Study On Synthesis, Properties Of Polyurethane And Its Copolymer With Hydrophilic/hydrophobic Transition

Polyurethane,as a kind of polymer material,is widely used in coatings,adhesives,elastomers and other fields.In recent years,environmental protection has increasingly become the focus of national and social attention,and traditional solvent-based polyurethane is difficult to meet the requirements,so waterborne polyurethane（WPU）has become a research hotspot.As an important environmentally friendly solvent,water has become the most important“green”dispersion medium for polyurethane.Waterborne Polyurethane（WPU）has the advantages of non-toxic,no odor and low VOC compared with solvent-based polyurethane.The introduction of ions or hydrophilic segments helps WPU to disperse stably in the water while changing the chains structure and the aggregation structure of WPU,affecting the drying and solidification process,resulting in deterioration of the water resistance of the film.For the above reasons,the application of WPU is limited.In this study,CO₂ was used as"switch"that controls hydrophilicity/hydrophobicity of WPU.CO₂-triggered hydrophobic/hydrophilic switchable polyurethane（S-PU）were prepared by introducing functional monomer into the polyurethane.Subsequently,we used SPU-HEA as emulsifier to prepare CO₂-triggered hydrophobic/hydrophilicswitchablepolyurethane-co-polymethacrylate（SPU-co-PMMA）composites by soap-free emulsion polymerization,and obtained the emulsion（SPU-PMMA-CO₂）prepared by carbonic acid solution.The reversible self-emulsification of S-PU and SPU-co-PMMA in water was achieved by protonation of tertiary amine group in CO₂ aqueous solution and deprotonation after CO₂ removal.We mainly studied the microstructure of the two emulsion particles under CO₂ stimuli-response and the properties of the emulsion after film formation,and discussed the mechanism of the water resistance improvement of the film compared with the control.（Control samples were prepared by replacing CO₂ with acetic acid as a salt forming agent:WPU-Ac and PU-PMMA-Ac.）Firstly,S-PUwassynthesizedwithafunctionalmonomer（N-（3-dimethylaminopropyl）-N,N-diisopropanolamine,DPA）,and a stable waterborne polyurethane dispersion with transparent pan-blue light was prepared in the deionized water bubbling with CO₂.In the test of hydrophilic/hydrophobic regulation,it can be seen from TEM that the initial S-PU is spherical particles and evenly dispersed in the water,the particle size of the DLS test is less than 30nm.After heating at 65^oC for 30min instead,the particle size of the microspheres increased to270nm and even aggregation.When bubbled CO₂ into the system again,S-PU dispersed in the water to form microspheres again,and the particle size is similar to the initial state.The results of water contact angle test showed that the data（114±0.8°）of S-PU film is far greater than the control（92±1°）.At a constant temperature of 40°C,the S-PU water uptake was 4.5 wt.%after 24 h,while the control film partially dissolved and the mass loss was severe.Secondly,SPU-HEA was prepared by sealing end S-PU with HEA.Aqueous emulsion of methacrylate monomer was prepared by using SPU-HEA as emulsifier in an aqueous solution of CO₂.SPU-co-PMMA composites was prepared by soap-free emulsion polymerization,and obtained the emulsion（SPU-PMMA-CO₂）made by carbonic acid solution.According to the DLS test,the particle size of the emulsion increased with the increase of the mass ratio of SPU:MMA（30nm-50nm）,and the change of particle size has cyclical response to CO₂ regulation.Water uptake and tensile tests（dry/wet state）showed that the water resistance of SPU-PMMA-CO₂ film was significantly better than that of the control（SPU-PMMA-Ac film）.According to the results of TGA test,after the film forming,the macromolecular chain of control still contained ions,so that the water plasticizes the material,which weakened the interaction between the macromolecular chains,destroyed the aggregate structure,and reduced the mechanical properties of the material.Due to quaternary ammonium being deprotonated,SPU-PMMA-CO₂ film is not affected by the plasticization of the water molecule after removal of CO₂.