Self-diffusion of hydrophobically end-capped polyethylene oxide urethane resin by using pulsed-gradient spin echo NMR spetroscopy

Abstract

Hydrophobically End-capped polyethylene oxide Urethane Resin(HEUR)-associating polymers, HEUR 35(8), HEUR 35 (12), and HEUR 35 (18), comprise a polyethylene oxide (PEO) having a molecular weight of 35,000 that is end capped with two C 8 H 17 , C 12 H 25 , and C 18 H 37 alkyl chains, respectively. These associating polymers were synthesized by condensation reactions with polyethylene oxides and alkyl isocyanates. The self-diffusion coefficients of HEUR-associating polymers were measured in aqueous solution by pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) spectroscopy. All polymers underwent a decrease in their mean diffusion coefficients as the concentration was increased. However, the dispersion of the diffusion coefficients, β, about the mean fluctuated with changes in concentration. The large dispersion at low concentrations of HEUR 35(8) and HEUR 35 (12) is related to the interaction between hydrophobic end groups, and the large dispersion at high concentrations of HEUR 35(18) is correlated with transient network formation. These results are valuable for predicting the associating mechanism of the large aggregates before and after their critical micelle concentration.

Understanding associative polymer self-assembly with shrinking gate fluorescence correlation spectroscopy

“…35,36 We also observe a monotonic decrease in the anomalous diffusion coefficient with increasing concentration above 0.25 wt% HEUR for t g = 0 which reflects either an increasing contribution of bound dye or obstructed diffusion of the free dye. 57 Regardless of model, the observations in the plateau region are consistent with experiments 8,9 and simulations 58 that show the intermediate hydrophobicity of C12 HEUR variants leads to a heterogeneous size distribution of self-assembled aggregates.…”

“…Associative polymers are key components in a wide range of liquid formulations, as they impart non-Newtonian rheological behaviour to products such as paints 1,2 and lubricants. 3,4 Their useful properties arise from the formation of concentrationdependent self-assembled structures, 5 which have been studied by a range of techniques including dynamic [6][7][8] and static 6,7 light scattering, nuclear magnetic resonance, 9 fluorescence spectroscopy, 6,10,11 and rheology. 5,6 Obtaining a full picture of the self-assembly process requires combining observations from multiple techniques.…”