Synthesis And Properties Of Amino Acid Based Multiblock Polymers

Amino acids are the basic building blocks of proteins.With the continuous advancement of bioengineering technology and the maturation of the synthesis process,the production cost of amino acids has gradually decreased,and it has become a kind of natural renewable resource with abundant yields.On the other hand,natural amino acid polymers,namely proteins,have precise primary sequence structures,which endow them with unique assembled structures,catalytic properties,and biological activities.In fact,before modern civilization,humans have a long history of using natural amino acid polymers(animal fur,silk,etc.).Theoretically,amino acid polymers are the most abundant and excellent in structure and performance among all synthetic biodegradable plastics.However,there is still a lack of efficient,scalable,and controllable sequence and structure polymerization methods to convert renewable amino acid monomers into high-value-added poly(amino acid)materials.The traditional amino acid polycondensation or solid-phase synthesis method is time-consuming and labor-intensive,and the obtained polymer has a low molecular weight,so it is difficult to realize the scalable application of poly(amino acid)s.Amino acid-based N-carboxyanhydride(NCA)and O-carboxyanhydride(OCA)can be subjected to ring-opening polymerization to prepare poly(amino acid)s and amino acid-based polyesters.It is an important monomer route for the scale-up synthesis of high-value-added amino acid-based polymers from renewable amino acid resources.Therefore,in this paper,we will aim to establish efficient monomer synthesis routes,develop sequence-controllable polymerization methods,and study the relationship between polymer sequence structure and properties to bridge the gap between renewable amino acid resources and high-value-added amino acid-based high-performance polymers.The main research results obtained in this paper are as follows:1.The traditional synthetic route of amino acid NCA monomers has been optimized and improved.The addition of high-efficiency acid scavengers enables the timely removal of acidic impurities,thus establishing an efficient and easy-to-scale synthesis route for NCA monomers.Based on this method,8 functionalized NCA monomers were synthesized at the 100-gram scale.On the other hand,a general synthesis method for amino acid-derived OCA monomers has been developed,and the high-yield synthesis of OCA monomers based on 11 amino acids such as valine and leucine,which are difficult to obtain by traditional routes,has been realized.2.One-pot synthesis of sequence-controlled block copolymers from monomer mixtures of amino acid-derived OCAs and epoxides using TEB)/PPNCl Lewis-pair catalyst.TEB can stabilize the polymer chain ends to achieve selective ring-opening polymerization of OCA monomers in a coordinated decarboxylation manner and inhibit racemization.At the same time,TEB can fully activate the epoxide monomers,which ensures the alternating copolymerization of CO2 released in the OCA polymerization and epoxide and maintains sufficient polymerization activity under 1 atm pressure.Finally,one-pot synthesis of sequence-selective polyester-polycarbonate block copolymers was achieved.The experimental and density functional theory(DFT)results demonstrate a chemoselective and synergistic polymerization mechanism.The high polymerization activity of the OCA monomers ensures the precise sequence selectivity of the switchable polymerization,and the TEB-stabilized chain end is synergistically decarboxylated to achieve a smooth transition from carbonate anion to alkoxy anion at the chain end.Using a simple but highly selective TEB/PPNCl catalyst,perfect block copolymers were obtained,and quantitative CO2 conversion(>99%)was achieved.A series of functionalized and sequence-selective polyester-polycarbonate block polymers can be easily obtained using various amino acid-derived OCAs and epoxy monomers with different substituents.Further,the catalytic concept of the Lewis-pair catalysis was extended to the ROP of biomass-derived cyclic acetal ester monomer,affording a random copolymer of poly(γ-butyrolactone)and poly(acetal ester).3.Inspired by the subtle hierarchical structure and unparalleled mechanical properties of natural spider silk,based on the scalable preparation of amino acid NCA monomers,we developed a sequential addition of NCA ring-opening polymerization method and synthesized hepta-block poly(amino acid)s mimicking the sequences of spider silk.By screening the appropriate hard segment composition and content in the polymer,a biomimetic poly(amino acid)material with high strength and modulus was synthesized,and its tensile strength and elongation at break surpassed commercial polylactic acid and Nylon 6.The characterization of the polymer secondary structure demonstrated that the excellent mechanical properties of the spider silk-like poly(amino acid)materials originated from the β-sheet crystallites widely dispersed in the amorphous region in the polymer structure.Furthermore,the heptablock poly(amino acid)materials were synthesized scalably,and the biomimetic fiber was prepared by solution spinning.The obtained fibrous material exhibits high strength and modulus,similar to the natural spider silk.