One-pot synthesis of brush-like polymers via integrated ring-opening metathesis polymerization and polymerization of amino acid N-carboxyanhydrides

One-Pot Synthesis of Strong Anionic/Charge-Neutral Amphiphilic Block Copolymers

Despite the ever more versatile polymerization techniques that are becoming available, the synthesis of macromolecules with tailored functionalities can remain a lengthy endeavor. This becomes more conspicuous when the implementation of incompatible chemistries (i.e., strong polyelectrolytes) within sequence-controlled polymers is desired, often requiring (i) polymerization, (ii) chain extension, and (iii) postpolymerization modification. Herein, we explore the production of strong anionic/charge-neutral block copolymers (BCPs) in a one-pot fashion. This straightforward three-step process includes the synthesis of a macroinitiator and chain extension via rapid and efficient photomediated atom transfer radical polymerization, followed by in situ deprotection to expose the polyanionic domains. The resulting BCPs, which are strong amphiphiles by nature, are capable of self-assembly in aqueous media, as evidenced by dynamic light scattering, small-angle X-ray scattering, ζ-potential measurements, and transmission electron microscopy. We further demonstrate the versatility of our methodology by producing several BCPs through sampling of a single reaction mixture, enabling the straightforward production of strong polymer amphiphiles.

Tunable, biodegradable grafting-from glycopolypeptide bottlebrush polymers

The cellular glycocalyx and extracellular matrix are rich in glycoproteins and proteoglycans that play essential physical and biochemical roles in all life. Synthetic mimics of these natural bottlebrush polymers have wide applications in biomedicine, yet preparation has been challenged by their high grafting and glycosylation densities. Using one-pot dual-catalysis polymerization of glycan-bearing α-amino acid N-carboxyanhydrides, we report grafting-from glycopolypeptide brushes. The materials are chemically and conformationally tunable where backbone and sidechain lengths were precisely altered, grafting density modulated up to 100%, and glycan density and identity tuned by monomer feed ratios. The glycobrushes are composed entirely of sugars and amino acids, are non-toxic to cells, and are degradable by natural proteases. Inspired by native lipid-anchored proteoglycans, cholesterol-modified glycobrushes were displayed on the surface of live human cells. Our materials overcome long-standing challenges in glycobrush polymer synthesis and offer new opportunities to examine glycan presentation and multivalency from chemically defined scaffolds.

Synthetic mimics of glycoproteins and proteoglycans have wide applications in biomedicine, yet preparation has been challenged by their high grafting and glycosylation densities. Here the authors show one-pot dual-catalysis polymerization of glycan-bearing α-amino acid N-carboxyanhydrides to form glycopolypeptide brushes.

Multicatalytic Transformation of (Meth)acrylic Acids: a One-Pot Approach to Biobased Poly(meth)acrylates

Shifting from petrochemical feedstocks to renewable resources can address some of the environmental issues associated with petrochemical extraction and make plastics production sustainable. Therefore, there is a growing interest in selective methods for transforming abundant renewable feedstocks into monomers suitable for polymer production. Reported herein are one-pot catalytic systems, that are active, productive, and selective under mild conditions for the synthesis of copolymers from renewable materials. Each system allows for anhydride formation, alcohol acylation and/or acid esterification, as well as polymerization of the formed (meth)acrylates, providing direct access to a new library of unique poly(meth)acrylates.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Star polymerization of norbornene derivatives using a tri-functionalized Blechert's olefin metathesis catalyst

A tri-functionalized initiator (IV) based on Blechert's catalyst as a highly efficient ROMP initiator for the living polymerization of norbornene derivatives.

Grubbs' and Schrock's Catalysts, Ring Opening Metathesis Polymerization and Molecular Brushes-Synthesis, Characterization, Properties and Applications

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented in order to understand the problems and the solutions provided through the years. The synthetic strategies towards bottlebrush copolymers are demonstrated and each one discussed separately. The initiators/catalysts for the synthesis of the backbone with ROMP are discussed. Syntheses of molecular brushes are presented. The most interesting properties of the bottlebrushes are detailed. Finally, the applications studied by different groups are presented.

Stimuli-Responsive Polypeptides for Biomedical Applications

Stimuli-responsive polypeptides have gained attention because desirable bioactive properties can be easily imparted to them while keeping their biocompatibility and biodegradability intact. In this review, we summarize the most recent advances in various stimuli-responsive polypeptides (pH, reduction, oxidation, glucose, adenosine triphosphate (ATP), and enzyme) over the past five years. Various synthetic strategies exploited for advanced polypeptide-based materials are introduced, and their applicability in biomedical fields is discussed. The recent polypeptides imparted with new stimuli-responsiveness and their novel chemical and physical properties are explained in this review.

Shape-changing linear molecular bottlebrushes with dually pH- and thermo-responsive diblock copolymer side chains

The collapse of inner pH-responsive blocks drives cylindrical-to-globular shape transition while outer thermoresponsive blocks provide additional control of solution state.

Two-Dimensional Controlled Syntheses of Polypeptide Molecular Brushes via N-Carboxyanhydride Ring-Opening Polymerization and Ring-Opening Metathesis Polymerization

Well-defined molecular brushes bearing polypeptides as side chains were prepared by a "grafting through" synthetic strategy with two-dimensional control over the brush molecular architectures. By integrating N-carboxyanhydride ring-opening polymerizations (NCA ROPs) and ring-opening metathesis polymerizations (ROMPs), desirable segment lengths of polypeptide side chains and polynorbornene brush backbones were independently constructed in controlled manners. The N2 flow accelerated NCA ROP was utilized to prepare polypeptide macromonomers with different lengths initiated from a norbornene-based primary amine, and those macromonomers were then polymerized via ROMP. It was found that a mixture of dichloromethane and an ionic liquid were required as the solvent system to allow for construction of molecular brush polymers having densely-grafted peptide chains emanating from a polynorbornene backbone, poly(norbornene-graft-poly(β-benzyl-l-aspartate)) (P(NB-g-PBLA)). Highly efficient postpolymerization modification was achieved by aminolysis of PBLA side chains for facile installment of functional moieties onto the molecular brushes.

Synthesis of controlled, high-molecular weight poly(l-glutamic acid) brush polymers

We report the synthesis and characterization of high-molecular weight poly(l-glutamic acid) based brush polymers. Utilizing a combination of ring-opening metathesis polymerization of norbornene based monomers and ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride, high-molecular weight γ-benzyl protected poly(l-glutamic acid) brush polymers are synthesized. Controlled and complete deprotection of the benzyl groups using trimethylsilyl iodide resulted in poly(l-glutamic acid) based brush polymers with molecular weights up to 3.6 MDa, which may potentially be used to prepare size-controlled unimolecular polymeric nanomedicine for drug delivery applications. Camptothecin brush poly(l-glutamic acid) conjugates were prepared and their stability, drug release kinetics, and in vitro toxicity were studied.

Folding Cooperativity of Synthetic Polypeptides with or without "Tertiary" Interactions

Model-based studies on helix-coil transition and folding cooperativity of synthetic polypeptides have contributed to the understanding of protein folding and stability and to the development of polypeptide-based functional materials. Polypeptide-containing macromolecules with complex architectures, however, remain a challenge in the model-based analysis. Herein, a modified Schellman-Zimm-Bragg model has been utilized to quantitatively analyze the folding cooperativity of polypeptide-containing macromolecules. While the helix-coil transition of homopolypeptides (e.g., poly(ε-benzyloxycarbonyl-l-lysine) (PZLL)) can be described by the classic model, the folding of grafted polypeptide chains in the comb macromolecules (e.g., polynorbornene-g-poly(ε-benzyloxycarbonyl-l-lysine) (PN-g-PZLL)) cannot be accurately predicted by the existing theories, due to the side-chain interactions between grafted polypeptides in the comb macromolecules. Incorporating nonlocal interaction explicability into the statistical mechanics treatment is found to be instructive to account for the possible "tertiary" interactions of polypeptides in the macromolecules with complex architectures.

Revisiting the Helical Cooperativity of Synthetic Polypeptides in Solution

Using synthetic polypeptides as a model system, the theories of helix-coil transition were developed into one of the most beautiful and fruitful subjects in macromolecular science. The classic models proposed by Schellman and Zimm-Bragg more than 50 years ago, differ in the assumption on whether the configuration of multiple helical sequences separated by random coil sections is allowed in a longer polypeptide chain. Zimm also calculated the critical chain lengths that facilitate such interrupted helices in different solvent conditions. The experimental validation of Zimm's prediction, however, was not carefully examined at that time. Herein, we synthesize a series of homopolypeptide samples with different lengths, to systematically examine their helix-coil transition and folding cooperativity in solution. We find that for longer chains, polypeptides do exist as interrupted helices with scattered coil sections even in helicogenic solvent conditions, as predicted in the Zimm-Bragg model. The critical chain lengths that facilitate such interrupted helices, however, are substantially smaller than Zimm's original estimation. The inaccuracy is in part due to an approximation that Zimm made in simplifying the calculation. But more importantly, we find there exist intramolecular interactions between different structural segments in the longer polypeptides, which are not considered in the classic helix-coil theories. As such, even the Zimm-Bragg model in its exact form cannot fully describe the transition behavior and folding cooperativity of longer polypeptides. The results suggest that long "all-helix" chains may be much less prevalent in solution than previously imagined, and a revised theory is required to accurately account for the helix-coil transition of the longer chains with potential "non-local" intramolecular interactions.

Synthesis, Characterization and Thermal Properties of Poly(ethylene oxide), PEO, Polymacromonomers via Anionic and Ring Opening Metathesis Polymerization

Branched polymers are a valuable class of polymeric materials. In the present study, anionic polymerization techniques were employed for the synthesis of low molecular weight poly(ethylene oxide) (PEO) macromonomers bearing norbornenyl end groups. The macromonomers were characterized by SEC, MALDI-TOF and NMR spectroscopy. Subsequent ring opening metathesis polymerization (ROMP) of the macromonomers using ruthenium catalysts (Grubbs catalysts of the 1st, 2nd and 3rd generations) afforded the corresponding polymacromonomers. The effects of the macromonomer molecular weight, the type of the catalyst, the nature of the solvent, the monomer concentration and the polymerization temperature on the molecular characteristics of the branched polymers were examined in detail. The crystallization behavior of the macromonomers and the corresponding polymacromonomers were studied by Differential Scanning Calorimetry (DSC). The thermal stability and the kinetics of the thermal decomposition of the samples were also studied by Thermogravimetric Analysis (TGA). The activation energies of the thermal decomposition were analyzed using the Ozawa–Flynn–Wall and Kissinger methodologies.

One-Pot Synthesis of Block Copolymers by Orthogonal Ring-Opening Polymerization and PET-RAFT Polymerization at Ambient Temperature

Well-defined poly(ε-caprolactone)-b-poly(methyl acrylate) (PCL-b-PMA) block copolymers were synthesized at ambient temperature by one-pot combination of diphenyl phosphate (DPP)-catalyzed ring-opening polymerization (ROP) and photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Full orthogonality of PET-RAFT polymerization and DPP-catalyzed ROP was confirmed by kinetic studies, which allowed facile synthesis of PCL-b-PMA block copolymers without a specific polymerization sequence. The resulting PCL-b-PMA block copolymers synthesized by either sequential or simultaneous ROP and PET-RAFT polymerization showed remarkably low molecular weight distributions (≤1.15), indicating that both ROP and PET-RAFT polymerizations proceeded in a controlled manner. In contrast to previous synthetic methods to prepare block copolymers, this facile one-pot method allows for rapid synthesis of block copolymers controlled via visible light.

Hydrogels assembled from star-shaped polypeptides with a dendrimer as the core

A second or fourth generation dendrimer with primary amine as the peripheral terminal group was first synthesized via Michael addition and thiol-yne addition. A series of star-shaped polypeptides was synthesized by ring opening polymerization (ROP) of γ-(2-(2-methoxyethoxy)ethyl) l-glutamate (l-EG2Glu) N-carboxyanhydride (NCA) using the amine group terminated dendrimer as the initiator. Taking advantage of the well-defined dendrimer and ROP, the arm number and arm length can be easily controlled. These star-shaped poly(l-EG2Glu) can spontaneously form hydrogels instead of micelles in water at low concentration. The critical gelation concentration (CGC) and hydrogel strength displayed a stronger dependence on arm numbers than the arm length under similar conditions. These properties can be easily modulated by varying the poly(l-EG2Glu) arm length and arm number. The hydrogels showed shear thinning and rapid recovery properties. TEM and AFM characterization revealed that the hydrogel networks were constituted by entangled and branched fibrils.

Ionic α-helical polypeptides toward nonviral gene delivery

The advent of polymeric materials has significantly promoted the development and rapid growth of various technologies in biomedical applications, such as tissue engineering and controlled drug and gene delivery. Water-soluble polypeptides bearing functional side chains and adopting stable secondary structures are a new class of functional polymeric materials of potentially broad applications in medicine and biotechnology. In this article, we summarize our recent effort on the design and synthesis of the water-soluble α-helical ionic polypeptides originally developed in our laboratory and highlight their applications in cell membrane penetration and nonviral gene/small interfering RNA (siRNA) delivery.

Brush macromolecules with thermo-sensitive coil backbones and pendant polypeptide side chains: synthesis, self-assembly and functionalization

Macromolecular brushes with thermo-sensitive coil backbones and pendant poly(γ-benzyl-l-glutamate) side chains were synthesized by reversible addition–fragmentation chain transfer and ring-opening polymerization. Functionalization and self-assembly of the macromolecules were investigated.

Self-folded redox/acid dual-responsive nanocarriers for anticancer drug delivery

Self-folded redox/acid dual-responsive nanocarriers (RAD-NCs) are developed for physiologically triggered delivery of anticancer drugs. The evidenced redox/acid responsiveness, facile decoration of ligands, and active tumor-targeting capability of RAD-NCs suggest their potential as a promising formulation for tumor-targeted chemotherapy.

Folding graft copolymer with pendant drug segments for co-delivery of anticancer drugs

A graft copolymer with pendant drug segments can fold into nanostructures in a protein folding-like manner. The graft copolymer is constructed by directly polymerizing γ-camptothecin-glutamate N-carboxyanhydride (Glu(CPT)-NCA) on multiple sites of poly(ethylene glycol) (PEG)-based main chain via the ring open polymerization (ROP). The "purely" conjugated anticancer agent camptothecin (CPT) is hydrophobic and serves as the principal driving force during the folding process. When exposed to water, the obtained copolymer, together with doxorubicin (Dox), another anticancer agent, can fold into monodispersed nanocarriers (with a diameter of around 50 nm) for dual-drug delivery. Equipped with a PEG shell, the nanocarriers displayed good stability and can be internalized by a variety of cancer cell lines via the lipid raft and clathrin-mediated endocytotic pathway without premature leakage, which showed a high synergetic activity of CPT and Dox toward various cancer cells. In vivo study validated that the nanocarriers exhibited strong accumulation in tumor sites and showed a prominent anticancer activity against the lung cancer xenograft mice model compared with free drugs.

One-step synthesis of hollow polymeric nanospheres: self-assembly of amphiphilic azo polymers via hydrogen bond formation

We introduce a facile and novel way that describes the random amphiphilic azo copolymer to construct hollow nanospheres via hydrogen bond formation.

PEG-Polypeptide Dual Brush Block Copolymers: Synthesis and Application in Nanoparticle Surface PEGylation

Amphiphilic polypeptide-containing hybrid dual brush block copolymers with controlled molecular weights and narrow molecular weight distributions were synthesized in one pot via ring-opening metathesis polymerization of sequentially added norbornyl-PEG and N-(2-((trimethylsilyl)amino)ethyl)-5-norbornene-endo-2,3-dicarboximide (M1) followed by ring-opening polymerization of amino acid N-carboxyanhydrides. Polylactide nanoparticles coated with these am phiphilic dual brush block copolymers showed significantly improved stability in PBS solution compared to those coated with amphiphilic linear block copolymers such as PEG-polylactide and PEG-polypeptides.