ARTICLE Received 29 Jan 2013 | Accepted 8 May 2013 | Published 13 Jun 2013 Synthetic regimes due to packing constraints in dendritic molecules confirmed by labelling experiments Baozhong Zhang 1 , Hao Yu 1 , A Dieter Schlu ¨ter 1 , Avraham Halperin 2 & Martin Kro ¨ger 3 Classical theory predicts that branching defects are unavoidable in large dendritic molecules when steric congestion is important. Here we report first experimental evidence of this effect via labelling measurements of an extended homologous series of generations g ¼ 1y6 of dendronized polymers. This system exhibits a single type of defect interrogated specifically by the Sanger reagent thus permitting to identify the predicted upturn in the number of branching defects when g approaches g max and the polymer density approaches close packing. The average number of junctions and defects for each member of the series is recursively obtained from the measured molar concentrations of bound labels and the mass concentrations of the dendritic molecules. The number of defects increases at g ¼ 5 and becomes significant at g ¼ 6 for dendronized polymers where the g max was estimated to occur at 6.1 rg max r 7.1. The combination of labelling measurements with the novel theoretical analysis affords a method for characterizing high g dendritic systems. DOI: 10.1038/ncomms2993 1 Laboratory of Polymer Chemistry, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, HCI J 541, CH-8093 Zurich, Switzerland. 2 Universite ´ Grenoble 1/CNRS, LIPhy UMR 5588, 38041 Grenoble, France. 3 Polymer Physics, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, HCI J 541, CH-8093 Zurich, Switzerland. Correspondence and requests for materials should be addressed to A.H. (email: avraham.halperin@ujf-grenoble.fr). NATURE COMMUNICATIONS | 4:1993 | DOI: 10.1038/ncomms2993 | www.nature.com/naturecommunications 1 & 2013 Macmillan Publishers Limited. All rights reserved. For your personal use only. Not for redistribution related contributions available from the author(s) at www.complexfluids.ethz.ch