Liquid Crystalline Behaviour And Adsorption Properties Of Poly(Ethyleneimine)s With Pendent Mesogenic Groups

Polyethyleneimine-based side-chain liquid-crystalline polymers(SCLCP) and their adsorption properties for heavy metal ions were studied.New series of PEI-based SCLCP containing biphenyl mesogenic groups and their ionic familiy with the spacer length from 2 to 6 methylene units were synthesized upon the study of the relationship between chemical structure and properties for SCLCP.The structures of the synthesized polymers were confirmed by IR and ¹H NMR spectroscopy.The substitution degrees of the mesogenic side groups on N-H units of PEI and the quaternization ratios the amino group in the backbone were calculated from ¹H NMR.It is shown that the substitution degree of mesogenic groups depends on the solvent used for the polymerization and the reaction time.The substitution degree of mesogenic groups increased as the reaction proceeded.Polymerizations carded out in the homogeneous medium result in higher substitution degree than those in the heterogenous medium.In addition,the substitution degree of mesogenic groups decreases with the increasing spacer length under the same reaction conditions.The poor swelling of the polymer backbone and the large size of the mesogenic groups are probably the causes.The thermal properties of these polymers were investigated by differential scanning calorimetry(DSC),polarized optical macroscopic(POM) and X-ray diffraction(XRD).It is shown that poly(ethyleneimine) is flexible and acts as a suitable main chain component for side-chain liquid crystalline polymers.The thermal properties and LC formation of the polymers are shown to be strongly affected by the type of mesogens,the length of spacer units and the degree of substitution in the side chain.POMen(n＞2) exhibits S_B-type thermotropic liquid-crystalline behaviour with fan textures.There is a lamellar order in these polymers.PHn performs a mesomorphic behaviour of S_E phase with mosaic textures.PCNn shows liquid-crystalline phases of nematic type with schlieren textures,and there is no order in the direction of the molecular long axes.The clearing temperatures decreased as the spacer length increased.A pronounced odd-even effect was observed.There is a minimum substitution degree for liquid crystal formation.The phase transition temperatures increase and the mesomorphic properties become stabilized as the substituting degree increases. DSC,POM and XRD indicate that POMe4CH₃ and POMe4OMe4 exhibit thermotropic smectic A phases and PCNnCH₃ show thermotropic nematic phases. The ionic liquid crystalline polymers formed a partial bilayer structure in the smectic A phase.The ionic liquid crystalline polymers(POMe4CH₃,POMe4OMe4) show wider mesomorphic temperature ranges(ΔT) compared to the non-ionic liquid crystalline polymers.It seems that the quaternization enhances and stabilizes the mesomorphic properties.The effect of the quaternization ratios of the amino group in the backbone on the thermal properties was investigated.Thermogravimetry anylasis shows that the quaternization leads to thermal degradation of the PEl-base SCLCPs at lower temperatures.The adsorption properties of the chelating resins for Hg(â…¡),Pb(â…¡),Cu(â…¡),Cd(â…¡),Co(â…¡),Zn(â…¡) were studied.It is shown that the resins can well absorb Hg(â…¡),Pb(â…¡),Cd(â…¡) and Cu(â…¡) rather than Co(â…¡) and Zn(â…¡).Besides,the resins have excellent absorptive selectivity for Hg(â…¡).By quenching at liquid crystalline phase and isotropic phase,aggregation structures with different orders were obtained.The adsorption results indicate that liquid-crystalline ordered aggregation structure of the chelating resins dramatically improves the adsorption properties and the absorptive selectivity.For PH4,the adsorption capacity for Hg(â…¡) dramatically increased at the temperature above Tg.The dynamics investigation of the resins indicated that the adsorption equilibrium time for Hg(â…¡) and Pb(â…¡) is very short.In addition,the PEI-based polymer resins have excellent regeneration properties.