A New Strategy For Construction Of Amide Bond-Containing Polymers Based On Catalytic S-V Reaction

Natural and synthetic amide bond-containing polymers are ubiquitous in our daily life.Natural amide bond-containing polymers(peptides and proteins)play a vital role in living systems,such as enzymatic catalysis(almost all known enzymes are proteins),mechanical support of collagen,immune protection of antibodies as well as transport and storage of hemoglobin.Synthetic polyamides are widely used as engineering plastics and fiber products due to their high strength,chemical resistance,heat resistance,abrasion resistance and self-lubricating properties.Recently,some emerging functional polyamides with excellent biocompatibility and degradability have attracted great attention,which have great application prospects in the biomedical research field,such as gene delivery,drug delivery,tissue engineering,antibody proteins,wound healing and biological mineralization.Traditionally,polyamides are synthesized by condensation polymerization of diamines and dicarboxylic acids or dicarboxylic acid derivatives.However,relatively harsh reaction conditions exist in these reactions.Considering the efficiency and the substrate scope,only a few novel amidation reactions can be applied to synthesize amide bond-containing polymers.The catalytic Staudinger-Vilarrasa(S-V)reaction of carboxylic acids with organic azides,using 2,2'-dipyridyl diselenide(PySeSePy)as a catalyst or activator,is a highly efficient reaction for the synthesis of amides.The catalytic S-V reaction has many advantages,such as a broader substrate scope,high efficiency,mild reaction condition,easy operation,and metal-free condition.However,to the best of our knowledge,the catalytic S-V reaction has rarely been referred for the preparation of amide-containing polymers by direct polymerization or post-polymerization,even though great advancements have been made in organic synthesis.Considering these highlights of the catalytic S-V reaction,we want to delve into the research that whether it can be used as a novel click reaction for the construction of amide-containing polymers.In this thesis,we successfully employed the catalytic S-V reaction for the synthesis of amide bond-containing polymers for the first time.First,the catalytic S-V reaction between dicarboxylic acid and diazide was used to prepare various polyamides by stepwise polymerization.The effect of the alkyl chains of monomer on polymerization was further investigated and the structures of the obtained polyamides were characterized in detail.Second,the catalytic S-V reaction was applied to the end-functionalization of polymers by post-modification of and the construction of polymers with complex topologies.Various amide-functionalized polymers and amide-linked(multi)block copolymers as well as star polymers were prepared.The detailed research contents were summarized as the following:(1)Synthesis of polyamides based on the catalytic S-V reactionWe synthesized the catalyst PySeSePy of the catalytic S-V reaction and diazides,which were characterized by proton nuclear magnetic resonance(1H NMR),carbon nuclear magnetic resonance(13C NMR)and elemental analysis.Then we chose 1,12-diazidododecane and tetradecanedioic acid as the model monomers for the polyamidation reaction to optimize the polymerization conditions,including the solvent,reaction time,catalyst loading and polymerization temperature.Under the optimized polymerization conditions,various aliphatic and aromatic polyamides were prepared and structures of the obtained polyamides were comprehensively characterized by H NMR,matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOF-MS),fourier transform infrared spectroscopy(FT-IR)and size exclusion chromatograph(SEC).The effect of the alkyl chains of monomer on the polymerization was also investigated.(2)The end-functionalization of polymers based on the catalytic S-V reactionThe linear precursors PS-N3 and N3-PS-N3 were synthesized by combination of atom transfer radical polymerization(ATRP)and a nucleophilic substitution reaction.And PEG-N3 was also prepared via a substitution reaction.Subsequently,we modified the end-group of PS-N3 with piperonylic acid,which was as the model reaction to optimalize the reaction conditions.Under the optimized post-polymerization conditions,various carboxylic acids were employed to prepare various chain-end functionalities of PS.The catalytic S-V reaction was further employed to conduct end amide-functionalization of PEG and double end amide-functionalization of PS under similar conditions,providing a useful platform for the synthesis of various chain-end functionalized polymers.The linear precursor PtBA-N3 was synthesized by combination of ATRP and a nucleophilic substitution reaction.The terminal carboxyl functionalized PEG-COOH and HOOC-PEG-COOH were prepared via an esterification reaction.Then the catalytic S-V reaction between Polymer-N3(PEG-N3,PS-N3)and carboxyl-containing multifunctional compounds were carried out to prepare amide bond-linked homopolymers(PEG-PEG,PS-PS)and three-arm star polymers((PEG)3,(PS)3).Finally,amide-linked diblock polymers(PS-b-PEG,PtBA-b-PEG)and triblock polymers(PS-b-PEG-b-PS,PtBA-b-PEG-b-PtBA)were quantitatively obtained by the catalytic S-V coupling reaction between Polymer-N3 and PEG-COOH/HOOC-PEG-COOH.The above obtained polymers were characterized by 1H NMR and SEC.Therefore,the catalytic S-V reaction can be used as a highly efficient click reaction to construct various complex topological amide bond-containing polymers.