| The thickness of dendronized polymers can be tuned by varying their generation g and the dendron functionality X. Systematic studies of this effect require (i) synthetic ability to produce large samples of high quality polymers with systematic variation of g, X and of the backbone polymerization degree N, (ii) a theoretical model relating the solvent swollen polymer diameter, r, and persistence length, λ, to g and X. This article presents an optimized synthetic method and a simple theoretical model. Our theory approach, based on the Boris-Rubinstein model of dendrimers predicts r . n1/4g1/2 and λ~n2 where n = [(X - 1)g - 1]/(X - 2) is the number of monomers in a dendron. The average monomer concentration in the branched side chains of a dendronized polymer increases with g in qualitative contrast to bottle brushes whose side chains are linear. The stepwise, attach-to, synthesis of X=3 dendronized polymers yielded gram amounts of g=1-4 polymers with N ≈ 1000 and N ≈ 7000 as compared to earlier maxima of 0.1 g amounts and of N ≈ 1000. The method can be modified to dendrons of different X. The conversion fraction at each attach-to step, as quantified by converting unreacted groups with UV labels, was 99.3% to 99.8%. Atomic force microscopy on mixed polymer samples allows to distinguish between chains of different g and suggests an apparent height difference of 0.85 nm per generation as well as an increase of persistence length with g. We suggest synthetic directions to allow confrontation with theory.
for LaTeX users @article{YGuo2009-131,
author = {Y. Guo and J. D. van Beek and B. Zhang and M. Colussi and P. Walde and A. Zhang and M. Kr\"oger and A. Halperin and A. D. Schl\"uter},
title = {Tuning polymer thickness: Synthesis and scaling theory of homologous series of dendronized polymers},
journal = {J. Am. Chem. Soc.},
volume = {131},
pages = {11841-11854},
year = {2009}
}
\bibitem{YGuo2009-131} Y. Guo, J.D. van Beek, B. Zhang, M. Colussi, P. Walde, A. Zhang, M. Kr\"oger, A. Halperin, A.D. Schl\"uter,
Tuning polymer thickness: Synthesis and scaling theory of homologous series of dendronized polymers,
J. Am. Chem. Soc. {\bf 131} (2009) 11841-11854.YGuo2009-131
Y. Guo, J.D. van Beek, B. Zhang, M. Colussi, P. Walde, A. Zhang, M. Kr\"oger, A. Halperin, A.D. Schl\"uter
Tuning polymer thickness: Synthesis and scaling theory of homologous series of dendronized polymers
J. Am. Chem. Soc.,131,2009,11841-11854 |
mk@mat.ethz.ch
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