bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elasticity of real networks: Comparison of molecular theory with experiments
Authors: Erman Burak 
Published: April 2007

AbstractPredictions of the theory of elasticity of real networks are compared with results of experiments. The shape of the stress‐strain curve for networks in the dry and swollen states and over wide ranges of strain, both in tension and compression, agrees with results of calculations based on the theory. The theory is also in close agreement with results of multiaxial stress‐strain experiments and with the predictions of the degree of crosslinking obtained from measurements of the modulus. The theory may additionally be applied to the analysis of birefringence. The assumption of the linear additivity of the elastic and mixing free energies in a swollen network leads to results which are in agreement with experimental findings on different crosslinked systems.
Kinetics of gelation of aqueous gelatin solutions
Authors: Djabourov Madeline , Maquet Jean , Theveneau Hélène , Leblond Jacques , Papon Pierre 
Published: April 2007

AbstractThe kinetics of gelation of gelatin + water solutions have been investigated by several experimental methods, in particular optical rotation, 1H nuclear magnetic resonance and rheological measurements. During quenching and isothermal annealing of the solutions, the gelatin chains undergo a conformational coil→helix transition which is responsible for the network growth. The amount of helix (derived from optical rotation measurements) shows a time evolution which could be analysed as the combination of two processes, the first obeying an Avrami equation, the second proceeding logarithmically in time. The water 1H n.m.r. measurements reveal that the spin‐spin relaxation time T2 is affected by these processes, thus implying that a fraction of water contributes to the network structure. Finally, the sol‐gel transition could be followed with a Weissenberg rheogoniometer in oscillatory shear, for a suitable range of temperatures, when the system changes from a purely viscous liquid (the shear modulus G′=0), to an almost purely elastic solid (the loss modulus G″=0).
The elastic behaviour of hydrogels
Authors: Oppermann Wilhelm , Rose Sigrid , Rehage Günther 
Published: April 2007

AbstractThe mechanical properties and the swelling behaviour of aqueous poly(acryl amide) and poly(acryl amide‐co‐Na acrylate) gels were investigated. The ionic networks were prepared by hydrolysis of the nonionic ones, in this way preserving the network topology. By measurement of the modulus it was detected that networks prepared in solution contain a rather large portion of elastically ineffective rings. Hydrolysing a part of the amide groups resulted in a considerably increased swelling ratio. The modulus of such ionic gels did not show the predicted decrease with rising swelling ratio, but on the contrary increased up to a fivefold value. The reason for this behaviour is seen in the limited extensibility (non‐Gaussian behaviour) of the network chains. At constant swelling ratio, the modulus of gels having identical topology decreased with rising degree of hydrolysis. This reflects the influence of the ionic groups on the mean‐square end‐to‐end distance of the free polymer chains.
Rate theory of random polymerisation: RA3 polymerisation
Authors: Lloyd Anthony C. , Stepto Robert F. T. 
Published: April 2007

AbstractThe limiting form of rate theory using the first generation subset of states of monomer units is applied to the self‐polymerisation of RA3 monomers. It affords a description of the polymerisation process which specifies how species interconvert. The case of no intramolecular reaction is considered first and it is shown how characteristics of the polymerisation, unit fractions and number fractions of molecular and continuing species, the gel point, the sol fraction and the network at complete reaction, may be evaluated. The gel point is defined in terms of a quantity called the critical total. Intramolecular reaction is then introduced and analytical expressions for the unit fraction of ring structures and for the gel point are derived. They are valid provided the ring‐forming parameter (λ) is not too large. However, in general, numerical evaluation of the characteristics of the polymerisation is required when intramolecular reaction is present. In the paper, emphasis is placed on correlations between the extent of reaction at gelation (Pc) and the structure of the network at complete reaction formed in the presence of pregel and postgel intramolecular reaction. The correlations are compared in general terms with those obtained experimentally for RA2 + RB3 polymerisations.
Computer simulation of urethane formation
Authors: Shy L. Y. , Eichinger B. E. 
Published: April 2007

AbstractComputer model calculations have been used to simulate the reaction of polyoxypropylene triol with hexamethylene diisocyanate. Various molecular weight distributions and degrees of polymerisation are used in the calculation. The effect of side reactions is investigated and compared with experiment. Good agreement for both cyclisation and gel points is found for bulk and concentrated solutions. The model can be used to simulate random polycondensation reactions with a reliability approaching that of experiments, and it gives crucial results that cannot be obtained in any other way.
Effects of functionality and temperature on gel points in random polymerisation
Authors: Ahmad Zahoor , Stepto Robert F. T. , Still Richard H. 
Published: April 2007

AbstractFirst, the relationship between gel point and average functionality for an RA2+R′Bf type polymerisation has been investigated by measuring the product of extents of reaction at gelation (αc) for sebacoyl chloride (SC)/polyoxyproplyene (POP)diol/POP triol mixtures reacting at various initial dilutions in diglyme as solvent at 60°C. Intramolecular reaction always delays gelation and a generalisation of the Ahmad‐Stepto gel point expression has been used to interpret the gelation data in terms of the ring‐forming parameter λ′ab. From the variation of λ′ab with initial dilution, values of b, the effective bond length of the chain forming the smallest ring structure, have been derived. It is found that b decreases with average polyol functionality (fw). This decrease apparently compensates for the increase in λ′ab with fw, so that ring formation is less sensitive to functionality than may have been expected. It is found that the Ahmad‐Stepto expression does not predict a consistent relationship between λ′ab, fw and the gel dilution of reactive groups.Second, the effect of temperature on the gel point has been studied by measuring αc for SC/POP triol mixtures reacting at various initial dilutions in diglyme as solvent at 27° C, 40° C and 60° C. At a given temperature, b decreases as triol molar mass increases, indicating that the POP residue of the chain forming the smallest ring structure is more flexible than the SC residue. This result is in keeping with those from previous investigations,1,2 For a given triol, αc decreases as temperature increases, indicating an increase in chain stiffness with temperature. Values of d In <r2>/dT are derived and found to be larger than those for linear chains.
In situ investigation by quasi‐elastic light scattering of an irreversible sol‐gel transition
Authors: Candau S. J. , Ankrim M. , Munch J. P. , Hild G. 
Published: April 2007

AbstractWe report a dynamic light scattering study of semi‐dilute solutions of polydisperse branched polymers. The autocorrelation function of the intensity of scattered light exhibits two decay modes. Experiments performed in situ on the sol phase of a system undergoing irreversible gelation show that the slow relaxation time diverges at the sol‐gel transition.
Inhomogeneity of gel and microsyneresis in porous styrene‐divinylbenzene copolymers
Authors: Galina Henryk , Kolarz Bozena N. , Wieczorek Piotr P. , Wojczynska Maria 
Published: April 2007

AbstractThe porosity of styrene‐divinylbenzene copolymers prepared by suspension copolymerisation of the monomers carried out in the presence of inert diluent changes due to solvent pretreatment is investigated. The changes seem to reflect the inhomogeneity of copolymer gel. Various portions of it are transferred from the rubber‐like into the glassy state at different stages of either swelling solvent exchange or the drying process. A microsyneresis, i.e. a local collapse of loosely crosslinked gel portions not followed by a shrinkage of the whole system, leads to the porosity changes.
Inhomogeneity during the bulk polymerisation of divinyl compounds: Differential scanning calorimetry experiments and percolation theory
Authors: Boots H. M. J. , Kloosterboer J. G. , Van Hei G. M. M. De , Pandey R. B. 
Published: April 2007

AbstractExperiments are presented that indicate inhomogeneity in bulk divinyl polymerisation which persists far beyond the gel point and a percolation model is given by which this inhomogeneity is simulated. Isothermal differential scanning calorimetry experiments indicate trapping of radicals in regions of low mobility long before overall vitrification occurs. The results on pendant double bonds in divinyl polymerisation are similar to those obtained by Malinsky et al. for styrene/divinyl benzene copolymerisation. The percolation model used shows inhomogeneity in snapshots and provides a qualitatively correct description of the high extent of cyclisation at low conversion, in contrast to classical chemical kinetics. The model overestimates the crosslinking at high conversion.
Epoxy mechanical properties: Function of crosslink architecture
Authors: Timm Delmar C. , Ayorinde Ayodeji J. , Foral Ralph F. 
Published: April 2007

AbstractA thermoset resin's molecular architecture is characterised by extent of reaction, crosslink average molecular weight and the average size of constituent macromolecules. Molecular analyses of extracts from cured resins via gel permeation chromatography yield microscopic estimates of this infrastructure. The number‐average molecular weight within the soluble oligomeric fraction correlates with crosslink average molecular weight: the extent of monomer conversion assists in developing a description of the molecular weight of constituent marcomolecules within the network structure. Macroscopic conformation couples observations by dynamic mechanical spectroscopy, compressive stress‐strain phenomena and impact resistance.
Novel precursors suitable for RIM polyurethane networks
Authors: Cawse John L. , Stanford John L. , Still Richard H. 
Published: April 2007

AbstractThe synthesis and development of novel, furan‐based diisocyanates (FDI) and myrcene‐based polyols (PM) with potential for polyurethane production are presented. Pure FDI compounds, similar in structure to 4,4'‐methylenediphenylene diisocyanate (MDI) were prepared unambiguously from fur‐furylamine as liquids of low volatility, stable down to 0° C. making them particularly suitable for RIM. Comparative kinetics studies with n‐butanol show the FDIs to behave as benzylic compounds with reactivities intermediate between those of aryl and alkyl diisocynates. Studies were made on segmented copolyurethanes prepared from FDI and polyol mixtures of 1,4‐butane diol (BD) and polytetrahydrofuran (Mn. 1010).Hydroxyfunctional polymyrcenes were prepared from myrcene in n‐butanol at 100° C using hydrogen peroxide as initiator. The liquid rubbers formed (Mn, 2000‐4000; with fn, 2.3‐1.3 respectively) were shown by n.m.r. to comprise mainly substituted 1,4‐butadiene units and are similar to the commercially available polybutadienes (PB). Copolyurethane elastomers were prepared from polyol blends of PM and 1,4‐butane diol reacting with MDI.Both series of FDI‐and PM‐based copolyurethanes were shown by d.s.c. d.m.a. and tensile measurements to possess properties comparable to analogous materials formed from, respectively, MDI‐ and PB‐based systems. In addition to their suitability for RIM, the results show the feasibility of deriving polyurethane feedstocks from naturally‐occurring, non‐oil based sources.
The influence of processing on biopolymeric structures
Authors: Richmond Peter , Smith Andrew C. 
Published: April 2007

AbstractMaize grits and maize starch were extruded under a number of conditions using a twin screw extruder. Under equilibrium operation the extruder was dead stopped and the barrel contents removed. Samples from the raw input to the extrudate were examined using scanning electron microscopy, water solubility and aqueous dispersion rheology. The extrusion process results in deformation of the starch granular structure and the production of a new texture corresponding to a marked increase in solubility. Raw maize dispersions are characterised by low viscosity and dilatancy, whereas their heat treatment results in a viscous, shear thinning response. Extrusion results in a tendency to Newtonian behaviour in the limit of high shear and low moistures. This behaviour has been attributed to the reduced swelling functionality of the starch as a function of extrusion which causes a breakdown of the starch granules.
The microstructure of polypropylene welds as a guide to processing history
Authors: Oliveira M. J. , Hemsley D. A. 
Published: April 2007

AbstractThe well known occurrence of different crystalline forms in polypropylene and their easy recognition in the polarising microscope has provided a method of analysing the behaviour of this material during the production of hot plate welds. The different thermal behaviour of the α‐ and the β‐forms of crystalline polypropylene allows estimation of the thermal history of the polymer in the region of the weld. In particular it is possible to estimate the amount of material actually melted by contact with the hot plate. The effect of the original crystalline microstructure of the components being welded on the microstructure of the recrystallised material forming the weld bond has also been explored. It is possible to characterise the general crystalline texture in the weld bead in terms of the shear and thermal history of the material. The influence of pre‐ and post‐welding annealing of the polypropylene has been investigated and a difficulty is encountered in explaining an apparent ‘memory’ of β‐form crystallisation which conflicts with established x‐ray diffraction results.
The characterisation of polycarbonate‐containing graft copolymers and the kinetics of graft polymerisation
Authors: Eastmond G. C. , Harvey L. W. 
Published: April 2007

AbstractThis paper examines several procedures for selective degradation of the preformed polymer component (polycarbonate) of certain types of graft copolymers. A procedure based on a two‐phase alkaline hydrolysis of the polycarbonate is identified as the preferred technique because it provides a clean system for the quantitative recovery and subsequent characterisation of the grafts. The application of the technique to a series of polycarbonate/polystyrene graft copolymers is reported. The kinetics of free‐radical graft polymerisation of styrene and the molecular weight distributions of the polystyrene grafts are compared with those for styrene homopolymerisation performed at the same rates of initiation. This comparison allows several differences between the kinetics of graft and homopolymerisation to be identified, both prior to and after gelation. These factors are interpreted in terms of modifications to the rate coefficient for bimolecular termination of the propagating grafts. Two (possibly three) factors are identified which influence the polymerisation kinetics prior to gelation; their influences are contrary and their relative importances depend on the rate of initiation. After gelation an additional effect, termed the network effect, comes into force and dominates both the rates of graft polymerisation and the molecular weight distributions of the grafts.
Topochemical polymerisation of a diacetylene: Studies of lattice parameters and thermal expansion coefficients
Authors: Bloor David , Day Richard J. , Ando David J. , Motevalli Majid 
Published: April 2007

AbstractThe solid‐state polymerisation of the disubstituted diacetylene, 2,4‐hexadiynylene bis(p‐toluene sulphonate). has been studied by x‐ray diffraction in the temperature range 223 to 295 K. The variation in lattice parameters is shown to be similar to that reported in previous less extensive studies. This data is used to determine the behaviour of the thermal expansion coefficients as a function of polymer content. The relevance of these results to the question of polymer chain lengths at low conversion is discussed.
Statistical evaluation of methylol‐free melamine‐formaldehyde oligomer distributions: Empirical formulae from elemental analysis
Authors: Gebregiorgis T. , Gordon M. 
Published: April 2007

AbstractThe problem of measuring quantitatively and reliably the proportions of methylene‐ and ether bridges in melamine‐formaldehyde resins has resisted chemical and spectroscopic approaches. Such measurements are specially required for refining statistical models of the overall crosslinking reaction. Pregel samples contain oligomer mixtures which can be freed from pendent methylols by treatment with ammonia. They obey the empirical formula (C3N6H6)1(CH2)R(H2O)z, where R and z can be found by optimising over measurements of %C, %N and %H. The accepted structures lead to prediction of z = −0.5R if only ether bridges are present or z= −R if only methylene bridges are present. In principle, intermediate values of −0.5R>z>‐R could allow the proportions of the two kinds of bridges to be determined. However, over a wide range of ratios R of formaldehyde to melamine, results are found to obey z = −0.2R, indicating retention of free water in the samples. Prolonged vacuum drying at room temperature may overcome the problem.
Copolymer melt rheograms from melt flow index
Authors: Shenoy A. V. , Saini D. R. 
Published: April 2007

AbstractAvailable literature data on the variation of melt viscosity with shear rate are shown to coalesce together to give unique curves for each copolymer type, independent of temperature and copolymer grade, based on a normalising technique using the Melt Flow Index. The unified curves obtained are useful for estimating the flow curves of the copolymers at the temperature of interest if the Melt Flow Index of the copolymer at the specific temperature is known. Coalesced curves are presented for a number of commonly known copolymers such as acrylonitrile‐butadiene‐styrene, styrene‐butadiene‐styrene. vinyl chloride‐vinyl acetate, ethylene‐vinyl‐acetate, polyester elastomer and an olefinic‐tyype thermoplastic elastomer.
Analysis of a homologous series of non‐reducing oligosaccharides from Arnica montana L. Roots
Authors: White Charles A. , Kennedy John F. , Lombard Anna , Rossetti Valeria 
Published: April 2007

AbstractThe oligosaccharide component compositions of a series of non‐reducing oligosaccharides extracted from the roots of Arnica montana L. has been determined by gel permeation chromatography (g.p.c.). The range of oligosaccharides present was found to extend beyond the octasaccharide previously reported. with 16% to 19% of the oligosaccharides having a degree of polymerisation of between 11 and 19 and almost 3% having a degree of polymerisation greater than 20. The chromatographic behaviour of this series of oligosaccharides is compared with that observed for series of D‐gluco‐oligosaccharides.
Ultrasonic study of molecular association of poly(vinyl chloride) solution in tetrahydrofuran
Authors: Hassun Subhi K. , Al‐Madfai Suham H. F. , Al‐Jarrah Mustafa M. F. 
Published: April 2007

AbstractUltrasonic absorption, velocity, adiabatic compressibility, relaxation time and relaxation amplitude measurements are reported on poly(vinyl chloride) (PVC) solution in tetrahydrofuran (THF) using pulsed ultrasonic apparatus operating at 2 MHz and 313 K. Results show a linear increase of velocity. density, viscosity, absorption coefficient, relaxation time and relaxation amplitude values with the increase of PVC concentration in THF. In contrast the compressibility decreases with increasing PVC concentration. This suggests interaction between PVC and THF molecules.
Investigations on the cyanogen bromide activation of xanthan gum
Authors: Kennedy John F. , Hussain Meriam Adam 
Published: April 2007

AbstractThe CNBr activation procedure has been investigated as a means of synthesising derivatives of xanthan gum. Both the titration and buffer methods of the procedure were compared. While the degrees of activation obtained from both methods were pH‐dependent, the buffer method gave a slightly greater concentration of active groups. Imidocarbonates constituted the major reactive species in the activated polysaccharide. This indicated that the mechanism of activation and hence, coupling with amino‐ligands, of CNBr‐activated xanthan was similar to that postulated for Sephadex and other polyglucose polysac‐charides. However, the degree of activation of xanthan gum was considerably reduced in comparison to values obtained with Sephadex activated in a similar manner. It was concluded that this was due to the complex structure and conformation of xanthan gum in solution which was also thought to be responsible for the ability of the unreacted polysaccharide to interact non‐covalently with small amino‐ligands. The activated xanthan gum exhibited a reduced viscosity in solution compared to that of the native polysaccharide.
A preliminary study of blends of bisphenol a polycarbonate and poly(ethylene terephthalate)
Authors: Chen Xin‐Yue , Birley Arthur W. 
Published: April 2007

AbstractThe microstructure of blends of bisphenol A polycarbonate (PC), and poly(ethylene terepthalate) (PETP) has been studied by solvent extraction, infrared spectrophotometry, differential scanning calorimetry and dynamic mechanical thermal analysis. The blends appear to contain two amorphous phases over the whole composition range. The tensile behaviour and the Charpy impact strength of some of the blends have been determined, before and after heat treatment at 125°C for 18 hours. Improved performance of the blends, compared with that of the homopolymers PC and PETP, has been demonstrated.
Curing of epoxy resin of 1,1'‐bis(4‐hydroxy phenyl) cyclohexane with phthalic anhydride. A differential scanning calorimetric investigation
Authors: Shah Praful P. , Parsania Pursottam H. , Patel Shanti R. 
Published: April 2007

AbstractCuring reactions of epoxy resin of 1,1'‐bis(4‐hydroxy phenyl) cyclohexane with phthalic anhydride have been investigated by differential scanning calorimetry. The overall kinetics of curing have been found to follow a simple Arrhenius‐type rate‐temperature dependence, with an average overall activation energy of 75.4 ± 8.0 kJ mol−1 and natural log of Arrhenius frequency factor of about 18 min−1 up to at least 90% conversion. The curing reaction is found to follow overall first‐order kinetics.
Electron irradiation of polymerisable langmuir‐blodgett multilayers as model resists for electron‐beam lithography
Authors: Boothroyd Brian , Delaney Paul A. , Hann Richard A. , Johnstone Robert A. W. , Ledwith Anthony 
Published: April 2007

AbstractAmphiphilic molecules containing a polymerisable oxiran (epoxide) group have been assembled into Langmuir‐Blodgett multilayers. Lines were drawn on the multilayers by exposure to an electron beam and subsequent development by rinsing in toluene. Line widths and heights were examined for various doses of electrons of energies 10, 5 and 2 kV. Generally, for the higher energies and shorter exposures, narrow well defined lines were obtained of height similar to the thickness of the original multilayers. Conversely, at lower energies and exposure times, troughs rather than lines were observed following incomplete development. The implications of these results are compared with theoretical predictions of bbnd forming and bond scission processes during electron irradiation of organic molecules.