Structure-to-glass transition temperature relationships in high temperature stable condensation polyimides

The presence of a hexafluoroisopropylidene (6F) connecting group in aryl dianhydrides used to prepare aromatic condensation polyimides provides high glass transition temperature (T sub g) polyimides with excellent thermo-oxidative stability. The purpose of this study was to determine if a trifluorophenyl-ethylidene (3F) connecting group would have a similar effect on the T sub g of aromatic condensation polyimides. A new dianhydride containing the 3F connecting group was synthesized. This dianhydride and an aromatic diamine also containing the 3F connecting group were used together and in various combinations with known diamines or known dianhydrides, respectively, to prepare new 3F containing condensation polyimides. Known polyimides, including some with the 6F connecting linkage, were also prepared for comparison purposes. The new 3F containing polymers and the comparison polymers were prepared by condensation polymerization via the traditional amic-acid polymerization method in N,N-dimethylacetamide solvent. The solutions were characterized by determining their inherent viscosities and then were thermally converted into polyimide films under nitrogen atmosphere at 300 to 500 C, usually 350 C. The T sub g's of the films and resin discs were then determined by thermomechanical analysis and were correlated as a function of the final processing temperatures of the films and resin discs. The results showed that similarities existed in the T sub g's depending on the nature of the connecting linkage in the monomers used to prepare the condensation polyimides

PMR polyimides with improved high temperature performance

Studies were performed to investigate the effect of substituting a hexafluoro isopropyl idene connecting group for a carbonyl group of a PMR polyimide monomeric reactant on the thermo-mechanical properties processability of graphite fiber reinforced PMR polyimide composites. Composites were fabricated utilizing PMR methodology. Monomeric reactant solutions of various stoichiometric ratios were used to impregnate Hercules HTS graphite fiber. The processing characteristics and elevated temperature (600 F) mechanical properties of the composites are described

Effect of substituted phenylnadimides on processing and properties of PMR polyimide composites

Three nitrophenylnadimide cure initiators and two phenylnadimides (without nitros) were evaluated as additives to PMR-15 resins and Celion 6000 graphite fiber composites. The results of a resin screening study eliminated all of the additives except 3-nitrophenylnadimide (NO2PN) for use as a low temperature curing additive for PMR-15. Thus, NO2PN and the two control additives were investigated in PMR-15 formulations from which Celion 6000 graphite fiber/PMR-15 composites were processed both with low temperature (274 C) and normal (316 C) cure cycles. Comparisons of the two processing cycles, the resultant glass transition temperatures (Tg), the ambient, 274 and 316 C composite mechanical properties determined before and after 316 C postcure, the 316 C thermo-oxidative weight losses and the retention of 316 C composite mechanical properties are presented. Empirical correlations of the type and amount of nadimide additives with processing parameters, Tg, composite mechanical properties, composite thermo-oxidative stability and long term retention of 316 C composite mechanical properties are also presented

Stability of PMR-polyimide monomer solutions

The stability of alcohol solutions of norborneyl capped PMR-polyimide resins was monitored during storage at ambient and subambient temperatures. Chemical changes during storage were determined spectroscopically using nuclear magnetic resonance. Resin processability and cured resin quality were determined by fabrication of unidirectional, graphite fiber composites using aged solutions and testing of selected composite properties. PMR-15 solutions exhibit nominally two weeks of useful life and PMR-2 solutions exhibit nominally two days of useful life at ambient conditions. The limiting factor is precipitation of imide reaction produces from the monomer solutions. Both solutions exhibit substantially longer useful lifetimes in subambient storage. PMR-15 shows no precipitation after several months storage at subambient temperatures. PMR-2 solutions do exhibit precipitates after extended subambient storage, however, the precipitates formed under these conditions can be redissolved. The chemical implications of these observations are discussed

Effects of graphite fiber stability on the properties of PMR polyimide composites

The effect of the stability of graphite fibers on composite properties after exposure in air at 600 F was investigated. Composites were fabricated from PMR-15 and PMR-2 monomer solutions, using HTS-2 and Celion 6000 graphite fibers as the reinforcement. The effect of long-term exposure in air at 600 F on composite weight loss and mechanical properties was determined. These composites exhibited a significantly increased lifetime at that temperature compared to composites fabricated from HTS fiber sold prior to 1975. The effect of the PMR-15 and PMR-II resin compositions on long-term composite performance at 600 F is also discussed

Service Standards in Higher Education: Lasswell\u27s Communication Model as a Training Tool

This paper examines a service standards training process established during the 2016/2017 academic year for Prairie State College (PSC), a two-year community college located in Chicago Heights Illinois. The goal of examining and revising the service training process was to enhance the quality of service after the college received poor service reviews from a recent satisfaction survey. Lasswell\u27s Communication Model was used to create content and structure for a training manual and workshop as part of the overall service training process at PSC. The service standards and training manual was successfully developed and is currently being tailored to accommodate the needs of the college. PSC plans to facilitate its first customer service training session in summer 2017 and a second session in the fall

Shifting ground: agricultural R&D worldwide

This brief summarizes the book, Agricultural R&D in the Developing World: Too Little, Too Late?, edited by Philip G. Pardey, Julian M. Alston, and Roley R. Piggott. The authors of the brief look at topics such as: International spillovers of public agricultural R&D; patterns of worldwide public investments in agricultural research; pervasive underfunding of agricultural research; divergent research agendas. The brief examines policy implications and concludes that "The issues are large scale and long term and demand serious attention, including further, more specific analysis. The national governments of developing countries can take some initiative, as indicated by the analysis of case studies in the book, in areas of national agricultural research policy such as: (1) enhancing IPR and tailoring the institutional and policy details of intellectual property to best fit local circumstances, (2) increasing the total amount of government funding for their national agricultural research systems, (3) introducing institutional arrangements and incentives for private and joint public–private funding, such as matching grants and check-off funds, and (4) improving the processes by which agricultural research resources are administered and allocated." From textAgricultural R&D, Public investments, Agricultural economics and policies, Agricultural innovations, Agricultural policy, Government spending policy, intellectual property,

European Cherry Fruit Fly Rhagoletis cerasi (Linnaeus)

European cherry fruit fly (ECFF) is a new invasive cherry-infesting pest from Europe. It was first detected in the U.S. in New York in 2017. This fact sheet describes it and includes life history, plant hosts, damage symptoms, monitoring, and management

NOTES ON TAXONOMY AND NOMENCLATURE IN THE GENUS LYGODIUM (SCHIZAEACEAE)

Due to various causes, the early history of both taxonomy and no menclature in the genus Lygodium is very confused. As a result,a numberof problems arise which need fuller discussion than is possible in Flora Malesiana.Such problems are here discussed, concerning most of the species native in Malaysia.The new combination Lygodium auriculatum (Willd.) Alston is published, and a new typification of the species Ophioglossum scandens L. is proposed