Synthesis And Self-assembling Behavior Of Azobenzene Based Liquid Crystalline Block Copolymers Containing Polydimethylsiloxane

In this thesis,the self-assembling behavior in bulk and thin films of the block copolymers composed of polydimethylsiloxane(PDMS)and azobenzene-based liquid crystalline polymers with different end groups were studied.The microphase separation structures of block copolymer thin films after thermal annealing and photoinduced orientation were studied with emphasis.The mechanism of microphase separation structure change was investigated by atomic force microscopy(AFM),UV-Vis absorption spectrometer and small/middle angle scanning X-ray scattering(GI-SAXS/MAXS).In block copolymer thin films,it's the first time that PDMS nanocylinders with orientation perpendicular to the substrate was obtained benefitting from the optical orientation of azobenzene liquid crystal polymer.In addition,the thermal stability of the oriented structure was improved by introducing chalcone liquid crystal elements with photocrosslinking properties.On this basis,thin films' application in nanometer template is preliminarily explored.This paper is mainly divided into the following parts:(1)Using n-butyl as the end groups of azobenzene liquid crystalline monomer,a series of different molecular weight of diblock copolymer PDMS65-bPM11 Azo C4n(D65An,65 and n represent the PDMS and PM11 Azo C4 polymerization degree)were synthesized with relatively narrow distribution by atom transfer radical polymerization(ATRP),whose self-assembled structures in bulk were studied by SAXS.Samples with hexagonal columnar phase(HEX)in bulk were used to prepare block copolymer thin films by solution spin coating.The films with 120 nm were annealed at 95 ? and 145 ? respectively.It was observed from AFM that the higher the annealing temperature,the more regular the microphase separation structures of the thin films.(2)The end group of azobenzene was changed to the cyanide group,and the pseudo-astragaloid azobenzene liquid crystal polymer was prepared,whose light response was faster.Diblock copolymer PDMS65-b-PM11 Azo CN35(D65CN35,65 and35 is the polymerization degree of PDMS and PM11 Azo CN,respectively)was synthesized,in which the volume fraction of PDMS was 24%.The self-assembling structure of the block copolymer was proved to be HEX by SAXS.Block copolymer thin films were prepared by spin coating with different solution concentrations.The dependence of film thickness on the orientation of microphase separation structure was investigated by using two light sources(linearly polarized light and unpolarized light).The study found that: the orientation of microphase separation structure have certain dependence on film thickness.With the increase of film thickness,the arrangement of PDMS nanocylinders ccurred the transition from parallel to perpendicular to the substrate induced by the linearly polarized light.When the light source is unpolarized light,the structure is out-of-plane uniaxial orientationin in the whole film thickness range.(3)In order to strengthen the thermal stability of microphase separation structure of block copolymer thin films,the photocrosslinked chalcone liquid crystal monomer was copolymerized with the pseudo-astragaloid azobenzene liquid crystal monomer,PDMS-b-(PM11Azo CN-co-PM11 Ch C4)was synthesized which the self-assembling structure is HEX in bulk.First,PDMS nanocylinders arranged perpendicular to the substrate was prepared by unpolarized light orientation,then was irradiated under ultraviolet light at the temperature of liquid crystal phase,so that the chalcone group was cross-linking to fix the microphase separation structure,thus the block copolymer thin film with certain self-supporting property was obtained.AFM,GI-SAXS and transmission electron microscopy(TEM)were used to characterize the structure of the cross-linked thin films.The results showed that the microphase separation structure with PDMS nanocylinders perpendicular to the substrate were maintained during the cross-linking process.