Oxygen plasma resistant phosphine oxide containing imide/arylene copolymers

A series of oxygen plasma resistant imide/arylene ether copolymers were prepared by reacting anhydride-terminated poly(amide acids) and amine-terminated polyarylene ethers containing phosphine oxide units. Inherent viscosities for these copolymers ranged from 0.42 to 0.80 dL/g. After curing, the resulting copolymers had glass transition temperatures ranging from 224 C to 228 C. Solution cast films of the block copolymers were tough and flexible with tensile strength, tensile moduli, and elongation at break up to 16.1 ksi, 439 ksi, and 23 percent, respectively at 25 C and 9.1 ksi, 308 ksi and 97 percent, respectively at 150 C. The copolymers show a significant improvement in resistance to oxygen plasma when compared to the commercial polyimide Kapton. The imide/arylene ether copolymers containing phosphine oxide units are suitable as coatings, films, adhesives, and composite matrices

Effect of molecular weight on polyphenylquinoxaline properties

A series of polyphenyl quinoxalines with different molecular weight and end-groups were prepared by varying monomer stoichiometry. Thus, 4,4'-oxydibenzil and 3,3'-diaminobenzidine were reacted in a 50/50 mixture of m-cresol and xylenes. Reaction concentration, temperature, and stir rate were studied and found to have an effect on polymer properties. Number and weight average molecular weights were determined and correlated well with viscosity data. Glass transition temperatures were determined and found to vary with molecular weight and end-groups. Mechanical properties of films from polymers with different molecular weights were essentially identical at room temperature but showed significant differences at 232 C. Diamine terminated polymers were found to be much less thermooxidatively stable than benzil terminated polymers when aged at 316 C even though dynamic thermogravimetric analysis revealed only slight differences. Lower molecular weight polymers exhibited better processability than higher molecular weight polymers

A Hierarchical Dirichlet Process Model with Multiple Levels of Clustering for Human EEG Seizure Modeling

Driven by the multi-level structure of human intracranial electroencephalogram (iEEG) recordings of epileptic seizures, we introduce a new variant of a hierarchical Dirichlet Process---the multi-level clustering hierarchical Dirichlet Process (MLC-HDP)---that simultaneously clusters datasets on multiple levels. Our seizure dataset contains brain activity recorded in typically more than a hundred individual channels for each seizure of each patient. The MLC-HDP model clusters over channels-types, seizure-types, and patient-types simultaneously. We describe this model and its implementation in detail. We also present the results of a simulation study comparing the MLC-HDP to a similar model, the Nested Dirichlet Process and finally demonstrate the MLC-HDP's use in modeling seizures across multiple patients. We find the MLC-HDP's clustering to be comparable to independent human physician clusterings. To our knowledge, the MLC-HDP model is the first in the epilepsy literature capable of clustering seizures within and between patients.Comment: ICML201

LaRC-ITPI/arylene ether copolymers

As part of an effort to develop high performance structural resins for aerospace applications, work has continued on block copolymers containing imide and arylene ether segments. The arylene ether block used in this study contains a bulky fluorene group in the polymer backbone while the imide block contains an arylene ketone segment similar to that in the arylene ether block and has been named LaRC-ITPI. A series of imide/arylene ether block and segmented copolymers were prepared and characterized. Films were prepared from these copolymers and mechanical properties were measured

Imide/arylene ether copolymers with pendent trifluoromethyl groups

A series of imide/arylene ether block copolymers were prepared using an arylene ether block containing a hexafluoroisopropylidene group and an imide block containing a hexafluoroisopropylidene and a trifluoromethyl group in the polymer backbone. The copolymers were characterized and mechanical properties were determined and compared to the homopolymers

Imide/arylene ether copolymers

Imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly(arylene ethers) in polar aprotic solvents and by chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The resulting block copolymers have one glass transition temperature or two, depending upon the particular structure and/or the compatibility of the block units. Most of these block copolymers form tough, solvent resistant films with high tensile properties

Imide/Arylene Ether Copolymers

Three different series of imide/arylene ether block copolymers were prepared using two different imide blocks and two different arylene ether blocks. Block molecular weights studied were 3110 and 6545 g/mole for each block and all four combinations possible were prepared in each series. Also, several segmented copolymers were prepared by forming the imide segment and the copolymer in the presence of the pre-formed arylene ether block. Two amine-terminated poly(arylene ether) blocks (ATPAE) were prepared by reacting 1,3-bis(4-fluorobenzoyl)benzene with either 2,2-bis(4-hydroxyphenyl)propane (BPA) or 9,9-bis(4-hydroxyphenyl)fluorene (BPF) and 4-aminophenol. Two anhydride-terminated poly(amic acid) blocks were prepared by reacting 4,4\u27-oxydianiline (ODA) or 1,3-bis(4-aminophenoxy-4’- benzoyl)benzene (BABB) with 3,3\u27,4,4\u27-benzophenonetetracarboxylic dianhydride (BTDA). The ATPAEs were reacted with the anhydride- terminated poly(amic acids) to provide block copolymers which were either thermally or solution imidized. Thermal imidization was accomplished by heating 1 h each at 100, 200 and 300°C while solution imidization was accomplished by adding toluene to the reaction, heating to 155°C overnight and collecting the toluene/water azeotropic mixture in a Dean-Stark trap. Some of the block copolymers displayed two Tgs indicating incomptability and phase separation, especially for the higher molecular weight blocks. The copolymer series preapred by reacting the ATPAE (BPA) blocks with the ODA/BTDA blocks in N,N-dimethylacetamide (DMAc) had inherent viscosities as high as 1.37 dL/g. The copolymer series prepared by reacting ATPAE (BPA) blocks with BABB/BTDA blocks in DMAc or N-methyl- pyrrolidinone (NMP) had inherent viscosities as high as 1.73 dL/g. The copolymer series prepared by reacting ATPAE (BPF) blocks with BABB/BTDA blocks in DMAc, NMP or m-cresol had inherent viscosities as high as 1.08 dL/g. The copolymers were characterized by differential scanning calorimetry (DSC), torsional braid analysis (TBA), thermogravimetric analysis (TGA) and wide angle x-ray diffraction (the BABB/BTDA imide is semi-crystalline). Mechanical properties were measured on copolymer films and fracture energies were measured on moldings. One copolymer was end-capped at a controlled molecular weight to improve processing and evaluated as an adhesive and graphite composite matrix. The chemistry and properties of the copolymers will be discussed and compared to those of the homopolymers

Reactions of trifluoroiodomethane on metal surfaces

To further understand reactions of fluorocarbons relevant to a number of technological applications, several surface-sensitive analytical techniques are applied to an investigation of the thermal and electron-induced chemistry of trifluoro-iodomethane (CF3I) on Ru(001) and Ni(100) surfaces;Ni(100) is found to be very active toward C-F bond scission, as a significant amount of CF3I thermally decomposes to its atomic constituents following adsorption at 100 K. Thermal desorption spectroscopy (TDS) shows that desorption of NiF2 and I increases linearly with CF3I exposure until reaching a saturation level. A small amount of CF3 desorption is detected as the exposure approaches saturation, indicating that adsorbed CF3 is stabilized as the surface sites required for decomposition become less available;Electron-induced decomposition (EID) of multilayer CF3I occurs with a cross-section of 1.5x10-16 cm2. F+ is the dominant product detected during electron irradiation. A number of new thermal desorption products are observed following electron irradiation. Of particular interest is a series of carbon-carbon bond formation products likely produced in the multilayer as a result of EID. The mechanism through which these products form may mimic the proposed electron-induced cross-linking of fluoropolymer chains;Exposure of CF3I to Ru(001) at 100 K results in a complex mixture of CF n (n = 2-4) thermal desorption products. X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and H2 coadsorption experiments suggest that the reactions which lead to these desorption products are regulated by the availability of surface sites. High-resolution electron energy loss spectroscopy (HREELS), in conjunction with electron-stimulated desorption ion angular distribution (ESDIAD), suggests that adsorbed CF3 adopts a tilted configuration in which one C-F bond is oriented normal to the surface plane;ESDIAD identifies a number of interesting patterns which give insight into the surface chemistry of CF3I on Ru(001), as well as the surface structure of the resulting products. A small hexagonal pattern is attributed to electron-stimulated desorption (ESD) of atomic fluorine adsorbed at step and defect sites, while two larger hexagons are attributed to various orientations of adsorbed CF3