetonitrile. Higher initial rates were obtained when dichloroethane was used as solvent.
Transient currents in poly(vinyl alcohol)–poly(vinyl pyrrolidone) polymer blend films
Authors: Narayana K. Lakshmi , Dasaradhudu Y. , Rao V. V. R. Narasimha
Published: April 2003

Transient currents (charging and discharging currents) in poly(vinyl alcohol) (PVA)–poly(vinyl pyrrolidone) (PVP) polymer blend films were measured over the temperature range 30–150°C at field strengths of 2.32–23.2 × 106 Vm−1. Polymer films were prepared by the isothermal immersion technique. Activation energies were evaluated from quasi‐steady‐state currents. A single relaxation peak was observed both from isochronal currents and low frequency dielectric relaxation. Activation energies evaluated from these two methods are found to be in fairly good agreement. The polarization is considered to be due to space charge origin along with some contribution from dipolar groups. The maximum loss was observed in Sample I (PVA: PVP = 25:75), suggesting maximum heterogeneity in this blend ratio.
Immobilization of urease and estimation of effective diffusion coefficients of urea in HEMA and VP copolymer matrices
Authors: Demircioǧlu Hüsniye , Beyenal Haluk , Tanyolaç Abdurrahaman , Hasirci Nesrin
Published: April 2003

Enzyme urease was immobilized in copolymer matrices of 2‐hydroxyethyl methacrylate (HEMA) and N‐vinyl pyrrolidone (VP). The activities of immobilized urease stored in phosphate buffer solution of pH 7.0 at 4°C were examined periodically for up to 90 days. For the matrices of higher VP/HEMA mole ratio in the structure, a higher volume increase and enhanced apparent activity were observed, while HEMA polymer alone proved to have the most stable matrix for prolonged activity. No appreciable amount of enzyme leakage was experienced for any of the matrices prepared. The effective diffusion coefficients of urea through these polymer matrices were calculated with a ‘diffusion and reaction’ model and the highest effective diffusion coefficient was found with pure HEMA matrix, possibly due to its laminated structure.
Electrical conductivity in iodine‐doped ethyl cellulose
Authors: Khare P. K. , Keller J. M. , Gaur M. S. , Singh Ranjeet , Datt S. C.
Published: April 2003

The electrical conductivity of solution‐grown ethyl cellulose (EC) films, 5–30 μm thick, has been studied in the sandwich configuration (metal–EC–metal) as a function of iodine concentration from 0.5 to 5.0 wt% ratio. The studies were conducted in the temperature range 333–383 K, while the field was varied over the range (3.0–5.5) × 104V/cm. Aluminium was used as the lower electrode, while the upper electrode was of Al, Ag, Cu, Au or Sn. Certain transient effects such as a large burst of current immediately after the application of field were observed. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories of electrical conduction. The results show that the electrical conduction follows Ohm's law at lower fields, while at higher fields, space‐charge limited current (SCLC) was observed. It was also found that Richardson–Schottky emission was responsible, to some extent, for the transport of charge carriers in the polymer. The conductivity of the films increased on doping with iodine. The dopant molecules are considered to act as additional trapping centes and provide links between the polymer molecules in the amorphous region, thus resulting in the formation of charge transfer complexes.
Synthesis and characterization of cryogenic adhesives based on epoxy‐modified polyurethane resin systems
Authors: Ma Chen‐Chi M. , Hsia Hung‐Chung , Chen Der‐Shyang , Li Ye‐Shiu , Li Ming‐Shiu
Published: April 2003

Polyurethane adhesives containing the polyether backbone exhibit a good joint strength in cryogenic environments. In practice, many of the commercially available polyurethane adhesive systems contain free or chemically blocked isocyanates which have some limitations. This study presents the synthesis and characterization of a modified polyurethane type adhesive. Glycidol was used to convert the isocyanate‐terminated polyurethane prepolymer to glycidylterminated polyurethane prepolymer. A series of glycidyl‐terminated polyurethanes, based on polyoxypropylene glycol (PPG) soft segments having different molecular weights, were synthesized and their adhesive properties on aluminium were evaluated. The effect of the soft segment length on adhesion was examined.

The adhesive properties at room temperature and cryogenic temperature are in line with the phenomenon observed in dynamical mechanical analysis (DMA) and in the phase separation behavior of the polyurethanes. Differential scaning calorimetry (DSC) was used to assess the phase separation content. An improvement in the adhesive strengths at room temperature is achieved by adding epoxy resins to the glycidyl‐terminated polyurethane resins.
Polyether and polyester polyol based glycidyl‐terminated polyurethane modified epoxy resins: Mechanical properties and morphology
Authors: Li Ye‐Shiu , Li Ming‐Shiu , Ma Chen‐Chi M. , Hsia Hung‐Chung , Chen Der‐Shyang
Published: April 2003

A glycidyl‐terminated polyurethane prepolymer was synthesized and used to enhance the properties of epoxy resins. Some properties of glycidyl‐terminated PU/epoxy with polyether based (PPG) and polyester based (PBA) glycidyl‐terminated PU were investigated in this research. The polyether based glycidyl‐terminated PU(PPG) modified epoxy resin proved to be superior to conventional epoxy resins in improved impact strength and fracture energy, but not tensile strength, tensile modulus, flexural strength and flexural modulus. On the other hand, the polyester based glycidyl‐terminated PU(PBA) modified epoxy resin had increased mechanical properties while showing slight variation of impact strength and fracture energy. Different mechanisms for this behaviour are advanced in this paper.
Study of polystyrene–polyethylene IPN system by the spin probe method
Authors: Tiňo J. , Borsig E. , Hloušková Z. , Fiedlerová A.
Published: April 2003

The spin probe method has been used to study the structure and molecular mobility of PS–PE IPN with various ratios of PS:PE. The dependence of the correlation times of motion of the spin probe and the linwidths of the EPR spectra on the composition of the IPN system and its thermal processing has been studied. The results imply that rotation correlation time of the probe is highest at the ratio PS:PE 1.5:0.5 and lowest at the ratio 0.75:1.25. The value of τ decreases with decreasing content of PS. At the transition from the ratio PS:PE 1.25:0.75 to 1:1 τ decreases sharply to a value close to the correlation time of PE. In the temperature range 173–373 K there are two domains which differ in molecular mobility. At temperatures above Tm of PE, heterogeneity is observed for samples with ratio of PE 1 or 0.75. Annealing at 473 K makes the samples homogeneous, which means that mixing of the chains of both polymers is observed in the interpenetrating regions.
Plastic zone radius of crosslinked bismaleimide resins
Authors: Pritchard Geoffrey , Swan Martin , Rose R. G.
Published: April 2003

There appear to be very few literature estimates of the size or the shape of the plastic zone in polybismaleimides, whether calculated or observed experimentally. Bismaleimides are characteristically much more brittle on a macroscopic scale than other thermosetting resins and might be expected to have exceptionally small plastic zone radii. In this paper, experimental investigations are described, which conclude that the plastic zone must be much smaller in bismaleimides than in epoxies, even after rubber toughening, and before the network is fully developed by postcure. No direct observation of the zone radius could be made, but model calculations were carried out using Irwin, Dugdale, Tresca and von Mises expressions. The estimated zone radii declined with cure time, and became more or less negligible for all except the highest rubber concentrations after postcure. Plane stress models gave higher radii than plane strain ones. The very small calculated plastic zones of bismaleimides were consistent with the low observed ratio of tensile to compressive strength. This ratio implies marked resistance to yielding compared with that to crack propagation, and suggests a morphology consisting of exxtensive regions of continuous, rigid crosslinked structures, with minimum scope for shear.
Partial specific volume of poly(D‐β‐hydroxybutyrate) in chloroaliphatic solvents
Authors: Bakoš Dušan , Ortega Francisco , Hernández‐Fuentes Irmina
Published: April 2003

Partial specific volumes, v02, of poly(D‐β‐hydroxybutyrate), PHB, were determined by density measurements in several chloroaliphatic hydrocarbons. We observed that v02 of PHB in tetrachloroethane is influenced only very little by temperature. This can be generalized for the group of solvents used. The experimental results are comapred with the data obtained theoretically using the concept of additivity of group contributions.
Study of transient currents in discharging mode in pure and iodine doped ethyl cellulose films
Authors: Khare P. K. , Chandok R. S.
Published: April 2003

A study of transient currents in discharging mode in vacuum aluminized pure and iodine doped ethyl cellulose (EC) films, approximately 20 μm in thickness, measured at various temperatures (303–353K) and applied fields (2.0 × 104−4.5 × 104 V/cm) is described. The order of current has been found to increase considerably with increase in poling temperature, field and iodine mixing. The currents have been found to show I ∝︁ t−n (i.e. Curie–Von Schweidler law) time dependence with different slopes in the short and long time regions. The conductivity of the films is increased on doping with iodine. The dopant molecules are considered to act as additional trapping centres and provide a link between the polymer molecules in the amorphous region, thus resulting in the formation of a charge transfer complex. The results of the experiments and the mechanisms involved are discussed on the basis of available theories.
Polymerization of 1,3‐butadiene with MgCl2‐supported cobalt catalysts activated by ordinary alkylaluminums
Authors: Takeuchi Masaki , Shiono Takeshi , Soga Kazuo
Published: April 2003

MgCl2‐supported CoBr2 catalysts were prepared from mixture of MgCl2 and CoBr2L2 (L = triphenylphosphine or pyridine) in toluene. Polymerization of 1,3‐butadiene was conducted over the catalysts combined with ordinary alkylaluminums as cocatalyst. The CoBr2(PPh3)2/MgCl2 catalyst gave polybutadiene with approximately 80% of 1,2 units, whereas cis‐1,4‐poly‐butadiene was obtained with the CoBr2(C5H5N)2/MgCl2 catalyst.

Addition of triphenylphospine to the latter catalyst caused a marked increase in the content of 1,2 units. The content of 1,2 units could be thus controlled in the range from 0 to 80% by changing the amount of triphenylphosphine.

On the other hand, the CoBr2(PPh3)2/MgCl2 catalyst with very low content of CoBr2(PPh3)2 hardly displayed any activity. Addition of dimethoxydiphenylsilane to the catalyst gave polybutadiene containing 90 % of 1,2 units with a fairly high activity.
Preparation and thermal characterization of graft copolymer obtained by radiation grafting of individual and binary monomer systems
Authors: Osman Massarat B. S. , Hegazy El Sayed A. , Mostafa Abo El‐Khair B. , Abdel‐Maksoud Afaf M.
Published: April 2003

Graft copolymers were obtained by radiation‐induced grafting of vinyl acetate (VAc) and N‐vinylpyrrolidone (NVP) individually and in binary mixture on to polypropylene (PP) films. The effect of some grafting conditions on the grafting yield was determined. The addition of Cu2Cl2 as inhibitor to the reaction medium inhibited the homopolymerization of the comonomer. The grafting process was remarkably enhanced by using dioxan as a diluent compared with other solvents used. The addition of some inorganic salts has a great influence on the individual grafting of both monomers. The gel percent in the graft copolymer was determined; it increased as the grafting yield increased. The swelling behaviour and electrical conductivity for the grafted films slightly increased by grafting. The changes in thermal parameters such as glass transition (Tg), melting (Tm) and recrystallization (Trc) temperatures and heats of melting (ΔHm) and recrystallization (ΔHrc) of the graft copolymers were also followed by differential scanning calorimetry (DSC). These thermal parameters of PP were varied by grafting with VAc and NVP and depend on the graft yield, which reflects the change in its crystalline domains and formation of crosslinks in the graft chains. The heat of recrystallization of the graft copolymer by cooling from the molten state decreases by grafting which is a good indication of crosslink formation, since crosslinking decreases the crystallizability of the polymer matrix.
Synthesis of ultra‐high molecular weight polyacrylonitrile with highly isotactic content (mm > 0.60) using dialkylmagnesium/polyhydric alcohol system as catalyst
Authors: Nakano Yasuhiro , Hisatani Kunio , Kamide Kenji
Published: April 2003

An attempt was made to synthesize a catalyst having high activity for synthesis of highly isotactic polyacrylonitrile (PAN) with high molecular weight by anionic polymerization. The reaction products of di‐n‐hexylmagnesium [(n‐C6H13)2Mg] with alicyclic alcohols such as 1,4‐cyclohexanediol or 1,5‐decalindiol were found to be effective as polymerization catalysts for preparation of PAN samples whose triad isotacticity [the content of mm (m, meso configuration)] is about 0.64 and viscosity‐average molecular weight (Mv) exceeds 1 × 105. The triad tacticities [mm, mr, and rr contents (r, racemo configuration)] of the polymers obtained were analysed by 13C NMR and their Mvs were determined by viscometry in dimethylsulphoxide at 25°C using Kamide et al.'s Mark–Houwink–Sakurada equation.

Mv of PAN increased significantly by after‐treatment of the catalysts, prepared from (n‐C6H13)2Mg and alicyclic alcohols, with triethylalyminium (Et3Al). Ultra‐high molecular weight PAN samples ranging in Mv from 2 × 106 to 6 × 106 [(mm) = 0.57–0.66] were obtained in anisole at 135°C by using the above catalyst system. A main role of Et3Al in these catalyst systems is considered to reduce, in advance, OH groups on the catalyst, resulting in a significant suppression of termination reactions of propagating PAN chains during the polymerization.
Mixing of rubber and viscoelasticity—III. Viscoelastic characterization of gum rubber
Authors: Nakajima N.
Published: April 2003

This paper is the third in a series where the author attempts to provide scientific interpretation for mixing of rubber. Each gum rubber exhibits its own characterstic behavior during mixing. In the previous paper, the behavior was identified with viscoelastic properties and failure. This paper describes characterization of gum rubbers based on viscoelastic properties.

Methods of describing deformation are discussed with a proposal to use material functions for the present purpose. Non‐linear viscoelasticity is discussed with a proposal to use a particular linearization scheme. The conventional characterization methods are discussed concerning the limitations and shortcomings of dilute solution methods and the Mooney index. The linearization scheme is applied as the characterization method most suitable for gum rubbers. A number of examples are given to demonstrate the effectiveness of this characterization method in relating the results to molecular architecture. Finally, the discussion covers processability of gum rubbers and their molecular structure.
A free volume study of miscible polyester blends
Authors: Zipper Marcus D. , Simon George P. , Tant Martin R. , Small J. Douglas , Stack Gary M. , Hill Anita J.
Published: April 2003

Four blend systems (miscible binary polyester blends) have been examined by positron annihilation lifetime spectroscopy (PALS). The ortho‐Positronium pick off lifetime, τ3, is related to the mean free volume cavity size in these miscible blends. The measured free volume cavity size for the blends is compared to the size predicted from linear additivity of the homopolymers. A negative deviation from linear additivity is observed for τ3 in each of the blend systems, and this behaviour is interpreted as a contraction of the mean free volume cavity size due to the changes in molecular packing that occur on blending. The consequence of these free volume results for the mechanical properties of miscible polyester blends is discussed and tested for the polycarbonate/Kodar system. The glass transition data suggest weak specific interactions in the blends; however, the mechanical properties are significantly affected by blending.
Intramolecular energy transfer in polyesters and model compounds containing anthracene and naphthalene groups separated by methylene and oxyethylene spacers
Authors: Mendicuti F. , Saiz E. , Bravo J. , Mattice Wayne L.
Published: April 2003

Steady state fluorescence has been used to study the efficiency of nonradiative single energy transfer for naphthalene → naphthalene and naphthalene → anthracene for polyesters and their bichromophoric model compounds. Polyesters containing only naphthalene groups were derived from 2,6‐naphthalene dicarboxylic acid as the rigid unit, and two series of glycols, HO(CH2)mOH and HO(CH2CH2O)n;OH, where m=2–6 and n=1–4, as flexible spacers. Bichromophoric model compounds were derived from 2‐naphthoic acid and the same glycols. In order to study the transfer for naphthalene → anthracene, a first attempt was made by studying bichromophoric model compounds D(CH2)mA, where D and A denote 2‐naphthoate (donor) and 9‐anthranoate (acceptor) groups, respectively. The fluorescence anisotropy measurements in a solid matrix of glassy poly(methyl methacrylate), for the compounds containing only naphthalene groups, and the simple excitation and emission spectra, for the compounds containing naphthalene and antharacene groups, clearly demonstrate the presence of non‐radiative singlet–singlet energy transfer, the efficiency of which depends mainly on n (or n). A theoretical treatment using the rotational isomeric state model of the conformatin of these molecules has also been performed. The combination of the experiments and the theoretical analysis establishes that the Förster radii are 1.2 and 1.4 nm for the naphthalene → naphthalene transfer in the bichromophoric model compounds and polyesters, respectively, and 1.6 ± 0.2 nm for the naphthalene → anthracene transfer in the model compounds studied.
Interface formation of Ca with poly(p‐phenylene α,α′‐diphenyl vinylene) and poly(p‐phenylene α‐phenyl vinylene)
Authors: Razafitrimo H. , Park K. T. , Ettedgui E. , Gao Y. , Hsieh B. R.
Published: April 2003

We have investigated the interface formation of Ca with poly(p‐phenylene α,α′‐diphenyl vinylene) (PPV‐DP) and poly(p‐phenylene α‐phenyl vinylene) (PPV‐P) using X‐ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of CaO, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Å of Ca deposition. At the same time, a new C 1s component became noticable at about −1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form CaC species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Å of Ca overlayer is contaminated by the CaO and CaC species and the overlayer is pure beyond 15 Å of Ca coverage.
Reactive blending via coordination chemistry—extraordinary mechanical response for atactic 1,2‐polybutadiene complexed with palladium chloride
Authors: Belfiore Laurence A. , Bossé Francis , Das Pronab
Published: April 2003

Experimental evidence in solution and in the solid state suggests that atactic 1,2‐polybutadiene and palladium chloride form coordination complexes with unusual mechanical properties. Ternary phase diagrams with tetrahydrofuran as the solvent highlight regions where gelation is favored relative to precipitation. The strongest evidence for a network structure is based on the facts that (i) solid films swell in heptane, and (ii) infrared spectroscopy identifies a new absorption characteristics of three‐membered rings and dihapto coordination of the olefinic sidegroup in 1,2‐polybutadiene to the metal center in palladium chloride‐bis(acetonitrile). Carbon‐13 solid state NMR spectroscopy suggests that the polymeric palladium complex is a glass when the salt concentration is 4 mol%. NMR linewidth data together with the pulse sequence parameters suggest that the chain backbone of the polymeric palladium complex experiences a significant reduction in molecular mobility which is consistent with diamagnetic glassy materials. Most importantly, the elastic modulus of polybutadiene increases by three orders of magnitude during the transition from rubbery to glassy behavior. This type of mechanical response cannot be explained by a filler effect, crystallite reinforcement, or antiplasticization. Transition‐metal coordination concepts applied to polymeric materials suggest that the enhancement in mechanical properties is a direct consequence of ‘coordination crosslinks’ where the palladium salt bridges different polymer chains. However, palladium‐catalyzed rections of the olefinic sidegroup, generating a chemically crosslinked network, represent a second explanation of the significantly enhanced macroscopic physical properties of 1,2‐polybutadiene in the presence of the transition‐metal salt. Reactive blending via metal‐ligand coordination represents a new mechanism to compatibilize polymeric mixtures that would otherwise exhibit phase separation.
Utility of pulsed‐field gradient—HMBC indirect detection NMR experiments for polymer structure determination
Authors: Rinaldi Peter L. , Ray Dale G. , Litman Vincent E. , Keifer Paul A.
Published: April 2003

The utility of pulsed‐field gradient (PFG)–heteronuclear multiple bond correlation (HMBC) 2D NMR experiments for characterizing polymer structure is demonstrated. Heteronuclear multiple quantum coherence (HMQC) and HMBC indirect detection experiments provide correlations indicating the presence of one‐bond and two‐or three‐bond connectivities, respectively; this information is vital for polymer structure determination. When HMBC methods are combined with PFG techniques artifacts are eliminated which normally limit the utility of HMBC. The elimination of these artifacts lowers the detection limit by almost two orders of magnitude, making it feasible to detect signals from the small number of repeat units bonded to defect structures, chain ends, branch points and block junctions, despite the presence of much larger resonances from the main‐chain repeat units. Spectra of poly(isobutylene‐b‐butadiene) diblocks and poly(isoprene‐b‐styrene) diblocks are used to illustrate these advantages.
Viscoelastic constitutive equations and rheology for high speed polymer processing
Authors: Leonov Arkady I.
Published: April 2003

Many attempts to formulate viscoelastic constitutive equations (CEs) for polymeric liquids have resulted in a situation where as many as several tens of popular CEs are in competition nowadays. None of these can describe the available data for simple flows, consistently, and almost all of them display nonphysical instabilities in high Deborah number flows. This paper discusses the most important classes of viscoelastic CEs, present recent results on their stability, recommends some principles of choice of CEs for practical use, and highlights a certain class of CEs for the description of the available set of rheological data for the most well characterized polymers, while satisfying all the stability constraints.
13C CP–MAS NMR spectra of tropical hardwoods
Authors: Sosanwo Olumide A. , Fawcett Allan H. , Apperley David
Published: April 2003

The carbon‐13 cross‐polarisation and magic angle spinning nuclear magnetic resonance spectroscopy studies of more than 20 tropical hardwoods are presented. Because of their productivity and area, the tropical evergreen forests are the location of more than one‐third of the net primary production of the terrestrial biosphere, a product which is currently of the order of 5.1 × 1016 g of carbon per year. Samples are mainly from Nigeria, predominantly timberwoods such as Diospyros mespiliformis (ebony), Tectona grandis (teak), Nauclea diderichii (opepe), Chlorophora excelsa (iroko), Khaya ivorensis (lagos mahogany), Khaya senegalensis (sapele mahogany), Daniellia oliveri (ojia), Sterculia oblonga (aye), Brachystegia kennedyi (okwen), and Mitragyna cilliata (abura); also included are Hevea braziliensis (rubber tree) and Gmelina arborea, a source of paper pulp.

Assignments of the various peaks of the spectra are given to the main components, lignin and holocellulose, and to other minor structures. The holocellulose features are those of cellulose, hemicellulose being masked, at least in woods in which it is known to be present. The signals from the holocellulose component indicate that about 35% of the material is cellulose in a recognisable crystalline form, presumably located at the centre of fiberes, but the type of crystal structure could not be identified because of interference from the rest of the holocellulose signals. The aromatic lignin signals were distinct, and were perceived to fall within a pattern of a smooth transition from the wood of aye, based upon a syringyl type of residue, to the woods of omo and mpingo, based on guaiacyl residues, the exceptions being the Khayas, ebony, teak and opepe, which contained a third structure. The proportion of lignin, according to the area of the aromatic region and the O—Me signals, was highest in mpingo (50%), a savanna wood; within the woods from the Nigerian rain forest, the population ranged from 22% for iroko to 44% for teak, a reasonable allowance being made for the extra lignin in the aliphatic network.
Structure and properties of polyolefin blends
Authors: Ślusarski Ludomir , Bieliński Dariusz , Włochowicz Andrzej , Ślusarczyk Czesław
Published: April 2003

Blends of ethylene–propylene–diene rubber (EPDM) and low density polyethylene (PEid) or isotactic polypropylene (iPP) crosslinked by dicumyl peroxide (DCP) have been prepared. Their morphology, reactivity of the components and crystallinity have been studied. The blends are microheterogeneous. Both plastomers, but particularly iPP, decrease the crosslinking efficiency of EPDM by DCP. It was found that they also influence the mechanical properties of the blends. The effect of iPP is far more pronounced than that of PEId, because of an increase in crystalline phase content. iPP particles play a role as nuclei for propylene monomer units in EPDM, whereas PEId particles are solvated by the elastomer matrix.
Thermally modified acrylic polymers as sorbents
Authors: Simitzis Johannis
Published: April 2003

Acrylic fibres were modified with ethylene diamine and pyrolysed at temperatures up to 600°C. According to IR spectroscopy, polymers pyrolysed at 300°C contain nitrile and other groups which are present in the initial polymer. The specific surface area is decreased by increasing the pyrolysis temperature. The pore size distribution reveals mainly the presence of macropores. Acrylic polymers and those pyrolysed at 300°C sorb more methylene blue and alizarin yellow from aqueous solution than a non‐polar commercial sorbent of high specific surface area. The experimental results for dye sorption were treated theoretically using a diffusion‐limited sorption method. The polymers can be ranked by the parameters of this method or their sorption ability. The dye sorption is little affected by the pores of the polymers and is mainly affected by the interactions between the functional groups of the polymers and those of the dyes.
Dielectric investigation on poly(methylmethacrylate) films doped with p‐nitroaniline
Authors: Shafee E. El.
Published: April 2003

The dielectric behaviour of solution‐grown thin films of poly(methylmethacrylate) containing p‐nitroaniline (p‐NA) as a dopant was investigated within the temperature range 60–90°C and a 20–105 Hz frequency band. It is shown that these mixtures exhibit only one relaxation process similar to that of pure PMMA. However, the addition of p‐NA increases both the height and the relaxation strength of the peaks and also shifts log fm to higher frequencies. The additive causes narrowing of the loss curves and increases the activation energy for relaxation. These results are interpreted in terms of the hydrogen bonding effects of p‐NA on localized motions of carboxymethyl dipoles in PMMA. An insight into the possible origins of the β‐ and α‐relaxations in PMMA is also presented.
Synthesis and rheological properties of soluble poly(hydroxyethyl methacrylate) and some copolymers
Authors: Perera Don I. , Shanks Robert A.
Published: April 2003

Methods to synthesise soluble poly(2‐hydroxyethyl methacrylate) (PHEMA) with varying molar mass were developed. Conversions over 90% were achieved without losing solubility. Steady state tests (range 0.01–590 Pa) and oscillatory tests (range 0.001–40 Hz) were carried out on 40% solutions in dimethyl formamide using a Carri‐Med rheometer. Only PHEMA having molar mass over 500000 showed significant shear thinning and viscoelastic properties. The copolymers of 2‐hydroxyethyl methacrylate (HEMA) with n‐butyl acrylate (BA) and 2‐hydroxypropyl acrylate (HPA) showed higher viscosities and viscoelastic properties compared with PHEMA homopolymer prepared under identical conditions. Also, viscosity and viscoelasticity increased with increase in acrylate content in the initial mixture. This was attributed to the higher molar mass of copolymers, which resulted from faster polymerisation rates owing to the inclusion of relatively highly reactive acrylates. However, in the case of HEMA : BA copolymers, first, the viscosity and viscoelasticity increased with increasing BA content and then dropped again, giving a maximum around HEMA : BA 75 : 25. This anomaly was explained by taking the effects of changes in inter‐and intra‐molecular hydrogen bonding as well as conformational differences caused by inclusion of BA in the PHEMA chain into account.
Chain‐scission and yellowing in high impact polystyrene
Authors: Singh R. P. , Raj R. A. , Prasad A. Vishwa , Sivaram S. , Lacoste J. , Lemaire J.
Published: April 2003

Different grades of impact‐modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain‐scission during photo‐oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturation content.
Electrical properties of an insulating varnish
Authors: Bishai Augenie M. , Hakim Itedal K.
Published: April 2003

A systematic dielectric study was carried out over a frequency range 60 Hz–300 kHz and at temperatures between 5 and 90°C on dehydrated castor oil mixed with different concentrations of styrene monomer to produce an insulating varnish. The volume resistivity was also studied. The results show that, when dehydrated castor oil is mixed with 10% styrene content by weight of the oil, epoxidised and then chemically treated with melamine resin and other additives, a varnish is produced with favourable electrical insulation properties.
Size‐exclusion chromatography of solutions of block copolymers in selective solvents
Authors: Quintana José R. , Villacampa Manuel , Katime Issa
Published: April 2003

Solutions of polystyrene‐block‐poly(ethylene/propylene) and polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene copolymers in 5‐methyl‐2‐hexanone and 4‐methyl‐2‐pentanone were studied by size exclusion chromatography. The association equilibrium was studied shifting from micelles to free copolymer chains by increasing the temperature. A remarkable tailing was observed in diblock copolymer micelle peaks that may be explained by the disturbance and restablishment of the association equilibrium during separation in the chromatographic column. This phenomenon was very small for triblock copolymers. In this case, micelle hydrodynamic volumes obtained from SEC curves were compared to those calculated from light scattering and viscosity measurements. The data agreement was very good. Comicellization was analysed by mixing two different micelle solutions and injecting the solution mixture at different elapsed times. The SEC curves showed an intermediate peak corresponding to mixed micelles. The results show that three micelle species coexist in solution during the first period after mixing, which suggests that comicellization proceeds via dissociation of pure micelles and association of both copolymer free chains to form uniform mixed micelles.
Sorption and diffusion of n‐alkanes into bromobutyl rubber membranes
Authors: Aminabhavi Tejraj M. , Munnolli Ravindra S. , Ortego J. Dale
Published: April 2003

Sorption and diffusion of n‐alkanes into bromobutyl rubber membranes were investigated in the temperature interval 25–60°C by a sorption gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes, their interactions with the chain segments of the polymer and temperature. The diffusion coefficients varied from 0.34×10−7 cm2/s (n‐hexadecane) to 9.94×10−7 cm2/s (n‐hexane). The activation energy for diffusion varied from 14kJ/mol (n‐hexane) heptane to 2.0kJ/mol for n‐hexadecane. The sorption/swelling results are discussed in terms of first and second order kinetic equations. The molar mass between chain‐entanglement‐crosslinks was estimated from swelling data. The experimental and calculated results showed a systematic dependence on the increasing size of the alkanes. None of the solvents showed any degradative effects on the polymer.
Synthesis and characterization of epoxidized phenolic novolacs modified by furfuryl alcohol
Authors: Salabarría Inraini Ramos , Oyanguren Patricia A. , Fasce Diana P. , Williams Roberto J. J.
Published: April 2003

The possibility of reacting furfuryl alcohol with the p‐position of phenolic rings, under acid conditions, was proved using different experimental techniques: size exclusion chromatography, Fourier transform infrared spectroscopy and 13C NMR. This reaction was then used in the modification of phenolic novolacs with furfuryl alcohol. After reaction with epichlorohydrin, epoxidized phenolic novolacs (EPN) modified with furan rings were obtained. They could be cured with aromatic diamines in a similar way to conventional EPNs. The presence of furan rings should improve burning resistance and smoke emission characteristics of the resulting networks.
Transient currents in charging and discharging modes in ethyl cellulose
Authors: Gaur M. S. , Singh Reeta , Khare P. K. , Singh Ranjit
Published: April 2003

Transient current in vacuum aluminized ethyl cellulose foil samples of thickness 75 μm were investigated in charging and discharging modes at different temperatures and fields. The occurrence of a peak in the current–time characteristics of charging current (Ic), and the dependence of such currents on field, characterized by a negative resistance region and followed by a superlinear region, are considered to indicate injection controlled transient currents modified by space‐charge arising from the localization of carriers in various traps. Carrier mobility values calculated from a knowledge of the peak in the charging current versus time characteristics were found to range from 10−11 to 10−9 cm2/V s.

As times larger than the peak time, the charging current follows the relation I ∝ t−n at low temperatures with different poling fields (Vp). However, the current increases with time and finally tends to saturate for samples poled at higher temperatures with higher values of field.

The isochronal characteristics (i.e. current–temperature plots at fixed times) constructed from discharge current versus time plots are characterized by a peak at 70°C or 100°C, depending upon the poling field values.