Quantitative determination of dynamic heterogeneities in core-shell latices by H-1 solid-state NMR

Solid-state H-1 NMR dipolar filter experiments an used to quantify the dyna mic heterogeneities in different core-shell latex systems. An adjustable di polar filter is used to destroy selectively the magnetization of rigid regi ons and to retain that in more mobile regional analogous to the classical G oldman-Shen NMR experiment. The subsequent application of filters with incr easing strength yields a characteristic decay curve for each sample. The di stribution of pure and mixed phases can then be determined by comparing the data with a linear superposition of the data from the pure substances. The system of interest consists of a three-stage emulsion polymer with three d ifferent layers. The core and the outer shell consist primarily of poly(met hyl methacrylate) (PMMA), and the inner shell consists of a copolymer (poly (butyl acrylate)/polystyrene; PBuA/PS). The overall morphology of the phase s is onion-like as determined by transmission electron microscopy. Only the core of the latex was found to contain pure phases, whereas the two shells showed mixed phases. It was found that the amount of interface exceeds 50% of the entire particle.