Hydrodynamic size and scaling relations for linear and 4 arm star PVAc studied using PGSE NMR

In this work the hydrodynamic radius and scaling relations of linear and 4 arm polyvinyl acetate (PVAc) were calculated from self-diffusion measurements. Self-diffusion coefficients at infinite dilution were estimated from measurements of self-diffusion at 25 degrees C in deuterated chloroform and in the dilute regime using pulsed gradient spin-echo (PGSE) nuclear magnetic resonance (NMR). Scaling laws were observed but unexpectedly these star polymers showed slightly larger hydrodynamic radii than the linear equivalents. Hydrodynamic radii were calculated for different Perrin or shape factors (i.e. spherical, cylindrical and ellipsoidal), and the equivalent hydrodynamic radii for the cylinders and ellipsoids were compared to those obtained for a spherical shaped molecule. These were also compared to an approximate equivalent hydrodynamic radius estimated using approximate dimensions of the polymers at maximum extension for the cylinder/ellipsoid molecular shapes. Results for cylinder and ellipsoid shapes were almost identical for the same aspect ratios as expected. (C) 2010 Elsevier B.V. All rights reserved.