Crystallography and equilibrium solubility for ammonium and potassium orthophosphites and hypophosphites

The composition and solubility properties of eight ammonium and potassium orthophosphites and hypophosphites were determined to evaluate the potential of these classes of materials for increasing the plant nutrient content of liquid fertilizers. Phase relationships for the systems (NH₄)₂O-P₂O₃-H₂O, K₂O-P₂O₃-H₂O, (NH₄)₂O-P₂O-H₂O, and K₂O-P₂O-H₂O were determined along with the crystallographic properties (X-ray and optical) of the solid phases. Toxicity and phosphite response was tested in greenhouse experiments for the compounds.     

Orthophosphates and Diphosphates Containing Zinc and Copper and Zinc and Cobalt

Solid solutions of diphosphates of zinc and copper and of zinc and cobalt were synthesized from mixtures of pure diphosphates at temperatures up to 1000°C. Their X-ray diffractometry patterns varied continuously from one end member to the other. Solid solutions of orthophosphates of composition Zn_3−xCox(PO₄)2, with x = 0.4–1.6, were formed at temperatures up to 950°C; all exhibited the structure of γ-Zn₃(PO₄)2. Solid solutions of orthophosphates of composition Zn_3−xCu_x(PO₄)2 exhibited more-complex behavior. At 1000°C and copper contents of 20–80 mol%, a phase that is related to Cu₃(PO₄)2, termed here the "ε-phase," predominated. At 850°–950°C and in the region from 20 mol% to ∼33 mol% of copper, the solid solutions (the "η-phase") adopted the structure of graftonite. At 800°–900°C and 10–15 mol% of copper, the solid solutions exhibited a new structure (the "δ-phase"), which we found to be related to the mineral sarcopside. At temperatures 950°C, the solutions that contained 5–15 mol% of copper (the "β-phase") had the structure of β-Zn₃(PO₄)2, whereas at 800°–850°C, solutions with 5 mol% of copper (the "-phase") exhibited the structure of γ-Zn₃(PO₄)2. Attempts to synthesize Cu⁺ZnPO₄ and Cu⁺Cu²⁺Zn₃(PO₄)3 were unsuccessful.     

Synthesis and Characterization of Cis- and Trans-Trimethyltriphenylcyclotrisiloxane

2,4,6-Trimethyl-2,4,6-triphenylcyclotrisiloxane (P₃) exists as cis and trans-stereoisomers. Herein, we present the detailed synthesis and characterization of the cis- and trans-P₃ isomers. After preparation of the mixed cyclic methylphenylsiloxanes, it was found that vacuum distillation was the best method for separating P₃ from the mixture of P₃ and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenylcyclotetrasiloxane (P₄) on a large scale and that pure cis-P₃ can be isolated by washing the mixed P₃ isomers with methanol. It is also shown that a selective crystallization method was successful for isolating cis-P₃ from the mixture of P₃ and P₄ directly and that large crystals may be obtained. Using gas chromatography and nuclear magnetic resonance (NMR) spectroscopy, the two different isomers and four different isomers in P₃ and P₄, respectively, are easily identified. The nuclear magnetic resonance (NMR) spectra, differential scanning calorimeter (DSC) thermograms, and infrared (IR) spectra with various ratios of cis-P₃ and trans-P₃ were also analyzed. A melting point depression of the cis-P₃ was observed with an increased amount of trans-P₃ for the mixed isomers, as expected. These P₃ stereochemical isomers provide valuable starting materials for the preparation of stereoregular siloxanes using ring-opening polymerization.     

On the relationship between Aris and Sherwood numbers and friction and effectiveness factors

We present a general solution of the diffusion-reaction problem for linear kinetics and an expression for the effectiveness factor (η) in terms of the shape normalized Thiele modulus (Φ) for a catalyst particle of arbitrary shape and with an arbitrary activity profile. We also show that the Sherwood number (Sh_Ω) or the dimensionless mass transfer coefficient between the interior of a particle or region (denoted by Ω) and its boundary (∂Ω) is related to the effectiveness factor and Thiele modulus by η=1/(1+Φ²/Sh_Ω). Further, the coefficients in the expansion of η in terms of Φ (the Aris numbers, Ar_i) are related to the asymptotic Sherwood number (Sh_Ω∞) obtained in the limit of slow reaction. We show that the curve Sh_Ω versus Φ is universal for most common particle or channel geometric shapes and for the case of uniform activity is described by the two asymptotes Sh_Ω=Sh_Ω∞=1/Ar₁ for Φ?1 and Sh_Ω≈Φ for Φ?1. For two-dimensional ducts we show that the friction factor times Reynolds number (fRe) is equal to 8Sh_Ω∞ and provide a physical interpretation of this result. In the second part of this work, we derive low-dimensional models for solving multicomponent nonlinear diffusion-reaction problems using the concept of an internal mass transfer coefficient. We also present low-dimensional models for catalytic reactors using external and internal mass transfer coefficients. Finally, the Aris/Sherwood numbers are presented for some commonly used catalyst particles in packed-bed reactors and washcoat shapes in catalytic monoliths.     

Synthesis and polymerization of p-bromomethylstyrene and p-lodomethylstyrene

Summary Synthesis of p-bromomethylstyrene (3) and p-iodome-thylstyrene (4) is reported. 3 was obtained by the bromomethylation of 2-phenylethyl bromide followed by dehydrobromination of the resultant p-(2-bromoethyl) benzyl bromide (2) with t-BuOK, as well as by cleaving p-vinyl-benzyl methanosulfonate with LiBr in the presence of 18--crown-6. 4 was obtained from p-chloromethylstyrene (1) via the Finkelstein reaction. 3 was polymerized successfully in the presence of free-radical initiators, but 4 was found to be too unstable to give a well-defined polymer.     

Characteristics and Composition of Some Convolvulaceae and Leguminosae Seeds and the Oils

The seeds of Quamoclit coccinea, Ipomaea horsfalliae, Argyria aggregata, Merremia pentaphylla (Convolvulaceae), Indigofera hirsuta, Dalbergia melanoxylon and Bauhinia vahlii (Leguminosae) as well as the oils extracted therefrom were analysed for physico-chemical characteristics and composition. The oil content was appreciable in Q. coccinea (22.6%), I. horsfalliae (19.8%), A. aggregata (13.5%) and D. melanoxylon (13.8%) seeds. The protein content was high (21.8–26.9%) in all except in M. pentaphylla and B. vahlii seeds. The iodine values ranged from 87.6 to 132.8. The content of unsaponifiable matter was low in all the oils. The predominant fatty acid was linoleic (34.3–59.7%), the other major acids being palmitic (14.4–23.8%) and oleic (6.5–22.1%). Significant quantities of stearic and longerchain saturated acids were also present.     

Radical polymerization of butyl acrylate and random copolymerization of styrene and butyl acrylate and styrene and methyl methacrylate mediated by monospiro- and dispiropiperidinyl-N-oxyl radicals

Radical polymerization of butyl acrylate (BA) and random copolymerizations of styrene (St) and BA and St and methyl methacrylate (MMA) in the presence of 7-aza-15-hydroxydispiro[5.1.5.3]hexadecane-7-yloxyl (1) and 1-aza-2,2-dimethyl-4-hydroxyspiro[5.6]dodecane-1-yloxyl (2) were carried out. Radical polymerization of BA at 120 °C in the presence of 1 gave poly(BA) with M_n=20200 and M_w/M_n=1.30 at 23% conversion. The termination of polymerization observed around ∼20% conversion was solved to a certain extent by an addition of small amounts of dicumyl peroxide, and poly(BA) with M_n=37400 and M_w/M_n=1.33 was obtained in 46% yield. Random copolymerizations of St and BA and St and MMA in the presence of 1 and 2 at 80 °C gave the corresponding random copolymers with narrow polydispersities of 1.12-1.38 at the molar fraction above 0.30 of St in feed. The kinetic study for the NO-C bond homolysis of the corresponding alkoxyamines prepared from 1 and 2 were carried out, and evaluation of the preexponential factors (A_act) and the activation parameters (E_act) showed that the steric factors of the nitroxides are reflected mainly on E_act.     

Synthesis,Structure and Thermal Properties of Copper and Silver Polyynides and Acetylides

Polyynes or oligoynes having general formula H–(C≡C)_n–H with n = 1,2,3,4,…, are a class of molecules that has become easily accessible in recent years due to new synthetic approaches. These molecules form copper and silver salts, which have been called, respectively, Cu-polyynides and Ag-polyynides. Here we show the synthesis of these salts and discuss their FT-IR spectra and thermal behaviour, which is studied by Differential Scanning Calorimetry (DSC). These properties are compared to the spectra and thermal behaviour of Cu₂C₂ and Ag₂C₂. It is shown that Cu₂C₂ can be oxidized to Cu-polyynides thereby loosing its original structure and becoming a polymeric coordinative structure. The structural changes make Cu-polyynides no more explosive than the parent Cu₂C_2. Similarly, Ag-polyynides, which decompose exothermally when heated, are not explosive compared to Ag₂C₂. The explosive decomposition of Cu₂C₂ occurs at 127 °C (DSC) whereas Ag₂C₂ decomposes explosively at 169 °C under the same conditions. Conversely, Cu-polyynides, when heated in the DSC, show a broad exothermal peak at about 243 °C. Ag-polyynides decompose near 94 °C and the release of energy is sufficiently gradual that no explosion is detected.     

Bioactivity and osteoinductivity of glasses and glassceramics and their material determinants

Bioactive glasses and glassceramics have been used in both bone repair and tissue engineering applications. An important feature of bioactive glasses and glassceramics, which enables them to be used for desired application, is their biological activity. This activity is manifested by the ability of these materials to form a stable bond with bone tissue (bioactivity) and, in some cases, their ability to promote/initiate osteogenesis (osteoinductivity). A stable material-bone bonding (i.e. bioactivity) results from specific material surface reactions leading to hydroxyapatite (HAp) formation on the material surface. Bioactivity of materials is often evaluated in vitro and the ability of materials to form HAp-like surface layer is usually studied after immersion/incubation of materials in simulated body fluid (SBF). Biological activity of materials can be also defined as their ability to induce specific cell responses leading to faster regeneration of bone tissue. It may be manifested by materials supporting bone cell attachment, proliferation and differentiation (biocompability/osteconductivity), and/or by materials inducing/promoting the expression of multiple bone-related genes that drive osteogenesis (osteoinductivity). Osteoinductivity is often verified in vivo by the materials capability to form bone at etopic (i.e. extraskeletal) sites. However, a lot of in vitro call-based experiments are now offered to determine osteoinductive properties of biomaterials. This review focuses on the silica-based glasses and glass-ceramics, in particular, the sol-gel derived ones, and summarizes their bioactivity and osteoinductivity as major determinants of their biological activity. We highlight the chemistry of bioglasses and glassceramics that affects not only the formation of a stable implant/bone bonding by HAp layer, but also drives the cell response in vitro and in vivo.     

Synthesis and characterization of pyridine and anthracene containing bismaleimides,bisnadimides and polyaspartimides

Three different novel diamines containing pyridine and anthracene moiety were prepared and subsequently converted into bismaleimides (BMI) and bisnadimides (BNI) and their structure was confirmed by elemental analysis, FT-IR, ¹H-NMR and ¹³C-NMR techniques. Chain extension of bismaleimides and bisnadimides was accomplished by incorporating various ether or ester groups. Owing to pendant anthracene moiety, pyridine unit and flexible linkages, the bismaleimides and bisnadimides were found to possess an excellent balance of properties; solubility and thermal stability and the curing behaviour was investigated by differential scanning calorimeter. In addition, a series of polyaspartimides containing anthracene and pyridine unit was prepared by the polyaddition of bismaleimides with various diamines via a Michael-type addition. The thermal stability of bismaleimides, bisnadimides and polyaspartimides was evaluated by thermo gravimetric analysis. All the polyaspartimides are soluble in many organic solvents and exhibit T _g in the range of 189–242 °C and 10% weight loss (T ₁₀) takes place in the range of 389–487 °C in N₂.     

Surface characterization and catalytic properties of supported tungsten and platinum-tungsten carbide and oxycarbide

Bulk tungsten carbide has been prepared from ammonium paratungstate. Oxidic oxygen in relatively small amount is always present on the WC surface regardless of the method of carburization. Tungsten(VI) oxide in Al₂(WO₄)₃ can be reduced directly and in apparently one single step to the elemental W(0) state by Ar⁺ bombardment. Under H₂ the reduction starts at 720 K. In 12 and 28% W03 supported on -Al₂O₃ and in Al₂(WO₄)₃, almost 90% of the tungsten could be converted to the carbide form. Extensive hydrogenolysis products for n-hexane reactions on freshly prepared WC were observed while selectivity to isomerization associated with decrease in activity occurs upon exposure of the WC to oxygen at 620 K. Supported tungsten carbide(s) and oxycarbide(s) on -Al₂O₃ have comparable catalytic behaviour to those obtained on the bulk systems. The presence of Pt in these supported systems did not improve the catalytic performances and even did not show the catalytic properties of Pt. This was attributed to the severe conditions of catalyst preparations. Although the catalytic activity of tungsten carbide(s) obtained from the carburization of Al₂(WO₄)₃ is very low, the selectivity suggests the presence of tungsten carbide plus some WO, species.     

Synthesis and characterization of novel organotin monomers and copolymers and their antibacterial activity

Two novel organotin monomers, (N‐tri‐n‐butyltin) maleimide and m‐acryloylamino‐(tri‐n‐butyltin benzoate), were synthesized. Copolymerization of these two monomers with styrene was carried out in the bulk at 65°C using asobisisobutyronitrile as the free radical initiator. The monomers and copolymers were characterized by elemental analysis; the molecular weights of the copolymers were determined by GPC, solubility, IR, and ¹H‐NMR spectral studies. The antibacterial activities of the synthesized organotin monomers and copolymers toward various types of bacteria were also reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 740–745, 2000     

Thermal stresses and birefringence in quenched tubes and rods: Simulation and experiment

Measurements and simulations of the radial distribution of the thermal birefringence components, Δn and n_θθ ? n_rr, and the average birefringence, <n_zz ? n_θθ>, in free quenched tubes and rods of polystyrene (PS) and polycarbonate (PC) at different initial temperatures were carried out. The thermal stress and birefringence components were simulated using the linear viscoelastic and photoviscoelastic constitutive equations combined with the first‐order rate equation for volume relaxation and the master curves for the Young's relaxation modulus and strain‐optical coefficient functions of polymers. The numerical procedures used to discretize the governing equations using finite difference method were described. The obtained numerical results provided the evolution of stress and birefringence components with time during and after quenching and an explanation of the measured residual birefringence distribution in quenched tubes and rods. It was also found that the thickness of the slices removed from the samples to measure the thermal birefringence components, Δn and n_θθ ? n_rr, was critical, in particular, when the initial temperatures were close to the glass transition temperature of polymers. With an increase of the initial temperature during quenching, a better agreement between the simulated and measured birefringence components was obtained. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Crystalline and magnetic properties of Er and Yb chromites modified by Mn and Ca cations

The structural and physical properties of some chromites–manganites solid solutions (RE,Ca)Cr_0.5Mn_0.5O₃, RE = Er, Yb, have been studied by X-ray diffraction and magnetic measurements. Powders were prepared by solid state reaction between the component oxides. Complete solid solutions were obtained, except for YbCr_0.5Mn_0.5O₃ in which traces of hexagonal YbMnO₃ remain through all the synthesis and sintering processes. Incorporation of Mn³⁺ cations does not alter the perovskite O-type structure of the chromites. Ca-containing solid solutions maintain the O-type structure.Magnetic measurements indicate an increase of the ferromagnetic behavior when Ca²⁺ is incorporated into the lattice, with an expected transformation of Mn³⁺ into Mn⁴⁺, and its associated ferromagnetic exchange interactions. Competition between ferromagnetic Mn³⁺–Mn⁴⁺, Mn³⁺–Cr³⁺ and antiferromagnetic Cr³⁺–Mn⁴⁺, Yb–TM interactions (TM: transition metal) leads to complex magnetic ordering in the ytterbium chromites, although double exchange Mn³⁺–Mn⁴⁺ interactions predominate and suppress the spin reversal expected for the pure YbCrO₃ material.     

Dehydrogenation and hydrogenation activity of palladium-tin-silica and nickel-tin-silica

The dehydrogenation of cyclohexanone, cyclohexylamine, cyclohexane, and 2-propanol and the hydrogenation of ethylene on palladium-tin-silica and the hydrogenation of benzene on nickel-tin-silica were studied. With nickel-silica and nickel-tin-silica, the deposition of carbonaceous materials was studied kinetically. The X-ray photoelectron spectra of palladiumtin and nickel-tin were observed. The catalytic activities of both of the catalyst systems changed in similar ways with the change of the $\text{Pd}\text{Sn}$ and $\text{Ni}\text{Sn}$ ratios (atomic) of the catalysts. The dehydrogenation activity increased to a maximum and then decreased, with a decrease in the $\text{Pd}\text{Sn}$ and $\text{Ni}\text{Sn}$ ratios. The hydrogenation activity of the tin-containing catalysts was much lower than that of the tin-free catalysts. Carbonaceous materials were observed to be deposited more easily on the nickel-silica than on the nickel-tin-silica. The palladium-4d and nickel-3d band peaks of the alloy systems obtained by X-ray photoelectron spectroscopy were observed to shift to higher binding energies as the $\text{Pd}\text{Sn}$ and $\text{Ni}\text{Sn}$ ratios decreased. From the amount of carbon monoxide adsorbed, the surface concentration of palladium and that of nickel on the catalysts were suggested to be the minor determining factor of the catalytic activity studied here. It is concluded that tin is not just a diluent for the active metal but is an effective component to weaken the adsorption bond.     

Mass transfer and structure of asbestos and non-asbestos diaphragms for chlorine and caustic production

Models and equations describing aspects of diaphragm performance are discussed in view of recent experiences with non-asbestos diaphragms. Excellent control of wettability and, therefore, of the amount of gases inside the diaphragm, together with chemical resistance to the environment during electrolysis, was found to be an essential prerequisite to performances of non-asbestos diaphragms that are comparable to those of asbestos diaphragms. Equations, derived and supported by experimental evidence from previous work, are shown to describe and predict hydrodynamic permeability and ohmic voltage drop of diaphragms, even in cases where the amount of gases inside the diaphragm slowly increases during electrolysis. Current efficiency is observed to be only dependent to a slight extent on the effective electrolyte void fraction inside the diaphragm. Major effects that determine current efficiency at 2 kA m^–2 and 120 gl^–1 caustic are shown to be diaphragm thickness, pore diameter distribution and the number of interconnections between pores inside the diaphragm. A discussion on design of the structure of non-asbestos diaphragms is presented.Nomenclature B permeability coefficient (m²) - c _i,x concentration of ionic species i at position x (mol m^–3) - c _k concentration of hydroxyl ions in catholyte (mol m^–3) - CE current efficiency - d thickness of diaphragm (m) - thickness of layer (m) - D _i ionic diffusion coefficient of species i (m²s^–1) - D _e dispersion coefficient (m²s^–1) - electrolyte void fraction - E potential inside diaphragm (V) - F Faraday constant, 96487 (C mol^–1 of electrons) - F _j,i flux of ionic species i in the stagnant electrolyte inside small pores of layer j - H hydrostatic head (N m^–2) - i flux of current =j/F (mol m^–2s^–1) - j current density (A m^–2) - k _i,l constant representing diffusion in diaphragm (m²s^–1) - k ₂ constant representing migration in diaphragm (m^–1) - v _p hydraulic pore radius according to [15] (m) - N number of layers - N _j,i flux of ionic species i in layer j (mol m^–2s^–1) - P hydrodynamic permeability (m³ N^–1s^–1) - R gas constant, 8.3143 (J mol^–1 K^–1) - density of liquid (kg m^–3) - R ₀ electric resistivity of electrolyte (ohm m) - R _d electric resistivity of porous structure filled with electrolyte (ohm m) - R _m resistance of the diaphragm (ohm m²) - R _a resistance of anolyte layer (ohm m²) - R _e resistance of electrodes (ohm m²) - s specific surface of porous structure (m^–1) - s ₀ standard specific surface of solids in porous structure (m^–1) - tortuosity defined according toR _d/R ₀=/ - T absolute temperature (K) - u superficial liquid velocity (m s^–1) - U cell voltage (V) - dynamic viscosity (N s m^–2) - v kinematic viscosity (m²s^–1) - x diaphragm dimensional coordinate (m) - y radial coordinate inside pores (m) Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands, September 17th and 18th 1987.     

Characterization and solubility measurement and prediction of selected arylamines in hexane, methanol and benzene

The solubility of nine arylamine molecules in benzene, methanol and hexane was measured. These molecules were: triphenylamine, N-(4-methyl phenyl) N,N bis phenyl amine, N-(3-methyl phenyl) N,N bis phenyl amine, N,N-bis(4-methyl phenyl) N-phenyl amine, N,N-bis(3-methyl phenyl) N-phenyl amine, tritolylamine (N,N,N-tris-(4-methylphenyl)amine), N,N-bis-(4-methylphenyl)-N-(3-methylphenyl)amine, N,N-bis-(3-methylphenyl)-N-(4-methylphenyl)amine, and N,N,N-tris-(3-methylphenyl)amine. The solubility of these molecules was estimated using ideal solution theory, the Hildebrand equation, and UNIQUAC method. The ideal solution theory and the Hildebrand equation were not able to estimate solubility with high precision. However, UNIQUAC method was able to estimate the solubility with good accuracy. It was found that substitution of methyl group regardless of its number in aryl ring increases the solubility. In addition, meta-substitution always results in higher solubility regardless of the nature of the solvent. Physical properties, as well as electrochemical properties of these materials were also provided. Based on these data, the most promising candidates for device preparation should be: mTTA, TTA, mmmTTA, and mono-TPA. However, the only way to prove the above ranking would be to test the candidates in actual devices, which is outside the scope of this paper.     

EXAFS and XPS Investigations of Cu/ZnO Catalysts and Their Interaction with CO and Methanol

Several investigations have been carried out on Cu/ZnO catalysts by employing extended Xray absorption fine structure (EXAFS) and Xray photoelectron spectroscopy (XPS). EXAFS investigations of Cu/ZnO catalysts subjected to hydrogen reduction show the presence of Cu¹⁺ species and Cu microclusters. The proportion of Cu¹⁺ depends on the rate of increase of the reduction temperature and on the amount of alumina added. An XPS study of the interaction of CO with model Cu/ZnO catalysts prepared in situ in the electron spectrometer shows the formation of CO₂ ^-, CO₃ ^2- and C₂O₄ ^2- species, their proportion relative to CO increasing with the Cu¹⁺/Cu⁰ ratio. A study of the interaction of CH₃OH with Cu clusters deposited on ZnO films reveals reversible molecular adsorption and the formation of CH₃O on clean Cu clusters. If the Cu clusters are pretreated with oxygen, however, both CH₃O and HCOO^- species are produced. Model Cu/ZnO catalyst surfaces containing both Cu¹⁺ and Cu⁰ species show interesting oxidation properties. On a Cu⁰-rich catalyst surface, only the CH₃O species is formed on interaction with CH₃OH. On a Cu¹⁺rich surface, the HCOO^- ion is the predominant species.     

Preparation and characterization of polyisoprenes and polybutadienes having 1,2- and 3,4-linkages preferentially

Polyisoprenes (PI) and polybutadienes (PB) both having vinyl-type side chains preferentially were prepared and characterized. Both polymers were anionically polymerized with cumyl potassium or pottassium naphthalenide as initiators in a polar solvent, tetrahydrofuran, at low temperature. From the ¹H NMR measurement, the PI contains 3,4- and 1,2-microstructures and PB does 1,2-microstructure preferentially. All the samples covering the molecular weight range of 37 k ≤ M_w ≤ 724 k for PI and 35 k ≤ M_w ≤ 197 k for PB were confirmed to have narrow molecular weight distribution. Measured glass transition temperatures, i.e., 11.0 °C for PI and ?0.7 °C for PB are both considerably high compared with those of 1,4-microstructure-rich analogues. Intrinsic viscosity measurements in 1,3-dioxane for PI and 2-octanol for PB were carried out, and the segment lengths of the 3,4-/1,2-rich PI and 1,2-rich PB were estimated to be 0.60 nm and 0.59 nm, which are both considerably shorter than the values for two polydienes having 1,4-microstructures preferentially, i.e., 0.66 nm for both 1,4-rich PI and PB. Furthermore plateau moduli of both polymers are determined by dynamic viscoelastic measurements.     

Theoretical and experimental studies of network formation and properties

A survey of recent work on pre-gel intramolecular reaction and gelation in oxypropylene-triol and tetrol-based polyester and polyurethane network-forming systems is presented, and relationships between the properties of the networks formed at complete reaction and the product of extents of reaction at gelation (α_c) are discussed. In contrast to that in corresponding linear reaction systems, the amount of pre-gel intramolecular reaction in the triol-based polyurethanes is never negligible, even in bulk. Kilb's model of RA₂ + RB_f type gelling systems has been reanalysed and a more accurate condition for gelation evaluated. The shear moduli and T_gs of dry networks are found to increase as α_c increases, indicating that these properties are strongly dependent on the amount of pre-gel loop formation. Extrapolated values of the shear moduli indicate that perfect, affine rather than phantom networks would be formed by reaction systems having the ideal gel point [α_c = (f ? 1)^?1].