Preparation and Applications of Optically Active Porous Materials Constructed by Helical Substituted Polyacetylenes

Author:Liang Jun Ya

Supervisor:deng jian ping


Degree Year:2018





Chiral compounds are indispensable from living organisms.For example,the amino acids and sugars required in human bodys are all chiral.Chiral enantiomers although have similar chemical and physical properties,drastically differ in their biological properties such as distribution,metabolism,and excretion.Thalidomide is a well-known chiral drug,of which S-enantiomer has a therapeutic effect while R-enantiomer is teratogenic.Moreover,currently more than 25%of clinically used drugs are chiral,and often only one of the enantiomers has therapeutic effects,while the other enantiomer is ineffective and may even cause side effects.Therefore,chiral resolution is of great significance in the areas of both biomedicine and materials science.Helical polymers with one-handed screw sense have special properties,such as optical activity,chiral amplification effect and enantioselectivity,due to the unique helical conformations.These properties render helical polymers with potential applications in asymmetric catalysis,enantioselectively induced crystallization,and enantioselective adsorption/release.Considering porous structures possessing the advantages of large specific surface area,good permeability,and easy accessibility towards guest molecules,in this dissertation a series of optically active porous materials constructed by helical substituted polyacetylenes was designed and prepared,including monolithic materials,interpenetrating polymer networks,hybrid microspheres,molecularly imprinted microspheres,and composite microspheres.Based on these materials,the enantioselectivity of helical substituted polyacetylenes in induced crystallization,chiral adsorption and release was investigated;meanwhile,the effects of multichiral sources on enantioselectivity were also studied.The main research contents are as follows:1.Porous materials consisting of substituted polyacetylenes were prepared by high internal phase emulsion polymerization using substituted acetylene monomer solution as continuous phase and deionized water as disperse phase.The as-obtained materials had regular and uniform pore structures,high porosity and low density.The pore size and porosity of the porous materials can be easily adjusted by varying the fraction of the disperse phase.Due to the chirally helical conformation of substituted polyacetylenes,the porous materials possessed optical activity.The optically active porous materials were used as chiral inducers and effciently induced enantioselective crystallization of threonine and alanine racemates.L-Threonine and L-alanine were preferably induced to form crystals from the respective racemic solutions.2.The porous materials prepared above were used as chiral framework to provide abundant space for a functional boronic acid-containing monomer to polymerize inside the pores,providing chiral interpenetrating polymer network(IPN)constructed by substituted polyacetylenes.The pore size in the resulting chiral IPNs can be tuned by adjusting the content of the boronic acid-containing polymer.Circular dichroism and UV-vis absorption spectra demonstrated that the helical polymer chains in both the pre-formed chiral framework and the final IPNs took preferential helicity,which rendered the IPNs with considerable optical activity.The as-prepared IPNs could adsorb glucose through esterification reaction occurring between the boronic acid groups contained in the networks and cis-diol in glucose.More importantly,the successful combination of boronic acid groups with the chiral framework enabled the IPNs to simultaneously exhibit enantioselectivity and pH sensitivity in the glucose adsorption process.The reversibility of the boronic acid-derived ester structure facilitated desirable reusability of IPNs.3.Optically active helical copolymers bearing siloxane groups in side chains were designed and synthesized.The copolymers were employed as macromolecular silane couplers to prepare the desired chiral porous hybrid particles consisting of helical substituted polyacetylene bonded with organosilica through a sol-gel reaction with TEOS.Abundant pores formed in the hybrid particles.The obtained hybrid particles exhibited remarkable optical activity due to the presence of the helical copolymers.Taking advantage of the optical activity,the chiral porous hybrid particles were employed as drug carriers and demonstrated enantioselectivity in releasing cinchona alkaloid.The enantioselective release was found to depend on temperature:low temperatures favored the enantioselective process.4.The optically active materials synthesized above are all composed of a single chiral source(chirally helical substituted polyacetylene).However,it remains unknown how the enantioselectivity will be affected when two or more chiral components are integrated in one material.To study this problem,molecularly imprinted polymer microspheres(MIPMs)were prepared by suspension polymerization of achirally and chirally substituted acetylenic monomers in the presence of chiral template molecules,Boc-D/L-proline.The MIPMs retained the chirally helical conformation of substituted polyacetylene and the chiral configuration cavities of template molecules.The MIPMs were utilized in enantioselective adsorption.The chiral configuration cavities and the chirally helical conformations worked synergistically and largely increased the chiral MIPMs’ enantioselective adsorption ability.5.The effect of interaction between chiral helical conformation and chiral configuration on enantioselectivity was investigated in the preceding section.Herein,we also studied the interaction of two different chirally helical polymers.First,chirally helical polylactides bearing polymerizable alkynyl group were prepared.Then,the polylactides were employed as macromers to copolymerize with a chiral alkynyl monomer through suspension polymerization,fabricating chiral microspheres consisting of helical polylactide and helical substituted polyacetylene.Terminal hydroxyl groups in polylactide chains performed emulsification effect,leading to pores in the final microspheres.Circular dichroism shows that the helical substituted polyacetylene had an important influence on the helical screw sense of polylactide chains,thereby affecting the enantioselectivity of the chiral microspheres in releasing chiral drug,naproxen.Compared with the enantioselectivity of PLA-based microsheres,copolymerizing PLA with chiral alkynyl monomer improved PLA’s enantioselectively discriminating ability in naproxen release and even can reverse the microspheres’ preferential enantioselectivity in releasing naproxen enantiomers.