TOUGHENING OF A TRIFUNCTIONAL EPOXY SYSTEM .1. NEAR-INFRARED SPECTROSCOPY STUDY OF HOMOPOLYMER CURE

The cure mechanism of a trifunctional epoxy resin with an amine cataly st has been studied using near infra-red spectroscopy. The concentrati ons of primary and secondary amine and epoxide groups have been monito red directly as a function of cure by the use of this technique. This was compared to thermal analysis of the cure process at a range of cur e temperatures by d.s.c. The conversion of the various functional grou ps and the increase in the glass transition temperature was found to b e uniquely determined by the degree of cure and unaffected by cure tem perature. The primary amines were found to be largely reacted by gelat ion, followed by the commencement of the secondary amine reaction. By monitoring hydroxyl production it was possible to determine the degree to which side reactions (reactions other than the main epoxy/amine re action) occurred. These side reactions, such as etherification, occurr ed at conversion values above gelation and become prominent at high le vels of crosslinking when the reactive functionalities become strongly diffusion controlled and their movement sterically hindered. At these high conversions unreacted secondary amines become trapped in the gla ssy network and these groups may result in disadvantageous properties of the final material.