Influence of substituted structure of Percec-type mini-dendritic end groups on aggregation and rheology of hydrophobically modified ethoxylated urethanes (HEURs) in aqueous solution

Percec-type substituted benzyl alcohol mini-dendrons as new hydrophobic end-cappers can effectively improve the thickening performance of hydrophobically modified ethoxylated urethanes (HEURs) in aqueous solution. To demonstrate the effects of substituted structure of Percec-type mini-dendritic end groups on aggregation and rheological properties of HEURs in aqueous solution and latex, three model HEURs end-functionalized by mono-, di- and tri-substituted benzyl alcohol mini-dendrons were synthesized, respectively. For a reasonable comparison, the total carbon number of substituted alkyl tails is set to be 24 for the three mini-dendritic end groups: HOCH2-Ph-C24H49 (C24), HOCH2-Ph-(C12H25)2 (2C12) and HOCH2-Ph-(C8H17)3 (3C8), which respectively correspond to single-, two- and three-tail according to their substituted degrees. Interestingly, rheological properties of these HEURs in aqueous solution and latex significantly depend on the substituted degree of mini-dendritic hydrophobes. The high-substituted mini-dendritic hydrophobes help HEURs to form a strong physical network with high thickening performance and fast relaxation in both aqueous solution and latex, because shorter alkyl tails in high-substituted dendritic hydrophobes will lead to a smaller aggregation number and a lower rheological activation energy. This work not only provides new insights into the connection of networks in solutions of mini-dendron functionalized HEURs but also offers a new approach to preparation of high performance thickeners used in water-borne systems.