Fluorescence probes for investigation of epoxy systems and monitoring of crosslinking processes

The fluorescence behavior of 1,1'-dimethyl-2,2'-carbocyanine and p-N,N-dime thylamino-styryl-2-ethylpyridinium was investigated in several epoxy system s. Time-correlated single photon counting was used for all fluorescence mea surements to obtain the rate constant for viscosity or mobility-dependent n onradiative processes of the probe. Microviscosity effects were discussed o n the basis of a model describing the microfriction between matrix and prob e molecules. The probes investigated are able to detect the glass-transitio n temperature of the materials investigated. These compounds also show a de pendence on the mobility in the glassy state. The probes applied in this wo rk also can be used to monitor the crosslinking process of several epoxy sy stems containing 4,4'-diaminodiphenylmethane (DDM) as curing agent. The epo xides used for the crosslinking process were 2,2'- [(1-methylethylidene)bis (4,1-phenyleneoxymethylene)bis-oxiranemethaneamine] [common name, diglycidy l ether of bisphenol A (DGEBA)], N-oxiranylmethyl-N-phenyl-oxiranylmethane [common name, diglycidyl aniline (DGA)], and epoxy novolacs of different fu nctionality. The networks obtained have a different morphology, which was s tudied by the fluorescence probe technology. The structure of the epoxy com pound has an important influence on the probe behavior because both network density and size of the free volume influence the photochemical behavior o f the probe. (C) 1999 John Wiley & Sons, Inc.