Chemical Engineering

Three series of crosslinked poly(ethylene oxide) rubbers have been prepared by photopolymerization of prepolymer solutions containing: (1) poly(ethylene glycol) diacrylate (PEGDA) and H 2 O, (2) PEGDA and poly(ethylene glycol) methyl ether acrylate (PEGMEA), and (3) PEGDA and poly(ethylene glycol) acrylate (PEGA). All of these polymers have similar chemical composition (approximately 82 wt.% ethylene oxide), but the crosslink density and the content and chemistry of chain end groups are different. The effect of chain end groups and crosslink density on mass density, glass transition temperature (T g), free volume, and H 2 , N 2 , CH 4 and CO 2 transport properties of the polymers was determined. The effect of temperature on gas permeability and solubility was also investigated. Many of the samples were amorphous. However, samples with high concentrations of PEGMEA could crystallize, and the formation of crystalline regions significantly decreased permeability. A generalized free volume model was used to interpret the effect of crosslink density and chain end groups on gas permeability and diffusivity, where free volume was characterized using two techniques: (1) density and group contribution theory, and (2) positron annihilation lifetime spectroscopy. Finally, the potential application of these materials for CO 2 /light gas separations was explored.

Six polybenzimidazoles have been prepared by a dispersion polycondensation process using polyphosphoric acid as a dehydrating reagent. Two of these contained an additional pyridine residue in the mainchain, and three of them additional imidazole groups. The molecular structures have been characterized by u.v., i.r. and 1H n.m.r, spectra. Physical characterization has involved solubility measurements, solution viscosity evaluation and thermal stability assessment via thermogravimetric analysis. The latter has confirmed that the inherently high thermo-oxidative stability of polybenzimidazoles is retained in the case of polymers and copolymers with additional nitrogen heterocycles in the mainchain.

460.6 cm-', F(OOO) = 205.4, room temperature, R = 0.064 for 130 unique reflections greater than 5o(F). The compounds are isostructural. The oxygen ion at the idealized position L IO is displaced along [ 1101 by about 0.5 A. The thallium and lead ions at %z origin have r.m.s. vibrational amplitudes in the basal plane that are twice as large as those perpendicular to the plane. Static displacements of the cation and oxygen in the basal plane can result in an octahedral environment with reasonable metal-oxygen bond lengths, i.e. 2.3 A or less. The copper and cobalt ions are in a distorted octahedral coordination. The two apical distances for Cu-0 are 2.489(16) A and for CoO = 2.38(4) A. The four equatorial bond lengths are Cu-0 = 1.8672(2) A and CoO = 1.880(2) A. The strontium ion is in nine-fold coordination to the oxygens that are at the corners of a monocapped square antiprism; the capping ion is the disordered oxygen. In the thallium compound four Sr-0 = 2.718(4) A, four Sr-0 = 2.626(l) A and the capping Sr-0 = 2.687(3) A. In the lead phase four Sr-0 = 2.716(8) A four Sr-0 = 2.616(2) A and the capping Sr-0 = 2.700(8) A. The partial replacement lead by copper does not occur at the same site but is displaced along [ 1001 by 0.6 A. The copper exists in a tetrahedral environment. *Dedicated to Professor LeRoy Eyring on the occasion of his 70th birthday.

Preparation and Physical Properties of One-Dimensional Structures: Ba p (Fe2S4)(? Compounds with the stoichiometry Bai+^FeaSi or Ba,j(Fe2S4)g, p and q integers, were first synthesized and investigated in this laboratory by Hong and Grey (7). These phases are part of a group of compounds which have been given the name "infinitely adaptive" proposed by J. S. Anderson (2). Infinitely adaptive structures are crystalline materials ... for which, within certain composition limits, every possible composition can attain a unique, fully ordered structure, without defects arising from solid solution effects and with no biphasic, coexisting ranges between successive structures. Some of the well-known structures falling into this classification include crystallographic shear structures (3), ladder type structures (4, 5) and compounds such as tetrathiafulvalene pentaiodide, (TTF) 7(1)5, a member of the general series (TTF)m (I)n (6). Other examples of these structures are the Aurivillius layered structures (7) with c-axis periodicities as long as 76 A, and the ferrites of the magnetoplumbite series (8) with c-axes up to 1500 A in length. All of these phases are characterized by structures formed from sublattices which have "incommensurate" repeat distances in one or two directions. We report here a review of the structure, preparation and physical properties of the Ba1(.IFe2S4 series of com

Preparation and Physical Properties of One-Dimensional Structures: Ba p (Fe2S4)(? Compounds with the stoichiometry Bai+^FeaSi or Ba,j(Fe2S4)g, p and q integers, were first synthesized and investigated in this laboratory by Hong and Grey (7). These phases are part of a group of compounds which have been given the name "infinitely adaptive" proposed by J. S. Anderson (2). Infinitely adaptive structures are crystalline materials ... for which, within certain composition limits, every possible composition can attain a unique, fully ordered structure, without defects arising from solid solution effects and with no biphasic, coexisting ranges between successive structures. Some of the well-known structures falling into this classification include crystallographic shear structures (3), ladder type structures (4, 5) and compounds such as tetrathiafulvalene pentaiodide, (TTF) 7(1)5, a member of the general series (TTF)m (I)n (6). Other examples of these structures are the Aurivillius layered structures (7) with c-axis periodicities as long as 76 A, and the ferrites of the magnetoplumbite series (8) with c-axes up to 1500 A in length. All of these phases are characterized by structures formed from sublattices which have "incommensurate" repeat distances in one or two directions. We report here a review of the structure, preparation and physical properties of the Ba1(.IFe2S4 series of com

Three series of crosslinked poly(ethylene oxide) rubbers have been prepared by photopolymerization of prepolymer solutions containing: (1) poly(ethylene glycol) diacrylate (PEGDA) and H 2 O, (2) PEGDA and poly(ethylene glycol) methyl ether acrylate (PEGMEA), and (3) PEGDA and poly(ethylene glycol) acrylate (PEGA). All of these polymers have similar chemical composition (approximately 82 wt.% ethylene oxide), but the crosslink density and the content and chemistry of chain end groups are different. The effect of chain end groups and crosslink density on mass density, glass transition temperature (T g), free volume, and H 2 , N 2 , CH 4 and CO 2 transport properties of the polymers was determined. The effect of temperature on gas permeability and solubility was also investigated. Many of the samples were amorphous. However, samples with high concentrations of PEGMEA could crystallize, and the formation of crystalline regions significantly decreased permeability. A generalized free volume model was used to interpret the effect of crosslink density and chain end groups on gas permeability and diffusivity, where free volume was characterized using two techniques: (1) density and group contribution theory, and (2) positron annihilation lifetime spectroscopy. Finally, the potential application of these materials for CO 2 /light gas separations was explored.

323 unique reflections >Su(F,). The Pb atoms are in octahedral coordination; the octahedra form a chain parallel to c by edge-sharing. Sr is coordinated by nine oxygen atoms that form a capped trigonal prism. The trigonal prisms form a chain parallel to c by face-sharing. The SrlPb site is surrounded by seven oxygen ions. The polyhedron can be described as a tricapped trigonal prism with one edge of the prism missing. The octahedra and trigonal prisms articulate by comer sharing into a three-dimensional framework. Two crystallographically independent Cu atoms are disordered and occupy tetrahedral interstices. One oxygen site is partially occupied. The presence of Pb*+ on the Pb site distorts the octahedron by lengthening two bonds to 2.4413) A; the average of the other four bond lengths is 2.137(19) A. The Sr-0 bond lengths to the six apices of the prism are 2.632(14) and 2.935(3) 8, to the three capping atoms. The disordered Sr/Pb atom site has four oxygen neighbors at 2.544(17) A, two at 2.621(5) A, and one at 2.42(2) A. The compound is an electrical insulator.

460.6 cm-', F(OOO) = 205.4, room temperature, R = 0.064 for 130 unique reflections greater than 5o(F). The compounds are isostructural. The oxygen ion at the idealized position L IO is displaced along [ 1101 by about 0.5 A. The thallium and lead ions at %z origin have r.m.s. vibrational amplitudes in the basal plane that are twice as large as those perpendicular to the plane. Static displacements of the cation and oxygen in the basal plane can result in an octahedral environment with reasonable metal-oxygen bond lengths, i.e. 2.3 A or less. The copper and cobalt ions are in a distorted octahedral coordination. The two apical distances for Cu-0 are 2.489(16) A and for CoO = 2.38(4) A. The four equatorial bond lengths are Cu-0 = 1.8672(2) A and CoO = 1.880(2) A. The strontium ion is in nine-fold coordination to the oxygens that are at the corners of a monocapped square antiprism; the capping ion is the disordered oxygen. In the thallium compound four Sr-0 = 2.718(4) A, four Sr-0 = 2.626(l) A and the capping Sr-0 = 2.687(3) A. In the lead phase four Sr-0 = 2.716(8) A four Sr-0 = 2.616(2) A and the capping Sr-0 = 2.700(8) A. The partial replacement lead by copper does not occur at the same site but is displaced along [ 1001 by 0.6 A. The copper exists in a tetrahedral environment. *Dedicated to Professor LeRoy Eyring on the occasion of his 70th birthday.

This research demonstrates the influence of laser speed and the drug particle size on the manufacturing of amorphous solid dispersions (ASD) and dosage forms thereof using selective laser sintering 3-dimensional (3D) printing. One-step manufacturing of ASD is possible using selective laser sintering 3D printing processes, however, the mechanism of ASD formation by this process is not completely understood and it requires further investigation. We hypothesize that the mechanism of ASD formation is the diffusion and dissolution of the drug in the polymeric carrier during the selective laser sintering (SLS) process and the drug particle size plays a critical role in the formation of said ASDs as there is no mixing involved in the sintering process. Herein, indomethacin was used as a model drug and introduced into the feedstock (Kollidon® VA64 and Candurin® blend) as either unprocessed drug crystals (particle size > 50 µm) or processed hot-melt extruded granules (DosePlus) with reduc...

Bi 18 P 4 O 42 , were studied using short-wavelength synchrotron X-ray radiation. The compound is monoclinic, I2/m, a ‫؍‬ 11.885(2) A s , b ‫؍‬ 11.540(2) A s , c ‫؍‬ 15.636(3) A s , ‫؍‬ 90.23(3)3, Z ‫؍‬ 2. The crystal is twinned by pseudo-merohedry. The structure re5nement converged to R ‫؍‬ 0.0366. There are 5ve crystallographically independent Bi atoms. The oxygen coordination polyhedron around Bi(1) is a slightly distorted cube with Bi+O bonds varying from 2.381(11) to 2.662(10) A s. The other four Bi atoms are in a severely distorted oxygen environment with bond lengths varying from 2.102(5) to 3.16(2) A s. A greater variation of the oxygen coordination polyhedra exists around the three crystallographically independent Pb atoms changing from a somewhat elongated cube to a monocapped pentagonal bipyramid; bond distances vary from 2.13(2) to 3.38(2) A s. Of 20 crystallographically independent oxygen ions 11 are disordered. The structure consists of two Bi+O layers parallel to (101). They are interconnected perpendicular to [010] by layers consisting of Pb and PO 4. The two crystallographically independent PO 4 moieties are disordered. This compound displays a-Bi 2 O 3 6uorite superstructure. The locations of the nonbonded lone-pair electrons were calculated and vary from 0 to 1.1 A s. These displacements from the cation nucleus are indicative of the extent of s+p hybridization, where zero displacement represents the spherical nonbonded 6s 2 orbital. The extent of hybridization is a function of the distortion of the oxygen coordination polyhedron around the cation.

Magnesium oxide nanoparticles (3 nm) were dispersed in 1,2-polybutadiene via solution casting. Particles were observed to be dispersed into submicron aggregates using atomic force microscopy and transmission electron microscopy. The nanocomposite density was consistently lower than that anticipated on the basis of an additive model, suggesting the presence of voids in the nanocomposites. The incorporation of nanoparticles into 1,2-polybutadiene increased acid gas (i.e., CO 2) and nonpolar gas (i.e., CH 4 , N 2) permeability with increasing particle loading. For instance, CO 2 permeability increased from 52 barrer in the unfilled polymer to 650 barrer in a nanocomposite containing 27 vol % (nominal) MgO, at 35°C and a feed pressure of 12 atm. CO 2 /nonpolar gas selectivity decreased with increasing particle loading, while CH 4 /N 2 selectivity was not influenced by the particles. Gas solubility increased systematically with increasing particle loading. In contrast, gas diffusion coefficients initially decreased with increasing particle loading and then increased with increasing loading at particle loadings greater than 10 vol % (nominal).

Magnesium oxide (MgO) nanoparticles were dispersed via solution processing in trimethylsilylsubstituted polyacetylenes to form polymer nanocomposites. In the presence of these particles, the polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA), were partially desilylated. Some PTMSDPA/MgO nanocomposites were insoluble in common solvents (e.g., toluene or chloroform), and the solubility characteristics depended on particle loading and preparation conditions. When possible, the reaction products were characterized using XPS, FTIR, and NMR. Small molecule model compounds were also used to study the reaction of trimethylsilyl groups with MgO nanoparticles. The CO 2 permeability in these nanoparticle-filled films was over 6 times higher than in the analogous unfilled polymers. This phenomenon may provide a route for preparing highly permeable, chemically stable membranes for gas separations.

Brookite (i.e., titanium dioxide) nanoparticles having a nominal diameter of 3 nm were dispersed in 1,2-polybutadiene (PB) via solution processing to form polymer nanocomposites. Atomic force microscopy and scanning transmission electron microscopy were used to characterize particle dispersion. A significant population of nanoparticle aggregates exhibited characteristic dimensions below 50 nm. However, some aggregates were over 1 mm in size. At high nanoparticle loadings (e.g., 27 nominal volume percent TiO 2), the permeability coefficients of CO 2 , CH 4 , N 2 and H 2 were more than 3 times higher than that in unfilled PB, which is opposite to the trend typically observed when impermeable particles are added to rubbery polymers. Gas solubility coefficients generally increased with increasing particle loading, whereas diffusion coefficients decreased with increasing particle loading. Therefore, the increase in permeability was due to an increase in gas solubility upon incorporating highly sorbing nanoparticles into the polymer. Interestingly, there was virtually no change in pure gas selectivity in the nanocomposites as compared to unfilled PB.