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The homopolymers of tetrahydrofuran, polytetramethylene glycols, may be chain‐extended to form polyurethane elastomers. These materials, while possessing a low glass point temperature, suffer from cold hardening, and it was decided to investigate copolymers of tetrahydrofuran and propylene oxide as elastomer ingredients. The preparation of these copolymers has been achieved by use of a boron trifluoride etherate polymerization catalyst. Details are given of the properties of both the copolymer and derived elastomers at nominal compositions in the range 50–85 wt.‐% of tetrahydrofuran. The copolymers described were synthesized as ingredients for castable elastomers, and in consequence viscosity effects are important. It has been found that no significant increase in viscosity occurs until the tetrahydrofuran content exceeds 75 wt.‐%. This indicates that each side methyl group exerts a screening effect over an average of 13 atoms of the polymer backbones. The mechanical testing of the derived elastomers indicates that the copolymerization of tetrahydrofuran and propylene oxide leads to material possessing a low glass point temperature and much better physical properties than the homopolymer of propylene oxide. The elastic properties of a chain‐extended diol are dependent on the degree of crosslinking and on the incidence of network deficiencies. Network deficiencies are caused by the presence of monofunctional species in the copolymeric diols, and a novel technique for determining diol monofunctionality based on analysis of physical test data was evolved for these studies.

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The use of trioxygen difluoride (O3F 2 ), a metastable compound of oxygen and fluorine, has been proposed as an additive to render liquid oxygen (LO 2 ) hypergolic with a wide range of fuels. The prime aim of the work reported was to determine the environmental limits of reliable hypergolic ignition of LO 2 : OsF 2 with liquid and gaseous hydrogen (LH2 and GH2). The results indicate that hypergolicity of OzFz is associated with its thermal decomposition, which contributes to the formation of reactive radicals. A significant dependence of ignition delay on the time-averaged weight ratio of oxidant to fuel (O/F) was found for all injector types. It is believed that the experimental results provide the engineering background necessary for any future consideration of scale-up to larger rocket engines. This study has shown that rather critical requirements must be met if satisfactory ignition is to be achieved; hence, OsF 2 is not a simple panacea for eliminating ignition or combustion problems in rocket systems that use LO 2 . Included is a review of the advantages and disadvantages of using LO 2 : O^Fz from the standpoint of the project engineer. NomenclatureF = total integrated flow of fuel up to ignition time, Ib g -gravity, ft/sec 2 / = ion-probe channel L* = chamber volume/nozzle-throat area, in. 0 = total integrated flow of oxidizer up to ignition time, Ib O/F = oxidizer-fuel mass flow rate ratio O/F = mass ratio of the total integrated oxidizer-fuel flow to the combustor up to the time of ignition P = pressure, psi S = area, ft 2 t = time, sec T = absolute temperature, °K V = velocity, fps Z = height, ft p = density, lb/ft 3 Subscripts C = combustor hardware IH, IO = hydrogen injector and oxygen injector, respectively

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