Synthesis of High Generation Dendronized Polymers and Quantification of Their Structure Perfection

Abstract

The sixth generation (g = 6) dendronized polymer (DP) PG6 was synthesized on a 2 g scale with Pn ∼ 500 in 60% chemical yield and with a coverage degree of 87–90% using a recently developed “n + 2” approach from its structurally virtually perfect, deprotected g = 4 congener dePG4. This synthesis represents the first fully reliable access to a g = 6 representative of this DP series and was therefore used for the synthesis of two higher generation representatives, the g = 7 and g = 8 DPs, PG7 and PG8, which are the highest g DPs ever reported. The structure perfection of the obtained DPs was analyzed by the conventional UV-labeling method and compared with the results from TGA, with which the amount of cleaved-off Boc-protecting groups was quantified. The accuracy of the TGA method was assessed as ±3% by using a Boc-containing dendron and well-characterized low generation DPs as reference. For the high generation DPs obtained by “n + 2” approach the TGA results confirmed the UV-determined coverages. For PG7, the TGA result slightly exceeds the error range (3.3%), which may suggest a possible overestimation of the coverage determined by UV quantification. AFM imaging shows a so far uncommon inhomogeneous appearance for PG7 and PG8, which may be a result of structural defects in both DPs.