Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which could be utilized to reduce vehicle weight for the X-33 and Reusable Launch Vehicle (RLV) programmes. The activity at NASA Langley Research Center focuses on developing polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohols. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g cc−1 to 0.32 g cc−1. Polyimide foams at densities of 0.032 g cc−1 and 0.08 g cc−1 were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, a good thermal conductivity at 25°C of 0.03 W m−1 K−1, compressive strengths as high as 0.84 MPa at 10% deflection and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from −253°C to 204°C. The foams survived the cyclic testing without debonding or cracking. Thermal forming of the 0.032 g cc−1 foam was performed and a minimum radius curvature of 0.0711 m was achieved. The foams exhibited excellent properties overall and are shown to be viable for use as cryogenic insulation on the next generation RLV.

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This article reviews two types of novel catalyst systems for the polymerization of substituted acetylenes; i.e., i) MoOCl4-based catalysts and ii) metal carbonyl-based catalysts. The MoOC14-nBu4Sn-EtOH( 1 : 1 : 1) catalyst achieves living polymerization of 1 -chloro-1 -octyne, tert-butylacetylene, and phenylacetylenes having bulky ortho substituents. The initiator efficiency for the polymerization of o-CF3-phenylacetylene reaches about 40% in anisole. Et3A1, EtzZn, and n-BuLi also work as useful cocatalysts in the MoOCl4-based system; the polydispersity ratios of poly( 0-CF3-phenylacetylene) are as small as I .06 to 1.02. The binary MoOCl4-n-BuLi system serves without ethanol. Block copolymers of 0-CF3-and o-MqSi-phenylacetylenes can be obtained by using MoOC14-Et3Al- EtOH( 1 : 1 :4). Whereas CC14 is used as solvent in the polymerization of phenylacetylene by W(C0) 6-CC14-hn, only a few equivalents of Ph2CC12 to tungsten is needed in the W(C0)6-Ph2CC12-hn system. A tungsten complex, WC12(CO)3-(AsPh3)~ by itself mduces the polymerization of phenylacetylenes.

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