Synthesis And Characterization Of Liquid Crystal Polyurethane

Liquid crystal polyurethane?LCPU?,as a new type of high performance material,has been widely used in the fields of shape memory,data storage,and photoelectric display,etc.Depending on the molecular structure,LCPU can often be classified into the main chain type liquid crystal polyurethane,the side chain type liquid crystal polyurethane,and the main/side chain type liquid crystal polyurethane.In liquid crystal polyurethane?LCPU?,urethane bond is a very important group,including the structure of amide and ester,which is formed by the reaction of polyol and diisocyanate.It combines the rigid hard segment of the liquid crystal polymer chain with the flexible soft segment,and then changes the interaction between the molecular forces?such as hydrogen bonds?in the polymer chains and the mesogenic units,thus affecting the formation of polymer liquid crystals and various physical and chemical properties.The research value of urethane bonds is important due to the variety of synthetic liquid crystal polyurethanes and the flexibility of reaction.Therefore,in this paper,a series of novel liquid crystal polyurethane and liquid crystal polyurethane block copolymers were based on the molecular structure design.By changing the combination of urethane bonds and polymer chains,The effect of intermolecular forces on the structural properties of the polymer was investigated.its main content is as follows:1)The phase structure and phase behavior of the main chain liquid crystal polyurethane MLCPU material can be controlled by studying the effective combination of molecular structure of polyols and polyisocyanate.Bis?n-hydroxyalkoxy?benzophenone?BHABP_n,n=3,5,6,8,11?is prepared by reacting bis?p-hydroxy?benzophenone?DHBP?with a 1-haloalkyl alcohol to obtain mesogenic unit with different flexible intervals.Then,bis-?6-hydroxyhexyloxy?-benzophenone?BHABP₆?with good liquid crystallinity was used as a polyol to react with polyisocyanates of different chain structure to synthesize the first type of main chain liquid crystal polyurethane?MLCPU?.The effects of different chain structures of polyisocyanates on the phase behavior and phase structure of the polymer were investigated in detail by IR,WXRD,DSC,and POM.The results showed MLCPU_6-1 obtained from1,6-hexadiisocyanate?HDI?with flexible chain structure has liquid crystal properties;The second type of main chain liquid crystal polyurethane MLCPU was synthesized by using HDI as polyisocyanate and liquid crystal based BHABP_n with different flexible spacing.The results show that with the increase of spacer length of themesogenic diol,the both MLCPU have liquid crystal texture and transition temperature is gradually reduced.2)Through the design and optimization of the synthesis route,phenol,4-butylaniline,1-haloalkyl alcohol,2-isocyanatoethyl methacrylate,etc.are used as raw materials to synthesize three kinds of azo liquid crystal monomers?methacrylic azobenzene?containing different flexible intervals by azotization,etherification and urethanization.Then,using conventional free radical polymerization method?AIBN as an initiator?,azobenzene?urethane-containing?side chain type liquid crystal polymers?PU_n,n=5,6,8,which is the number of the methylene units between the main chain and azo mesogenic unit in the side chains?with different flexible spacer lengths were prepared.The structures of mesogenic unit,monomers and polymers were characterized by NMR.The phase behavior and phase structure of polymer liquid crystals were studied by DSC,POM and WXRD.The effects of alkyl chains of different lengths on the phase behavior and phase structure of azobenzene side chain liquid crystal polyurethane were investigated.The experimental results show that the synthesized PUs have liquid crystallinity.When the alkyl chain length is short?n=5?,the azobenzene mesogenic units are closely distributed around the main chain due to the side chain being bound by the main chain,showing the phase behavior of the smectic liquid crystal.The azobenzene liquid crystal unit and the main chain together form a layered phase structure.Characterization by SAXS revealed that the stability of this lamellar phase structure disappeared as the length of the alkyl chain increased.3)An amphiphilic liquid crystal block copolymer PEO-b-P?M?_n was synthesized by ATRP polymerization with PEO-Br having different molecular chain length as initiator,CuBr/HMTETA as catalyst and self-made azo liquid crystal monomer as raw material,which is consisted of hydrophilic poly?ethylene oxide??PEO?and hydrophobic polymethacrylate with azobenzene?containing urethane bond?liquid crystal side chain.The effects of PEO on the structure and liquid crystal properties were investigated by ¹H-NMR,DSC,POM and SAXS for the two series of hydrophilic liquid crystal block copolymers with different chain lengths.The microphase separation of liquid crystal block copolymers membrane was observed by AFM.The results show that all the liquid crystal block copolymers have a distinct liquid crystal texture.Due to the introduction of the PEO segment,the azobenzene group in the P?M₆?_n series together with the main chain and flexible segments form a layered phase structure.PEO₁₁₄ series polymer films have microphase separation after heat treatment.