Small-angle neutron scattering of solutions of arborescent graft polystyrenes

Small-angle neutron scattering was used to measure the size and shape of arborescent graft polymers as a function of generation in solution. The radius of gyration of arborescent graft polymers was found to be almost independent of temperature in both deuterated cyclohexane (above the cloud point) and deuterated toluene. For dilute deuterated cyclohexane solutions the optically measured cloud point was found to be 15 +/- 1 degrees C. Two peaks were observed in the SANS data for the phase-separated (below the cloud point) deuterated cyclohexane solutions of the largest polymers (generation 3). The first peak (at smaller scattering vector) is attributed to the interference between molecules while the second peak arises from the single particle form factor which was also observed at temperatures above the cloud point. In deuterated cyclohexane the position of the form factor peak was constant at temperatures above 15 degrees C. In the phase-separated deuterated cyclohexane solutions the form factor peak shifted to higher q, indicating a fractional decrease in molecular diameter of about 15% upon phase separation. The spacing of the interference peak (at low q) in the phase-separated solutions was consistent with the molecules aggregating in clusters with little interpenetration of the molecules. A power law function was used to model the real space density profile from which scattering curves were calculated and compared to the experimental data. This power law functional form for the density profile gave fits with smaller deviations from the experimental data when compared to either a hard or hollow sphere model.