Syntheses And Viscoelasticity Studies Of UPy-Contained Main Chain Supramolecular Polymers

As a new kind of polymer material,the supramolecular polymer based on ureidopyrimidone structure(UPy)with non-covalent bond exhibites specific properties and has a good application prospect.The viscoelasticity of the polymer determines its mechanical properties and applicable conditions,and the viscoelasticity of the polymer is closely related to its own chemical structure,as is the case with supramolecular polymers.The supramolecular polymer is composed of a UPy structure,isocyanate structure and main chain polymer.Among them,the 6-substituent in the UPy structure,the isocyanate structure and the main chain polymer can affect the viscoelastic properties of the supramolecular polymer.Based on the problems above,the effects of chemical structure on viscoelasticity were studied by designing and synthesizing supramolecular polymers with different structures.First,seven different structures of UPy synthons and their derivatives were prepared by changing the isocyanate and isocytosine 6 substituents in the synthon.The intrinsic aggregation structure of the synthon and its derivatives was studied by FT-IR,'H-NMR,XRD,UV,SEM,TEM,AFM and other methods.Thereafter,13 corresponding supramolecular polymers were synthesized by reacting with the terminal hydroxyl polymer based on the UPy synthons of the different structures synthesized above.The effects of chemical structure changes on the viscoelasticity of supramolecular polymers were investigated by FT-IR,1H-NMR,SAXS,TEM,AFM and other methods.Finally,two kinds of thermodynamically incompatible supramolecular polymers were selected to prepare different ratios of supramolecular polymer blends,The phase separation phenomenon and the influence on viscoelasticity of different proportions of supramolecular polymer blends were studied by FT-IR,1H-NMR,DSC,DMA and static tensile mechanical tests.In summary,the following conclusions were obtained:The 6-substituent on the UPy structure would affect the density of the ?-electron cloud With the increase of the electron-donating effect of the 6-substituent,the density of the?-electron cloud increased gradually,which resulted a strong hydrogen bond.Due to the increase of the density of the ?-electron cloud,the electron repulsion among ? bonds was enhanced,resulting in increasing of the(001)interplanar spacing in the derivative.The rising of the steric hindrance of the isocyanate structure has hindered the ?-? interaction between the pyrimidine rings,which would increase the spacing of(001)crystal plane for the derivative.A distinct nanofiber structure could be observed in the supramolecular polymer with small steric hindrance at the 6-position of pyrimidone,which would lead to a significant microphase separation.With the growth of steric hindrance for the 6-position substituent and the isocyanate structure,the nanofiber structure destructed,as well as the phase separation degree in the supramolecular polymer gradually declined.The maximum value of storage modulus of the supramolecular polymer decreased exponentially along with the microphase separation degree,while the maximum value of the loss modulus and the peak area of the loss modulus decreased linearly.The content of nanofiber structure showed a decreasing trend by reducing the UPy content in the same structure mainchain polymer.The increase of the UPy content could improve the mechanical properties of the material.It could be observed that a large size and amount of the hard segment was formed by self-assembly of the UPy dimmer with a soft and flexible mainchain polymer soft segment,which also led to a low melting point and glass transition temperature of the polymer.The empirical formula for the linear increase of the loss modulus peak area versus the hard segment content was obtained according to the experimental data.The slope in the formula was the integral of the contribution difference between the soft and hard segments to the loss modulus versus temperature,and the intercept was the integral of the contribution of the soft segment to the loss modulus versus temperature.For the binary mixed system,this study focused on a method for studying the degree of phase separation of thermodynamic incompatible systems using the glass transition enthalpy of the polymer.The two thermodynamically incompatible soft segments of the mainchain polymer were restricted in a certain region due to the aggregration of the UPy end group so that the soft segment mainchain polymer would have interaction between each other,thereby forming a third phase.When the binary component molar ratio was between 80:20 and 70:30,there were the highest content of the third phase,which leading to the maximum elastic modulus,elongation at break and the storage modulus.In the binary component,the loss modulus peak area was related to the content of the soft and hard segments.According to mathematical induction,we applied the empirical formula of the binary component blend polymer to the polymer blend of the n-component.