Control of the Urethane Cure Reaction with Solid, Blocked Isocyanates

摘要

The objectives of this program were to demonstrate that solid, blocked isocyanates could control the urethane cure reaction by providing indefinite potlife below the melting point of the solid, and a rapid, controllable cure above the melting point. More generally, the approach addressed the question of differences in reactivity of molecules in solution and in the solid state. The relationship of melting temperature, solubility in the binder and particle size of the blocked isocyanate as it relates to polyurethane chemistry was also investigated. This program was divided into three tasks. Tasks 1 was concerned with synthesizing a group of solid, blocked isocyanates with various melting temperatures, and preparing a catalog of cure agents/ 'trigger' temperatures. The crystallinity of the compounds was also determined. In Task 2 the solid, blocked isocyanates were examined by infrared spectroscopy, and the solubility of candidate compounds in common urethane forming polymers and plasticizers was investigated. In Task 3 cure studies were performed, and the effect of particle size, catalysts and temperature on cure time and quality was investigated. Several solid, blocked isocyanates were evaluated in common liner and propellant formulations.