A Model System for the Thermodynamic Analysis of Reaction-Induced Phase Separation: Solutions of Polystyrene in Bifunctional Epoxy/Amine Monomers

ILEANA A. ZUCCHI; MARÍA J. GALANTE; JULIO BORRAJO; ROBERTO JJ WILLIAMS

MACROMOLECULAR CHEMISTRY AND PHYSICS

Wiley - VCH

Lugar: Weinhem; Año: 2004 p. 676 - 683

1022-1352

A model system consisting of a linear polymer dissolved in a bifunctional monomer/co-monomer solvent, was selected to test the applicability of the Flory- Huggins (FH) theory in the absence of usual assumptions present in the analysis of modified thermosetting polymers. Solutions of two almost monodisperse polystyrenes (PS, Mn = 83000 or 217000), in diglycidylether of bisphenol A (DGEBA), and in stoichiometric DGEBA/BA (benzylamine) solutions, exhibited an upper-critical-solution-temperature (UCST) behavior. Cloud-point curves (CPC) were fitted with the F-H model using an interaction parameter depending on both temperature and concentration, c = (a+b/T)/(1-cf2), where f2 represents the volume fraction of PS. A group-contribution method provided a reasonable explanation of the observed trends. Cloud-point times in the course of the DGEBA/BA stepwise polymerization, carried out at 70 ºC and 80 ºC, were determined for solutions containing 2.5 to 15 wt % PS ( Mn = 83000). Times were transformed to conversions using kinetic curves determined by Fourier-Transformed Infrared Spectroscopy (FTIR) and Size Exclusion Chromatography (SEC). The analysis of cloud-point conversions with the FH model was performed considering the (ideal) distribution of epoxy/amine species generated as a function of conversion. An empiric fitting of cloud-point curves was possible with the use of an interaction parameter decreasing with conversion. Possibilities of improving the thermodynamic description of a polymerization-induced phase separation, are discussed.