Commercially available fourth and fifth generation poly(propyleneimine) (PPI) dendrimers were functionalized with acetyl chloride and deuterated acetyl chloride. Their solution properties in water and D2O were measured with dilution viscometry, densitometry, rheology, and small‐angle neutron scattering (SANS) and compared to molecular modeling. Both the acetylated and PPI dendrimers exhibited Newtonian rheology in solution at all concentrations, but the functionalized dendrimers were less viscous than the nonacetylated dendrimers at an equal weight fraction (50 wt %). The acetylated dendrimers exhibited a pronounced structure peak in SANS, however, that was not evident for PPI in solution and a greatly enhanced solubility. This structure peak, evident at concentrations as low as 0.2 wt %, was evidence for long‐range electrostatic interdendrimer forces, which were screened by added salt. A quantitative agreement was obtained between the dilute‐limiting absolute scattering spectra of both the nonacetylated and acetylated dendrimers in solution with model calculations via a homogeneous spherical model and input parameters independently obtained from dilution viscometry or direct calculation. The combined measurements verified significant solvent penetration for both dendrimer types. The form factors measured in this manner were also in good quantitative agreement with the results of molecular dynamics simulations, which pointed to significant backfolding of the terminal groups. SANS and rheology measurements at higher concentrations suggested dendrimer clustering and interpenetration with increasing concentration, leading to less structure and lower viscosity than would be predicted from the dilute‐limiting behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 857–873, 2000

The effect of adding acetylated poly(propyleneimine) dendrimers to the structure and rheology of aqueous solutions of high molecular weight poly(ethylene oxide) (PEO) was investigated by rheology and small‐angle neutron scattering in a temperature range of 10–40 °C. In the semidilute regime, the steady shear rheology of PEO solutions was unmodified by the addition of dendrimers at a comparable weight concentration. At the highest concentrations studied, the addition of acetylated dendrimers suppressed the onset of a low‐frequency elastic modulus at the lowest temperature investigated. For comparison, the addition of PEO of a comparable molecular weight at the same weight fraction resulted in a milder suppression but, unlike the dendrimers, greatly increased the solution viscosity. The addition of acetylated dendrimers to a semidilute PEO solution at 10 °C substantially reduced the solution turbidity. These effects on the rheology and optical properties were confirmed by small‐angle neutron scattering measurements of the molecular structure of the mixture. Additional SANS measurements in the dilute regime (0.1 wt % PEO) showed quantitatively that the dendrimers decorated the PEO chains in a necklace structure, such as that observed previously for micelles. The results suggested a mechanism of rheology modification whereby the dendrimers disrupted the association network structure in the PEO solution at lower temperatures by preferentially associating with the PEO chains in solution. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 874–882, 2000