Web Release Date: December 12,
Conformation of Arborescent Polymers in Solution by Small-Angle Neutron Scattering: Segment Density and Core-Shell Morphology
and
Institute for Environmental Research, Australian Nuclear Science & Technology Organization, PMB 1, Menai, NSW 2234, Australia, Center for Neutron Scattering, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, Department of Chemistry, Institute for Polymer Research, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8541
Received September 19, 2007
Revised Manuscript Received November 12, 2007
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 
s = (Rg)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-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 
(r) obtained by indirect Fourier transformation and deconvolution methods (P(r), pair distance
distribution function and (r) = (r) - (solvent), scattering length density contrast profile).
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