Hydrolysis And Condensation Behavior Of Polypolyacids And APTES Supramolecular Self-assembly System

Recently,silicon-based hybrid materials have been extensively attracted because of that they possess both inorganics stability and organics functionality.Sol-gel method is one of the most widely used ways to prepare various kinds of silica-based hybrid materials.Based on the sol-gel process,the precursor,siloxane,has been applied for self-assembling with different functional additive molecules when they are hydrolyzed and condensed to form different organic-inorganic hybrid materials.Compared with other technology,the process for design and preparation of silicon-based hybrid materials based on the sol-gel method is conducted on the molecular level and,consequently,that it has significant advantages such as controllability for reaction course,material structure and performance,as well as good dispersion of the product.Generally,the study on supramolecular self-assembly of siloxane are mainly focused on the self-assembly behavior of hydrolysis species of siloxane,and few attentions is paid for the self-assembly behavior between organic siloxane and exogenous species.Undoubtedly,the self-assembly of exogenous species and organic siloxane by the specific interactions of recognizable groups would supply more novel ideas for the preparation of silicon-based composite.Therefore,the study about self-assembly of organic siloxane and exogenous species not only enrich the corresponding theory,but also provide application for producing silicon composite with high-performance.In the present work,by using the acidic groups（i.e.phenolic hydroxyl and phosphate group）and amino as recognizable groups,the supramolecular self-assembly system of poly-acid（tannins and phytic acid）and 3-ammonia propyl triethoxy silane（APTES）was conducted.The influence of temperature,molar ratio,electronic effect,solvent effect and water content on the self-assembly was investigated.The paper mainly includes the following two parts:1.The research of self-assembly behavior of tannic acid and APTESThis experiment explored the supramolecular self-assembly system of APTES and TA in different solvents.The self-assembly product could be gel or microsphere,which was decided by the dielectric constant of solvent.The hydrolyzation and condensation of the only APTES would form six-member ring cluster by the interaction of silicon hydroxy and amino,which inhibited the condensation between Si-OH to generate a gel product.When TA was introduced in the APTES system,some recognizable groups from TA interacted with amino on APTES to restrict the formation of cluster Hence,the condensation of Si-OH on APTES would go on to produce a gel or microsphere.A typical gel and microsphere system of APTES and TA were chosen as the object,and the influence of reaction temperature,molar ratio,water content on the self-assembly behavior were investigated.The self-assembly mechanism was explored by characterising product at different period with NMR,XPS,FT-IR,TGA and elemental analysis.The results showed that:（1）In the process of self-assembly,the interaction of amino on APTES and the hydrogen from TA exhibited the property of ionic bond,which was seriously affected by the dielectric constant of solvent.The protonated ability of amino,a decisive factor of the electrostatic interaction between TA and APTES,decreased as the increase of dielectric constant of solvent and vice versa.Namely,the APTES was more easily gelatinized by TA in the solvent with a smaller dielectric constant.（2）In the solvent of dimethyl sulfoxide（DMSO）,a gel system was formed by the self-assembly of APTES and TA.The gel with a three-dimensional network structure was mainly constituted through the ionic bond（NH₃⁺-OAr）,hydrogen bonding（Si-OH…HO-Ar）and condensation of Si-OH;the interaction of NH₃⁺-OAr inhibited the formation of cluster of APTES,which improved the condensation of Si-OH to produce a linear skeleton.The linear skeleton was associated with TA by multi-site crosslinkers of ionic bonding and hydrogen bonding and therefore to form a gel product.In a certain range,the increase of water content and the increment of temperature would accelerate the hydrolysis of APTES and,thus facilitate the supramolecular self-assembly of TAand APTES to form gel.（3）In anhydrous ethanol（CH₃CH₂OH）,TA interacted with the hydrolyzate of APTES by ionic bonding and hydrogen bonding to form self-assembled microspheres.The particle size of microsphere increased as the increase of TA content.The particle size of microsphere increased as the increase of TA content.The particle size increased with the water content,and decreased as the further increase of water.2.The study of supramolecular self-assembly behavior of phytic acid and APTESThe supramolecular self-assembly behavior of APTES and PA in different dielectric constant and the acetone was studied in this part.The influences of temperature,molar ratio and water content on the supramolecular self-assembly behavior were studied by utilizing NMR,XPS,FT-IR,TGA and element analysis.The results showed that:（1）The self-assembly of APTES and PA severally formed the gel-free,transparent gel,semitransparent gel and opaque gel products in the solvent of water,DMSO,acetone and tetrahydrofuran as the decrease of dielectric constant.This was consistent with the above-mentioned conclusion that the electrostatic interaction of self-assembly was affected by the dielectric constant of solvent.The solvent with greater dielectric constant was adverse to the formation of ionic bond as well as intramolecularly six-member ring and,hence gone against the condensation of APTES.The solvent with small dielectric constant could not solvate the self-assembly unit.This further proved the influence of dielectric constant on the electrostatic interaction in the self-assembly system.（2）The content of trace water significantly affect supramolecular self-assembly of APTES and PA by altering the crosslinking condensation of APTES hydrolysate.In the water-free system,APTES could not hydrolyze and therefore the crosslinking condensation of APTES as well as the products of gel or precipitate would not form.However,the water,with a greater dielectric constant,destroyed the stability of ionic bond between APTES and PA.So,in a certain range,the transparency of self-assembly gel decreased as the increase of water,and finally precipitated.This is due to that the increase of water promoted the hydrolyzation and condensation of APTES but suppressed the electrostatic interaction of NH₃⁺-OP,resulting in a destruction of the gel.Then,the hydrolysate of APTES condensed and crosslinked to cause an insoluble sphere product.（3）Elevation of the self-assembly temperature no only promoted the further hydrolyzation and condensation of APTES-PA but also seriously affected the morphology of the product.The solvent could be volatilized as the increase of temperature,resulted in a separation of product and solvent,which turned the product from sphere to irregularity.（4）The self-assembly of APTES and PA changed gradually from the transparent gel to the precipitation constituted by spherical particles as the increase of PA.A small number of PA could combine several APTES,which leaded to a crosslinking condensation between APTES hydrolysates and formed a gel.However,more APTES was bonded in the system containing much PA,which promoted the crosslinking condensation of APTES hydrolysate and increased the crosslinking density of the self-assembly.Then,a granular product with clear interface was obtained.It is difficult to controllably prepare functional silicon-based material under the ordinary condition because the hydrolysis product of aminopropyl siloxane contains the both alkaline-NH₂ and acidic Si-OH,which react readily with each other.A massive works about the self-assembly of aminopropyl siloxane and exogenous molecule containing carboxyl have been done in our group.Two natural poly acids（TA and PA）were selected as the exogenous species for the controllable self-assembly with APTES for the first time.Similar to the carboxyl,the phenolic hydroxyl of TA and phosphate group of PA could form the aptamer with amino,which prompted the production of supramolecular self-assembly system from APTES and gained diversified organic silicon composite materials.Our work had values both in theory and application for the design and preparation of organic silicon composite materials.