Particles with a copolymer soft core of poly(n-butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) and a homopolymer hard shell of PMMA were characterized using transmission electron microscopy and solid-state NMR spectroscopy. Two synthesis parameters were investigated: (1) the phase ratio of the core and the shell and (2) the compatibility of the two phases. A series of core-to-shell ratios from 100/0 to 25/75 were synthesized and characterized. The compatibility between the phases was changed (1) by using acrylic acid in either the core and the shell or in both, (2) by synthesizing a homopolymer or a copolymer core or (3) by introducing crosslinking points in the core. The combination of transmission electron microscopy and solid-state NMR spectroscopy allows quantitative determination of the extent of coverage of the core by the shell polymer and the interphase thickness; both were found to depend on the shell content and the compatibility of the phases.
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Kirsch et al. (1999) studied this question.