Preparation Of Reactive Polyurethane Associative Thickener And Its Rheological Behavior In Aqueous Systems

Hydrophobically modified ethoxylated urethane（HEUR）,as a typical class of amphiphilic associative polymer,has been widely applied into the application of waterborne coatings,emulsions,inks etc for thickening.Conventional HEUR associative thickeners are all non-reactive,which may slowly migrate or penetrate from the final cured films over time.Facing to above problem,a new concept of reactive HEUR was proposed in this study and a series of novel reactive HEUR polymers were prepared.Rheology and curing behavior of these reactive HEURs in pure water and/or emulsion were systematically investigated.The main contents and results of this dissertation are as follows:1.A novel benzophenone functionalized hydrophobically modified ethoxylated urethane(BPC₁₁HEUR)was prepared.Rheology measurements show similar rheological properties of BPC₁₁HEUR aqueous solution to those reported non-reactive HEUR.UV-vis absorption spectroscopy,¹H-NMR and rheology measurements collectively demonstrate that BPC₁₁HEUR possesses typical UV-induced hydrogen abstraction coupling characteristic and photo-initiated reactivity to initiate the polymerization of acrylate compounds.Rheology measurements of BPC₁₁HEUR in UV polyurethane acrylate emulsions indicate that BPC₁₁HEUR can not only effectively mediate the emulsions viscosity(such as 50 folds of low-shear viscosity enhancement with addition dosage of BPC₁₁HEUR as low as 1 wt%),but also efficiently initiate the polymerization of these UV resins in emulsion.Therefore,the work may be of guidance for fabrication of photo-sensitive HEUR thickener and application of BPC₁₁HEUR in UV emulsion.2.Considering the unsatisfactory thickening capability of BPC₁₁HEUR in aqueous systems,a new benzophenone functionalized HEUR（C18-BP-HEUR）bearing long alkyl chain was prepared.Surface tension,DLS and rheology measurements clarify that C18-BP-HEUR possesses stronger hydrophobic association ability and superior thickening performance compared to BPC₁₁HEUR under identical additive content.For example,the zero shear viscosity of 30 g/L BPC₁₁HEUR is just near 5.81 Pa.s,while the viscosity can attain 810.9 Pa.s in 30 g/L C18-BP-HEUR solution.In UV emulsions,0.2 wt%additive amount of BPC₁₁HEUR can elevate the zero shear viscosity of pure emulsion from 0.026 Pa.s to 1.05 Pa.s.While in 0.2wt%C18-BP-HEUR additive emulsion,the zero-shear viscosity can be improved to 19.22 Pa.s.UV-vis,¹H-NMR and in situ rheology measurement reveal a typical and similar photo-initiating reactivity of C18-BP-HEUR to BPC₁₁HEUR.The work aims to offer a new feasible route to develop more efficient photo-sensitive HEUR thickener and its application in UV emulsion.3.A novel clickable,olefin-functionalized hydrophobically modified ethoxylated urethane（Vinyl-HEUR）was prepared.Surface tension,DLS,and rheology measurement of Vinyl-HEUR aqueous solution demonstrate a significant concentration dependence of its solution aggregation and rheology behavior,zero shear viscosity of 30 g/L Vinyl-HEUR solution can reach 2895 Pa.s.Moreover,the solution rheology can be largely affected by temperature and meets the single-Maxwellian relaxation behavior in solution.The zero-shear viscosity of pure emulsion can be improved from 2.8 Pa.s to 100 Pa.s after 0.2 wt%additive amount of Vinyl-HEUR,which is comparable to reported non-reactive Perce-type HEUR thickener.Multiple alternating shear rate testing demonstrate benign thixotropy of the Vinyl-HEUR thickened emulsion.¹H-NMR reveals that it is hard for Vinyl-HEUR to be initiated by generally thermal（AIBN）or photo-initiator（DMPA）,while shows highly efficient ene-thiol clickable reactivity between terminal-ene double bond and multiple mercaptane which is confirmed by in situ rheology measurement under UV irradiation.Comparative in situ rheology experiments of Vinyl-HEUR with C18-HEUR in UV emulsion demonstrate that the use of Vinyl-HEUR as thickener can help shorten the gelation time and accelerate the growth of shear elastic modulus of the curing system.The work provides a few guidance for preparation of efficient,quickly clickable reactive HEUR thickener and may offer a new alternative for the application of Vinyl-HEUR into UV emulsions.4.In view of the restricted polymerization reactivity of the end-ene group of Vinyl-HEUR,a novel polymerizable acrylic-type hydrophobically modified ethoxylated urethane（Acrylic-HEUR）was prepared.Rheology measurements show excellent thickening performance of Acrylic-HEUR to pure water,for example,zero shear viscosity of Acrylic-HEUR solution can attain to about 75 Pa.s which is comparable to a non-reactive C18-HEUR thickener.Meanwhile,the steady and oscillatory shear measurements of Acrylic-HEUR aqueous solutions display similar single-Maxwellian relaxation behaviors to reported common HEURs.¹H-NMR,dynamic light scattering（DLS）,and in situ rheology measurements prove that the side methacrylate group located in the end of Acrylic-HEUR can be efficiently initiated by photo-initiator to trigger radical polymerization.Thickening experiments in UV emulsion suggest that Acrylic-HEUR behaves comparable thickening efficiency to a non-reactive HEUR（C18-HEUR）.Moreover,the viscosity of emulsion thickened by Acrylic-HEUR can synchronously response to external alternating high-low-high shear and exhibits a low-high-low value variation,representing a good thixotropy of the formula.Through a contrast experiment,in situ rheology measurements of emulsion thickened by above two HEURs clarify the co-polymerization reactivity of Acrylic-HEUR with this UV resins in emulsion,and can help elevate elastic shear modulus and slow down the stress relaxation behavior of cured UV emulsion.The work may be of guidance for providing a new route to synthesize polymerizable acrylic-HEUR polymer and promoting the development of efficient and superior HEUR thickener product in industry.