Influence of Terminal Hydrophobe Branching on the Aqueous Solution Behavior of Model Hydrophobically Modified Ethoxylated Urethane Associative Thickeners

Abstract

The influence of terminal hydrophobe branching on the micellar properties of Hydrophobically modified Ethoxylated URethanes (HEURs) is addressed through fluorescence, dynamic light scattering (DLS), solution rheology, and Raman spectroscopy. Model HEURs used in this study are monodisperse and fully substituted with hydrophobic groups of different structures. Two linear hydrophobes (l-C12H25 and l-C16H33) and three branched hydrophobes [b-(C12H26), b-(C16H34), and b-(C20H42)]are coupled to the hydroxyls of POE670 and POE195 through 4,4-methylene bis(dicyclohexyl)diisocyanate (H12MDI) units. Prior low molecular weight surfactant studies observed that a CH2 group, introduced as a branch from a linear hydrophobe, contributes approximately half to the surfactant's hydrophobicity that the same CH2 unit would add to the linear chain. Within hydrophobe equivalent comparisons, greater hydrophobic domains are indicated in pyrene's I1/I3 emission ratio for the linear hydrophobe HEURs, denoting a more hydrophilic core in branched HEURs. An increase in the number of -CH2-groups notably influences aqueous solution viscosities, as expected, but among equivalent hydrocarbon comparisons, the moderate-size linear hydrophobe is more viscosifying than the branched hydrophobe at high concentrations. Viscosity increases correlate with the aggregation sizes estimated from DLS studies as aggregate sizes approach 500 nm, covering small to large hydrophobes and different oxyethylene spacer lengths. Conformational differences (Raman spectroscopy) of poly(oxyethylenes) and HEURs under stagnant and flow conditions are also examined. The presence of byproduct impurities can markedly influence these results.

Influence of Hydrophobe, Surfactant and Salt Concentrations in Hydrophobically Modified Alkali-Soluble Polymers Obtained by Solution Polymerization

“…Figure 3 shows the η0 as a function of SDS concentration (C SDS ) for the three polymers studied. It is observed that the addition of surfactants to the solutions of associative polymers has dramatic effects on the viscosity of the medium because links represent associative polymer micellar high-affinity domain interactions with surfactants [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. In many cases, has been found that this effect is strongly dependent on the nature and level of addition of surfactant.…”

Effects of polymer concentration and chain length on aggregation in physically associating polymer solutions

“…It is demonstrated that the change of N has a greater effect on HS-MFH transition than that on MFH-micelle transition. The aggregation number of micelles, which is used to account for some properties, for example, the rheological behavior of associative polymers, is a major focus in many experimental [36][37][38] and theoretic [39] studies. In this paper, the average volume fraction of stickers at micellar cores φ s (r co ) is similar to the average aggregation number of the micelle.…”

Spray applications: Part IV. Compositional influences of HEUR thickeners on the spray and velocity profiles of waterborne latex coatings

“…To better define the structural effects of HEUR thickeners that could influence this behavior requires an examination of specific HEUR structures. [45][46][47] Our time for such studies is over and we leave this challenge to others. …”