Columnar Phase Of Side-chain Liquid Crystalline Polymers Based On Multi-chain Model

The side chain liquid crystal polymers(SCLCP)with extended conformation,such as Mesogen-jacketed liquid crystalline polymer(MJLCP)and dendron-jacketed liquid crystalline polymer(DJLCP),can self-organize into columnar phases.For the columnar phase,it is generally believed that the supramolecular column formed by a single polymer chain is the building block of the columnar phase,multi-chain supramolecular column formed by a bundle of chains is rarely mentioned.Therefore,we take phasmidic SCLCPs as the research object to illustrate that the"multi-chain supramolecular column"is an important form of microphase separation in the columnar phase of side-chain liquid crystalline polymers,in-depth study of its formation mechanism has important scientific significance for discovering the new function of SCLCP.The middle of the phasmidic mesogens is a long rigid core,and the two ends are percec type first generation dendronized end-groups.We first synthesized two phasmidic mesogens MS-n(n=8,12,n is the number of carbon atoms per alkyl chain).Subsequently,we synthesized four phasmidic MJLCPs(PE-n and PNB-n,n is the number of carbon atoms per alkyl chain)with polyethylene(PE)and polynorbornene(PNB)as the backbone and MS-n as the side-chains.Combined differential scanning calorimetry(DSC),polarized light microscopy(POM),one-dimensional(1D-)and two-dimensional X-ray diffraction(2D-XRD)analysis experiments demonstrate that MS-n(n=8,12)can form a long-range-ordered hexagonal columnar phase(?_H),and four phasmidic molecules arranged side-by-side form a supermolecular tetramer,and the tetramers then formed the supermolecular column,with their molecular long axis perpendicular to the column axis.The phase behavior of PE-n and PNB-n depends on the length of the alkyl tail chain(n).PE-8 and PNB-8 form a smectic A phase(Sm A),and PE-12 and PNB-12 form a hexagonal columnar phase(?_H).PE-12 form a double-chain supermolecular column and PNB-12 form a four-chain supermolecular column.We synthesize a series of double-sided chain DJLCP(P-n,n is the number of carbon atoms per alkyl chain)with PE as the backbone and hemiphasmidic mesogens as the side-chain.We study the self-assembling characteristics of its monomer M-n and polymer P-n.the results show that the monomer M-n(n=8,10,12)and the polymer P-n(n=6,8,10,12)form?_Hphase,P-n form a double-chain supermolecular column,and M-12 and P-12 have a 2₁supramolecular helix.Finally,we synthesized a series of hemiphasmidic mesogens dendrimer oligomers(OM_p-W_m,p=1,2,p is the number of biphenyl units;m=0,1,2,3,m is the number of benzene in rigid component)with biphenyl units as the backbone and hemiphasmidic mesogens as the side-chain.The results show that the oligomers OM₁-W_m(m=2,3)and OM₂-W_m(m=1,2,3)form?_H phase,but their molecular packing is different:OM₁-W_m form a supramolecular column which the molecular backbone perpendicular to the column axis;OM₂-W_m form a supramolecular column which the molecular backbone parallel to the column axis.For OM₂-W_m,as the length of the rigid core increases,the number of chains per supramolecular column increases from 7 to 11.