Blends of epoxy/anhydride thermosets with a high-molar-mass poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA, M-n = 232 000) was used to modify a stoich iometric epoxy (diglycidyl ether of bisphenol A; DGEBA)-anhydride (methyl t etrahydrophthalic anhydride; MTHPA) thermoset. PMMA concentrations in the r ange 3-7wt% led to morphologies consisting of a continuous PMMA-rich region that appeared rough and striated in scanning electron micrographs and larg e domains of the thermoset exhibiting a dispersion of PMMA-rich particles i n the micrometre range. These morphologies are the result of the critical p oint location, estimated at 2.1wt% PMMA as a result of the high molar mass of the additive. A 5 wt% PMMA led to an increase of the stress intensity fa ctor K-IC from 0.65 MPa m(1/2), for the neat thermoset, to 0.94 MPa m(1/2). However, T-g was reduced from 117 degrees C for the neat thermoset to abou t 105 degrees C for the PMMA-modified material. The T-g decrease is ascribe d to the differential segregation of both monomers to the PMMA-rich phase. No influence of PMMA addition on the cure kinetics was observed. An upper c ritical solution temperature was observed, meaning that cloud-point convers ions increased with cure temperature. Phase separation took place before ge lation in the temperature range investigated in this study. (C) 1999 Societ y of Chemical Industry.