Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2. REPORT TYPE 3. DATES COVERED (From -To) SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)Air Force Research Laboratory (AFMC) AFRL/PRS SPONSOR/MONITOR'S Pollux Drive NUMBER(S)Edwards AFB CA 93524-7048 AFRL-PR-ED-JA-2006-178 DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release; distribution unlimited (AFRL-ERS-PAS-2006-132) SUPPLEMENTARY NOTESTo be published in the ACS journal Macromolecules. AbstractA new cyanate ester monomer was prepared from bis(4-cyanatophenyl)-dimethylsilane (SiMCy) and fully characterized by analytical and spectroscopic techniques. The monomer was found to have a melting point about 20 °c lower than that of the commercial bis(4-cyanatophenyl)dimethylmethane (BADCy) with similar melt viscosity, curing kinetics, and post-cure glass transition temperature. Analysis of the single-crystal molecular structure by x-ray diffraction showed that intermolecular packing was dominated by weak hydrogen-bonding attractions between the aromatic rings and the -OCN nitrogen atoms. In contrast, the packing interactions found in BADCy are dominated by dipole-dipole interactions of the OCN groups. These differences may explain the 50% reduction in moisture uptake observed in SiMCy as compared to BADCy during exposure to boiling water. In addition, thermogravimetric analysis revealed that SiMCy exhibited a significantly higher char yield in air than BADCy, presumably due to the formation of silicates at high temperature. The combination of improved thermooxidative stability and reduced moisture absorption without significant loss in ease of processing or mechanical properties makes SiMCy an important potential "drop in" replacement for BADCy, and demonstrates the power of the molecular level approach to designing new hightemperature polymer materials. SUBJECT TERMS SECURITY CLASSIFICATION OF:17 Abstract.A new cyanate ester monomer was prepared from bis(4-cyanatophenyl)-dimethylsilane (SiMCy) and fully characterized by analytical and spectroscopic techniques. The monomer was found to have a melting point about 20 °C lower than that ...

The structure of nanocomposites produced by melt-mixing polypropylene and 5 wt % of organically modified layered silicates with varying amounts of different maleated polypropylene compatibilizer grades has been analyzed with X-ray diffraction, transmission electron microscopy (TEM), and melt rheology. The extent of delamination in different nanocomposites has been quantified from analysis of several TEM images for each specimen by a product of the single particle volume fraction and the intrinsic viscosity of such particles. This measure correlated directly with the low shear relative viscosity of the molten composites (relative to the silicate free mixture of polypropylene and compatibilizer). The results also indicate that the acid number alone is not a good predictor of compatibilizer effectiveness, i.e., the amount required for exfoliation. The molar ratio of functional groups to compatibilizer chains is found to be a better parameter for ranking compatibilizer effectiveness than the acid number, which is a weight ratio. With higher values of the molar ratio, lower concentrations of compatibilizer are required for significant exfoliation. With the highest molar ratio compatibilizer, an optimum compatibilizer concentration of about 10 wt % leads to a composite with the most exfoliated structure.

A process for producing hollow microcapsules as ultrasound contrast agents was optimized using a 2(3) factorial experimental design method with two replicates. Spray drying, a conveniently scalable encapsulation technique, was used to encapsulate a volatile core material, such as ammonium carbonate, using biodegradable 50-50 poly(D,L-lactide-co-glycolide). Various effects due to changes in processing variables and their interactions were studied using the factorial grid. The high- and low-incremented variables examined included the temperature difference between the inlet and outlet of the spray dryer (5 degrees and 15 degrees C), air atomization pressure (80 and 100 psi), and polymer concentration in solvent (0.005 and 0.025 g/mL). Responses analyzed for computing the main effects and interactions were microcapsule morphology, yield, mean size, and zeta potential. Experimental results showed that polymer concentration was most important for determining microcapsule morphology. The temperature difference for drying prominently affected mean size, and atomization pressure was the main effect for microcapsule yield. Interactions among variables were not present in this case. The best conditions for producing PLGA microcapsules was a temperature difference of 5 degrees C, an initial polymer concentration of 0.005 g/mL, and an atomization pressure of 80 psi. The microcapsule zeta potentials were unaffected by spray-drying conditions.

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