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1H, 19F and 11B nuclear magnetic resonance characterization of BF3: amine catalysts used in the cure of C fibre-epoxy prepregs

1985; Elsevier BV; Volume: 26; Issue: 6 Linguagem: Inglês

10.1016/0032-3861(85)90124-7

1873-2291

James A. Happe, Roger J. Morgan, Connie M. Walkup,

Fiber-reinforced polymer composites

1H, 19F and 11B nuclear magnetic resonance studies are reported which characterize the complexes of boron trifluoride with monoethylamine and with piperidine, BF3:NH2C2H5 and BF3:NHC5H10, respectively. These complexes are used as catalysts for the cure of high performance C fibre-epoxy composities from prepregs. The chemical compositions of commercial BF3:amine complexes are variable and contain BF4− and BF3(OH)− salts together with other unidentified highly reactive species. The BF3:amine complexes, which are susceptible to hydrolysis, also partially convert to the BF4− salt (i.e. BF4−NH3+C2H5) upon heating. This salt formation is accelerated in dimethyl sulphoxide solution and in the presence of the epoxides that are present in commercial prepregs. Commercial C fibre-epoxy prepregs are shown to contain either BF3:NH2C2H5 or BF3:NHC5H10 species together with their BF4− salts and a variety of boron-fluorine or carbon-fluorine prepreg species. Considerable variation in the relative quantities of BF3:amine to its BF4− salt was observed from prepreg lot to lot, which will cause variable viscosity-time-temperature prepreg cure profiles. It is concluded that the chemically stable and mobile BF4− salt is the predominant catalytic species, acting as a cationic catalyst for the prepreg cure reactions. During the early stages of cure the BF3:amine catalysts convert to the BF4− salts in the presence of epoxides, whereas the BF3-prepreg species are susceptible to catalytic deactivation and immobilization.