Dendrimers in Solution: Insight from Theory and Simulation

Abstract

A variety of experimental and theoretical approaches show that, akin to linear polymers, dendrimers in good solvent conditions are best described as flexible macromolecular aggregates with a dense core and fluctuating monomer groups. We present theoretical and simulational evidence of how the shape and inner structure of dendrimers depends on the generation number as well as the effective interactions that exist between dendrimers in solution. These approaches based on simplified dendritic structures show there is a tunable and ultrasoft interaction between the centers of the solublized dendrimers. Results from small-angle neutron scattering data confirm the theory and indicate that dendrimers are model systems of ultrasoft colloids that bridge the gap between polymers and hard spheres. Dendrimers can form a class of materials analogous to the related systems of star polymers and block copolymer micelles which exhibit special properties.

Synthetic regimes due to packing constraints in dendritic molecules confirmed by labelling experiments

“…In turn, these last two features enable the theoretical analysis of the labelling data of the homologous series of DP in order to quantify the number of defects for different g. As we shall discuss, the number of defects increases significantly for 1,000 PG6 thus suggesting the onset of SIS in the vicinity of g max . Importantly, the effects are evident only in the long 1,000 PGg but not in the short 45 PGg. This supports the SIS interpretation as defect accumulation due to imperfect reaction conversion should affect all DP irrespective of N. In contrast, SIS effects in the g range explored are envisioned only in long, locally cylindrical DP because of their lower g max .…”

“…Importantly, the observed deviations occur only for the locally cylindrical 1,000 PGg series. There are no comparable effects for the 45 PGg homologous series, which exhibit ideal DP behaviour as specified by equation (4). This is an important observation supporting the interpretation of the data in terms of g max -related SIS effects.…”

“…We investigated two homologous series differing in the polymerization degree of the backbone, N: long DP of NE1,000 ( 1,000 PGg) and short DP with NE45 ( 45 PGg). The 1,000 PG1... 1,000 PG5 series was reported already 48 , while the 1,000 PG6 and the 45 PG1... 45 PG6 series are new (Methods). As we shall discuss, the differences between the two have a key role in identifying the g max effects and the onset of SIS.…”

“…This supports the SIS interpretation as defect accumulation due to imperfect reaction conversion should affect all DP irrespective of N. In contrast, SIS effects in the g range explored are envisioned only in long, locally cylindrical DP because of their lower g max . They are not expected in the 45 PGg series because of their higher g max arising since short DP adopts a dendrimer-like, near spherical, shape traceable to backbone end effects.…”

“…This is experimentally challenging because the performance of standard characterization techniques, such as nuclear magnetic resonance (NMR) [39][40][41] , mass spectrometry (MS) 39 and gel permeation chromatography (GPC) 42,43 , attain their limits at high g and high MM. While scattering techniques provide information about the dimensions of the dendritic molecules and their density profiles they are not sensitive to branching defects 44,45 . On the theory side, computer simulations probed the onset of dense packing in perfect dendritic molecules by monitoring properties such as bond strain and equilibration rates 38,46,47 .…”