Synthesis Of Liquid Crystalline Polymers Containing Diverse Functionality Controlled By Polybutadiene

Side chain liquid crystal polymers（SCLCPs）possess excellent properties due to the combination of amorphous polymer skeletons and anisotropic side chains.Through reasonable design of polymer skeletons and liquid crystals（LCs）with different function,polymers that will show some special functions can be obtained,which have resulted in a great progress in integrated and intelligent advanced polymer materials.With the development of polymer science in recent years,the diversity of liquid crystal polymers（LCPs）containing complicated structures has put forward a new challenge in the construction of structure-property relationship and their precise mechanism.The design of functionality that alters the molecular interaction becomes a new research topic.Living anionic polymerization（LAP）with easy implement has been always utilized to create diverse polymeric architectures with well-defined molecular weight and narrow polydispersity index（PDI）,which has become one of most efficient methods for the synthesis of general rubber and elastomers.Polybutadienes（PBs）as the typical synthetic rubber produced from LAP not only have double bonds served as the post-functionalized site with microstructural and morphological diversity,but also show a low glass transition temperature（T_g）available for LCPs with a room temperature T_g.From the perspective of molecular design,this work hence investigated the microstructural control of properties of the synthetic LCPs containing diverse functionality controlled by PB microstructures.Furthermore,the influence of molecular design and processing design on properties of LCPs is explored.（1）PBs with control of microstructures,i.e.,1,2-olefins ranging from 8%to 94%（mole fractions）,were readily synthesized using living anionic polymerization（LAP）.It shows the determination of refractive index increasement（dn/dc）and weight-average molecular weitht（Mw）of PBs using gel permeation chromatography equipped with differential refractive index（RI）and low angel laser light scattering（LALLS）detectors（GPC-RI/LALLS）.These PB backbones were subsequently used as precursors for the synthesis of PB-based liquid crystal polymers（LCPs）（PB-M₁ and PB-M₂）with microstructural control of grafting densities of 15%,30%and 50%（moles）after the longitudinal attachement of azobenzene moieties（Azo-M₁ and Azo-M₂）along to PBs.The experimental results have demonstrated that PB-M₁ and PB-M₂show an increased grafting density up to 50%followed by increasing the1,2-olefin content of PBs.More importantly,the unchanged grafting density（almost 50%）with increasing 1,2-olefin fractions was observed for both PB-M₁ and PB-M₂,which explained the 1,2-olefin microstructural control in terms of phase transitions regardless of whether Azo-M1 or Azo-M2was used as a side attachment,where the temperature range of mesogenic formation（ΔT）and LC-to-isotropic phase transition（Ti）increased with the 1,2-olefin fractions.（2）Based on commercial three block copolymer（styrene-butadiene-styrene）SBS,liquid crystal elastomers（LCEs）have been synthesized in combination of"thiol-ene"click and esterification reactions,where azobenzene LC moieties（Azo-M₃）have been incorporated into PB block with control of the double bond and SH groups ratios in feeding,as well as the content of hydrogen-bonding(2-urea-4[1H]pyrimidone（Upy）（5%,10%,20%）as a dynamic crosslinking agent.In addition,LCEs with different ratios of Azo-M₃ and Azo-M₄ LCEs were designed and synthesized by introducing Azo-M₄.The experimental results have demonstrated that the synthesized LCEs show a good film-formation property.The infrared dichroism of the N=N bond is different after stretching.More importantly,after mechanical stretching,the mesogenic orientation of LCE films was studied.And reversible photodeformation and insignificant thermal deformation were observed.Dynamic crosslinking is reversible and LCEs membrane reprocessing can be realized.Furthermore,by controlling the feeding ratio of Azo-M₃ and Azo-M₄,T_g and T_i values of LCPs have been modulated,which is the fundamental research for further exploration.