Conformation of arborescent polymers in solution by small-angle neutron scattering: Segment density and core - Shell morphology

Abstract

The radius of gyration (Rg) was determined as a function of generation number for arborescent polystyrenes with two different side chain mass average molecular mass (Mw ≈5000, 5K, versus 30 000, 30K) by small-angle neutron scattering (SANS) measurements. The Rg values obtained were analyzed in terms of the Zimm-Stockmayer model for randomly branched polymers, the scaling relation Rg ∝Mwv", and the expansion factor αs = (R g)goodsolvent/(Rg)⊖solvent.. The Rg and scaling exponent v = 0.26 ± 0.01 found for G0 through G3 polymers with 5K side chains in cyclohexane-d correspond to the values predicted by the Zimm-Stockmayer model. The Rg for G0 through G3 polymers with 30K side chains deviate from the model with v = 0.32 ± 0.02, corresponding to v = 0.33 expected for hard spheres. Deuterated polystyrene (PS-d) side chains were grafted onto G2 and G3 polystyrene (PS) cores. These copolymers, G2PS-graft-PS-d and G3PS-gra/f-PS-d, were characterized as spheres with a well-defined PS core-PS-d shell structure by the SANS contrast matching method. The shape and the segment radial density profile of the core and shell for GPS-graft-PS-d were determined based on P(r) and Δρ(r) obtained by indirect Fourier transformation and deconvolution methods (P(r), pair distance distribution function and Δ ρ(r) = ρ(r) - ρ(solvent), scattering length density contrast profile). © 2008 American Chemical Society.