bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and properties of copolypyromellitimides
Authors: Yang Chin‐Ping , Hsiao Sheng‐Huei 
Published: April 2003

AbstractCopolyamic acids with different proportions of diamine component were prepared by polymerizing different molar ratios of diamines—benzidine (B)/4,4′‐diaminodiphenyl ether (E) and p‐phenylene diamine (P)/4,4′‐diaminodiphenyl methane (M)—with pyromellitic dianhydride (PMDA) in dimethylacetamide (DMAc) at room temperature. Diamine component can be arranged in regular sequence through various reaction processes, such as alternating, block, and partial block copolymers. In addition, it can also be arranged in random sequence to obtain random copolymers. Thermal cyclodehydration of polyamic acids results in the corresponding polyimides. Polymers are characterized by viscosity, thermal stability, crystallinity, and mechanical strength. It was found that an increase in the proportion of more flexible diamine component (such as E and M) incorporated in polymer chain results in copolyimides with better mechanical strength and causes a fall in viscosity of copolyamic acids and a decrease in thermal stability and crystallinity of copolyimides. Within the copolymers of the same composition, the thermal stability, crystallinity, and mechanical strength of ordered polymers are superior to those of random polymers. The results of viscosity measurements imply that the anhydride‐terminated prepolymer is easily destroyed by water in the solution, so that the ultimate viscosities of alternating and block copolyamic acids are inferior to those of random ones, but this phenomenon can be improved through the preparation of the partial block copolymers.
Dynamic mechanical properties and adhesive strengths of epoxy resins modified with liquid rubber. II. Modification with CTBN
Authors: Takemura Akio , Shiozawa Kimihide , Tomita Bun‐Ichiro , Mizumachi Hiroshi 
Published: April 2003

AbstractThe dynamic mechanical properties and the adhesive strengths of epoxy resins‐CTBN blend systems and epoxy resins‐CTBNX blend systems were investigated.Both CTBN blend and CTBNX blend systems were proved to be partially compatible with the dynamic mechanical measurement. In the case of CTBN blend systems, the more blending of CTBN, the more the compatibility increased. On the other hand, CTBNX‐20 was more compatible than CTBNX‐30 but less than CTBNX‐40. In any case, the blending of CTBN or CTBNX reduced the nonreacted part of the epoxy resins cured at room temperature.The adhesive strengths were evaluated as a function of the storage modulus with altering temperature and altering rubber content. Both procedures were proved to be equal.
Dielectric properties of an epoxy resin and its composite I. Moisture effects on dipole relaxation
Authors: Reid Jonathan D. , Lawrence William H. , Buck Richard P. 
Published: April 2003

AbstractDipole relaxation dielectric loss behavior of a fiberglass–epoxy composite has been studied as a function of moisture uptake. A single widely distributed loss peak, centered at −16°C for 10 kHz measurement, is observed in the dry composite. Very low moisture concentrations (<0.1%) interact with the composite, through either dipole pairing or by inducing chemical changes, to decrease loss intensity. At moisture concentrations from 0.1 to 1.4%, loss peak intensity generally increases with moisture uptake. Over this moisture concentration range water dipoles presumably relax in phase with the epoxy segments or side groups upon which they adsorb. Arrhenius relaxation activation energy decreases, and improved loss peak definition at increasing moisture concentrations is interpreted as indicating resin plasticization by adsorbed moisture. At moisture concentrations above 1.4%, the appearance of a second loss peak suggests formation of a new colloidal or weakly adsorbed moisture phase, as well as the saturation of primary adsorption sites.
Lower critical solution temperature behavior of ethylene propylene copolymers in multicomponent solvents
Authors: Irani C. A. , Cozewith C. 
Published: April 2003

AbstractThe lower critical solution temperature (LCST) locus for ethylene‐propylene copolymers has been determined as a function of pressure in a variety of single and multicomponent solvents. The lower critical end‐point temperature (LCEP), which is the intersection of the LCST locus with the vapor‐pressure curve, was found to be predictable from the solvent density as previously established for single‐component solvents by Charlet and Delmas.1 Dissolving a low‐molecular hydrocarbon gas such as propylene in an alkane has a dramatic effect on lowering the LCEP, and can reduce phase‐separation temperatures to levels at which this technique becomes attractive as a practical method for polymer recovery from diluents such as those used in solution polymerizations. Temperatures considerably above the LCEP are needed to minimize the residual polymer concentration in the solvent in the two‐liquid‐phase region. The solvent critical temperature must be approached for essentially complete elimination of the polymer from the solvent phase. The LCST locus was found to be a linear function of pressure for all of the systems investigated, and the slope of the line, d(LCST)/dP, could be well correlated as a function of solvent density and critical temperature. From the relationship between the LCEP and solvent density and the correlation for d(LCST)/dP, the location of the LCST locus can be readily predicted from a knowledge of solvent properties.
Melt viscosity and electrical conductivity of carbon black‐PVC composite
Authors: Noguchi Tsutomu , Nagai Tohru , Seto Jun'etsu 
Published: April 2003

AbstractThe effect of the structure of carbon black aggregates on the melt behavior and electrical conductivity of carbon black‐vinylchloride‐vinylacetate copolymer systems was analyzed. As the amorphous carbon aggregates are roll‐milled, they become cylindrical, then, as the milling time is prolonged, spherical. During milling, polymer adsorption and dispersivity increases in the same manner, causing the viscosity of the composite to decrease. It was established that during a certain milling time, conductivity rises to a peak, after which it falls. We attribute this phenomenon to there being an optimum aspect ratio and degree of dispersion of the cylindrical carbon aggregates. A model explaining the relationship between milling time and change in conductivity is proposed. When oxidized carbon black was dispersed into the copolymer, it was found that it disperses better than unoxidized carbon black, although the conductivity of the resulting composite is lower.
Latex interpenetrating polymer networks based on acrylic polymers. II. The influence of the degree of network compatibility on morphology
Authors: Hourston D. J. , Satgurunathan R. , Varma H. 
Published: April 2003

AbstractTwo latex interpenetrating polymer networks, one prepared from a pair of supposedly compatible polymers and the other from an incompatible pair, were investigated using transmission electron microscopy and dynamic mechanical analysis. From the results, it was proposed that both interpenetrating polymer networks consisted of latex particles with essentially coreshell morphologies. Evidence for a core‐shell structure was more marked for the materials synthesised from the incompatible polymers. The other polymer pair showed indications of a significant amount of mixing.
Mathematical analysis of transport properties of polymer films for food packaging. VI. Coupling of moisture and oxygen transport using langmuir sorption isotherms
Authors: Howsmon Gregg J. , Peppas Nikolaos A. 
Published: April 2003

AbstractDeterioration of food products stored in flexible packaging materials can be attributed to the presence of both water and oxygen in the environment surrounding the food. Mathematical models for the simultaneous permeation of moisture and oxygen through the packaging polymeric film and subsequent adsorption on the food surface are presented for the case of competitive adsorption of the two diffusing species. These models are then used to predict internal packaging conditions over time for selected food products. Oxygen and moisture permeation are treated as independent phenomena, and the competition is regarded as occuring on a surface described by the Langmuir adsorption isotherm. It is found that for certain polymer physical properties and relative surface coverages, water and oxygen molecules can dislodge each other from the food surface and, even for situations where the initial partial pressure of oxygen is less than the external partial pressure, can cause an outward flow of the more weakly adsorbed material. This theory is then extended to incorporate varying external conditions of storage.
Relationship between phenolic adhesive chemistry and adhesive joint performance: Effect of filler type on fraction energy
Authors: Ebewele Robert O. , River Bryan H. , Koutsky James A. 
Published: April 2003

AbstractThe performance of adhesive bonded joints depends on many factors, one of which is the adhesive formulation. The effects of organic and inorganic fillers upon the fracture toughness of phenol–resorchinol–formaldehyde adhesive in hard maple joints were explored in this study. Analytical techniques (DSC, IR, SEM, and GPC), and solubility studies were employed to relate physical effects to chemical effects of teh fillers. The resin showed two distinct stages of cure: (1) a low temperature exotherm associated with resorcinol and paraformaldehyde and (2) a high temperature endotherm associated with the base resin. Filler was found not to affect the cure. Fillers did have a profound effect on the morphology of the wood‐adhesive interphase and upon the bulk adhesive properties. These effects, revealed in both SEM and fracture toughness studies, are discussed at lenghth.
Rheological characterization of dextran‐enzymatic synthesis media
Authors: Tecante A. , C. A. López‐Munguia , García‐Rejón A. 
Published: April 2003

AbstractThe bacteria Leuconostoc mesenteroides (strain NRRL‐B512) has been used for the fermentative production of the polysaccharide dextran from sucrose. The polysaccharide production was carried out via a four‐step process involving (1) production of the enzyme dextransucrase (DS), (2) bacteria removal from the culture broth, (3) enzyme purification by gel permeation chromatography, and (4) enzymatic synthesis of dextran in a cell‐free reaction medium.The enzymatic reaction was followed measuring the change in rheological properties of the reaction medium with time at different initial substrate concentrations. The influence of other parameters, such as temperature, addition of acceptor molecules (maltose), and enzyme purity, were also considered.The microbial extracellular polysaccharide is responsible for the non‐newtonian character of the reaction media. At low shear rate values the flow behavior was newtonian, whereas at higher shear rates the reaction media exhibited a marked shear‐thinning behavior. The Carreau equation appears to fit fairly well the experimental data over several decades of shear rate. The reaction media showed elastic behavior as well.
Calculation of temperature and pressure dependence of heat capacities in polymer melts
Authors: Hartmann Bruce , Balizer Edward 
Published: April 2003

AbstractA new PVT equation of state PV5 = T1/2 − ln V where P = P/B0, and T = T/T0, was used to calculate the temperature and pressure dependence of Cp − Cν for polymer melts. The results are in the form of universal master curves in terms of reduced variables. As a function of temperature, a maximum in Cp – Cν is predicted, while as a function of pressure a minimum is predicted. Supplementing the PVT equation with experimental Cp (T) data from the literature, Cp/Cν was also found to have a maximum as a function of temperature. Two useful approximations were also found. One is related to the Nernst–Lindemann equation for Cp – Cν and the other is the approximate constancy of RT0/B0V0.
Solvent‐vapor‐induced crystallization of branched polydisperse polycarbonate
Authors: Daniewska I. , Dobkowski Z. , Członkowska‐Kohutnicka Z. 
Published: April 2003

AbstractPreliminary results on the investigation of solvent‐vapor‐induced crystallization of polycarbonate/PC/ are presented. The influence of solvent solubility parameters δs on the sphrulite radius R and crystallinity degree α is taken into account. It has been found that both R and α depend on δs for PC samples of different molecular characteristics.
Effect of catalyst residues on the degradation of rigid foam polyurethane
Authors: Abu‐Zeid M. E. , Nofal E. E. 
Published: April 2003

AbstractImmediately after heating rigid foam polyurethane (PU) at 165°C, it degrades in accordance with the degradation mechanisms suggested by Abu‐Zeid et al. in earlier publications. However, after three days all photoacoustic spectra (PAS) bands indicative of PU degradation almost disappeared, and the samples were found to resist both UV and thermal degradation for a wide range of temperatures and UV dosages. Residual catalysts left from PU polymerization were found to be the main cause of its degradation. When these residues were consumed in the process of solid repolymerization, PU becomes immune to heat and UV degradation.
Swelling of cotton in ethylene diamine: Variation of the spiral angle and the angle of crystallite dispersion with stress
Authors: Kalyanaraman A. R. 
Published: April 2003

AbstractThe swelling of cotton in ethylene diamine is well known. This paper analyzes the variation of the spiral angle and the angle of crystallite dispersion with variation in applied stress to a bundle of EDA‐treated fibers. EDA treatment causes regular variation in the spirality of cotton. The variation in the angle of crystallite dispersion is irregular signifying the onset of decrystallization. Mechanical deformation of cotton fibers involves extension and compression of crystallite helices. The present analysis seems to point out that EDA treatment of cotton fibers cause a kind of order in the mechanical deformation of the fibers by aligning the helices and disordering the crystallites.
Characterization of polyisobutylene‐based model urethane networks
Authors: Miyabayashi Toshio , Kennedy J. P. 
Published: April 2003

AbstractPolyisobutylene‐based model urethane networks have been prepared by crosslinking liquid α, ω‐di(hydroxyl)polyisobutylenes, i.e., PIB‐diols carrying exactly two CH2OH functions, Fn = 2.0 ± 0.1, and rather narrow molecular weight distributions, Mw/Mn = 1.5−1.6, with tritriphenylmethyl isocyanate \documentclass{article}\pagestyle{empty}\begin{document}$$\rm{HC}\ (\hskip-6pt\hbox{---}p\rm{C}_6\rm{H}_4\hbox{---}\rm{NCO})_3$$\end{document}. Networks prepared with Mn = 1400 and 7500 PIB‐diols, and with 90/10 and 80/20 mixtures of these PIB‐diols (bimodal networks), have been characterized by extraction, by the Flory–Rehner swelling method, and by the Mooney–Rivlin equilibrium modulus method, and tested by stress–strain measurements. Mc values of the Mn = 1400 PIB‐diol network obtained by swelling (1550) and by equilibrium modulus studies (1500) were in excellent agreement with the Mn of the prepolymer. Also the C2 parameter was negligible in comparison to C1, suggesting the absence of interchain entanglements. This is the first hydrocarbon‐based polyurethane network that exhibits a negligible C2 value by stress–strain measurements of unswollen samples. The Mc values of the Mn = 7500 PIB‐diol were also in good agreement with the Mn of the prepolymer; however, C2 was larger than C1, indicating interchain entanglements. Evidence for strain‐induced toughening was observed with both networks prepared with the Mn = 1400 and 7500 PIB‐diols. The ultimate properties of the two bimodal networks did not show improvement over those of the individual constituents; however, the Mn's of the constituents were not very different.
Gas transport in partially fluorinated low‐density polyethylene
Authors: Kiplinger C. L. , Persico D. F. , Lagow R. J. , Paul D. R. 
Published: April 2003

AbstractLow‐density polyethylene film was subjected to direct fluorination on one surface by exposure to a dilute fluorine gas stream for various periods of time. Various analyses indicate partial fluorination of a thin surface layer. The permeability coefficients for He, CO2, and CH4 were measured at 35°C. The permeability of He was not changed by fluorination; whereas, values for CO2 and CH4 were decreased by as much as two orders of magnitude. The selectivity of transport for gas pairs of different molecular size was greatly improved, suggesting applications of this technique for membrane separation processes.
Improvement in properties of poly(vinyl acetate): Emulsion with dibasic acids
Authors: Verma S. K. , Bisarya S. C. 
Published: April 2003

AbstractWe report an attempt to graft cis (maleic and citraconic) and trans (e.g., fumaric and mesaconic) unsaturated dibasic acids onto poly(vinyl acetate) in emulsion system, in the presence of an initiator and a small quantity of vinyl acetate. The resulting emulsions showed better adhesiveness, higher shear strength, and varied viscosity, and yielded relatively translucent films with faster drying properties. Grafting in the case of these acids was poor, but the cis acids were better grafted than the trans acids. Furthermore, saturated acids (e.g., oxalic and succinic acid) and an inorganic acid (boric acid) were only physically incorporated in the poly(vinyl acetate) emulsion (PVAc emulsion); the resulting product also showed similar improvement in the end properties.
Swelling of particulate polymers enmeshed in poly(tetrafluoroethylene)
Authors: Errede L. A. , Stoesz J. D. , Sirvio L. M. 
Published: April 2003

AbstractIt was demonstrated that swelling of cross‐linked polymers can be monitored much more conveniently and reproducibly after that polymer has been comminuted to a fine powder, and then fabricated mechanically into a tough microporous composite film consisting of the particulate matter (> 80%) enmeshed in poly(tetrafluoroethylene) [PTFE; < 20%]. The latter component provides the physical integrity that affords ease of handling and ensures permanent entrapment of the particles even after 100 cycles of swelling and desiccation to the original dry state. The PTFE microfiber network, however, does not affect adversely either the physicochemical properties of the particles or the permeability to fluids. Kinetic studies in 10 replicates have shown that the void space (0.3 to 0.6 mL/g of composite) is filled by capillary action within the first few minutes of contact with the liquid, and that swelling to the equilibrium state (2 to 90 mL/g of composite) usually occurs within 0.5 to 2 hours thereafter, depending primarily upon the surface to volume ratio of the particles. The magnitude of swelling at equilibrium, however, is depended only on the thermodynamic state of the gelled polymer in excess liquid, and is reproducible usually within 0.2%.
Specific‐enzyme release of cellulose‐bound drugs, experimental and theoretical study
Authors: Lapicque F. , Dellacherie E. 
Published: April 2003

AbstractVarious polymeric prodrugs of pholcodine were prepared by covalently linking a substrate ester of the hydroxylic drug to cellulosic derivatives. The ester derivatives of the drug were chosen so that the resulting insoluble cellulosic prodrugs became substrates of α‐chymotrypsin. The hydrolysis of such compounds was studied for various spacer arms in conditions simulating the intestinal medium. A theoretical model was developed to describe the enzymatic catalysis of this hydrolysis, taking into account the adsorption of the enzyme onto the polymer, the hydrolysis reaction, and the enzyme denaturation. The resulting equations using independently determined parameter values such as the Langmuir adsorption constants, the enzyme denaturation constants, and the initial hydrolysis rate constant successfully correlated with the experimental data.
Sorption and transport of CO2 in PVF2/PMMA Blends
Authors: Chiou J. S. , Paul D. R. 
Published: April 2003

AbstractThe sorption and transport of CO2 in miscible PVF2/PMMA blends are reported at 35°C as a function of pressure from 1 to 25 atm. Significant plasticization by CO2 is evident for all blend compositions. This effect induced further crystallization of PVF2 for some blends, altered the shape of sorption isotherms for blends with a glassy amorphous phase, and resulted in permeabilities which increased with pressure for all compositions. Modified sorption and transport models to account for plasticization are used to analyze the data. The effect of crystallinity on observed behavior has been accounted for using approximate models to allow comparison of responses of sorption and transport with blend composition.
Improvements in the stress‐strain behavior of urethane rubbers by bimodal network formation
Authors: Kim C. S. Youn , Ahmad J. , Bottaro J. , Farzan M. 
Published: April 2003

AbstractUrethane rubbers find increasing application as binders for composites. Typical examples are solid propellants. The rubber networks are formed by end linking hydroxy‐terminated prepolymers with tri‐ or higher functional isocyanates. A recent trend in solid propellant technology is the replacement of the traditional low‐energy binders with “energetic” binders containing nitro, nitrato, or azido groups. Since these energetic polymers create relatively short interchain lengths between the cross‐link points, the binders give notoriously poor mechanical properties. Our study demonstrates that significant improvements in the stress‐strain behavior are attained with bimodal modifications of the energetic binders, that is, by blending these energetic short chains with very long chains prior to curing into rubbers.Molecular aspects of the improvement have been examined in terms of polymer types, crosslinkers, viscoelastic factors, and solid filler content. Results indicate that the improvement is primarily due to the extent of nonaffine deformation of the bimodal rubber network.
The SCOPE dynamic model for emulsion polymerization I. Theory
Authors: Dougherty Eugene P. 
Published: April 2003

AbstractThe SCOPE dynamic process model has been developed to treat batch and semibatch emulsion copolymerizations. This computer‐based model treats jacketed reactors of arbitrary size. It consists of a coupled set of ordinary differential and algebraic equations that describe material balances for the reacting species and energy balances for both the reactor and the cooling water jacket. The model also includes a feature that allows for proportional integral derivative (PID) control of the monomer emulsion and cooling water feed rates to a reactor temperature set point. The model is based largely upon the kinetic theories developed by Smith, Ewart, and Harkins to treat emulsion homopolymerizations. The SCOPE model improves upon and expands the classic theories by taking advantage of recent theoretical developments in emulsion polymerization. Such phenomena as diffusion‐controlled termination and radical desorption—important for predicting accurate polymerization rates—are included in the model. More modern theories of particle nucleation, including both homogeneous and micellar mechanisms, have been incorporated into the model to predict accurate particle size distributions. SCOPE also extends the classic theories to treat the emulsion copolymerization of an arbitrary number of monomers. Output from the model includes species concentrations, residual monomer levels, particle size distributions, molecular weight distributions, instantaneous and cumulative copolymer compositions, and reactor temperatures as a function of time. The SCOPE model can be used to evaluate various process control strategies and to study the effects of process dynamics on polymer properties. In Part II, SCOPE model predictions are compared with experimental data for styrene‐methyl methacrylate copolymerizations.