Douglas R. Swanson

Partial shell-filled core-shell tecto(dendrimers): A strategy to surface differentiated nano-clefts and cusps

Poly(amidoamine) (PAMAM) dendrimer shell reagents possessing either nucleophilic (i.e., primary amines) or electrophilic (i.e., carboxymethyl esters) functional groups have been covalently assembled around appropriate electrophilic or nucleophilic dendrimer core reagents to produce partial shell filled/core-shell tecto(dendrimers). Partial shell-filled products with saturation levels ranging from 28% to 66% were obtained. These metastable, remarkably monodispersed assemblies possess functionally differentiated nano-cusps and clefts that exhibit “autoreactive” behavior. Pacification of these autoreactive products with appropriate alkanolamine reagents produced robust, nonreactive, “hydroxy-amine-differentiated” surfaces that exhibit very active self-assembly properties. Based on the monodispersity, dimensional scaling, and electrophoretic similarities of PAMAM dendrimers to globular proteins, these assemblies may be viewed as crude biomimetics of classical core shell-type protein aggregates. These dimensionally larger, but analogous PAMAM core-shell tecto(dendrimer) architectures extend and complete a similar pattern of autoreactivity and pacification that was observed earlier for traditional mono PAMAM dendrimer core-shell modules possessing unsaturated shell levels.

Unique steric and geometry induced stoichiometries observed in the divergent synthesis of poly(ester-acrylate/amine) (PEA) dendrimers

This work describes the Michael addition of unprotected, branched, (A)x-type acrylate monomers (i.e., trimethylolpropane triacrylate (TMPTA); x = 3 or pentaerythritol tetraacrylate (PTA); x = 4) to various mono- and poly-alkyleneamine cores under mild conditions to produce (core: amine); G = 1; [dendri-poly(ester-acrylate)z]; (PEA) type dendrimers in one step. Quite remarkably, this strategy did not necessitate large excess reagent protocols as required for traditional Tomalia-type poly(amidoamine) (PAMAM) dendrimer syntheses, yet produced relatively little oligomeric/polymeric side product. Ideal, mathematically predictable dendrimer structures were obtained in high yield with only modest excesses (i.e., 4.0 moles of monomer/core-NH); whereas, at lower ratios (i.e., 0.5–2.0 moles of monomer/core-NH), non-ideal, geometrically controlled dendrimers possessing, macrocyclic (looped) structures (i.e., geometrically induced stoichiometry (GIS)) were formed when adequate reactivity space was available on the amine scaffolding. However, when amine core reaction sites became highly congested, one observed the formation of well defined, non-ideal dendrimers exhibiting sterically induced stoichiometries (SIS). It is postulated that Michael addition of these nanoscale (i.e., 1–1.5 nm) branched (A)x monomers onto these sub-nanosized linear-α,ω-alkylenediamine or poly(alkyleneamine) scaffoldings produces a highly congested reaction environment even at this early generational state (i.e., G = 1). The observed products appear to be influenced and directed by these consequential steric and geometric space constraints.

Dendritic Macromolecules: A Fourth Major Class of Polymer Architecture – New Properties Driven by Architecture

This new architectural class of macromolecules has received substantial attention during the past decade. Three dendritic subclasses, which include (a) random hyperbranched (i.e., one-pot AB x , polymerizations), (b) dendritic grafted (i.e., Combburst® polymers) and (c) regular dendrons/dendrimers (e.g., Starburst® dendrimers) have been synthesized and characterized at a well-defined level in our laboratory. It is clear that their precisely controlled, nanoscale dimensions and architecture play critical roles in influencing physical properties and performance characteristics. Furthermore, these parameters have also distinguished dendrimers as fundamental modules for many nanotechnology applications, as well as for the construction of a new class of larger nanoscale entities which we have termed core-shell tecto(dendrimers) . This account will overview these activities and focus on certain unique de Gennes dense packing (or congestion phenomena) and nanoscale container properties that have emerged from this novel architecture.