Study On The Synthsis And Performance Control Of Side Chain Liquid Crystalline Polymers

Side chain liquid crystalline polymers(SCLCPs)with an excellent combination of liquid crystalline(LC)and polymer characteristics have gained contentious attentions owing to the widespread applications.Recently,more attentions were paid to the appearing of new applications,the design of new molecular architectures and the discovery of new mosophases.It is always necessary for SCLCP materials to solve problems that the response time and applicable temperature(room T.and wider ?T).Changing the flexibility of main chains and choosing appropriate spacers are simple methods.SCLCPs exhibit excellent performances that are inseparable with molecular design.It was desired to modulate the properties by tailoring molecular design.Developing new LC polymers with well-defined structures and properties become a dramatic challenge but of vital importance.In view of above problem,this paper begins from reasonable molecular design.SCLCPs with the same mesogens(Chol-)but different spacers,flexibility of backbones,topologies and grafting density were synthesized via the methods in effective combination of living anionic polymerization and hydrosilylation.Based on the design of PS and PB rigid/flexible main chains,concerining the dynamic behavior and cooperative effect of different factors,the research about molecular design and performance regulation was realized:(1)Based on flexible main chains,new series of linear-comb and star-comb PB-SCLCPs with narrow PDI and well-controled molecular weight have been suscussfully synthesized,namely,hvPB/lvPB-SCLCPs bearing different PB-microstructures,presenting well-designed 70%and 40%grafting density respectively,the structure-property relationship focused on the cooperative effect of grafting density and topology was systematically studied.It was demonstrated that lvPB/hvPB-SCLCPs exhibited essentially constant bilayer SmA phase around room temperature(Tg=12-4?),and exhibiting wide ?T(85-197?).Surprisingly,compared lvPB-SCLCPs with hvPB-SCLCPs,the trend of lvPB-SCLCPs displaying the effects of topology on phase transitions and micro-structures was just different from that of hvPB-analogies owing to the differenc of grafting density.For hvPB-SCLCPs,S-hvPB-SCLCPs containing high density mesogens were desired to generate wider AT and higher molecular order in comparison with L-hvPB-SCLCPs,while for lvPB-SCLCPs,L-hvPB-SCLCPs containing high density mesogens were desired to generate wider ?T and higher molecular order in comparison with S-hvPB-SCLCPs.In particular,the unique differences of macromolecular aggregation state arrangement between L-hvPB-SCLCPs and S-hvPB-SCLCPs were observed from POM.The possible molecular arrangement model of two analogous architectures was constructed,that was used to systematically investigate the relationship of molecular force and the formation of LC phase.(2)Based on flexible main chains,new series of linear-comb and star-comb PS-SCLCPs with narrow PDI and well-controled molecular weight have been synthesized,containing SiH and Vinyl functionalized PS main chains,namely PVPDMS-SCLCPs and PVSt-SCLCPs,bearing the specific[Si-O-Si]and[Si-C]as spacers separatively.Herein,well-designed grafting density(90%,70%and 40%)was readily performed.The study compared the difference of[Si-O-Si]versus[Si-C]spacer followed by grafting density.It was demonstrated that PVPDMS-SCLCPs and PVSt-SCLCPs exhibited essentially constant SmA,PVSt-SCLCPs obtained lower Tg(22-46 ?)and larger d-spacing(40.1-52.4 A),PVPDMS-SCLCPs(122-158 ?)and PVSt-SCLCPs(130-151 ?)presented similar AT in more than 90%grafting density,in addition,the AT both exhibited the decreasing trend followed by decreased grafting density,while the decreasing trend in AT of PVSt-SCLCPs was fast[148-94-51 ?],in contrast,that of PVPDMS-SCLCPs was slow[144-120-115 ?],especially for the grafting density from 70%to 40%,AT kept constant.This phenomenon was further confirmed by POM,[Si-O-Si]as spacer was applicable to advantageous decoupling effect,presenting the better polarized optical property and wider AT.The design systematically allows for precision in flexible/rigid matrixes.It was demonstrated that PB-SCLCPs presented better performance,but PS-SCLCPs also displayed the better performances in more than 90%grafting density.(3)Based on rigid and flexible block copolymer main chains,new series of linear-comb and star-comb[PVSt-co-lvPB]-SCLCPs with narrow PDI and well-controlled molecular weight have been synthesized,PVSt and lvPB was grafted on the same LC mesogens.Well-designed 60%and 40%grafting density in total was readily performed,of which 100%,70%or 40%grafting density in PVSt was achieved,the bifunctional LC block copolymers have been synthesized,and the structure-property relationship was systematically studied.It was demonstrated that the effect of topology was indistinctive on the structure and performance,while Tg and AT increased,polarized optical property was better owing to the increasing grafting density.The structures of PVSt-SCLCPs and lvPB-SCLCPs LC blocks showed mutual promotion cooperatively in performance by varing the block ratio.In addition,the microphase separation of block copolymers focused on the varied grafting density was studied.It was demonstrated that PVSt-co-lvPB showed the typical island morphology structure of microphase separation in AFM,while the microphase separation of[PVSt-co-lvPB]-SCLCPs with 60%total grafting density was indistinctive,and the influence of topology and block ratio on phase separation was also indistinctive,but the microstructures of[PVSt-co-lvPB]-SCLCPs gradually varied into phase separation to some extent owing to the increasing grafting density.