A carbon-13 NMR characterization study of the core/shell latex particle interphase and an investigation of its role on the mechanical behavior of toughened PMMA

Toughening of brittle thermoplastics like poly(methyl methacrylate) (PMMA) can be achieved by incorporating particles which consist of radially alternating rubbery and glassy layers into the brittle matrix. Three layered core/shell latexes consisting of poly(divinylbenzene) (PDVB)/poly(butyl acrylate) (PBA)/poly(methyl methacrylate) (PMMA) were developed as toughening particles. The core/shell latex interphases, as well as the particle/matrix interphase have a considerable influence on the overall mechanical properties of the polymer composite. Two-layered PDVB/PBA and PBA/PMMA particles were synthesized for independent characterization and comparison with the three layered toughening particle.; Solid-state NMR was used to characterize the interphase of two layer PDVB/PBA and PBA/PMMA core/shell latex particles through measurement of spin-lattice relaxation times ( (H) T{dollar}sb1rho).{dollar} The PDVB core latex particles were synthesized by miniemulsion polymerization and the stage II butyl acrylate was added semicontinuously. The thickness and the amount of the interfacial PBA has been calculated from the (H) T{dollar}sb1rho{dollar} measurements by applying a model which was proposed for compatible blend systems. The thickness of the interphase of PDVB/PBA was calculated to be in the range of 5 to 7 nm.; A PMMA macromonomer was incorporated in the seed PBA latex using a miniemulsion process to compatibilize the seed polymer with the PMMA shell. Results from soap titration experiments and NMR relaxation studies revealed that the PMMA macromonomer predominantly partitions to the surface of the PBA latex. A PMMA shell was added to the uncompatibilized and compatibilized PBA seed latexes. The compatibilized latex had an interphase thickness in the range of 15 to 16 nm compared to the uncompatibilized core/shell latex which had a thickness of 10 to 11 nm.; Tensile and fracture properties of PMMA incorporating two-layer (PBA/PMMA with interphase thicknesses of 5-7 nm and 15-16 nm) or three-layer (PDVB/PBA/PMMA; PDVB/PBA interphase, 5-7 nm, and PBA/PMMA interphase, 15-16 nm) particles were compared. The fracture surface was examined with atomic force microscopy and scanning electron microscopy. It was found that composites prepared with three-layer particles had a higher fracture toughness compared to the two-layer particles, while those composites prepared with two-layer particles with a thicker interphase exhibited higher toughness values compared to ones with a thinner interphase thickness.