The objective of this three year program is the synthesis, formulation, and evaluation of FASIL fluoroalkylarylene-siloxanylene copolymers as curing and non-curing seals for fuel containment in high performance aircraft. This portion of the program was concerned primarily with the synthesis of monomers but a brief examination of selected polymerization systems was also conducted. Polymers containing the silphenylene structure have attracted the attention of a number of workers over the past twenty years because their thermooxidative stability is superior to that of Me2SiOx. Copolymers of silphenylenes and dimethylpolysiloxanes were envisioned as materials possibly possessing the desirable properties of both parent systems and this was realized to a certain extent. Thus incorporating silphenylene units into polydimethylsiloxane decreases the tendency to split out cyclic oligomers in a hot environment but raises the Tg because silphenylene tends to be crystalline.