Modification of Silicone Polyurethane
Jul 25, 2023
The synthesis of organosilicon modified waterborne polyurethane dispersion (CADPSUR) usually involves two main steps in the preparation of most ADPURs: the participation of oligomer diols in the formation of high molecular weight polyurethane or medium molecular weight polyurethane prepolymers Dispersion in water under shear force. The preparation of ADPUR usually adopts two types of methods: external emulsification method and self emulsification method. External emulsification method is to force polyurethane prepolymer or polyurethane organic solution to be emulsified in water in the presence of emulsifier and high shear force to form lotion. The polyurethane lotion prepared by this method has poor storage stability, and the physical properties of the film formed are poor.
Self Emulsifying Method of Polyurethane
Self emulsifying method is to directly introduce hydrophilic groups into the molecular chain, making the molecular parts hydrophilic and dispersing the entire molecule in water. According to the different Chain reaction, self emulsifying methods can be divided into acetone method, prepolymer dispersion method, melt dispersion method, keto imine/ketone azo method, end capping emulsification method, etc. The acetone method and prepolymer dispersion method are more mature among them.
The preparation of ADPSUR mostly adopts the prepolymer dispersion method, that is, the organic silicon polyurethane prepolymer containing hydrophilic groups with terminal NCO groups is dispersed in water under high shear force with little or no solvent when the molecular weight and viscosity are small. Water can be used as a chain extender, and high reactivity diamine chain extenders can also be used to expand the chain in water to generate high molecular weight polyurethane.
According to the type of functional group, it can be divided into tibial modification method, amino modification method, and silane coupling agent modification method. At present, there are four methods for copolymerization modification of polyurethane by organic silicon based on the structure of organic silicon: CD silicone alcohol modification method Aminoalkyl polysiloxane modification method Modification method of polysiloxane with light burning base sealing Alkoxysilane crosslinking modification method. In the modified copolymer, the soft segment of polysiloxane/or polyester chain segment gives the material good elasticity, while the hard segment of polyurethane and polymer chain segment increases the strength of the material.
Modification method of light base terminated siloxane
Organic silicon contains active light groups that can react with the isocyanate NCO in polyurethane, which is the main reason why organic silicon compounds can modify polyurethane, thus achieving the copolymerization of the two. According to the different connection methods between the silicon atom and the silicon atom, there are two types of organic siloxane modification methods: the siloxane type with the tibia group directly connected to the silicon atom, and the organic siloxane modification method with the alkane light group indirectly connected to the silicon atom.
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