Solvent induced phenomena in a dendronized linear polymer
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Solvent induced phenomena in a dendronized linear polymer Anja Kroeger & Baozhong Zhang & Christine Rosenauer & A. Dieter Schlüter & Gerhard Wegner
Received: 22 April 2013 / Revised: 6 June 2013 / Accepted: 7 June 2013 / Published online: 7 August 2013 # The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract The properties of a dendronized linear polymer (DP) in dilute solutions depending on solvent quality and temperature are described. The polymer has a contour length of Lc =1,060 nm. The sample of the fourth generation (PG4) was analyzed in the thermodynamically good solvents dioxane, chloroform, and methanol. The wormlike macromolecule has a persistence length lp =7 nm in dioxane and a cross-section radius determined by small angle X-ray scattering (SAXS) of Rc (SAXS) =2.8 nm. The bulk density of PG4 determined by SAXS was compared with solution density. Evidence for substantial swelling of the cross-section was found. Toluene acts as a thermodynamically poor solvent (θ solvent). Above the θ temperature Tθ, a strong temperature dependence of the size and the Young’s modulus E was observed. Following Odijk, E/kBT ∼1 was found. Below Tθ, a regime characterized by unswelling of the wormlike chains was observed. The results suggest that DPs can be described as soft colloid filaments, which are subject to commonly observed interactions in colloidal systems. A phase diagram indicates a regime below Tθ in which fluctuations of osmotic pressure inside the filaments result in periodic undulation of the chains. In summary, introducing a dense dendritic shell around the backbone converts conventional polymers into molecular colloids.
Electronic supplementary material The online version of this article (doi:10.1007/s00396-013-3007-9) contains supplementary material, which is available to authorized users. A. Kroeger (*) : C. Rosenauer : G. Wegner Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany e-mail: [email protected] B. Zhang : A. D. Schlüter Laboratory of Polymer Chemistry, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, HCI J541, 8093 Zurich, Switzerland
Keywords Dendronized polymers . Solution behavior . Phase separation . Colloidal filaments . Morphological instability
Introduction Ever since dendronized linear polymers (DPs) have come to the scene [1–17], the question was raised whether such structures exhibit properties fundamentally or—at least—substantially different from ordinary linear polymers that are furnished with small but sterically assuming side groups. Poly(tert-butyl-methacrylate) (PtBMA) is a simple example for such a case in which steric interactions among the side groups enlarge the stiffness of the macromolecule substantially. The latter is inferred from comparison of the characteristic ratio of PtBMA and polymethyl methacrylate (PMMA) [18]. It is ∼11 for the former, meaning that the respective Kuhn length lk, which is the length of the statistical element of the random flight cha
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