Aggregation And Rheological Behavior Of Hydrophobically Modified Ethoxylated Urethane In Aqueous Solution

Hydrophobically modified ethoxylated urethane?HEUR?,as a typical triblock telechelic hydrophobic associating polymer,has been extensively studied in synthesis and theoretical models.However,the preparation of novel functional HEUR and its aggregation and rheological properties have not been further studied.Therefore,novel functional hydrophobic end groups were designed and synthesized of and used as new end-cappers to prepare such HEURs.The effects of molecular structure,hydrophobic property of end groups on the aggregation and rheological behavior of the solution were investigated,and relations between associative structures and rheological properties were correlated.The main research contents and results of this dissertation are as follows:1.Three novel HEUR model polymers end-functionalized with substituted benzyl alcohol dendritic end-cappers were designed and prepared.For a reasonable comparison,the total alkyl carbon number of 24 is set for the three hydrophobes:C24OH for single-tail,2C12OH for two-tail and 3C8OH for three-tail according to their substituted degrees,respectively.A comparative study of the aggregation and rheological properties of these HEUR model polymers in aqueous solution and latex were carried out in detail.The results indicate that the HEURs functionalized by di-and especially tri-substituted mini-dendritic hydrophobes have stronger thickening efficiency and faster relaxation behavior in aqueous solution than mono-substituted benzyl alcohol with the identical total carbon number of alkyl tail.The high substituted mini-dendritic end groups help HEURs to form a strong physical network with a fast relaxation process in both aqueous solutions and latex.This is in line with the requirement of high viscosity and fast relaxation of thickener in actual industrial application.2.An azobenzene-functionalized HEUR polymer?AzoHEUR?was designed and prepared by the step-growth polymerization of PEG with a slight excess of diisocyanates in toluene followed by the reaction of the terminal isocyanate groups with the lauryl alcohol-substituted azobenzene(AzoC₁₂OH).The effect of hydrophobicity change of azobenzene hydrophobes on the aggregation and rheological properties of AzoHEUR aqueous solutions were investigated in detailed.The isomerization of azobenzene end groups induces a change in hydrophilic-lipophilic balance of polymer due the hydrophobicity response of end group,leading to different aggregation number of micelle.Meanwhile,the number density of the elastic chains and the relaxation hehavior of the network will change also.A reversible rearrangement of micellar junctions through the loop-bridge transitions or bridge-loop transitions was presented to understand the light-induced rheological property change of concentrated AzoHEUR aqueous solutions.3.A novel hydrophobically modified ethoxylated urethane model polymer?AzoFcHEUR?end-bifunctionalizedwithPerce-typemini-dendron3-?6-ferrocenyhexyloxyl?-5-?6-azobenzenehexyloxy?benzyl alcohol?AzoFcPhOH?was designed and prepared.The multiple stimuli-responsive aggregation and rheological behavior of AzoFcHEUR in aqueous solution were studied in detail.It has been demonstrated that the multiple stimuli-responsive hydrophobicity change of end groups induces a reversible micellar transition or a rearrangement of micellar aggregates in dilute AzoFcHEUR aqueous solution and a rearrangement of physical network from a dense network to a sparse network in dense AzoFcHEUR aqueous solution dependent on the magnitude of amphiphilicity change of end groups upon exposure to different external stimuli and vice versa,leading to quite distinct solution aggregation and rheological behavior.4.A novel telechelic hydrophobically modified ethoxylated urethane model polymer?CouHEUR?end-functionalized with coumarin was designed and prepared by the reaction of poly?ethylene glycol?with a large excess of diisocyanates followed by the end-capping of the terminal isocyanate groups with coumarin substituted undecanol(CouC₁₁OH).The effects of light intensity,irradiation time,polymer concentration,and temperature on the transient network and rheological behavior of the CouTAP aqueous solution were studied in detail.The rheological properties of the dimerized CouTAP aqueous solution shows weak temperature dependence,and the dynamics hardly depends on concentration,due to the transformation of triblock to multiblock polymer.It has been demonstrated that the dimerization of coumarin will connect the flower loops and bridges in the micellar cores to form multiblock polymer,leading to an unusual transient network.The resulting network shows weak temperature dependence,and the dynamics hardly depends on polymer concentration.Furthermore,a unique dynamic network model composed of dimerized bridges and train flower loops was presented to vividly describe the interesting aggregation and rheological properties.