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

摘要

The radius of gyration (R-g) was determined as a function of generation number for arborescent polystyrenes with two different side chain mass average molecular mass (M-w approximate to 5000, 5K, versus 30 000, 30K) by small-angle neutron scattering (SANS) measurements. The R-g values obtained were analyzed in terms of the Zimm-Stockmayer model for randomly branched polymers, the scaling relation R-g proportional to M-w(v), and the expansion factor alpha(s) = (R-g)(goodsolvent)/(R-g)(Theta solvent). The R-g 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 R-g for GO 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-graft-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 Delta rho(r) obtained by indirect Fourier transformation and deconvolution methods (P(r), pair distance distribution function and Delta rho(r) = rho(r) - rho(solvent), scattering length density contrast profile).