Synthesis And Properties Of Complicated Topological Polymers

For a long time,polymers with complex topologies such as linear,cyclic,Y type,seesaw type,8 type,H type,dendritic,hyperbranched,and Janus type,have been an important research field for scientists,because different topologically structured polymers have different properties.Among them,the topologies of dendritic,hyperbranched,and Janus type polymers are complex.The structure of dendrimer is precise and compact,and its terminal functional groups are abundant.In general,the synthetic procedures of dendrimer are numerous and the purification process is complicated.Hyperbranched polymer is also a kind of highly branched polymers,having the advantages of good solubility,low viscosity,and rich terminal functional groups.Although its structural regularity is poor,it is easy to obtain.The word "Janus"comes from the god of the gates of Roman mythology,who has two faces in the opposite direction.Janus type polymer generally consists of two asymmetric"hemispheres" with different structures and properties.This paper focuses on the synthesis and properties of many of the abovementioned topological polymers,such as long chain hyperbranched polymer,linear diblock polymer,linear block dendritic polymer,Janus type dendritic copolymer and Janus type hyperbranched polymer block polydendrons.The specific contents and main findings are as follows.1.Synthetic kinetics of long-chain hyperbranched polymers and inhibition of their self-cyclization side reactionsMany studies have synthesized long-chain hyperbranched polymers using AB2 macromonomers.A kind of AB2 macromonomers is a Y-type macromonomer which contains a reactive functional group A at one chain end and two functional groups B at the other chain end.There are some problems when synthesizing long-chain hyperbranched polymers using Y-type macromonomers.Due to the close proximity of the two B functional groups,when a functional group B participates in the reaction,it will provide steric hindrance to the other functional group B,inhibiting the further reaction of the other functional group B,and inevitably resulting the different distance between the branching points simultaneously.In addition,the intramolecular self-cyclization reaction of the Y-macromonomer also brings byproducts.Another AB2 type macromonomer is seesaw-type macromonomer.The seesaw-type macromonomer contains a reactive functional group A in the middle of the chain and two functional groups B at both ends of the chain.Because the functional groups are far away from each other,the effect of steric hindrance is effectively eliminated,so that the functional groups B can be fully reacted,resulting the distance between the branch points,namely the length of the branches uniform.However,there are also self-cyclization side reactions of macromonomers.Herein,we synthesized long chain hyperbranched polymers through the seesaw type macromonomer alkynyl-(PMMA-N3)2,who has one alkynyl group in the middle of the chain and two azide groups at the end of the chain.Since the reaction of the seesaw type macromonomer to form hyperbranched polymers is a multimolecular reaction process,and the intramolecular self-cyclization side reaction is a single-molecular reaction,we promoted hyperbranching reaction through high monomer concentration and suppressed intramolecular self-cyclization side reaction.In addition,the chain end of macromonomer alkynyl-(PMMA-N3)2 is a quaternary carbon,providing additional steric hindrance and inhibiting the self-cyclization side reaction.With the combination of high monomer concentration and steric hindrance,the self-cyclization side reaction was effectively inhibited,anduniform branch length long chain hyperbranched PMMA without self-cyclization by-product was synthesized.We also synthesized long chain hyperbranched polymer using a tertiary carbon terminated macromonomer poly(methyl acrylate)alkynyl-(PMA-N3)2,to demonstrate that steric hindrance indeed inhibited the self-cyclization side reaction by comparison.We monitored the reaction kinetics of hyperbranching polymerization of macromonomers by FTIR,1H NMR,GPC-MALLS and other characterization methods,and confirmed the kinetic equation for the growth of long-chain hyperbranched polymers.2.Preparation of antibacterial hyperbranched polymer by one-pot method combining ATRP and quaternizationThere are many methods to synthesize hyperbranched polymers,such as polycondensation of ABn type monomers,self-condensing vinyl polymerization(SCVP),self-condensation ring-opening polymerization,and proton transfer polymerization.In addition,the combination method of A2+Bn type monomers is also used to prepare hyperbranched polymers,but this method is not easy to control,and in the process of synthesizing hyperbranched polymers by this method,gelation reaction easily occurs.Therefore,this thesis developed a new method for preparing hyperbranched polymers by one-pot reaction combining ATRP and quaternization,which is simple and convenient.In this work,we used bromoethyl 2-bromoisobutyrate(Br-EBiB)and 2-(dimethylamino)ethyl methacrylate(DMAEMA)to prepare hyperbranched polymers.When Br-EBiB initiated the ATRP of DMAEMA,the quaternization reactions also occurred between them,resulting in the preparation of hyperbranched polymers.Since the reaction solvent was the mixture of THF and H2O2 as the degree of quaternization increased,the charge density of the product increased,and the solubility of the product in mixed solvents reduced,resulting the collapse of the molecular chain and favoring the intramolecular quaternization.Thus,the molecular weight distribution of the prepared hyperbranched polymer was narrow.Moreover,the hyperbranched polymer contains a large amount of quaternized structures that is positively charged,and can interact with negatively charged bacterial cell membranes,achieving the purpose of sterilization.In addition,the polyquaternium fungicides have the advantages of low toxicity.Killing assay confirmed that the obtained hyperbranched polyquaternium had certain bactericidal properties against E.coli and S.aureus.3.Influence of mixing dynamics and topology on self-assembly behavior of amphiphilic copolymersThe self-assembly of amphiphilic copolymers has application in drug loading,drug delivery and related fields.Different morphologies of the self-assemblies such as spherical micelles,rod micelles,vesicles,compound vesicles,layered structure,tubular structure,bread ring like structure and so on,can be prepared through self-assembly.There are many factors that affect the self-assembly of amphiphilic copolymers,such as the proportion of hydrophilic and hydrophobic segments,the initial concentration of the copolymer,the mixing dynamics,the topology of the polymer and so on.In this part of the work,we prepared the linear polymer L-PtB A-Br by ATRP of tert-butyl acrylate(tBA).L-PtBA-N3 was synthesized by azidation of bromine end group of the chain.Then monofunctional macroinitiator L-PtBA-PBiB was prepared by click reaction between L-PtBA-N3 and propiyl 2-bromoisobutyrate(PBiB).Further,we performed the ATRP of methyl methacrylate(MMA)and synthesized the linear diblock copolymer L-PtBA-b-L-PMMA.In addition,we performed the click reaction of L-PtBA-N3 and an AB2 initiator PBMP which contains two bromine groups to prepare the difunctional macroinitiator L-PtB A-PBMP,and further initiated ATRP of MMA to synthesize the linear block the first generation dendrimer L-PtBA-b-G1-PMMA.These steps were repeated to prepare the linear block second generation dendrimer L-PtBA-b-G2-PMMA.The selective deprotection of L-PtBA-b-L-PMMA,L-PtBA-b-G1-PMMA and L-PtBA-b-G2-PMMA was performed by trifluoroacetic acid to obtain amphiphilic copolymers with different topologies,namely L-PAA-b-L-PMMA,L-PAA-b-G1-PMMA and L-PAA-b-G2-PMMA.Finally,we prepared the self-assemblies of three topological copolymers under different mixing conditions by slow injection of distilled water into the DMF solution of the polymer as well as slow injection of the DMF solution of polymer into the distilled water.In the former mixing dynamic,the property of the copolymer solution changed slowly,and the copolymer mainly underwent intermolecular chain aggregation.It was observed that the morphology of the self-assemblies was mainly micron-sized caterpillar like micelle through TEM characterization.In the latter process of mixing dynamics,the property of the copolymer solution changed rapidly,and the copolymer mainly aggregated within the macromolecular chain.The morphology of the self assemblies was mainly nano-sized spherical micelles and short caterpillar like micelles.4.Synthesis of Janus-type long-chain dendritic poly(methyl acrylate)block dendritic polystyreneThe Janus type long chain dendrimers combine the precise,compact structure and richterminal group functionality property of dendrimer and the asymmetrical property of Janus polymer.In this work,we prepared short chain linear PtBA and short-chain linear PBoc-AEA via initiating the ATRP of tert-butyl acrylate(tBA)and tert-butyloxycarbonyl-aminoethyl acrylate(Boc-AEA)by the initiator of ethyl 2-bromoisobutyrate.Afterwards,their terminal bromines of chain ends were transferred to azide group and clicked with an AB2 type ATRP initiator containing one alkynyl group and two bromine groups.Subsequently,ATRP of methyl acrylate(MA)and styrene(St)were respectively initiated to synthesize L-PtBA-b-G1-PMA and L-PBoc-AEA-b-G1-PS.Then the above steps were repeated to synthesize L-PtBA-b-G2-PMA and L-PBoc-AEA-b-G2-PS.Subsequently we performed the deprotection of PtBA and PBoc-AEA blocks to prepare L-PAA-b-G2-PMA and L-PAEA-b-G2-PS.By slowly dropping the DMF solution of L-PAA-b-G2-PMA into diluted DMF solution of L-PAEA-b-G2-PS,Janus G2-PMA-b-G2-PS was prepared using the amidation reaction between L-PAA-b-G2-PMA and L-PAEA-Zb-G2-PS.Infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses confirmed that the two dendrons of G2-PMA and G2-PS were covalently bonded through their respective linear blocks;gel permeation chromatography characterization showed a substantial increase in molecular weight;differential scanning calorimetry analysis showed the presence of glass transition temperature of PMA and PS*The films prepared from the acetone,cyclohexane and DMF solutions of Janus G2-PMA-b-G2-PS showed different hydrophilicity and hydrophobicity,indicating that the Janus dendrimer had different microphase separation behavior in different solvents.5.Synthesis of amphiphilic Janus-type hyperbranched polyglycidol-block-polydendronsUp till now,there have been studies on different complex structures of Janus type polymers,including Janus bottle brush polymers,Janus hyperbranched polymers and Janus dendrimers.In this section,we synthesized the Janus hyperbranched polymer block polydendrons.Firstly,we prepared the first generation dendron of methacrylated lysine(HEMA-Boc-Lys(Boc)-G1)through the esterification of hydroxyethyl methacrylate(HEMA)and(S)-2,6-di-tertbutoxycarbonylaminohexanoic acid(Boc-Lys(Boc)-OH).Then the Boc group of HEMA-Boc-Lys(Boc)-G1 was removed by trifluoroacetic acid and amidation reaction with Boc-Lys(Boc)-OH was performed to synthesize the second generation dendron of methacrylated lysine(HEMA-Boc-Lys(Boc)-G2).Subsequently,we fabricated poly(hydroxyethyl methacrylate)-block-polylysine dendrons(PHEMA-b-PHEMA-Boc-Lys(Boc)-G2)by RAFT polymerization.The hydroxyl groups of the PHEMA block were used to initiate the anionic ring opening polymerization of glycidol,and hyperbranched polyglycidol-block-polylysine dendrons(HPG-b-PHEMA-Boc-Lys(Boc)-G2)was synthesized.The hyperbranched polyglycidol was hydrophilic,containing a large number of terminal hydroxyl groups,and the polylysine dendrons were hydrophobic.We prepared the self assemblies of HPG-b-PHEMA-Boc-Lys(Boc)-G2 by directly dissolving it in water.According to the TEM charaterization,the morphology of the self assemblies was mainly spherical micelle with the diameter of about 40 nm.