Distribution of End Groups within a Dendritic Structure: A SANS Study Including Contrast Variation

Abstract

We present an analysis of the distribution of end groups within a urea-functionalized poly(propyleneamine) dendrimer of the fourth generation by small-angle neutron scattering (SANS). The phenyl end groups have been deuterated to enhance their contrast. The SANS experiments are performed using solution of the labeled dendrimer in mixtures of protonated and deuterated dimethylacetamide (DMA). In this way the contrast between the solute and the solvent is varied in a systematic fashion (contrast variation). The analysis presented here gives three partial scattering functions that depend differently on contrast. From these data, the scattering length density within the dendritic structure can be derived. All results show that the end groups are dispersed throughout the dendrimer with a broad maximum located at a radial distance that corresponds to ca. half of the overall size of the molecule. Hence, there is no well-defined surface of a dendritic structure defined by the end groups, but the end groups are mo...