A thermodynamic simulation of the phase separation process in a modified thermosetting polymer was carried out. The polydispersity of the generated polymeric species was taken into account in the frame of a conventional Flory-Huggins equation. The example considered in the simulation was a diglycidyl ether of bisphenol-A (DGEBA)-ethylenediamine (EDA), epoxy-amine polymer, modified by the addition of 15 wt% castor oil (monodisperse modifier). The size increase of the oligomeric species and the corresponding decrease of the entropic contribution to the free energy of mixing made a modifier-rich phase (B-phase) segregate from the matrix (a-phase) at a particular conversion level. The B-phase is enriched in monomers and low-molecular-weight species of the polymer distribution. This produces a significant decrease of the B-phase conversion with respect to the overall conversion. The monomer with the smaller size and functionality is preferentially segregated into the B-phase, leading to a stoichiometric imbalance. When a semipermeable B-phase is assumed, i.e. no oligomeric species are allowed to transfer to the or-phase, a secondary phase separation inside the B-phase is generated. This leads to a sub-matrix (6-phase) which is rich in modifier, and a sub-segregated phase (),-phase) which is rich in thermosetting polymer. This process may continue well beyond the gelation of the a-phase, due to the low conversion level of the B-phase at the time the or-phase gels. The thermodynamic simulation explains some recent experimental observations in systems of commercial interest.
Посилання на статтю:
Thermodynamic analysis of phase separation in rubber-modified thermosetting polymers: influence of the reactive polymer polydispersity / Carmen C. Riccardi, Julio Borrajo and Roberto J. J. Williams // Polymer. – 1994. – Vol 35. – P. 5541-5550.