bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some fields of biomedical application of polyurethanes
Authors: Batyrbekov Erkesh O. , Moshkevich Sofia A. , Rukhina Larisa B. , Bogin Ruben A. , Zhubanov Bulat A. 
Published: April 2007

AbstractPolyurethane foams have been studied as drug carrier matrixes for sustained delivery application. The drugs used in the investigation were the specific antituberculous drug isoniazid, the antibiotic rifampicin, and the local anaesthetic novocain. The release of the drugs into model biological media was studied by UV spectroscopy. It has been found that drug release occurs in accordance with first‐order kinetics. The possibility of application of drug delivery systems for treatment of tuberculosis and haemorrhoids has been shown by some medical‐biological tests.
Solubilities, viscosities and unperturbed dimensions of poly (2,6‐diisopropylphenyl methacrylate)
Authors: Gargallo Ligia , Hamidi Nasrolah , Radić Deodato 
Published: April 2007

AbstractThe dilute solution properties of poly(2,6‐diisopropylphenyl methacrylate) (PDPP) in various solvents were studied by viscosity, exclusion chromatography and osmotic pressure measurements. The Mark‐Houwink‐Kuhn‐Sakurada relationships were established. The unperturbed dimensions, the rigidity factor σ, the characteristic ratio C∞ and the thermodynamic parameters were determined using the Stockmayer‐Fixman equation and from data in theta solvent (binary mixture). The rigidity factor of PDPP is abnormally high. The conformational behaviour of this polymer is analysed in terms of the effect of the side chain structure. The results are compared with other polymers of the same series.
Photostability of polyetherurethaneureas
Authors: Thapliyal B. P. , Chandra R. 
Published: April 2007

AbstractPolyetherurethaneureas (PEUUs) were synthesised from polyethylene‐glycols (PEGs) of molecular weight 400, 600 and 1000, 4,4′‐diphenylmethanediisocyanate (MDI) and aliphatic diamine chain extenders, 1,3‐propanediamine (PDA) and 1,6‐hexanediamine (HDA). Polymer films were irradiated with 365 nm light at 293 K and the effects of polyether soft segment length and urea hard segment on photo‐oxidative stability were studied by following the variation in weight‐average molecular weight (Mw), gel formation and stress‐strain properties. Changes in ultraviolet and infrared spectroscopy were monitored on photo‐oxidation and hydroperoxide content determined. The soft segment length was increased by increasing the molecular weight of PEG from 400 to 1000 and hard segment structure was changed by variation of diamine. It was noted that the structure of urea and polyether soft segment length plays an important role in photostability of PEUUs. PDA chain extended PEUUs were more stable than HDA chain extended PEUUs.
Comments on the accuracy of zero shear intrinsic viscosity of high molecular weight polyacrylamide
Authors: Tam K. C. , Tiu C. , Fang T. N. 
Published: April 2007

AbstractThe intrinsic viscosity of a polymer is traditionally measured with a capillary tube viscometer where the shear rate range is moderately high. Such method is valid when the polymers are non‐ionic and have low to moderate molecular weight. The viscosity‐shear rate curves obtained for dilute aqueous solutions of two high molecular weight polyacrylamides using two rotational viscometers indicate a strong shear‐dependent viscosity in the medium to high shear rate regions. The zero shear intrinsic viscosity of the polymers determined by extrapolation from the high shear rate region to the zero shear condition may result in large errors. Its implication in predicting the molecular weight of polymers using the Mark‐Houwink‐Sakurada equation is discussed. A rheological equation for intrinsic viscosity as a function of shear rate is proposed.
Thermotropic polyesters: Synthesis and properties of poly(p‐oxybenzoate‐co‐m‐phenylene terephthalate)s
Authors: Brown Philip J. , Karacan Ismail , Liu Jing , McIntyre J. Eric , Milburn Alexander H. , Tomka J. George 
Published: April 2007

AbstractDSC, TMA, hot‐stage microscopy and WAXS have been used to examine the effect of concentration of angular units and molecular weight on the thermal transitions of poly(p‐oxybenzoate‐co‐m‐phenylene terephthalate)s. Copolymers containing molar fractions of m‐phenylenedioxy units between 0·20 and 0·30 are melt processable nematogenic materials. In contrast, poly(p‐oxybenzoate‐co‐p‐phenylene isophthalate)s remain nematogenic over a wider concentration range (0·20–0·40) of angular isophthaloyl units. Comparison of fibres produced from copolymers with the same fraction of angular units (0·25) indicates that those with isophthaloyl units have a higher modulus than those with m‐phenylenedioxy units. These differences are ascribed to differences in planarity of chains containing isophthaloyl and m‐phenylenedioxy units, respectively.
Dielectric and viscoelastic studies of poly(ethyl methacrylate) containing cholesteric compounds
Authors: Deshpande Dinkar D. , Basu Chandana , Pandya Madhav V. 
Published: April 2007

AbstractPoly(ethyl methacrylate) (PEMA) containing small amounts of cholesteryl additives was studied by dielectric and dynamic mechanical spectroscopy. Dielectric data from pure PEMA and PEMA + additive systems were fitted to the WLF equation. Using the WLF constants obtained from the data for pure PEMA, the To values for PEMA + additive systems were determined in order to get the best fit of the experimental points to the WLF curve. Values of tan δmax (dielectric and mechanical) for all the PEMA + additive systems shift to higher temperatures compared with that for pure PEMA. In the glassy region, the moduli of PEMA + additive systems are higher than that of pure PEMA. Viscometric studies of PEMA + additive systems indicate the presence of some interaction. FTIR spectra of the polymer + additive systems show no shift in carbonyl bond frequency. The shift of Tg to higher temperatures indicates that chain motion in this region is hindered greatly by these additives and the reason for this may be the fitting or aligning of the additive molecules in the polymer matrix.
Chain transfer in vinyl chloride polymerization in the presence of polybutadiene
Authors: Beati E. , Pegoraro M. , Gianotti G. , Cassani F. 
Published: April 2007

AbstractVinyl chloride (M) was polymerized in the presence of a low molecular weight polybutadiene (S) at 60°C in the presence of x,x′‐azobisdiisobutyronitrile as initiator, which does not affect the transfer reaction.The raw material was fractionated for the purpose of separating the pure PVC homopolymer.The number‐average molecular weight of PVC homopolymer, determined by size exclusion chromatography (SEC), was used in Mayo's equation to obtain the value of the transfer constant Cs, which was found to be 11. A simplified reaction scheme is given according to which it is possible to explain why the reaction yield decreases and the crosslinking density increases by increasing the [S]/[M] ratio.
pH‐stat methodology in continuous monitoring of the kinetics of hydrolysis of phosphate esters catalysed by alkaline phosphatase from human placenta: Limitations, advantages and theoretical aspects
Authors: Roig M. G. , Serrano M. A. , Bello J. F. , Cachaza J. M. , Kennedy J. F. 
Published: April 2007

AbstractThe appropriateness of pH‐stat methodology in the dynamic monitoring of the kinetics of hydrolysis of phosphate esters catalysed by alkaline phosphatase (from human placenta) has been studied. This methodology involves autotitration of the H+ released or consumed during a given reaction time. The lack of specificity of the method, titrating the total H+, together with the known effect of the dissolution of environmental CO2 on the reacting system, giving rise to carbonic acid, implies an overtitration of the H+ released in the hydrolysis reaction. Because of this, parallel to each series of reaction kinetics, the dissolution kinetics of environmental CO2 under working conditions are quantified with suitable blanks, thus enabling one to subtract them from the global kinetics of the release of H+. Although no background buffers are added to the reacting system in order to maintain a constant pH, the buffering capacity of the system itself obliges one to quantify it by calibrations in order to calculate the true release rate of H+ in the reaction. These two principal limitations of the pH‐stat methodology, the dissolution of environmental CO2 and the inherent buffering capacity of the system, can be partially mitigated by working within an inert atmosphere of N2 and having a good knowledge of the acid/base characteristics of the reagents and reaction products, which together will permit the choice of a working pH range in which the second limitation will be negligible. Having studied theoretically the acid/base balances of the system in reaction, it is concluded that optimum working conditions for the pH‐stat methodology are between pH 8·5 and 11·0, since over this pH range the buffering capacity is null (thus eliminating the need for calibrations) and the stoichiometry of H+ (nH+) is close to unity. These theoretical predictions have been confirmed experimentally with calibrations and measurements of nH+ at different pH values.
Copolymerization propagation kinetics of styrene with alkyl acrylates
Authors: Davis Thomas P. , O'Driscoll Kenneth F. , Piton Mark C. , Winnik Mitchell A. 
Published: April 2007

AbstractPropagation rate constants have been determined at two temperatures (298 K and 323 K) for the copolymerizations of styrene (STY) with methyl acrylate (MA) and STY with n‐butyl acrylate (BA) over a range of monomer feed compositions. A pulsed UV laser was used as an initiation source and gel permeation chromatography (GPC) was utilized to analyse the products. None of the copolymerizations conformed to the Mayo‐Lewis model, with respect to their propagation rate constants. The results were interpreted on the basis of a penultimate effect on the propagation reaction. In addition, Mark‐Houwink constants were determined for poly(MA) and poly(BA) in tetrahydrofuran (THF) at 298 K. These constants are given as [K(dm3 kg−1),α]: 7·88 × 10−3, 0·885 and 8·57 × 103, 0·865 for poly(MA) and poly(BA) respectively.
Raman spectroscopy of Kevlar fibres during deformation—Caveat emptor
Authors: Young R. J. , Lu D. , Day R. J. 
Published: April 2007

AbstractIt has been demonstrated that when aromatic polyamide fibres such as Kevlar 49 are subjected to mechanical deformation, significant frequency shifts are obtained for the peak position of the 1610 cm−1 Raman band using both 632·8 nm and 488 nm laser radiation. Two earlier reports of the deformation of fibres in a 488 nm argon ion laser beam reported no such frequency shifts. It has been shown that this wavelength of laser light can degrade Kevlar fibres. This causes premature failure of the fibres through chain scission and the fibres break at low strains before significant levels of stress or strain can be achieved. Hence, the previous conflicts can be resolved and it has been demonstrated that simultaneous Raman spectroscopy and mechanical deformation is a powerful method of following the micromechanics of fibre deformation.
Synthesis and characterization of polyurethanes containing arylene sulfone ether linkages
Authors: Idage Susheela B. , Idage Bhaskar B. , Vernekar Subhash P. 
Published: April 2007

AbstractPolyurethanes containing arylene sulfone ether linkages were synthesized by solution polymerization of 4,4′‐bis(4‐isocyanatophenoxy)diphenylsulfone (SPI) and 4,4′‐bis(3‐isocyanatophenoxy)diphenylsulfone (SMI) with various aliphatic glycols such as ethylene glycol (EG), 1,2‐propylene glycol (PG), 1,4‐butylene glycol (BG), polyethylene glycol (PEG 300 and 1000), polypropylene glycol (PPG 300 and 1000) and polytetramethylene glycol (PTMG 1000. TERACOL) in dimethylacetamide (DMAC) at 120°C. The diisocyanates SPI and SMI were prepared from the corresponding diacid chlorides via Curtius rearrangement. The polyurethanes were obtained in high yields. The effect of structures of diisocyanate and aliphatic diols on the molecular weight and thermal properties of polyurethanes was also investigated. The polyurethanes prepared were characterized by infrared spectroscopy, solution viscosity, elemental analysis, thermogravimetric analysis and X‐ray diffraction. Physical and thermal properties of polyurethanes prepared from SPI and various aliphatic glycols were compared with the polyurethanes from SMI and various aliphatic glycols.
Studies on polymer latex films: I. A study of latex film morphology
Authors: Roulstone B. J. , Wilkinson M. C. , Hearn J. , Wilson A. J. 
Published: April 2007

AbstractPolymer films have been formed from poly (butyl methacrylate) latices prepared by surfactant‐free emulsion polymerisation. The latices having also been cleaned by microfiltration constitute model colloid particles and hence form ‘model’ films.A novel freeze fracture replication and transmission electron microscopy technique was employed to study film morphology. It demonstrated the presence of interparticle boundaries between latex particles deformed into dodecahedra and the particle packing order without the need for a staining technique. The time and temperature of film formation and storage was shown to affect the degree of particle coalescence. Solvent cast films were also studied for comparison purposes.
trans‐polyoctenylene as a processing aid for rubber: Influence on energy consumption and properties of rubber compounds
Authors: Lau Wayne W. Y. , Swee‐Hin Teoh , Suat‐Hong Goh 
Published: April 2007

Abstracttrans‐Polyoctenylene rubber, TOR, was melt blended with different types of rubber in various proportions in a Brabender Plasti‐corder. Energy consumption in mixing the blends indicated that TOR is an effective processing aid for a variety of rubber and inclusion of TOR in a blend can result in significant saving of energy. TOR of lower molecular weight (e.g. Vestenamer 8012) performs significantly better than TOR of higher molecular weight (e.g. Vestenamer 6213), both as a processing aid and as a dimension stabilizer.
Grafting of low density poly(ethylene) with butyl acrylate: Synthesis and characterisation
Authors: Raval Heta , Singh Y. P. , Mehta M. H. , Devi Surekha 
Published: April 2007

AbstractLow density poly(ethylene) was grafted with butyl acrylate using benzoyl peroxide as free radical initiator in an inert atmosphere and toluene as solvent. Various parameters such as reaction time, temperature, initiator concentration and ratio of monomer to polymer were varied to study their effects on percentage of grafting and grafting efficiency of butyl acrylate on to low density poly(ethylene). The graft copolymers were characterised by IR spectroscopy. The change in the solubility behaviour of low density poly(ethylene) due to grafting was studied by turbidometric titration. Thermal stability of graft copolymers was found to be higher than that of LDPE. Intrinsic viscosity data showed an increase in viscosity with increasing grafting percentage.
Polymerization of some oxiranes using the diphenylzinc‐butanone system in benzene at 60°C
Authors: López Francisco , Calcagno María P. , Contreras Jesús M. , Torrellas Zulay , Felisola Katania , Rabagliati Franco M. , Katime Issa A. 
Published: April 2007

AbstractThe diphenylzinc‐butanone system was used as polymerization catalyst for some oxiranes in benzene solution at 60°C. This system is greatly influenced by the molar ratio of butanone to diphenylzinc, and the maximum catalytic activity for propylene oxide and ethylene oxide was found for a ratio of unity. GPC results strongly suggest the presence of more than one active species for the system. 13C NMR analysis indicates that the resulting poly(propylene oxide) has a head‐to‐tail arrangement. For the polymerization of propylene oxide with butanone/diphenylzinc = 1, after an initial induction period, the reaction was first‐order with respect to monomer with k = 2·51 × 10−5 s−1. Ethylene oxide polymerizations using butanone/diphenylzinc = 1 and 5 were also first‐order with respect to monomer after an initial induction period with k = 7·80 × 10−6 s−1 and k = 5·71 × 10−6 s−1, respectively. The diphenylzinc‐butanone system was not an effective catalyst for styrene oxide polymerization.
Wood fibre‐polyester dough moulding compounds
Authors: Freischmidt G. , Michell A. J. , Lewis M. J. , Vanderhoek N. 
Published: April 2007

AbstractThe mixing of wood fibres into dough moulding compounds (DMC) has been enhanced through thickening the mix by using zinc oxide or by adding an increased amount of scrap polystyrene. In both cases, the requirement for expensive styrene monomer has been reduced. The time needed for mixing has been shortened from up to 10 h to only 0·5 h as a result of the more efficient mixing. The electrical insulation properties of the compounds easily meet industry standards. Attempts to reduce the brittleness and increase the mechanical properties of the compounds by pretreating the fibres have not been successful.
Behaviour of poly(β‐hydroxybutyric acid) in dilute solution
Authors: Huglin Malcolm B. , Radwan Mostafa A. 
Published: April 2007

AbstractThe refractive indices of poly(β‐hydroxybutyric acid) (PHB) at four wavelengths have been determined via different procedures. Viscometric and light scattering measurements have been made on solutions of eight samples of PHB (Mw = 20·9 × 103−929 × 103 g mol−1) in 2,2,2‐trifluoroethanol. From the dependences of intrinsic viscosity and of radius of gyration on molar mass, the conformation of PHB in dilute solution is shown to be that of a random coil. The findings are discussed in relation to existing conflicting evidence on the conformation of this polymer.
Tetramethylammonium 3‐aminopropyl dimethylsilanolate—aminopropyl dimethylsilanolate—a new catalyst for the synthesis of high purity, high molecular weight α,ω‐bis(aminopropyl) polydimethylsiloxanes
Authors: Hoffman Jerome J. , Leir Charles M. 
Published: April 2007

AbstractTetramethylammonium 3‐aminopropyl dimethylsilanolate, readily prepared from bis(3‐aminopropyl) tetramethyldisiloxane and tetramethyl‐ammonium hydroxide pentahydrate, has been found to serve as a highly effective catalyst for the ring opening polymerization of cyclic siloxanes with an end blocker such as bis(3‐aminopropyl) tetramethyldisiloxane to give aminopropyl terminated linear polydimethylsiloxanes. By following a novel two stage procedure, even high molecular weight (5,000–55,000 g/mol) silicone diamines were able to be prepared in a high state of purity; chain extension reactions of these diamines with diisocyanates gave a series of high molecular weight silicone polyureas with good elastomeric properties.
Magnetic resonance imaging studies of the polymerisation of methylmethacrylate
Authors: Jackson Peter , Clayden Nigel J. , Walton Nicholas J. , Carpenter T. Adrian , Hall Laurance D. , Jezzard Peter 
Published: April 2007

AbstractMagnetic resonance imaging has been used to spatially map the time course of the bulk polymerisation of methylmethacrylate. Both two‐dimensional projection and slice‐selective techniques have been employed. Image intensities give qualitative information about viscosity, reaction rates and the localised extent of polymerisation. The importance of proton relaxation measurements in drawing quantitative conclusions is stressed.
Photoresponsive peptide and polypeptide systems: Part 9. Synthesis and reversible photochromism of azo aromatic poly(L‐α,ω‐diaminobutyric acid)
Authors: Yamamoto Hiroyuki , Nishida Ayako 
Published: April 2007

AbstractPoly(L‐α,ω‐diaminobutyric acid) having azo aromatic side chains was synthesized by the water‐soluble carbodiimide procedure. The photoresponsive properties of the polypeptide poly[N7‐p‐(phenylazo)benzoyl‐L‐α,ω‐diaminobutyric acid] (PPABLDBA) due to the trans (about 71%, under visible light) cis (under ultraviolet light) photoisomerization of the azo aromatic moieties in the side chains were investigated by absorption and circular dichroism spectroscopy in hexafluoro‐2‐propanol (HFIP). The starting slightly turbid solution of trans‐PPABLDBA becomes clear on irradiation at 360 nm, accompanied by photoconversion of the conformer of the azo moieties to cis. The backbone conformation of PPABLDBA in HFIP is right‐handed helical (helical content, about 60%) when the azo moieties are trans (71%), while the conformation is random coil when cis. The backbone conformational transition of PPABLDBA from helical to coil is mostly reversible under the influence of light.
Physico‐chemical studies of polyetherurethaneurea in phosphate buffer solution
Authors: Ray Alok R. , Neelamegham Sriram , Bhowmick Ashis 
Published: April 2007

AbstractPolyetherurethaneureas are increasingly used as implants in the human body, where they come in contact with body fluid. Most of the reported properties of polyetherurethaneureas have been determined in the dry state. The present work deals with the properties of these materials in aqueous systems. A number of linear polyetherurethaneureas based on polyethoxyglycol and polypropoxyglycol of different molecular weights, 4,4′‐diphenylmethane diisocynate, 1,3‐propanediamine and 1,6‐hexanediamine have been prepared. Their swelling characteristics and phase composition in phosphate buffer solution are evaluated. The role of water in changing various properties of polyetherurethaneureas is discussed.
Ultrasonic degradation of polymer solutions. 1. Polystyrene revisited
Authors: Price Gareth J. , Smith Paul F. 
Published: April 2007

AbstractThe results of ultrasonic irradiation of polystyrene solutions in toluene, benzene and carbon tetrachloride are described. The effect of a range of conditions such as ultrasonic intensity, solution concentration and varying solvents were investigated. The non‐random nature of the degradation process was clearly demonstrated and the effect of different solvents was interpreted in terms of their thermodynamic properties.
Effects of plasticizer on shear modification of polystyrene
Authors: Qian J. W. , Rudin A. , Teh J. W. 
Published: April 2007

AbstractThe elastic and viscous properties of polymer melts may be affected by the shear history of the polymer. The extrudate swell of a polymer melt is primarily a manifestation of the elasticity of the polymer melt. In this study, a single screw extruder was used to impose different shear histories on a polystyrene polymer which was processed with and without added plasticizer. The extrudate swell and apparent viscosity of these melts were measured with a capillary rheometer. These characteristics of unplasticized polystyrene are almost not affected by the various preshearing processes. However, the extrudate swell and viscosity of polystyrene containing plasticizer are affected by plasticizer level, shear history and thermal history. After most of the plasticizer in the presheared plasticized polystyrene was extracted, the extrudate swell was still lower than that of the parent sheared polystyrene with the same shear history and the same plasticizer content. These results were obtained without significant changes in molecular weight.Shear modification by conventional process equipment may become impractical if the shear field intensity or dwell time of the material in the apparatus is limited. In such cases, shear refinability by standard process equipment may be observed if the coupling density in the polymer is reduced by some additional means, such as blending with a plasticizer.