Core-shell particles designed for toughening epoxy resins. I. Preparation and characterization of core-shell particles

A two-stage, multistep soapless emulsion polymerization was employed to prepare various sizes of reactive core-shell particles ( CSPs) with butyl acrylate (BA) as the core and methyl methacrylate (MMA) copolymerizing with various concentrations of glycidyl methacrylate (GMA) as the shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink: either the core or shell. The number of epoxy groups in a particle of the prepared CSP measured by chemical titration was close to the calculated value based on the assumption that the added GMA participated in the entire polymerization unless it was higher than 29 mol So. Similar results were also found for their solid-state C-13-NMR spectroscopy. The MMA/GMA copolymerized and EGDMA-crosslinked shell of the CSP had a maximum glass transition temperature (T-g) of 140 degrees C, which was decreased with the content of GMA at a rate of - 1 degrees C/mol %. However, the shell without crosslinking had a maximum T-g of 127 degrees C, which decreased at a rate of -0.83 degrees C/mol %. The T-g of the interphasial region between the core and shell was 65 degrees C, which was invariant with the design variables. The T-g of the BA core was -43 degrees C, but it could be increased to -35 degrees C by crosslinking with EGDMA. The T-g values of the core and shell were also invariant with the size of the CSP. (C) 1998 John Wiley & Sons, Inc.