Abstract: A pressure release device for sealably mounting on a vessel adapted to contain a fluid under pressure not to exceed a predetermined maximum pressurization limit.

Abstract: A stable solution of an aromatic polyamic acid of controlled molecular weight, of the type capable of being converted to polyimides, which undergoes relatively little change in viscosity or gelling over extended periods of time at room temperature. Such solution may be prepared by reacting impure aromatic dianhydride with aromatic diamine in a suitable solvent where the ratio of active aromatic diamines is approximately equimolar. Such solution may also be prepared by a two step process which comprises:Step I-Reacting a dianhydride of high purity (99+%) with a diamine in a molar ratio of about 0.95/1 dianhydride/diamine to yield a viscosity below about 10,000 cps, for example from about 2,000 to 6,000 at about a 10-15% solution.Step II-Then adding to I about 0.05 mole of a less pure dianhydride such as from about 97-99% pure dianhydride to yield a 10-15% solution of polyamic acid having a viscosity of about 10,000 cps.