Preparation And Property Of Cationic Waterborne Polyurethane Based On CO₂

Polyurethanes are large commodity polymers widely used in coatings,adhesives,foams and many other fields.With the increasing concern on volatile organic compound(VOC)in solvent-based polyurethanes,waterborne polyurethanes including anionic,cationic and neutral ones,should be the choices in the future.Currently,anionic waterborne polyurethanes are dominating in industry,while cationic waterborne polyurethanes(CWPUs)are sparsely found in the commercial list,and received much less systematic and in-depth research.The reason lies in the poor stability of CWPU dispersions,and excessive cationic hydrophilic chain extenders are used to assure stable dispersion,leading to poor water resistance and failure in commercial products.Therefore,improving the emulsification efficiency of cationic hydrophilic chain extender is of key importance,which may be solved if new structure polyols are created in combination of new design in cationic hydrophilic functional group.As far as raw materials are concerned,polyether and polyester polyols constitute the main polyols in polyurethane industry.Fortunately,a new polyol called CO2-polyol has been developed recently based on telomerization of carbon dioxide and propylene oxide.The coexistence of carbonate and ether units in CO2-polyol affords new structure polyurethane with advanced performance.In this thesis,various CWPUs based on CO2-polyol(CO2-CWPUs)will be explored in combination with delicate design of hydrophilic groups,and the main results are summarized as follows.1.CO2-CWPUs with cationic hydrophilic groups in main chain,side chain and terminus were prepared from CO2-polyol.For stable dispersion of CO2-CWPU,the influence of hydrophilic group position on the minimum usage of hydrophilic chain extender was investigated.When the hydrophilic group was located at the terminus,its emulsifying capacity was 3.5 times that of the hydrophilic group in the side chain and 4.4 times that of the hydrophilic group in the main chain.Therefore,when CWPU emulsion was induced to disperse stably by terminal hydrophilic groups,the amount of hydrophilic chain extender can be significantly reduced to only 1.0 wt%.This preparation strategy was versatile,not only suitable for the preparation of CWPU from CO2-polyol with different carbonate unit contents,but also effective for traditional polyester and polyether polyols.Thanks to the special structure of coexistence of carbonate units and ether bonds in CO2-polyol,CO2-CWPU had excellent hydrolysis and oxidation resistance,showing great application potential.2.Ultraviolet light(UV)curing in combination with terminal hydrophilicity induced dispersion strategy was employed to prepare water-resistant CWPU from CO2-polyol to fulfil the long-term use requirement.By adjusting the amount of photoinitiator,UV-dose,side chain double bond density and hydrophilic group content,the UV-cured CO2-CWPU film reached water absorption equilibrium at 72 h,maintaining water absorption rate as low as Ca.5.8%even immersed in water for 240 h.Compared with polyester or polyether based CWPUs,CO2-CWPU provided excellent water resistance in HCl solution.In addition,the tensile strength of CO2-CWPUs with different contents of carbonate units was adjusted from 12.0 MPa to 24.0 MPa,which retained above 90%in different corrosive media immersion.3.A solvent free route to eco-friendly cationic waterborne polyurethane derived from CO2-polyol was developed,using butyl acrylate(BA)as diluting agent to avoid the addition of organic solvent,while CO2-CWPU acted as macromolecular emulsifier during free radical emulsion polymerization of BA,forming CWPU grafted poly(butyl acrylate)dispersion.Compared with non-functional CWPU,the emulsion introducing double bonds was more stable,possessing higher Zeta potential and unimodal particle size distribution.Meanwhile,the film showed excellent thermal stability and widely adjustable mechanical properties,which was expected to show broad applications in polyurethane coatings and adhesives.