Efficient Divergent Synthesis of Dendronized Polymers with Extremely High Molecular Weight:  Structural Characterization by SEC-MALLS and SFM and Novel Organic Gelation Behavior

High molecular weight poly(p-hydroxystyrene) (PHS) was dendronized in high yield by the divergent grafting of aliphatic polyester dendrons using acetal and ketal protected anhydride derivatives of bis(hydroxymethyl)propionic acid. Relatively low polydispersities (PDI = 1.1-1.3) were maintained throughout the dendronization process. Detailed characterization of a series of these polymers by size exclusion chromatography (SEC) and SEC with multi-angle laser light scattering (SEC-MALLS) clearly shows the effect of dendron steric bulk on the persistence length (ξ) of the polymer main chain in solution. As a result of the fixed degree of polymerization (DP), the main chain rigidification that accompanies lateral dendron growth causes an unusual relationship between Rg,z and molecular weight across a series of generations. The rodlike structure and contour length of the alkylated dendronized polymers was also characterized by scanning force microscopy (SFM) on mica, highly oriented pyrolytic graphite (HOPG), and molybdenum disulfide (MoS2) surfaces. One of the G3 dendronized polymers with an alkylated periphery showed significant physical gelation behavior at concentrations below 1 wt % in several organic solvents, which constitutes additional evidence that the solution phase rigidity of a polymer chain can be enhanced by dendronization.