Polymerization Of N-carboxyanhydrides Research Articles

Self-promoted Controlled Ring-opening Polymerization via Side Chain-mediated Proton Transfer for the Synthesis of Tertiary Amine-pendant Polypeptoids.

Proton transfer is essential in virtually all biochemical processes, with enzymes facilitating this transfer by optimizing the proximity and orientation of reactants through site-specific hydrogen bonds. Proton transfer is also crucial in the rate-determining step for the ring-opening polymerization of N-carboxyanhydrides (NCAs), widely used to prepare various peptidomimetic materials. This study utilizes side chain-assisted strategy to accelerate the rate of chain propagation by using NCAs with tertiary amine pendants. This moiety enables hydrogen bond formation between the incoming NCA and the polymer amino growing end. The tertiary amine side chain of the NCA forms a proton shuttle, via a less constrained transition state, to facilitate the proton transfer process. Moreover, the tertiary amine side chains enable the precipitation of NCA monomers through in situ protonation during the monomer synthesis. This greatly facilitates the synthesis of these unreported monomers, allowing the direct controlled synthesis of tertiary amine-pendant polypeptoids. This side chain-promoted polymerization has rarely been reported. Additionally, the tertiary amine side chains, as widely used functional groups, endow the polymers with unique properties including pH- and thermo-responsiveness, tunable pKas, and siRNA transfection capability. The self-promoted synthesis, facile monomer preparation, and attractive properties make tertiary amine-pendant polypeptoids promising materials for various applications.

Open-vessel polymerization of N-carboxyanhydride (NCA) for polypeptide synthesis.

Synthetic polypeptides, also known as poly(α-amino acids), have the same polyamide backbone structures as natural proteins and peptides. As an important class of biomaterials, polypeptides have been widely used because of their biocompatibility, bioactivity and biodegradability. Ring-opening polymerization of N-carboxyanhydride (NCA) is a classical and widely used method for the synthesis of polypeptides. The dominantly used primary amine-initiated NCA polymerization can yield well-defined polymers and complex macromolecular architectures, but the reaction is slow and sensitive to moisture, making it necessary to use anhydrous solvents and a glovebox. One solution is to use lithium hexamethyldisilazide (LiHMDS) as the initiator, as described in this protocol. LiHMDS-initiated NCA polymerization is less sensitive to moisture and can be carried out in an open vessel outside the glovebox. It is also very fast; the reaction can be complete within 5 min to produce 30-mer polypeptides. In this protocol, poly(γ-benzyl-L-glutamate) is prepared as an example, but the protocol can easily be adapted to the synthesis of other polypeptides by generating NCAs from different amino acids, making it particularly suitable for the efficient parallel synthesis of polypeptide libraries. We provide detailed procedures for NCA synthesis and purification, the method of polymer end-group modification and measurement of polymerization kinetics and reactivity ratio. The procedure for synthesis of monomers and polymerization to form polypeptides requires <1 d. The superfast and open-vessel NCA polymerization method described here will probably enable a wide range of applications in the synthesis and functional study of polypeptide biomaterials.

Recent Advances and Future Developments in the Preparation of Polypeptides via N-Carboxyanhydride (NCA) Ring-Opening Polymerization.

Polypeptides have the same or similar backbone structures as proteins and peptides, rendering them as suitable and important biomaterials. Amino acid N-carboxyanhydrides (NCA) ring-opening polymerization has been the most efficient strategy for polypeptide preparation, with continuous advance in the design of initiators, catalysts and reaction conditions. This Perspective first summarizes the recent progress of NCA synthesis and purification. Subsequently, we focus on various initiators for NCA polymerization, catalysts for accelerating polymerization or enhancing the controllability of polymerization, and recent advances in the reaction approach of NCA polymerization. Finally, we discuss future research directions and open challenges.

Synthesis of Polypeptides by Ring-opening Polymerization: A Concise Review

Abstract: The most economical and efficient route to prepare polypeptides from synthetic chemistry is through the Ring-opening Polymerization (ROP) of amino acids using Ncarboxyanhydride (NCA) monomers. Peptide polymers, in contrast to proteins, consist of repeated amino acid units and are comparatively simpler macromolecules. Despite their simplicity, these polypeptides offer a unique combination of beneficial traits found in both synthetic polymers (such as solubility, processability, and rubber elasticity) and natural proteins (including secondary structure, functionality, and biocompatibility). Nevertheless, NCA polymerization faces significant challenges, including intricate monomer purification and the necessity for processing toxic solvents. In this context, this review presents the fundamental principles of this polymer chemistry, the synthesis of NCA monomers, and the different methodologies to access polypeptides by ROP. It also explores the most recent advances in this field of research, with a focus on how new methods enable the use of more reactive initiators and the development of original processes, including the use of aqueous solvents.

Toward Synthetic Intrinsically Disordered Polypeptides (IDPs): Controlled Incorporation of Glycine in the Ring-Opening Polymerization of N-Carboxyanhydrides.

Intrinsically disordered proteins (IDPs) do not have a well-defined folded structure but instead behave as extended polymer chains in solution. Many IDPs are rich in glycine residues, which create steric barriers to secondary structuring and protein folding. Inspired by this feature, we have studied how the introduction of glycine residues influences the secondary structure of a model polypeptide, poly(l-glutamic acid), a helical polymer. For this purpose, we carried out ring-opening copolymerization with γ-benzyl-l-glutamate and glycine N-carboxyanhydride (NCA) monomers. We aimed to control the glycine distribution within PBLG by adjusting the reactivity ratios of the two NCAs using different reaction conditions (temperature, solvent). The relationship between those conditions, the monomer distributions, and the secondary structure enabled the design of intrinsically disordered polypeptides when a highly gradient microstructure was achieved in DMSO.

An Undergraduate Laboratory Module Integrating Organic Chemistry and Polymer Science.

Polymer science is receiving wider acceptance in the organic chemistry community; thus, it is imperative to include it in the undergraduate organic chemistry curriculum. Despite the ever-increasing popularity of the topic of polymer chemistry in undergraduate curricula, a comprehensive laboratory experiment module describing a polypeptide synthesis by ring-opening polymerization of N-carboxyanhydride (NCA ROP) and a homopolymer synthesis by activators-regenerated by electron-transfer for atom transfer radical polymerization (ARGET ATRP) has yet to be proposed. Herein, we report a semester-long, ten week undergraduate laboratory module focusing on the synthesis and analytical characterization of polyalanine and polystyrene for an advanced organic chemistry class. Students received hands-on-experiences in synthesizing polymers followed by their characterization via proton nuclear magnetic resonance (1H NMR) spectroscopy, electrospray ionization-mass spectrometry (ESI-MS), gel permeation chromatography (GPC), thermogravimetry (TGA), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM), which are not well-presented in the typical organic chemistry curricula. These engaging hands-on lessons in the newly designed laboratory module not only increase students' interests in an interdisciplinary environment of organic chemistry and polymer science but also cultivate their research interests and communication skills and promote critical thinking.

Synthetic Antifreeze Glycoproteins with Potent Ice-Binding Activity.

Antifreeze glycoproteins (AFGPs) are produced by extremophiles to defend against tissue damage in freezing climates. Cumbersome isolation from polar fish has limited probing AFGP molecular mechanisms of action and limited development of bioinspired cryoprotectants for application in agriculture, foods, coatings, and biomedicine. Here, we present a rapid, scalable, and tunable route to synthetic AFGPs (sAFGPs) using N-carboxyanhydride polymerization. Our materials are the first mimics to harness the molecular size, chemical motifs, and long-range conformation of native AFGPs. We found that ice-binding activity increases with chain length, Ala is a key residue, and the native protein sequence is not required. The glycan structure had only minor effects, and all glycans examined displayed antifreeze activity. The sAFGPs are biodegradable, nontoxic, internalized into endocytosing cells, and bystanders in cryopreservation of human red blood cells. Overall, our sAFGPs functioned as surrogates for bona fide AFGPs, solving a long-standing challenge in accessing natural antifreeze materials.

Precision Synthesis of Polysarcosine via Controlled Ring-Opening Polymerization of N-Carboxyanhydride: Fast Kinetics, Ultrahigh Molecular Weight, and Mechanistic Insights.

The rapid and controlled synthesis of high-molecular-weight (HMW) polysarcosine (pSar), a potential polyethylene glycol (PEG) alternative, via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is rare and challenging. Here, we report the well-controlled ROP of sarcosine NCA (Sar-NCA) that is catalyzed by various carboxylic acids, which accelerate the polymerization rate up to 50 times, and enables the robust synthesis of pSar with an unprecedented ultrahigh molecular weight (UHMW) up to 586 kDa (DP ∼ 8200) and exceptionally narrow dispersity (D̵) below 1.05. Mechanistic experiments and density functional theory calculations together elucidate the role of carboxylic acid as a bifunctional catalyst that significantly facilitates proton transfer processes and avoids charge separation and suggest the ring opening of NCA, rather than decarboxylation, as the rate-determining step. UHMW pSar demonstrates improved thermal and mechanical properties over the low-molecular-weight counterparts. This work provides a simple yet highly efficient approach to UHMW pSar and generates a new fundamental understanding useful not only for the ROP of Sar-NCA but also for other NCAs.

Insight into the cross-linking of synthetic polypeptide gels prepared by ring-opening polymerization using l-cystine N-carboxyanhydride

Synthetic polypeptides have promising potential for various biomedical applications that often require a cross-linked network for stability against solvents or mechanical stress. Due to the natural occurrence and availability of the l-cystine α-amino acid, l-cystine N-carboxyanhydride (NCA) is commonly used as a cross-linker in the ring-opening (co)polymerization of α-amino acid NCAs to prepare covalently cross-linked synthetic polypeptides. In this work, we show that the l-cystine NCA tends to undergo undesired decomposition side reactions, i.e., β-elimination and formation of 2,5-diketopiperazine, which reduce the amount of the cross-linker available and make it difficult to control the final properties of the materials prepared from it. By using the analogous l-homocystine NCA instead, the decomposition side reactions can be completely avoided. We demonstrate the cross-linking performance of l-cystine NCA compared to l-homocystine NCA by studying the corresponding gels prepared by copolymerization with γ-benzyl-l-glutamate NCA.

Modulation of polymerization rate of N-carboxyanhydrides in a biphasic system

The recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) offer an effective strategy to simplify the preparation of polypeptide materials. However, the fine-tuning of polymerization kinetics, which is critical to differentiate the main polymerization and the side reactions, remains largely unexplored. Herein we report the modulation of polymerization rate of NCA in a water/oil biphasic system. By altering the aqueous pH, the initial location of the initiators, and the pKa of initiating amines, we observed the change in polymerization time from several minutes to a few hours. Due to the high interfacial activity and low pKa value, controlled polymerization was observed from multi-amine initiators even if they were initially located in the aqueous phase. This work not only improves our understanding on the biphasic polymerization mechanism, but also facilitates preparation of versatile polypeptide materials.

Accelerated Ring‐Opening Polymerization of α‐Amino Acid N‐Carboxyanhydridevia Inorganic Nano‐initiators†

Comprehensive SummaryWhile the accelerated polymerization of N‐carboxyanhydrides (NCAs) has been utilized to synthesize versatile polypeptide materials in an efficient manner with minimized side reactions, the preparation of polypeptide‐based inorganic/organic hybrid materials with the acceleration strategy remained largely unexplored. Herein, we report the accelerated ring‐opening polymerization (ROP) of NCAs mediated by amine‐modified inorganic nano‐initiators, such as mesoporous silica nanoparticles (MSN‐NH2), which is driven by the cooperative effect of the neighboring α‐helical polypeptide chains in a dichloromethane (DCM)/water biphasic system. Well‐defined nano‐hybrids were prepared within 15 min from non‐purified NCA monomers, through in situ purification and subsequent ultrafast polymerization process. NCAs can be rapidly initiated by amino groups of MSN uniformly dispersed at the interface of DCM and water, and subsequently formed the well‐defined polypeptides within 15 min. The prepared inorganic/organic nano‐hybrid with MSN as the core and polypeptide as the shell adopted spherical morphology and uniform size distribution due to the excellent controllability of ROP. Besides, this system is also suitable for a variety of NCAs and inorganic nano‐initiators. This research allows efficient and rapid preparation of inorganic/organic nano‐hybrids, and further promotes the extensive application of this material in the biomedical fields.

Cooperative Covalent Polymerization of N-carboxyanhydrides: from Kinetic Studies to Efficient Synthesis of Polypeptide Materials

ConspectusPolypeptides, as the synthetic analogues of natural proteins, are an important class of biopolymers that are widely studied and used in various biomedical applications. However, the preparation of polypeptide materials from the polymerization of N-carboxyanhydride (NCA) is limited by various side reactions and stringent polymerization conditions. Recently, we report the cooperative covalent polymerization (CCP) of NCA in solvents with low polarity and weak hydrogen-bonding ability (e.g., dichloromethane or chloroform). The polymerization exhibits characteristic two-stage kinetics, which is significantly accelerated compared with conventional polymerization under identical conditions. In this Account, we review our recent studies on the CCP, with the focus on the acceleration mechanism, the kinetic modeling, and the use of fast kinetics for the efficient preparation of polypeptide materials.By studying CCP with several initiating systems, we found that the polymerization rate was dependent on the secondary structure as well as the macromolecular architecture of the propagating polypeptides. The molecular interactions between the α-helical, propagating polypeptide and the monomer played an important role in the acceleration, which catalyzed the ring-opening reaction of NCA in an enzyme-mimetic, Michaelis–Menten manner. Additionally, the proximity between initiating sites further accelerated the polymerization, presumably due to the cooperative interactions of macrodipoles between neighboring helices and/or enhanced binding of monomers. A two-stage kinetic model with a reversible monomer adsorption process in the second stage was developed to describe the CCP kinetics, which highlighted the importance of cooperativity, critical chain length, binding constant, [M]0, and [M]0/[I]0. The kinetic model successfully predicted the polymerization behavior of the CCP and the molecular-weight distribution of resulting polypeptides.The remarkable rate acceleration of the CCP offers a promising strategy for the efficient synthesis of polypeptide materials, since the fast kinetics outpaces various side reactions during the polymerization process. Chain termination and chain transfer were thus minimized, which facilitated the synthesis of high-molecular-weight polypeptide materials and multiblock copolypeptides. In addition, the accelerated polymerization enabled the synthesis of polypeptides in the presence of an aqueous phase, which was otherwise challenging due to the water-induced degradation of monomers. Taking advantage of the incorporation of the aqueous phase, we reported the preparation of well-defined polypeptides from nonpurified NCAs. We believe the studies of CCP not only improve our understanding of biological catalysis, but also benefit the downstream studies in the polypeptide field by providing versatile polypeptide materials.

Size Control and Biological Properties of PAMAM-Cored Multiarm Block Copolymers.

Size is one of the crucial factors influencing the biological properties of nanomedicines. However, the size control of nanomaterials is still very challenging, and the size effect on their biological properties is worth studying. Herein, we present the synthesis and size control of a series of multiarm block copolymers with the third-generation PAMAM (G3 PAMAM) as the core. The multiarm copolymers were synthesized by the ring-opening polymerization of N-carboxyanhydride of the l-glutamic acid-5-tert-butylester [Glu(OtBu)-NCA] monomer with the amine-terminated PAMAM as the initiator, followed by the synthesis of the poly(carboxybetaine) (PCB) block via the atom transfer radical polymerization of the 2-(dimethylamino)ethyl methacrylate monomer, the reaction with tert-butyl bromoacetate, and the deprotection of the tert-butyl ester groups. The polyglutamic acid (PGA) block provided abundant reactive groups for the functionalization of the multiarm block copolymers, and the PCB block imparted excellent water solubility and anti-protein adsorption capability. We synthesized three multiarm copolymers with diameters of 15, 24, and 41 nm, respectively, by tuning the polymerization degrees of the arms. Doxorubicin was coupled to the PGA block through the acylhydrazone linkage, which resulted in a pH-sensitive drug release and a drug loading of over 20%. We systematically investigated the size effects on their cellular uptake, cytotoxicity, endocytic pathway, biodistribution, tumor penetration, and antitumor activity. This work is helpful for the design of polymeric nano-drug carriers for tumor therapy.

Adding Polypeptides to the Toolbox for Redox-Switchable Polymerization and Copolymerization Catalysis

Bis(imino)pyridine (BIP) iron alkoxide complexes act as catalysts to efficiently polymerize N-carboxyanhydrides (NCAs), including γ-benzyl-l-glutamate NCA (BLG-NCA) and sarcosine NCA (Sar-NCA), at room temperature. Reaction rates were greatly enhanced with the addition of mild Lewis acids, such as [CoCp2][BArF24], which work cooperatively with the iron-based catalysts to facilitate NCA polymerization. The reactivity of (2,6MeBIP)FeOCH2C(CH3)3 with Sar-NCA was combined with its known reactivity for ε-caprolactone polymerization to form diblock and triblock copoly(ester-b-peptides) through sequential addition of lactone and NCA monomers. Redox-switchable polymerization reactions were developed by iteratively exposing the catalyst to redox reagents and Sar-NCA or cyclohexene oxide. The orthogonal reactivity demonstrated by the catalyst in its oxidized and reduced states led to the synthesis of diblock and triblock copoly(ether-b-peptides). Polyether segments were synthesized with the catalyst in its oxidized state, while the polyamide segments were synthesized with the catalyst in its reduced state. Both copolymerization reactions developed here are rare examples where NCA polymerization reactions can be combined with other ring-opening polymerization reactions to make copolymers containing polypeptides and other functional monomers.

High Molecular Weight Polyproline as a Potential Biosourced Ice Growth Inhibitor: Synthesis, Ice Recrystallization Inhibition, and Specific Ice Face Binding.

Ice-binding proteins (IBPs) from extremophile organisms can modulate ice formation and growth. There are many (bio)technological applications of IBPs, from cryopreservation to mitigating freeze-thaw damage in concrete to frozen food texture modifiers. Extraction or expression of IBPs can be challenging to scale up, and hence polymeric biomimetics have emerged. It is, however, desirable to use biosourced monomers and heteroatom-containing backbones in polymers for in vivo or environmental applications to allow degradation. Here we investigate high molecular weight polyproline as an ice recrystallization inhibitor (IRI). Low molecular weight polyproline is known to be a weak IRI. Its activity is hypothesized to be due to the unique PPI helix it adopts, but it has not been thoroughly investigated. Here an open-to-air aqueous N-carboxyanhydride polymerization is employed to obtain polyproline with molecular weights of up to 50000 g mol-1. These polymers were found to have IRI activity down to 5 mg mL-1, unlike a control peptide of polysarcosine, which did not inhibit all ice growth at up to 40 mg mL-1. The polyprolines exhibited lower critical solution temperature behavior and assembly/aggregation observed at room temperature, which may contribute to its activity. Single ice crystal assays with polyproline led to faceting, consistent with specific ice-face binding. This work shows that non-vinyl-based polymers can be designed to inhibit ice recrystallization and may offer a more sustainable or environmentally acceptable, while synthetically scalable, route to large-scale applications.

Precision Synthesis of Polypeptides via Living Anionic Ring-Opening Polymerization of N-Carboxyanhydrides by Tri-thiourea Catalysts.

The chemistry of α-amino acid N-carboxyanhydrides (NCAs) has a history of over 100 years, but precise and efficient ring-opening polymerization methods for NCAs remain highly needed to facilitate the studies of polypeptides─that is, mimics of natural proteins─in various disciplines. Moreover, the universally accepted NCA polymerization mechanisms are largely limited to the "amine" and the "activated monomer" mechanisms, and the anionic ring-opening polymerization of NCAs has so far not been invoked. Herein, we show an unprecedented anion-binding catalytic system combining tripodal tri-thiourea with sodium thiophenolate that enables the fast and selective anionic ring-opening polymerization of NCAs. This method leads to the precision construction of various polypeptides with living polymerization behavior and is evidenced by narrow molecular weight distributions (Mw/Mn < 1.2), chain extension experiments, and minimal "activated monomer" pathway. Calculations and experimental results elucidate a living anionic polymerization mechanism, and high selectivities for monomer propagation relative to other deleterious side reactions, such as the "activated monomer" pathway, are attributed to the enhanced stabilization of the propagating carbamate anion, which is enforced by an intramolecular hydrogen bond within the tri-thiourea structure.

Thermoresponsive Glycopolypeptide Containing Block Copolymers, Particle Formation, and Lectin Interaction.

Amphiphilic block copolymers with a thermoresponsive poly(N-isopropylacrylamide) block and a glycopeptide block are synthesized and particle formation as well as interaction of the glyco-corona with lectins is investigated. The synthetic route comprises the preparation of block copolymers by N-carboxyanhydride polymerization and subsequent deprotection to obtain pH- and thermoresponsive poly(l-glutamic acid)-b-poly(N-isopropylacrylamide) (pGA-b-pNIPAM), which is then further modified with different amino sugars by a versatile coupling method with 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholin-4-ium chloride (DMT-MM). The glycosylated pGA-b-pNIPAM block copolymers are investigated with regard to cloud point temperatures (Tcp ), particle size, and stability. The morphology of the particles is visualized using cryo-SEM. Zeta potential measurements are indicating that the saccharide moieties are located on the surface of the particles. This assumption is further substantiated by quantitative lectin interaction assays with nonaggregated and aggregated glycosylated pGA-b-pNIPAM. The interaction of the model lectin ConA with the block copolymers is independent of the degree of substitution in the nonaggregated state at room temperature. However, at 37°C, when particles of pGA-b-pNIPAM are present, the interaction becomes stronger with increasing degree of substitution. This interaction with lectins can be used for targeting saccharide-modified particles in drug delivery.

Biomimetic Glycosylated Polythreonines by N-Carboxyanhydride Polymerization.

Glycosylated threonine (Thr) is a structural motif found in seemingly disparate natural proteins from deep-sea collagen to mucins. Synthetic mimics of these important proteins are of great interest in biomedicine. Such materials also provide ready access to probe the contributions of individual amino acids to protein structure in a controlled and tunable manner. N-Carboxyanhydride (NCA) polymerization is one major route to such biomimetic polypeptides. However, challenges in the preparation and polymerization of Thr NCAs have impeded obtaining such structures. Here, we present optimized routes to several glycosylated and acetylated Thr NCAs of high analytical purity. Transition metal catalysis produced tunable homo-, statistical, and block-polypeptides with predictable chain lengths and low dispersities. We conducted structural work to examine their aqueous conformations and found that a high content of free OH Thr induces the formation of water-insoluble β-sheets. However, glycosylation appears to induce a polyproline II-type helical conformation, which sheds light on the role of glyco-Thr in rigid proteins such as mucins and collagen.

Spherical α-helical polypeptide-mediated E2F1 silencing against myocardial ischemia-reperfusion injury (MIRI).

Apoptosis of cardiomyocytes is a critical outcome of myocardial ischemia-reperfusion injury (MIRI), which leads to the permanent impairment of cardiac function. Upregulated E2F1 is implicated in inducing cardiomyocyte apoptosis, and thus intervention of the E2F1 signaling pathway via RNA interference may hold promising potential for rescuing the myocardium from MIRI. To aid efficient E2F1 siRNA (siE2F1) delivery into cardiomyocytes that are normally hard to transfect, a spherical, α-helical polypeptide (SPP) with potent membrane activity was developed via dendrimer-initiated ring-opening polymerization of N-carboxyanhydride followed by side-chain functionalization with guanidines. Due to its multivalent structure, SPP outperformed its linear counterpart (LPP) to feature potent siRNA binding affinity and membrane activity. Thus, SPP effectively delivered siE2F1 into cardiomyocytes and suppressed E2F1 expression both in vitro and in vivo after intramyocardial injection. The E2F1-miR421-Pink1 signaling pathway was disrupted, thereby leading to the reduction of MIRI-induced mitochondrial damage, apoptosis, and inflammation of cardiomyocytes and ultimately recovering the systolic function of the myocardium. This study provides an example of membrane-penetrating nucleic acid delivery materials, and it also provides a promising approach for the genetic manipulation of cardiomyocyte apoptosis for the treatment of MIRI.

Superfast and Water‐Insensitive Polymerization on α‐Amino Acid N‐Carboxyanhydrides to Prepare Polypeptides Using Tetraalkylammonium Carboxylate as the Initiator

AbstractWe design the tetraalkylammonium carboxylate‐initiated superfast polymerization on α‐amino acid N‐carboxyanhydrides (NCA) for efficient synthesis of polypeptides. Carboxylates, as a new class of initiator for NCA polymerization, can initiate the superfast NCA polymerization without the need of extra catalysts and the polymerization can be operated in open vessels at ambient condition without the use of glove box. Tetraalkylammonium carboxylate‐initiated polymerization on NCA easily affords block copolymers with at least 15 blocks. Moreover, this method avoids tedious purification steps and enables direct polymerization on crude NCAs in aqueous environments to prepare polypeptides and one‐pot synthesis of polypeptide nanoparticles. These advantages and the mild polymerization condition of tetraalkylammonium carboxylate‐initiated NCA polymerization imply its great potential in functional exploration and application of polypeptides.