Synthesis, Characterization, and Rheological Behavior of Polyethylene Glycols End-Capped with Fluorocarbon Hydrophobes

Abstract

Two polyethylene glycols (PEG, M = 35 000) end-capped with short fluorocarbon tails were synthesized and characterized. In aqueous solution, the fluorocarbon portions associate strongly to form micelle-like structures which are bridged by PEG chains to form a three-dimensional network. As a result, these polymers in solution exhibit unusual rheological properties as a function of fluorocarbon length, polymer concentration, and shear rate (frequency). Their zero-shear viscosity increases with concentration, a common behavior of associating polymers. The viscosity is dramatically enhanced by replacing the end hydrophobe C6F13 with C8F17, a consequence of the stronger association interaction of C8F17 in aqueous solution. The polymer with the longer end group exhibits strong shear thinning once a critical shear rate is reached, whereas for the C6F13 end-capped polymer, we cannot with our equipment reach the shear-thinning regime. Our data indicate that between 2 and 6 wt %, and perhaps over a wider range of concentrations, both systems can be characterized in terms of identical values of the plateau modulus G N°, implying a similar concentration of chains bridging micelles in each system. The G N° values increase strongly with polymer concentration, consistent with a larger fraction of bridging chains and a smaller fraction of looping chains at elevated concentration. The viscosity difference between the two polymers can be explained in terms of a slower exit rate of the longer fluorocarbon from its micelle.

Macromolecular Assemblies in Solution: Characterization by Light Scattering

“…10,13 With increasing the polymer concentration, however, such flower micelles may be interconnected by bridging chains with termini entrapped in the core of two distinct micelles, and exhibit the characteristic viscoelastic behavior. 8,[50][51][52][53] The association behavior of flower micelles is a delicate problem, because repulsive forces between loops tend to prevent micellar association whereas the loop-to-bridge transition by the entropic penalty associated with loop formation favors association. 54,55 Recently, Nojima et al 9 investigated the association behavior of flower micelles formed by telechelic hydrophobicallymodified poly(N-isopropylacrylamide) (HM-PNIPAM) in 25 C water by static light scattering.…”

“…[8][9][10][11][12][13] Multi-stranded helical polymers may form assemblies of their unique architecture by the hydrogenbonding.…”

“…[2][3][4][5][6][7] On the other hand, if the chain possesses a number of attractive moieties, its assembly may be a uni-core or multicore flower micelle. [8][9][10][11][12][13] Multi-stranded helical polymers may form assemblies of their unique architecture by the hydrogenbonding. 14 The macromolecular assemblies formed by associating polymers in solution can be characterized in terms of the architecture, the size (i.e., the radius of gyration, hydrodynamic radius, or intrinsic viscosity), the average and distribution of the aggregation number, and inter-assembly interaction.…”

Silica nanoparticles dispersed in a self-assembled viscoelastic matrix: structure, rheology, and comparison to reinforced elastomers

“…Hydrogels may have this property, if the particles are hydrophilic and stable, which is why work on silica-filled oilin-water microemulsion networks has been undertaken [15]. Such networks are made of microemulsion droplets stabilized by a surfactant and bridged by a triblock copolymer with hydrophobic end-groups called telechelic polymer, which some- * julian.oberdisse@lcvn.univ-montp2.fr times micellizes also in absence of surfactant [16][17][18][19][20][21][22][23][24][25][26][27][28][29] . Very recently, networks of connected wormlike micelles have also attracted interest [29,30].…”

Rapid self-healing and anion selectivity in metallosupramolecular gels assisted by fluorine–fluorine interactions

“…49 In polymer science, polyethylene glycol derivatives with terminal fluoroalkyl groups have shown to exhibit peculiar rheological properties as "associative thickeners". 50 Similarly, polyacrylamide with a minute amount of fluorocarbon groups have shown to associate much stronger compared to simple hydrocarbon derivatives. 51 In recovering the gel strength after release of the step strain.…”