Synthesis of an anionically chargeable, high-molar-mass, second-generation dendronized polymer and the observation of branching by scanning force microscopy

An efficient synthesis of a methacrylate-based, second-generation (G2) dendronized macromonomer and its free radical polymerization to the corresponding high-molar-mass G2 dendronized polymer are described. The molar mass is determined by gel permeation chromatography (GPC), light-scattering, and analytical ultracentrifugation and compared with values estimated from a scanning force microscopy (SFM) contour lengths analysis of individualized polymer strands on mica. The polymer carries terminal tert-butyl-protected carboxyl groups, the degree of deprotection of which with trifluoroacetic acid is quantified by NMR spectroscopy using the highest molar mass sample. SFM imaging of both protected (noncharged) and unprotected (charged) dendronized polymers on solid substrates reveals mostly linear chains but also some with main-chain branches. The nature of these branches is investigated and the degree roughly estimated to which they are formed. Finally, a synthetic model experiment is described which sheds some light on the aspect of whether chain transfer, a process that could lead to covalent branching, is of importance in the synthesis of the present dendronized polymers.