| Waterborne polyurethanes(PU)are normally dispersed in water and are nonflammable,odorless and enviromentally friendly.Other advantages of waterborne PUs include convinient processing,good mechanical properties,super freeze resistance and alkali resistance,high elasticity and stable hardness-softness against temperature.In recent years,waterborne PUs have been widely used in textile,leather processing,coating,timber processing,bulding materials,papermaking,adhesives,etc.However some shortcomings such as their low resistance to high temperature and water limit the extensive utilization of PU materials.Compared with PU,Polyacrylate(PA)emulsion is good at water and weather resistance,but is easy to be solved by nonpolar solvents.Thus PA modified PU can combine the advantages of both and has been studied extensively in the past decades.The work presented here focused on the detailed studies of a special PA modified PU which was derived from m-tetramethylxylylene diisocynate(TMXDI).Chapter one reviewed recent research progress on PU,waterborne PU and their preparation methods.In this part,the solution properties and the structure-property relationship of different PU dispersions were also summarized.In chapter two,the influence of reaction parameters was investigated carefully on the TMXDI based PUs modified by polyacrylate.A stable emulsion can be obtained under the following conditions:using AIBN as initiator,R(NCO/OH molar ratio)=1.5,the DMPA content = 6.44%,the PEG content = 7.1%and the PU/PA weight ratio=3/2.Particle size,surface tension and solubilization capacity of the aqueous PU dispersions were also characterized.NMR and IR were used to determine the molecular structure of the PU chains.TEM showed that the synthesized PUs consist of spherical particles.In chapter three,in order to study the influence of hydroxyl acrylate monomers on the properties of waterborne polyacrylate modified PU,a method was established to verify the polymer distribution in the TMXDI-based PU prepolymer system.At low HPMA/NCO ratio,the main component of the PU prepolymer is mainly the form of PU1(only one polymerizable double bond exists in this prepolymer),acting as a kind of polymerizable emulsifier in later radical polymerization with arylic monomers.When HPMA/NCO increased,PU1 content decreased.While the content of PU2,the prepolymer with both polymerizable double bonds,gradually increased.At this stage,PU prepolymers act as not only emulsifiers but also cross-linking agents.Thermo and mechanic properties and the water absorption of the polymer film were measured to verify the proposed mechanism.In chapter four,the method for the one-step synthesis of functional waterborne acrylate modified PUs with high carboxyl(-COOH)content was established.It was found that,when low amount of methacrylic acid(MAA)is used,the yielded polymer has a core-shell structure with the hydrophilic PU shell and hydrophobic PA core.When MAA content is high,PAs congregate at the surface while PUs distributed within them.Additionally,the functional waterborne acrylate modified PUs with high carboxyl(-COOH)content was used as capping agent in the preparation of copper nanoparticles.In chapter five,polyacrylate modified PUs were modified by organic silicon monomers and inorganic silica nanoparticles.In organic silicon modified polyurethane method,the reaction between hydroxyl group of organic silicon and-NCO groups of TMXDI was used to establish the chemical modification of PU materials.Inorganic silica nanoparticle modified polyurethanes were conducted by two methods.One is to mix polyurethane dispersions directly with nanoparticles,and another is to use double bond on the surface of silica nanoparticles to chemically react with PUs.Organic silicon and inorganic silica modified polyurethane materials can obviously improve the water resistance property.The water resistance of C5 sample is much better than the physical mixed samples.The tensile strength of the C5 is the highest. |
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