Polymer swelling 2: A restudy of poly(styrene-co-divinylbenzene) swelling in terms of the cross-link density1

A very convenient and reliable gravimetric method was developed for measuring swelling of poly(styrene-co-divinylbenzene) in particulate form. The method is based on the gravimetric procedure reported earlier² for monitoring liquid uptake by thin (<0.3 mm) microporous composite films, consisting of swellable particulate (80% by weight) enmeshed in poly(tetrafluoroethylene) microfibers (20%). The swellability S (in milliliter of liquid absorbed per gram of polymer in equilibrium with excess liquid) for six sty-co-DVB polymers with crosslink densities ranging from 0.01 to 0.12 was measured in 19 organic liquids. In each study of S as a function of the relationship was given by where is the average number of carbon atoms in the “backbone” of the polystyrene segments between cross-link junction, C is the relative swelling power of the liquid, and is the critical cross-link density above which S is equal to zero.     

d-NMR-Untersuchungen der behinderten Rotation am Bindungsinkrement. IX. Behinderte Rotation um partielle Doppelbindungen in kernsubstituierten Phenyl-β-dimethylaminovinyl-thioketonen

d-N.M.R.-Investigations of the Restricted Rotation at the Bonding Increment. IX. Restricted Rotation about Partial Double Bonds in Nucleo-substituted Phenyl-β-dimethylaminovinyl-thioketones Due to resonance stabilization restricted rotations about partial and double bonds have been observed in some substituted phenyl-β-dimethylaminovinyl-thioketones 2. The free enthalpies of activation have been determined by means of d-n.m.r.-spectroscopy in dependence on the properties of the p-phenyl substituents and the solvent. The measured ΔG^≠-values depend on the σ-substituent constants and on the E_T-values of solvent polarity linearly. Substituents with electron-withdrawing properties and solvents with increasing polarity enhance the free enthalpies of activation of the restricted rotation.     

The Use of Inverse Gas Chromatography (IGC) to Determine the Surface Energy of RDX

The surface properties of RDX play an important role in enhancing mechanics performances of the propellants and explosives. In this work, thereby, inverse gas chromatography (IGC) using various probe liquids as the medium was used to determine the surface energy components of RDX containing both dispersive and polar components, which were acquired respectively from neutral probe liquids (such as n‐hexane, n‐heptane, n‐octane) and polar probe liquids (such as chloroform, benzene, methanol). The results show that RDX located in different column temperatures has difference in the surface energy and possesses more surface energy when there is high temperature. The calculated formula of the total surface energy with temperature is: , and it is also found that dispersive, polar, electron acceptor, and electron donor components of RDX are , , , and , respectively. These results demonstrate that the dispersive component is the primary part of the total surface energy, and RDX has an acid performance.     

Vapour pressure and vapourisation enthalpy of pyridine N‐oxide

The vapour pressure of pyridine N‐oxide was measured using a boiling point method at different temperatures from 389.02 to 546.33 K and the constants of the Antoine equation for the substance were determined. The vapourisation enthalpy of pyridine N‐oxide at the normal boiling point is calculated to be 58.8 ± 1.8 kJ mol^?1. Based on Othmer's method, the standard enthalpy of vapourisation is estimated to be 66.6 ± 0.1 kJ mol^?1 by using pyridine as the reference substance. Furthermore, Watson equation is employed to verify the reliability of and the results demonstrate that the value of is acceptable. © 2011 Canadian Society for Chemical Engineering     

Polymer protected reagents, 1. Esterification with polymer bound AIPO4

The advantageous use of a polymer protected reagent -AlPO₄ as a mild catalyst for esterification was studied.     

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy¹. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m², and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ～4000J/m² (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (r_yc) in that was a maximum when bond thickness was equal to 2 r_yc. At bond thicknesses less than 2 r_yc, there was a restraint on the development of the plastic zone resulting in lower values.     

Elongational flow studies of hinged rodlike molecules

Poly(amino acid) in an intermediate state of its helix-coil transition is known to be in a hinged rodlike conformation. In this work, the responses of poly(amino acids) in the hinged rodlike conformation against an elongational flow field were investigated by monitoring their flow-induced birefringence. Poly(L-glutamic acids) (PGA) and poly(γ-benzyl-L-glutamate) (PBLG) were examined as polyelectrolyte and noncharged poly(amino acids), respectively, and the results were compared. In the plots of flow-induced birefringence, Δn, against strain rate, $ {\dot \varepsilon } $, for hinged rodlike PBLG, there was a critical strain rate, $ \dot \varepsilon_0 $, below which Δn was not observed. Over $ \dot \varepsilon_0 $, the birefringence pattern observed was identical with that of rodlike molecules. The Δn vs. $ {\dot \varepsilon } $ plot for hinged rodlike PGA had characteristics of a rigid rod at any strain rate and there was no $ \dot \varepsilon_0$ observed. The rotational diffusion coefficient, D_r, of PBLG in the hinged rodlike conformation was larger than that for its helical conformation, while D_r, for the hinged-rodlike PGA was smaller than that for its helical conformation. It is concluded that the hinged-rodlike PGA molecule is in an extended form and that the hinged-rodlike PBLG is hydrodynamically more compact and rigid than that in its quiescent state. It is deduced that at $\dot \varepsilon_0$ hinged rodlike PBLG molecules collapse to a conformation optically anisotropic and mechanically rigid. © 1996 John Wiley & Sons, Inc.     

A corresponding states treatment of saturated density,surface tension and capillary constant of cryogenic liquids and refrigerants

Using a new set of energy (kT) and length (σ) parameters, a corresponding states treatment is applied to the calculation of some thermophysical properties in a generalised non-dimensional form. The saturated density is well represented by the following equation: for all the liquids studied here. The surface tension correlations are $ \gamma _r^* = 2.055\left({1.219 - T_r^*} \right)^{1.240} $ for cryogenic fluids and hydrocarbons and $ \gamma _r^* = 2.322\left({1.228 - T_r^* } \right)^{1.244}$ for refrigerants. An interpretation of the index in the density equation and the constants in the surface tension equations is given. Using these correlations, an equation is also proposed for the capillary constant.     

Nonlinear programming methods to determine surface free energy components of polymers using harmonic mean approximation

The dispersion and polar surface free energy components, γ and γ, and the critical surface free energy, γ_c, of polymers were determined from contact angle data by the application of a nonlinear programming method using harmonic mean approximation. The surface free energy components of the probe liquids, γ and γ, which reflect the conditions of the maximized interaction parameter, Φ, were also simultaneously determined by this method.     

In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry

Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.

Proposed control scheme.     

Tearing mode interlaminar fracture toughness of composite materials

The Simplified Split Cantilever Beam (SSCB) is proposed in this work and compared with the Split Cantilever Beam (SCB) to obtain the tearing mode interlaminar fracture toughness. The materials considered are single‐fiber system composites and interply hybrid composites. For interply hybrid composites, three different types of stacking sequence for SSCB specimens, which are [0/0//0],[0/0//0]. and [0/0//0], are tested to compare their suitability. Finite element analysis combined with a modified crack closure integral has been applied to separate the different components of the strain‐energy release rate. In addition, the method of compliance calibration was used to calculate Gc values. The effects of crack growth, initial crack length, specimen width, and number of glass fiber plies were also studied. The results show that SSCB testing has a more dominant Mode III component and more stable Gc values than SCB testing. For SSCB testing, the crack growth and the specimen width for the range considered have no clear effects on the interlaminar fracture toughness, but the initial crack length should be carefully selected to obtain corrected values. The tearing mode interlaminar fracture toughness of interply hybrid composites is higher than that of carbon/epoxy composites, and the three different types of stacking sequence considered are all suitable to approximate the Mode III interlaminar fracture toughness for interply hybrid composites.     

Synthesis and characterization of resins from urea and acrolein

The reactions of urea with acrolein in neutral and acidic media were studied by means of ¹H- and ¹³C-NMR spectroscopy. The addition of aldehyde groups to urea seems to be the first step of the reaction. In the second step in neutral medium the groups and the double bonds react with the amide groups. In the acidic medium the condensation of as second step was dominant. In the further course of the reaction highly crosslinked resins are formed which are insoluble and unmeltable. Chemical shifts of individual compounds are given. On the basis of these data, it was possible to set up tentative reaction schemes. The determination of the concentrations of reaction products as functions of reaction time allowed to establish the kinetics of individual reactions.     

Ammoxidation of propylene by pulse reaction technique

The ammoxidation of propylene on Fe-Bi-P mixed oxide catalyst was studied at 500 °C by the pulse reaction technique, to examine the effects of P(P = 0–4) and P (P/P = 0–3) on the catalyst activity. Since the ammoxidation of propylene proceeds through consumption of oxygen from the catalyst even in the absence of oxygen, the reduction of catalyst progresses with the number of O₂-free pulse, losing its activity. In the presence of oxygen, however, the conversion of propylene and the selectivities of acrylonitrile, acetonitrile, CO₂, and CO vary with the pulse number, but settle to some steady values corresponding to P/P. It is also found that the conversion and the selectivities depend on the oxidation state of the catalyst, the latter also depending on P/P in the reactants, and that the catalyst working in the flow system may be being reduced to some extent.     

Pyryliumverbindungen. 38. Zur Ringtransformation von 2,4,6-Triaryl-thiopyryliumsalzen mit Essigsäureanhydrid zu Arylbenzenen und Thiobenzophenonen

Pyrylium Compounds. 38. About the Ring Transformation of 2,4,6-Triarylthiopyrylium Salts by Acetic Acid Anhydride to Arylbenzenes and Thiobenzophenones 2,4,6-Triarylthiopyrylium salts 5 react in the presence of an appropriate condensing agent (sodium acetate, carbonate, methoxide, tert-butoxide or potassium acetate) with acetic acid anhydride to yield arylbenzenes 3 and thiobenzophenones 6 . This ring transformation represents the first example of the conversion of the moiety into the thiocarbonyl group Under the same conditions 3,5-dimethyl-2,4,6-triphenylthiopyrylium perchlorate ( 13 ) forms via [1,5]-sigmatropic rearrangement the thiobenzophenone 15 . The structure of the new compounds 6 was proved by spectroscopic methods as well as by degradation reactions. Thus, hydrogen peroxide converts 6a to the known benzophenone 4 . Alkaline saponification gives the 2-hydroxy-benzophenone 8 , whereas heating with hydrochloric acid causes a selective cleavage of the acetoxy group to the 2-hydroxy-thiobenzophenone 7 .     

Shear rate dependence of the viscosity of cellulose nitrate solutions in the dilute concentration regime revisited

A detailed rheological study of cellulose nitrate in ethylacetate had been carried out in the dilute concentration (c) regime, covering a degree of polymerization (DP) range between 300 < DP_η < 7000 and shear rates ($ \dot \gamma $) between 100 s^?1 < $ \dot \gamma $ < 2000 s^?1. The results show a strong dependence of the transition Newtonian to non-Newtonian behavior on the three variables $ \dot \gamma $, DP, and c, similar to that found recently on solutions of synthetic polymers. Emphasis has been put on the critical concentrations corresponding to the standard shear rate 1000 s^?1 to correspond to the standard conditions ($ \dot \gamma $ ? 1000 s^?1; 0.3 < [η] · c < 0.6; DS = 2.90 ± 0.02) proposed for the determination of the intrinsic viscosity [η] of cellulose nitrates. It is shown that solutions with concentrations adjusted according to the above given conditions still exhibit Newtonian behavior, up to the highest range of DP. It follows, therefore, that applying the standard conditions, an extrapolation to $ \dot \gamma $ = 0 as has been proposed often for the intrinsic viscosity determination of cellulose nitrate is not advisable and results in considerable error. Considering the relationship between [η] and DP, the present results indicate that the decrease of the exponent ( a ) from a = 1.0 to a = 0.76, taking place above a DP ? 1000, is not a consequence of the applied shear rate but rather of the molecular properties of the solutes themselves.     

Kinetics of ion exchange in monodisperse resin

Ion-exchange kinetics within a conventional strong base resin, Dowexl-8X®, and a resin with uniform particle size, Dowex® Monosphere® Tough Gel® TG550A®, were investigated using neutron activation analysis and radio-tracer techniques. The kinetics of ion exchange were measured in a batch and in a “shallow-bed” flow system. The experimental data were compared with the results of model computations. The diffusivities of several anions within TG550A and Dowexl-8X were deduced. It was found that at 25°C Br^-, Cl^-, OH^-, and Na⁺ diffuse within TG550A with the diffusion coefficients = 6.0 × 10^-7 cm²/s, = 1.2 × 10^-6 cm²/s, = 7.0 × 10^-8 cm²/s, and = 5 × 10^-7 cm²/s. Diffusion of anions within a conventional resin, Dowexl®, was slower: = 3.5 × 10^-7 cm²/s, = 6 × 10^-7 cm²/s, = 2.7 × 10^-8 cm²/s, and = 5 × 10^-7 cm²/s. A higher rate of ion diffusion and the bead-size uniformity may make monodisperse Dowex Monosphere Tough Gel TG550A resin attractive for analytical applications. The difference in properties between conventional and monodisperse resins is not sufficient to affect the large volume applications of resins. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1271–1283, 1997     

Untersuchungen zur Gegenionenstruktur bei der Kationischen Polymerisation von Isobutylvinylether mit iodhaltigen Initiatoren

Investigations on the Counter Ion Structure of the Cationics Polymerization of Isobutylvinylether with Iodine Based Systems The structure of counter ions of iodine based initiators for the cationic polymerization of isobutylvinylether is elucidated by means of u.v.-spectroscopy using as model system: Increasing electrophilicity of the cation causes a decrease of the counter ion stability. High concentrations of iodine lead to the formation of polyiodides, as I and I, respectively. The influence on chain propagation by iodine and monomer concentration as well have been followed by GPC and u.v.-spectroscopy. Both influences, strongly affects the propagation reaction. Triphenylmethylbromide in conjunction with iodine is a convenient initiating system, realizing a long living and transfer suppressed propagation, when solvents of higher polarity are used. An activated carbon-halide bond is concluded to be the active species.     

The relationship between the molecular weight and the critical miscibility composition of a solvent-nonsolvent-terpolymer system

A theoretical equation for the dependence of the apparent molecular weight measured by light scattering on the solvent used has been derived with regard to the composition heterogeneity. Terpolymers corresponding to a partial azeotrope were synthesized from styrene, acrylonitrile, and methyl methacrylate with mole fractions of 0.55, 0.16, and 0.29, respectively. The molecular weight measured by light scattering was found to be independent of the solvent used. Therefore the terpolymer was concluded to be apparently homogeneous in composition. The relationship between the molecular weight M of the terpolymer and the volume fraction of the nonsolvent γ in the solvent mixture at the precipitation point in a butanone-methanol-terpolymer system was experimentally proved to follow the equation where γ₀ and b′ are constants. Between the molecular weight and the limiting viscosity number [η] of the terpolymer the following relationships are valid at 35°C: and      

Study on the thermal stability of heterogeneous nucleation effect of polypropylene nucleated by different nucleating agents

The thermal stability of the heterogeneous nucleation effect of polypropylene (PP) nucleated with an organic phosphate (A) and two kinds of sorbitol derivatives (B and D) was investigated by DSC multiscanning. For pure PP, the peak temperature of crystallization (T) was little changed with an increasing number of DSC scans, indicating that nucleation of PP is thermally stable. For the PP nucleated with an organic phosphate (PPA), the temperatures at the onset of crystallization (T) and at the completion of crystallization (T); the peak temperature of crystallization (T) and melting (T); and the heat of crystallization (ΔH_c) and fusion (ΔH_m) of PP are higher than those of pure PP and were little influenced with an increasing number of DSC scans. For PP nucleated with the sorbitol derivatives (PPB and PPD), the T, T, T, and T decreased with an increasing the number of scans. These results indicated that the thermal stability of heterogeneous nucleation effect of the nucleating agent A is higher than that of nucleating agents B and D. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1643–1650, 2002     

Time temperature equivalence in plasticized PVC

The viscoelastic response of plasticized PVC was determined from stress-relaxation data over a wide range of time at different temperatures. The relaxation modulus as a function of time was determined from these data. The relaxation curves were then shifted horizontally to obtain a master curve at a reference temperature. The amount of shift was evaluated using the WLF equation. The coefficients C and C used in the equation for the PVC were determined according to the method of reduced variables.