Kinetically Induced Disorder Bicontinuous Structure Self-assembled By Block Copolymer

Bicontinuous phase refers to the phase regions of a system in which two phases composed of different components are continuous respectively and intersecting with each other at the same time.On the one hand,the formation of the bicontinuous phase will cause a significant effect on the macroscopic properties(such as mechanical properties,etc.)of the material.On the other hand,porous materials with continuous channels can be obtained by selective etching from the bicontinuous structure.Due to the three-dimensional interconnection and high specific surface area,this kind of porous material has great value in numerous applications,such as filtration,separation,catalyst loading and so on.Block copolymers are composed of two or more chain segments formed by different chemical structures connected by covalent bonds.In general,mesoscale ordered structures can be formed through microphase separation of block copolymers,including several ordered bicontinuous structures,such as double gyroid(DG),double diamond(DD),etc.However,these bicontinuous phase structures only appear in a very narrow window of the phase diagram and in most cases,are difficult to fabricate.Therefore,efficiently fabricating mesoscopic bicontinuous structures through block copolymers has significant research value and practical significance.In this paper,we studied the method and mechanism of the formation of the disordered bicontinuous phase(DBP)induced by kinetic control in the blend system of block copolymer and homopolymer.The disordered bicontinuous mesoporous material was prepared base on this,furthermore the templating method using the mesoporous material was explored.The main research contents and conclusions of this paper are as follow:(1)A series of polystyrene-b-polylactide block copolymers(PS-PLA)and homopolymers of polystyrene and polylactide were synthesized by atom transfer radical polymerization(ATRP)and ring-opening polymerization(ROP).In the blend system of PS-PLA and PLA,the disordered bicontinuous structure was obtained in a wide blending proportion through solvent evaporation induced self-assembly.The results show that only dichloromethane can be used as a solvent to obtain the structure,while toluene,1,2-Dichloroethane,chloroform and other solvents can not induce the formation of disordered bicontinuous structure.The disordered bicontinuous structure disappeared after thermal annealing or prolonging the evaporation time of solvent,which proved that the formation of the structure was a kinetically controlled process.By changing the molecular weight of PLA homopolymer,it was found that the final self-assembly structure was related to the relative molecular weight of block copolymer and homopolymer.(2)The blends of PS-PLA and PS were studied,and it was found that at a certain blending ratio,disordered bicontinuous structure could be obtained by solvent evaporation.By changing the content of PS homopolymer,the PS-PLA block copolymer underwent a morphology transition process of"lamellar—disordered bicontinuous—cylinder".The influence of solvents,thermal annealing and other factors on the self-assembly morphology was investigated.It was confirmed that the formation of disordered bicontinuous structure in the system was controlled by kinetic factors.(3)Through selective etching of PS-PLA blend system,mesoporous material with disordered bicontinuous channels was obtained.The average pore diameter of the porous material is 3.9?27 nm,and the specific surface area is 60?194 m~2/g.Using the porous material as a template,mesoporous silica was successfully prepared.In this paper,solvent evaporation induced self-assembly behavior of blend system of block copolymer and homopolymer was studied.A rapid and efficient approach to fabricate disordered bicontinuous structure was established.Disordered bicontinuous structure can be fabricated efficiently in a wide range of blending ratios through this method,and the method has high tolerance for the molecular weight and polydispersity of block copolymers,evaporation rate of solvents and other parameters.More importantly,mesoporous polymer materials can be obtained through this approach.This work provides a new pathway for the application of block copolymers in filtration,adsorption,catalysis and other fields.