Preparation Of Polyacrylates By Pickering Emulsion Polymerization And Its Modification To WPU

Pickering emulsion polymerization is a kind of emulsion polymerization method using solid particles instead of traditional emulsifier,which has been widely used in the field of preparation of organic-inorganic hybrid functional polymer composites.The waterborne polyurethane（WPU）material has the drawbacks of poor heat resistance and water resistance.In order to improve the comprehensive performance of WPU and expand its application,this paper innovatively adopt the way of Pickering emulsion polymerization to achieve double modification to WPU with polyacrylate and inorganic nanoparticles.In this paper,nano-SiO₂ particles with different size were prepared by St?ber sol-gel method.The surface wettability of nano-SiO₂ was modified by hexamethyldisilazane（HMDS）.The degree of hydrophobicity was changed by controlling the reaction conditions,so as to obtain the nano-SiO₂ particles with moderate hydrophilicity.And then used as the solid particle stabilizer to prepare polyacrylate/SiO₂ organic-inorganic hybrid emulsion by Pickering emulsion polymerization.The results show that the modified nano-SiO₂ particles with moderate hydrophilicity can replace the traditional surfactants and have good emulsifying ability in the emulsion polymerization of acrylic acid.In addition,the heat resistance,water resistance and mechanical strength of polyacrylate/SiO₂ composites were enhanced with the increase of the amount of nano particle SiO2.The polyacrylate/SiO₂ hybrid emulsion was further blended with the waterborne polyurethane to realize the double modification to WPU by polyacrylate and nano SiO₂ particles.The results show that the heat resistance and water resistance of the composite latex film were obviously improved compared with the single WPU.However,the biggest drawback of this blend compound emulsion is the poor compatibility,the stable storage period is less than six months,so it is difficult to meet the requirements of commercial applications.Aiming at the disadvantages of poor stability of the blended composite emulsion,the reactive polyurethane polymer emulsifier emulsion（WPU-HEMA）was synthesized by the reaction of hydroxyethyl methylacrylate（HEMA）with waterborne polyurethane prepolymer.And then cooperate with moderate hydrophilic nano-SiO₂ particles as the composite emulsifier of acrylic mixed monomers,and the chemical crosslinking WPU-HEMA-Pickering polyacrylate composite emulsion was prepared by Pickering emulsion polymerization.The results show that when the amount of acrylate compound is less than 40wt%,the composite emulsion can form film at room temperature,and the storage stability period is more than six months.Infrared test and NMR analysis show that C=C has been introduced into the WPU molecular chain,confirming the accuracy of the structure of the reactive polyurethane emulsifier（WPU-HEMA）.The surface tension test shows that WPU-HEMA has good emulsifying ability.The GPC test showed that the molecular weight of the composite film increased significantly compared with the single WPU.TG test showed that the temperature correspond to the maximum weight loss rate Tmax and completely degraded T_end of the composite film were improved greatly compared with the single WPU-HEMA latex film with the increase of the acrylate content in a certain range.The thermal stability was improved.The water absorption of the composite latex film decreased from 23.5wt%to 5.4wt%,and the tensile strength increased from 8.52MPa to 33.41MPa,and the water resistance and mechanical properties were improved obviously.