Phase Separation Induced by a Chain Polymerization: Polysulfone-Modified Epoxy /Anhydride Systems P. A. OYANGUREN, 1 C. C. RICCARDI, 1 R. J. J. WILLIAMS, 1 I. MONDRAGON 2 1 Institute of Materials Science and Technology ( INTEMA ) , University of Mar del Plata and National Research Council (CONICET), J.B. Justo 4302, 7600 Mar del Plata, Argentina 2 Departamento de Ingenierı B a Quı B mica y del Medio Ambiente, Escuela Universitaria de Ingenierı B a Te ´cnica Industrial, Universidad del Paı B s Vasco / Euskal Herriko Unibertsitatea, Avda Felipe IV, 1B, 20011 San Sebastia ´n/Donostia, Espan ˜a Received 3 July 1997; revised 31 October 1997; accepted 9 December 1997 ABSTRACT: The reaction-induced phase separation in a blend of a commercial polysul- fone ( PSu ) with diepoxide-cyclic anhydride monomers, was studied. The diepoxide was based on diglycidylether of bisphenol A ( DGEBA ) and the hardener was methyl tetrahy- drophthalic anhydride ( MTHPA ) , used in stoichiometric proportion. Benzyldimethy- lamine (BDMA) was used as initiator. PSu had no influence on the polymerization kinetics, the gel conversion, and the overall heat of reaction per epoxy equivalent. A kinetic model including initiation, propagation, and termination steps was used to estimate the distribution of linear and branched species in the first stages of the chain- wise copolymerization. This distribution, together with the PSu distribution, were taken into account in a thermodynamic model of the blend. The interaction parameter was fitted from experimental determinations of conversions at the start of phase separa- tion, obtained under different conditions. The thermodynamic model was used to ex- plain the complex morphologies developed in materials containing different PSu concen- trations as well as their dynamic mechanical response. The shift in glass transition temperatures was explained by the fractionation of different species during the phase separation process. Phase inversion produced a significant decrease of the elastic modu- lus in the glassy state and a thermoplastic-like behavior of the material in the rubbery region.  1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1349–1359, 1998 Keywords: reaction-induced phase separation; polysulfone – epoxy blends; epoxy – an- hydride networks; polysulfone-modified epoxies INTRODUCTION cal examples of a reaction-induced phase separa- tion during a step polymerization. The reaction of diepoxides with cyclic anhydrides Studies on thermoset / thermoplastic blends have constitutes an example of network formation increased significantly since the middle of the through a chain-wise polymerization. A kinetic 1980s. Several engineering thermoplastics associ- model for these systems has been recently pro- ated with different thermosetting polymers have posed. 1 Based on this model, a thermodynamic de- been investigated. But, for the most part, high-T g scription of phase separation in thermoplastic-mod- epoxy systems based on di-, tri-, or tetrafunctional ified epoxies cured with anhydrides, will be devel- epoxides, cured with aromatic diamines, have oped to explain the morphologies generated and the been selected due to their extended use in ad- dynamic mechanical properties of the resulting ma- vanced composites. These systems represent typi- terials. The selected thermoplastic was a polysul- fone ( PSu ) , due to its convenient solubility with epoxy monomers and the existence of several stud- Correspondence to: R. J. J. Williams ies, 2–13 reporting an increase in the fracture tough- Journal of Polymer Science: Part B: Polymer Physics, Vol. 36, 1349–1359 (1998)  1998 John Wiley & Sons, Inc. CCC 0887-6266/98 / 081349-11 ness of PSu-modified epoxy – amine systems. 1349 8Q5A 7005 / 8Q5A$$7005 04-02-98 15:51:42 polpal W: Poly Physics