Aggregation Behavior of a Symmetric, Fluorinated, Telechelic Polymer System Studied by¹⁹F NMR Relaxation

Abstract

19F NMR experiments are used to study the aggregation behavior of two telechelic polymer systems. These polymer systems consist of a water−soluble chain, here poly(ethylene glycol), with two hydrophobic endgroups. Because of the hydrophobic interaction of the fluorocarbon endgroups, these polymer chains associate in water to form aggregates at low concentrations. The aggregate comprises a core formed from the insoluble hydrophobic endgroups that are surrounded by a corona of long water-soluble polymer chains. With increasing polymer concentration, the polymer chains start bridging so that a three-dimensional, physical network with fluorinated aggregate cores as cross-link points is formed. This effect can be substantially enhanced by replacing the hydrophobic endgroup C6F13 with C8F17, a consequence of the stronger association of C8F17 in aqueous solution. By different 19F NMR parameters, i.e., 19F transverse relaxation and 19F chemical shift, we can distinguish aggregated and nonaggregated chain ends. This enables us to follow the formation of an infinite network.

Design and synthesis of a two compartment micellar system based on the self-association behavior of poly(N-acylethyleneimine) end-capped with a fluorocarbon and a hydrocarbon chain

“…For the short relaxation time T 2, short we find values around 200 ls, which is a factor 10 lower than T 2, long . Virtually the same values were found in our previous study of symmetric ABA block copolymers with fluorinated end groups 24) .…”

“…For this reason we also performed 19 F NMR experiments that should enable us to probe the aggregation behavior of the fluorocarbon chains. As described in detail elswhere 24) , the aggregation behavior of the fluorinated endgroups manifests itself by the appearance of a short component in the transverse relaxation (T 2 ) as well as in the decreasing 19 F chemical shift. We chose the FP 25 L 16 polymer, that forms micellar aggregates upon a critical concentration with a lipophilic core environment.…”

“…5 we compared these results with a symmetric polymer system C 8 F 17 1PEG 800 1C 8 F 17 studied earlier 24) . By comparing the two data sets, the fraction belonging to the short relaxation time of FP 25 L 16 is increasing much slower in comparison with the symmetric PEG polymer system.…”

Tumor pH-responsive flower-like micelles of poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(l-histidine)

“…Similar results have been observed with BAB (hydrophobic B blocks and hydrophilic A block) type amphiphilic copolymers which form flower-like micelles and often lead to micellar bridging (resulting in micelle aggregation) depending on environmental conditions [34][35][36][37][38]. For example, the formation of three-dimensional networks by bridging between micelles has been induced by high polymer concentration, salts and pH [34][35][36][37][38]. It is expected that as the pH of solution decreases, the PLA-b-PEG-b-polyHis micelles swell (Fig.…”

Adsorption properties of oligo(fluorooxetane)-b-poly(ethylene oxide)-b-oligo(fluorooxetane) triblock copolymers at the air–water interface: Comparison of hydroxyl and acetate end groups

“…Due to the structural diversity available, a variety of modifications can be made to the poly(ethylene oxide) block including end-capping with a variety of, typically, hydrophobic materials. End-capping moieties include hydrocarbons, [3][4][5][6][7] fluorocarbons, [8][9][10] mixed hydrocarbon/fluorocarbon systems [11] and lead to AB, ABA di-or triblock architectures, respectively, where A = hydrophobe and B = poly(ethylene oxide). In contrast, BAB triblock copolymers can be prepared where A is now the relatively more hydrophobic poly(propylene oxide) [12][13][14][15].…”