Investigation of Thermal Properties of Polyureas

Thermal properties of more than 20 different polyureas intended for the use as protective varnish for printed-circuit boards have been studied. Rate and completeness of the polyureas decomposition as well as their solubility in common solvents have been analyzed. It has been shown that the polyureas synthesized from branched diisocyanates, for example, isophorone diisocyanate or 1,3-bis-(isocyanatomethyl)cyclohexane, and diamines (N,N′-dialkylethylene and propylenediamine) are prone to fast and complete decomposition at relatively low temperature. For instance, the polymer formed via the reaction between piperazine and isophorone diisocyanate has been completely decomposed at 400°C within 1 min, whereas degree of decomposition of the polymer obtained from piperazine and hexamethylene diisocyanate has been as low as 31% under the same conditions. The relationship between the completeness of the polyureas decomposition and the shape of their thermogravimetric analysis curves has been stated.