Solvent induced phenomena in a dendronized linear polymer

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.FigureᅟElectronic supplementary materialThe online version of this article (doi:10.1007/s00396-013-3007-9) contains supplementary material, which is available to authorized users.

The Viscosity Law of Dendronized Linear Polymers

“…Note the decrease in [ η ] when the temperature increases by only 15 °C. This effect goes along with a small change in l p when increasing T . However, the rather strong dependence of [ η ] on the generation number of the DPs at constant degree of polymerization P is noteworthy and somewhat surprising at first.…”

“…A freshly prepared set of four samples, named PG1 to PG4, were investigated. The samples were dissolved in dioxane, which had been found to be a thermodynamically good solvent for all generations . Measurements of the specific viscosity η sp as a function of c were made as shown in Figure and extrapolation of the resulting data to lim( η sp / c ) L→0 = [ η ] at T = 25 °C results in the data summarized in Table .…”

“…This communication describes experiments by which the viscosity law for dendronized linear polymers (DPs) is established both as function of degree of polymerization P and persistence length l p . DPs are to be seen as wormlike molecular objects of cylindrical cross section . Since the mass per repeat unit of the polymer backbone increases nonlinearly with the number of generations G and thereby, the mass of the polymer at constant degree of polymerization it was an open question how the viscosity law would look like for these unconventional macromolecules.…”

“…Details of the synthesis including information on the structural perfection have been described in previous publications . Moreover, solutions of PG4 in thermodynamically good and poor solvents have been investigated recently . These studies resulted in a model description in which the DP behaves as a wormlike chain, assuming a random flight conformation in dilute solution.…”

“…For PG4, the sample that was analyzed in detail by static and dynamic light scattering (SLS and DLS), the following characteristics were found: a weight‐average molar mass of = 2.3 × 10 7 g mol −1 , a positive second osmotic virial coefficient of A 2 = 2 × 10 −9 mol dm 3 g −2 , a radius of gyration of R G = 128 nm, and a hydrodynamic radius of R h = 72 nm . The contour length L c = P W × d = 1060 nm was obtained from the weight‐average degree of polymerization P W = 4240 and the repeat distance between identical monomer units in the linear chain of d = 0.25 nm in accordance with previous work .…”