Side-Chain Liquid Crystalline Polyethers And Their Copolymers:Anionic Polymerization,Structures And Properties

Side-chain liquid crystalline?SCLC?polymers are of both theoretical and practical interest,since they combine the anisotropy of liquid crystals with polymeric properties.Among the various types of liquid crystalline polymers,polyether is particularly attractive for its important characteristics including high chemical stability,good elastic and adhesive properties.More importantly,besides the advantages mentioned above,it's a typical type-A polymer,which has a cumulative longitudinal dipole moment along its backbone,the global motion of this polymer could be reflected by its dielectric fluctuation of the end-to-end vector.However,synthesis of well-defined SCLC polyether with low polydispersity,controlled chain length and end functionality remains a great challenge.In this work,we have successfully synthesized a series of well-defined polyethers based SCLCs with different chain structures and architectures via anionic ring-opening polymerization.Both chain dynamics and phase behavior of homopolymers and phase structures of copolymers have been investigated.Side chain liquid crystalline polyethers with different molecular weights and well-defined chemical structures are successfully synthesized by anionic polymerization.The phase behavior and structures of the polyethers have been investigated by combining various techniques including DSC,X-ray scattering and POM.Three phase states are generally observed for all of the SCLC polyethers,the higher temperature state is identified as a SmA phase,lower temperature state exhibits a complex phase which is a mixture of a HexB phase and a frustrated HexB phase in analogy to smectic antiphase,and last state is amorphous.These three states are reversible in the cooling-heating cycles.The chain dynamics and statistics of type-A SCLC polymer are experimentally explored by using broadband dielectric spectroscopy.We find that the chain dynamics in the liquid crystalline phase?SmA?is slower than that in amorphous state,and has higher apparent activation energy comparing to the isotropic melt.The molecular weight M_w dependence of the normal mode relaxation time?_n in the isotropic melt conforms to the Zimm model,while in the SmA phase it shows Rouse behavior.The mean squared end-to-end distance of these different molecular weight SCLC polymer chain in the SmA phase decreases comparing to that in the isotropic melt.The main chain takes a self-avoiding walk in the isotropic melt,whereas a random walk in the SmA phase,consistent with the results from chain dynamics.A series of well-defined block copolymers with the exactly same length of LC block were synthesizied by introducing 1,2-Butene oxide into the reaction system.Combining with DSC and temperature dependence X-ray diffraction method,both micro-phase separation structure and liquid crystalline phase behavior of block copolymers were investigated.Most of the samples exhibit a HPC structure,and explored the relation between the content of PBO and the size of the phase separation structure.The introduction of PBO block broke the original HexB anti-phase in homopolymers,at room-temperature,block copolymers with low PBO content show HexB phase whereas high PBO content exhibit SmA phase.Two dimension phase diagram was drawn based on the results of temperature dependence of SAXS.By adding the liquid crystalline monomer and 1,2-Butene oxide into the flask at the same time,a set of well-defined liquid crystalline gradient copolymers were gained by taking an aliquot at a particular time during the polymerization.The thermal transitions,phase structures and the evolutions of liquid crystalline gradient copolymers with composition and temperature were systematically investigated.Compared with the corresponding liquid crystalline block copolymers,the gradient copolymers exhibited a broad glass transition region and a large breadth of liquid crystalline phase transformation associated with disordered mesogenic packing and a thickness distribution of liquid crystalline layers.The gradient copolymers exhibited distinct ordering and evolution processes with continuous liquid crystalline melting,which are different from the diblock copolymers.In order to obtain the insights into the copolymerization process,the consumption of monomers at each stage of the copolymerization has been followed directly by using real-time ¹H NMR spectroscopy technique,the reaction activity of EOBC monomer is faster than that of butylene oxide.For preparation of sequence-controlled liquid crystalline terpolymers,monomer containing functional azobenzene was added into the reaction system,the in-situ NMR results show that EOBC monomer and Azo monomer have equal reaction activity.Combining with the above copolymerization system of liquid crystalline monomer and 1,2-Butene oxide,the relationship of reactivity ratio between the three kinds of monomers is r_E?r_Azo>r_B.The consumption of the co-monomers during the anionic copolymerization process was monitored by using in-situ NMR technique.According to the different reactivity ratios of three monomers,the distribution of different monomers along with the molecular chain can be controlled.