Gradient interphase between reactive epoxy and glassy thermoplastic from dissolution process, reaction kinetics, and phase separation thermodynamics

Planar interfaces have been prepared by assembling high-jr, thermoplastics such as poly(phenylene ether) (PPE) or poly(ether imide) (PEI) and epoxy-am ine networks at different conversions of the epoxy groups, X-e, followed by a complete curing. Direct evidence of the structure of the interfacial reg ions was made by means of electron microscopies, SEM and TEM, and atomic fo rce microscopy, after a complete curing of the epoxy-amine. The morphologie s of the interfaces are explained from the competition between the dissolut ion process of a thermoplastic by nonreactive solvent and the thermodynamic s and the kinetics of reactive epoxy-amine/thermoplastic system. If the pha se diagram indicates that the epoxy-amine/thermoplastic system is nonmiscib le, the interface remains very thin (< 20 nm). in the opposite, a gap range of miscibility controlled by the polymerization rate allows a diffusion of the comonomers into the thermoplastic layer and its further dissolution. A s a consequence, 100-400 <mu>m thick interphases can be generated. A gradie nt morphology results from the gradient composition at phase separation. Th e gradient composition or concentration profile is shown to depend on the t ype of dissolution process that is mainly determined by the competition bet ween the thermodynamic osmotic pressure and the swelling resistance of the thermoplastic.