The Molecular Characteristics of Poly(propyleneimine) Dendrimers As Studied with Small-Angle Neutron Scattering, Viscosimetry, and Molecular Dynamics

Abstract

The molecular characteristics of the first five generations of poly(propyleneimine) dendrimers with two different types of end groups have been investigated using small-angle neutron scattering (SANS), viscosimetry, and molecular dynamics simulations. The dimension of the poly(propyleneimine) dendrimers, as measured by both SANS and viscosimetry, increases linearly with the generation number and roughly as M 1/3 , where M is the molar mass of the dendrimer. This relationship proves to be independent of the character of the end group and the solvent used and is indicative of a compact (space-filling) structure with a fractal dimensionality of approximately 3. The distinct maximum in the Kratky representation of the scattering data and the observed relation (i.e., R η = (5/3)R g ) between the hydrodynamic radius Rη and the radius of gyration Rg are consistent with such a structure. Molecular dynamics simulations for two different solvent qualities are in good accordance with the acquired experimental results. The probability distributions of the amine end groups, based on these simulations, exhibit a substantial degree of backfolding. The corresponding radial density distributions show a constant density plateau and a monotonic decrease of the density toward the exterior of the molecule. The above results indicate that the poly(propyleneimine) dendrimers can be considered as flexible molecules with a relatively homogeneous radial density distribution. This view clearly deviates from both the dense shell and dense core models.

Dynamics of star-burst dendrimers in solution in relation to their structural properties

“…Fractal dimensions of dendrimers have been a͒ Author to whom correspondence should be addressed. Electronic mail: s.rathgeber@fz-juelich.de evaluated by Murat and Grest 2 using molecular dynamics simulations as well as by Mansfield 3,4 5 and poly͑propyleneimine͒ dendrimers 6 seem to support the M ϳR g 3 scaling behavior. Most computer simulations seem to agree that the endgroups of a dendrimer are distributed throughout the molecule 2,3,[7][8][9] and are not located predominantly on the outside of the dendrimer, as was postulated by the theory of de Gennes and Hervet.…”

Z. Guan, Control of polymer topology through late‐transition‐metal catalysis, J Polym Sci Part A: Polym Chem (2003), 41(22), 3680–3692

“…A Kratky plot for the lowest pressure PE showed a peak. 66 To our knowledge, this phenomenon has only been observed for dendrimers, 72 not for hyperbranched polymers. The intrinsic viscosity of the PE made at 0.1 atm was only one-eighth of the value for polypropylene of a comparable molecular weight.…”

Thermoresponsive hyperbranched polyethylenimines with isobutyramide functional groups

“…12 The LCST for PAMAM and PPI terminated with IBAm groups dropped around 15 8C and 4 8C, respectively, with increasing one generation, and PPI terminated with IBAm groups exhibited much lower LCST compared with PAMAM terminated with the same number of IBAm groups. This phenomenon was explained as follows: The PPI dendrimer was much smaller than the PAMAM dendrimer with the same number of the chain ends, 29,30 thus, PPI dendrimer had higher density of the peripheral IBAm groups and stronger interaction between the IBAm groups, leading to efficient dehydra- tion at the relatively low-temperature region. As far as structure was concerned, HPEI was much similar to PPI.…”