Small-angle neutron scattering of blends of arborescent polystyrenes

Small-angle neutron scattering (SANS) was used to measure the size and shape of styrene-based arborescent polymers blended with linear deuterated polystyrene (d-PS) and linear deuterated poly(vinyl methyl ether) (d-PVME). For generation 0, 1, and 2 arborescent polymers, the Rg were essentially equivalent in going from d-PVME to d-PS as the matrix material while for generation 3 (G3) the Rg in d-PS was found to be smaller than in d-PVME. For comparison, the Rg of a sphere was calculated assuming the size of the sphere was equivalent to a G3 molecule collapsed to bulk density. The Rg obtained was 162 angstroms, which is quite close to the Rg of the G3 polymer in d-PS (Rg = 164 angstroms). This indicates that the G3 molecules should behave as essentially noninterpenetrating spheres with the linear d-PS matrix chains being largely excluded from the interior of the arborescent molecules. In the single phase region of the phase diagram it was difficult to establish a clear temperature dependence of the Rg for the generation 0, 1, and 2 molecules in d-PVME. For the G3 molecules in d-PVME a small decrease in Rg with increasing temperature was observed in the single phase region with an abrupt decrease of 21% on phase separation between 110 and 115 °C. The single particle form factor of arborescent polymers in blends was studied using a power law model for the density profile. In comparison with a hard sphere or a shell model, the scattering function calculated from the power law function for the density profile provided the best fit to the experimental scattering data.