Preparation And Rheological Behaviour Of Novel Hydrophobically Modified Ethoxylated Urethane Thickener

Novel Percec-type dendrons with different terminal hydrophobic tail number andterminal hydrophobic chain lengths, ferrocenyl compound with redox reversibilitybehavior and spiropyran compound with photochromism function were synthesizedand used as new end-cappers to prepare nional groups on the molecular structure,physicochemical properties, and rheological properties were observed. This workwould be useful for the development of novel functional HEUR thickener systems andopens a new perspective for more efficient thickeners and also promises the potentialof these HEUR polymers in waterborne coating, cosmetics, printing ink, adhesive andso on for the first time. The main contents and the results are as follows:Novel dendron hydrophobically modified ethoxylated urethanes (DHEUR) withidentical hydrophilic portion but different terminal hydrophobic group numbers wereprepared by using Percec-type dendrons as new end-cappers, respectively. ForDHEUR-1with4-mono(decyloxy) benzyl alcohol, the solutions exhibit Newtonianbehavior accompanied by shear-thinning at high shear rate region. DHEUR-2with3,5-di(decyloxy) benzyl alcohol in solutions processa relatively higher solutionviscosity and similar solution viscosity behavior to DHEUR-1. However, shearthinning behavior shifts to a lower shear rate region due to a relatively longerrelaxation time. Interestingly, the solutions of DHEUR-3with3,4,5-tri(decyloxy)benzyl alcohol show pronounced shear thinning behavior over the whole shear raterange. The oscillatory measurements further confirm that a gradually developingassociative network leads to their different solution rheological behavior, i.e., viscousfluid (DHEUR-1), viscoelastic fluid (DHEUR-2), and elastic body (DHEUR-3) withincreasing the hydrophobic tail number of dendrons. The activation energy increasewith the increase of terminal hydrophobic group numbers, indicating that DHEURwith more hydrophobic tail chain has stronger association strength and needs moreenergy potential barrier for the disengagement of hydrophobes from micelles. Ingeneral, the results demonstrate that the terminal hydrophobic tail number of dendronsplays a key role in determining the associative and rheological behavior of DHEUR in solutions.DHEUR with identical hydrophilic portion but different terminal hydrophobicchain lengths were prepared by using di-substituted benzyl alcohol dendrons withdifferent alkyl chain length as new end-cappers. DHEUR-2C8solutions aredominantly composed of the flower-like micellar junctions and a complete physicalnetwork have not been developed. Interestingly, DHEUR-2C12and DHEUR-2C16insolutions have developed a complete physical network through micellar junctions togive high solution viscosity. The rheological activation energy of these DHEURpolymers derived from temperature dependence measurements increase with theincrease of terminal hydrophobic chain length, indicating that the network formed byDHEUR polymers with longer hydrophobic chain has stronger association strengthand needs more energy potential barrier for the disengagement of hydrophobes frommicelles. Furthermore, the amount of DHEUR polymers requested for the formationof a complete physical network in latexes gradually decrease in the order of terminalhydrophobic chain length, i.e., DHEUR-2C8(0.6wt%), DHEUR-2C12(0.4wt%),DHEUR-2C16(0.2wt%). In general, the results demonstrate that the hydrophobicchain length of dendrons plays a key role in determining the associative andrheological behavior of DHEUR in solution and latex also.Novel ferrocenyl hydrophobically modified ethoxylated urethanes (Fc-HEUR)were prepared by using ferrocenyl alkyl alcohol molecule as new end-cappers.UV-visible spectroscopic characterization of Fc-HEUR aqueous solution for differentoxidation degree showed that the solution color deepened When Fc-HEUR have beenoxidized. The absorption peak of ferrocene groups at about428nm decreased, theabsorption peak of ferric ions at about627nm strengthened gradually. WhenFc-HEUR have been reduced, the color of the aqueous solution recovered lightyellow of original form, absorption peak at about627nm disappeared, absorptionpeak at about428nm reemerged. From the calculation of surface tension datedependence on polymer temperature for Fc-HEUR aqueous solution，the CMC beforeoxidation is0.2mM, CMC after oxidation is10mM oxidation. The particle size of Fc-HEUR polymer in aqueous solution increases with the increase of polymerconcentration, when the concentration has reached CMC, the value of the particle sizewas about130nm. The rheology behavior research results of Fc-HEUR in aqueoussolution and in latex show the proportion of hydrophobic groups reduced afteroxidation. With the increase of the degree of oxidation, the association weakened, theshear viscosity decreased. Hydrophilic ferric ions in the polymer chain becomehydrophobic ferrocene groups after reduction. Association strengthened and shearviscosity recovered to the initial value, showing that Fc-HEUR have reversible redoxregulation.Novel spiropyran hydrophobically modified ethoxylated urethanes (SP-HEUR)with photochromism function were prepared by using SP-(CH2)11OH as newend-cappers. The spiropyran group was introduced into the polyurethane system. Theultraviolet&visible absorption spectrum and fluorescence spectra shown that thespiropyran group of SP-HEUR have changed from the closed loop SP state to theopen-loop PMC state after UV and visible light irradiation. SP-HEUR thickener hasthe reversible response in the photochromic process. After UV irradiation, theassociation strengthened, the shear viscosity increased due to the formation of closedloop SP state of spiropyran group. After visible light irradiation, the associationweakened, the shear viscosity decreased due to the formation of the open-loopPMC state of spiropyran group. The results showed that the spiropyran polyurethanethickener has the reversible response in the photochromic process and the control ofthickening could be controlled by light.