Mild and Efficient Preparation of Block and Gradient Copolymers by Methanesulfonic Acid Catalyzed Ring-Opening Polymerization of Caprolactone and Trimethylene Carbonate

Synthesis and Characterization of Guanidinylated CO-Releasing Micelles Based on Biodegradable Polycarbonate

As one of the gaseous signals in living cells, carbon monoxide (CO) not only participates in many biological activities but also serves as a therapeutic agent for the treatment of diseases. However, the limited applicability of CO in gas therapy emerges from the inconvenience of direct administration of CO. Here we reported the construction of guanidinylated CO-releasing micelles, which are composed of poly(trimethylene carbonate) (PTMC)-based CO donors. The in vitro studies demonstrated that micelles in the presence of light irradiation can induce cancer death, whereas no obvious toxicity to normal cells was observed. Moreover, the functionalization of guanidine groups imparts improved cellular uptake efficiency to micelles owing to the specific interactions with the surface of cells, which synergistically increase the anticancer capacity of the system. The guanidine-functionalized CO-releasing micelles provide a new strategy for the construction of CO-releasing nanocarriers, which are expected to find applications in gas therapeutics.

Ring opening copolymerization of δ-valerolactone with 2-methyl-1,3-dioxane-4-one towards poly(3-hydroxypropionate-co-5-hydroxyvalerate) copolyesters

A straightforward strategy of ring-opening copolymerization (ROCOP) toward the synthetic copolyesters is gaining increasing interest. In present work, a novel series of poly(3-hydroxypropionate-co-5-hydroxyvalerate) P(3HP-co-5HV) copolyesters are obtained through ROCOP of...

Reducing the crystallinity of PCL chains by copolymerization with substituted δ/ε-lactones and its impact on the phase separation of PCL-based block copolymers

Various substituted δ/ε-lactones have been copolymerized with ε-caprolactone (ε-CL) with the aim to inhibit the crystallization of polycaprolactone (PCL). Among the studied co-monomers, the best results were obtained with the...

Sequentially bridging anionic addition and ring-opening polymerization by cooperative organocatalysis: Well-defined block copolymers from methacrylates and cyclic esters

Organocatalytic sequential block copolymerization of dissimilar monomers with distinct chemical characteristics is great challenging, usually involving the integration of different polymerization mechanism. In this contribution, we reported the synthesis of...

Recent Developments in Lactone Monomers and Polymer Synthesis and Application

Lactones are a group of compounds that have been known for several decades. The commercial importance of lactones results from the possibility of manufacturing of a broad scope of derivatives and polymers with a wide spectrum of applications. In this work the synthesis and characterization of simple lactones are described, which due to the easy methods of the synthesis are of high importance for the industry. The chemical as well as biochemical methods are included with special attention paid to the methods that avoid metal catalysts, initiators or toxic solvents, allowing the use of the final products for the medical applications, e.g., for controlled drug-release systems, resorbable surgical threads, implants, tissue scaffolds or for the production of drugs. Lactone-based derivatives, such as polymers, copolymers, composites or three-dimensional structures are also presented. The work is focused on the methods for the synthesis of lactones and lactones derivates, as well as on the special properties and application of the studied compounds.

Poly(trimethylene carbonate-co-valerolactone) copolymers are materials with tailorable properties: from soft to thermoplastic elastomers

Aliphatic poly(ester-carbonates) are receiving extensive research attention as tailorable materials suitable for multiple applications from tissue engineering and 3D scaffold printing to drug delivery. Thus, simple reliable procedures for producing easily tailorable poly(ester-carbonates) without metal residues are continuously sought after. In this work, we report on one-pot synthesis of random copolymers of TMC and δ-VL using metal-free biocompatible 1,5,7-triazabicyclo[4.4.0]dec-5-ene as a catalyst and benzyl alcohol and poly(ethylene oxide) as initiators. Random poly(ester-carbonates) with TMC : VL unit ratios ranging from 80 : 20 to 20 : 80 were synthesized via ring-opening polymerization while displaying excellent agreement of comonomers' ratios in the feed and copolymer chains. The copolymers' supramolecular structure, thermal and mechanical properties were thoroughly analyzed by various methods. The obtained results clearly indicated that the physicochemical properties can be controlled simply by varying the ratio of comonomers and the length of segments in the copolymer chain. Several copolymers exhibited behavior of thermoplastic elastomers with the most promising one exhibiting a 2200% increase in elongation at break compared to the poly(valerolactone) homopolymer while retaining tensile strength and Young's modulus suitable for biomedical applications. Overall, our work contributed to widening the portfolio of tailorable copolymers for specialized bioapplications and possibly paving a way for the use of more sustainable polymers in the biomedical field.

Dithiolane-Crosslinked Poly(ε-caprolactone)-Based Micelles: Impact of Monomer Sequence, Nature of Monomer, and Reducing Agent on the Dynamic Crosslinking Properties

Dithiolanes are used to obtain dynamic and reversible crosslinks between polymer chains. Copolymers of two different dithiolane-containing cyclic carbonate monomers and ε-caprolactone (CL) were synthesized by ring-opening polymerization using a methoxy-poly(ethylene glycol) (mPEG) initiator and different catalysts (diphenyl phosphate (DPP), methanesulfonic acid (MSA), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), or Sn(Oct)2). Each catalyst required a different temperature, which had a pronounced influence on the reactivity ratio of the monomers and occurrence of transesterification reactions and, therefore, the monomer sequence. Self-crosslinkable copolymers were obtained when the dithiolane units were connected closely to the polymer backbone, whereas the presence of a linker unit between the dithiolane and the backbone prevented self-crosslinking. The former amphiphilic PEGylated block copolymers formed micelles by nanoprecipitation in the aqueous environment and crosslinked spontaneously by disulfide exchange during subsequent dialysis. These dithiolane-crosslinked micelles showed reduction-responsive dissociation in the presence of 10 mM glutathione, making them promising drug delivery systems for the intracellularly triggered cargo release.

Organocatalytic sequential ring-opening polymerization of a cyclic ester and anionic polymerization of a vinyl monomer

Organocatalysis has provided new tools for making block copolymers, in particular active species able to polymerize monomers of different chemical nature such as cyclic esters, cyclic carbonates and epoxides. We report herein the first example of an organocatalytic active species able to polymerize sequentially a cyclic ester, ε-decalactone, and a vinyl monomer, methyl methacrylate. The resulting block copolymer shows the properties of thermoplastic elastomers.

Terpolymer-stabilized complex coacervates: A robust and versatile synthetic cell platform

The utilization of liquid-liquid phase separated systems has seen increased attention as synthetic cell platforms due to their innate ability to sequester interesting, functional, and biologically relevant materials. However, their applications are limited by the temporal stability of such condensed phases. While there are a number of strategies toward droplet stabilization, in our group we have developed a polymer-based approach to stabilize complex coacervate microdroplets. These protocells are remarkably robust and have been utilized to support a number of new protocellular applications. Here, we describe in detail the methodologies we have developed for the synthesis of the starting components, their formation into stable, cargo-loaded protocells, and how these protocells are treated post-formation to purify and analyze the resultant functional self-assembled systems.

π-π-Stacked Poly(ε-caprolactone)-b-poly(ethylene glycol) Micelles Loaded with a Photosensitizer for Photodynamic Therapy

To improve the in vivo stability of poly(ε-caprolactone)-b-poly(ethylene glycol) (PCL-PEG)-based micelles and cargo retention by π-π stacking interactions, pendant aromatic rings were introduced by copolymerization of ε-caprolactone with benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (TMC-Bz). It was shown that the incorporation of aromatic rings yielded smaller micelles (18–30 nm) with better colloidal stability in PBS than micelles without aromatic groups. The circulation time of i.v. injected micelles containing multiple pendant aromatic groups was longer (t½-α: ~0.7 h; t½-β: 2.9 h) than that of micelles with a single terminal aromatic group (t½ < 0.3 h). In addition, the in vitro partitioning of the encapsulated photosensitizer (meta-tetra(hydroxyphenyl)chlorin, mTHPC) between micelles and human plasma was favored towards micelles for those that contained the pendant aromatic groups. However, this was not sufficient to fully retain mTHPC in the micelles in vivo, as indicated by similar biodistribution patterns of micellar mTHPC compared to free mTHPC, and unequal biodistribution patterns of mTHPC and the host micelles. Our study points out that more detailed in vitro methods are necessary to more reliably predict in vivo outcomes. Furthermore, additional measures beyond π-π stacking are needed to stably incorporate mTHPC in micelles in order to benefit from the use of micelles as targeted delivery systems.

Wormlike Nanovector with Enhanced Drug Loading Using Blends of Biodegradable Block Copolymers

The application of nanoparticles comprising amphiphilic block copolymers for the delivery of drugs is a subject of great interest as they hold promise for more effective and selective therapies. In order to achieve this ambition, it is of critical importance to develop our understanding of the self-assembly mechanisms by which block copolymers undergo so that we can control their morphology, tune their ability to be loaded with biofunctional cargoes, and optimize their interactions with target cells. To this end, we have developed a strategy by which blends of (biocompatible) amphiphilic block copolymers generate nonspherical nanovectors, simultaneously enhancing drug loading without the need for subsequent purification owing to the use of the biocompatible direct hydration approach. The principal morphology achieved using this blending strategy are wormlike nanovectors (nanoworms, NWs), with an elongated form known to have a profound effect on flow behavior and interactions with cells. Unloaded nanoworms are not toxic toward human retinal (ARPE-19) cells and can be effectively endocytosed even after varying the surface charge. In terms of drug loading, we demonstrate that uptake of dexamethasone (DEX; a clinically relevant therapeutic agent) in nanoworms (DEX@NWs) can be enhanced using this process, increasing drug content up to 0.5 mg/mL (10 wt % in particles). Furthermore, such nanoworms are stable for at least 5 months and are, therefore, a promising platform for nanomedicine applications.

EGFR-Targeted Nanobody Functionalized Polymeric Micelles Loaded with mTHPC for Selective Photodynamic Therapy

meta-Tetra(hydroxyphenyl)chlorin (mTHPC) is one of the most potent second-generation photosensitizers, clinically used for photodynamic therapy (PDT) of head and neck squamous cell carcinomas. However, improvements are still required concerning its present formulation (i.e., Foscan, a solution of mTHPC in ethanol/propylene glycol (40:60 w/w)), as mTHPC has the tendency to aggregate in aqueous media, e.g., biological fluids, and it has limited tumor specificity. In the present study, polymeric micelles with three different diameters (17, 24, and 45 nm) based on benzyl-poly(ε-caprolactone)-b-poly(ethylene glycol) (PCL_n-PEG; n = 9, 15, or 23) were prepared with mTHPC loadings ranging from 0.5 to 10 wt % using a film-hydration method as advanced nanoformulations for this photosensitizer. To favor the uptake of the micelles by cancer cells that overexpress the epidermal growth factor receptor (EGFR), the micelles were decorated with an EGFR-targeted nanobody (named EGa1) through maleimide-thiol chemistry. The enhanced binding of the EGFR-targeted micelles at 4 °C to EGFR-overexpressing A431 cells, compared to low-EGFR-expressing HeLa cells, confirmed the specificity of the micelles. In addition, an enhanced uptake of mTHPC-loaded micelles by A431 cells was observed when these were decorated with the EGa1 nanobody, compared to nontargeted micelles. Both binding and uptake of targeted micelles were blocked by an excess of free EGa1 nanobody, demonstrating that these processes occur through EGFR. In line with this, mTHPC loaded in EGa1-conjugated PCL₂₃-PEG (EGa1-P₂₃) micelles demonstrated 4 times higher photocytotoxicity on A431 cells, compared to micelles lacking the nanobody. Importantly, EGa1-P₂₃ micelles also showed selective PDT against A431 cells compared to the low-EGFR-expressing HeLa cells. Finally, an in vivo pharmacokinetic study shows that after intravenous injection, mTHPC incorporated in the P₂₃ micelles displayed prolonged blood circulation kinetics, compared to free mTHPC, independently of the presence of EGa1. Thus, these results make these micelles a promising nanomedicine formulation for selective therapy.

DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

Organocatalysis is highly efficient in the ring-opening polymerization (ROP) of cyclic esters. A variety of initiators broaden the areas of organocatalysis in polymerization of different monomers, such as lactones, cyclic carbonates, lactides or gycolides, ethylene phosphates and phosphonates, and others. The mechanisms of organocatalytic ROP are at least as diverse as the mechanisms of coordination ROP; the study of these mechanisms is critical in ensuring the polymer compositions and architectures. The use of density functional theory (DFT) methods for comparative modeling and visualization of organocatalytic ROP pathways, in line with experimental proof of the structures of the reaction intermediates, make it possible to establish these mechanisms. In the present review, which continues and complements our recent manuscript that focused on DFT modeling of coordination ROP, we summarized the results of DFT modeling of organocatalytic ROP of cyclic esters and some related organocatalytic processes, such as polyester transesterification.

Polymer Assembly Encapsulation of Lanthanide Nanoparticles as Contrast Agents for In Vivo Micro-CT

Despite recent technological advancements in microcomputed tomography (micro-CT) and contrast agent development, preclinical contrast agents are still predominantly iodine-based. Higher contrast can be achieved when using elements with higher atomic numbers, such as lanthanides; lanthanides also have X-ray attenuation properties that are ideal for spectral CT. However, the formulation of lanthanide-based contrast agents at the high concentrations required for vascular imaging presents a significant challenge. In this work, we developed an erbium-based contrast agent that meets micro-CT imaging requirements, which include colloidal stability upon redispersion at high concentrations, evasion of rapid renal clearance, and circulation times of tens of minutes in small animals. Through systematic studies with poly(ethylene glycol) (PEG)-poly(propylene glycol), PEG-polycaprolactone, and PEG-poly(l-lactide) (PLA) block copolymers, the amphiphilic block copolymer PEG₁₁₄-PLA₅₃ was identified to be ideal for encapsulating oleate-coated lanthanide-based nanoparticles for in vivo intravenous administration. We were able to synthesize a contrast agent containing 100 mg/mL of erbium that could be redispersed into colloidally stable particles in saline after lyophilization. Contrast enhancement of over 250 HU was achieved in the blood pool for up to an hour, thereby meeting the requirements of live animal micro-CT.

Scope and limitations of ring-opening copolymerization of trimethylene carbonate with substituted γ-thiolactones

The reactivity of functional γ-thiolactones has been investigated in Ring Opening Copolymerization with trimethylene carbonate.

Hybrid block copolymers of polyesters/polycarbonates and polypeptides synthesized via one-pot sequential ring-opening polymerization

Polyester/polycarbonate-b-polypeptide hybrid block copolymers were synthesized by a sequential ring-opening polymerization in a one-pot manner.

Hierarchical Self-Assembly of a Copolymer-Stabilized Coacervate Protocell

Complex coacervate microdroplets are finding increased utility in synthetic cell applications due to their cytomimetic properties. However, their intrinsic membrane-free nature results in instability that limits their application in protocell research. Herein, we present the development of a new protocell model through the spontaneous interfacial self-assembly of copolymer molecules on biopolymer coacervate microdroplets. This hierarchical protocell model not only incorporates the favorable properties of coacervates (such as spontaneous assembly and macromolecular condensation) but also assimilates the essential features of a semipermeable copolymeric membrane (such as discretization and stabilization). This was accomplished by engineering an asymmetric, biodegradable triblock copolymer molecule comprising hydrophilic, hydrophobic, and polyanionic components capable of direct coacervate membranization via electrostatic surface anchoring and chain self-association. The resulting hierarchical protocell demonstrated striking integrity as a result of membrane formation, successfully stabilizing enzymatic cargo against coalescence and fusion in discrete protocellular populations. The semipermeable nature of the copolymeric membrane enabled the incorporation of a simple enzymatic cascade, demonstrating chemical communication between discrete populations of neighboring protocells. In this way, we pave the way for the development of new synthetic cell constructs.

Triblock Copolymers Based on ε-Caprolactone and Trimethylene Carbonate for the 3D Printing of Tissue Engineering Scaffolds

Background

Biodegradable PCL- b-PTMC- b-PCL triblock copolymers based on trimethylene carbonate (TMC) and ε-caprolactone (CL) were prepared and used in the 3D printing of tissue engineering scaffolds. Triblock copolymers of various molecular weights containing equal amounts of TMC and CL were prepared. These block copolymers combine the low glass transition temperature of amorphous PTMC (approximately -20°C) and the semi-crystallinity of PCL (glass transition approximately -60°C and melting temperature approximately 60°C).

Methods

PCL- b-PTMC- b-PCL triblock copolymers were synthesized by sequential ring opening polymerization (ROP) of TMC and ε-CL. From these materials, films were prepared by solvent casting and porous structures were prepared by extrusion-based 3D printing.

Results

Films prepared from a polymer with a relatively high molecular weight of 62 kg/mol had a melting temperature of 58°C and showed tough and resilient behavior, with values of the elastic modulus, tensile strength and elongation at break of approximately 120 MPa, 16 MPa and 620%, respectively. Porous structures were prepared by 3D printing. Ethylene carbonate was used as a crystalizable and water-extractable solvent to prepare structures with microporous strands. Solutions, containing 25 wt% of the triblock copolymer, were extruded at 50°C then cooled at different temperatures. Slow cooling at room temperature resulted in pores with widths of 18 ± 6 μm and lengths of 221 ± 77 μm, rapid cooling with dry ice resulted in pores with widths of 13 ± 3 μm and lengths of 58 ± 12 μm. These PCL- b-PTMC- b-PCL triblock copolymers processed into porous structures at relatively low temperatures may find wide application as designed degradable tissue engineering scaffolds.

Conclusions

In this preliminary study we prepared biodegradable triblock copolymers based on 1,3-trimethylene carbonate and ε-caprolactone and assessed their physical characteristics. Furthermore, we evaluated their potential as melt-processable thermoplastic elastomeric biomaterials in 3D printing of tissue engineering scaffolds.

Polymers from sugars and CO2: ring-opening polymerisation and copolymerisation of cyclic carbonates derived from 2-deoxy-d-ribose

We report the preparation of two anomeric cyclic carbonate monomers from CO₂ and natural sugar 2-deoxy-d-ribose, their ring-opening polymerisation and copolymerisation with trimethylene carbonate to produce aliphatic polycarbonates with tunable properties.

Switching from Controlled Ring-Opening Polymerization (cROP) to Controlled Ring-Closing Depolymerization (cRCDP) by Adjusting the Reaction Parameters That Determine the Ceiling Temperature

Full control over the ceiling temperature (Tc) enables a selective transition between the monomeric and polymeric state. This is exemplified by the conversion of the monomer 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC) to poly(AOMEC) and back to AOMEC within 10 h by controlling the reaction from conditions that favor ring-opening polymerization (Tc > T0) (where T0 is the reaction temperature) to conditions that favor ring-closing depolymerization (Tc < T0). The ring-closing depolymerization (RCDP) mirrors the polymerization behavior with a clear relation between the monomer concentration and the molecular weight of the polymer, indicating that RCDP occurs at the chain end. The Tc of the polymerization system is highly dependent on the nature of the solvent, for example, in toluene, the Tc of AOMEC is 234 °C and in acetonitrile Tc = 142 °C at the same initial monomer concentration of 2 M. The control over the monomer to polymer equilibrium sets new standards for the selective degradation of polymers, the controlled release of active components, monomer synthesis and material recycling. In particular, the knowledge of the monomer to polymer equilibrium of polymers in solution under selected environmental conditions is of paramount importance for in vivo applications, where the polymer chain is subjected to both high dilution and a high polarity medium in the presence of catalysts, that is, very different conditions from which the polymer was formed.

Tripodal hydrogen bond donor binding with sulfonic acid enables ring-opening polymerization

The first Brønsted acidic catalysis platform workable in all of the three major types of cyclic ester monomers including lactides, cyclic carbonates, and lactones, is described in this paper.

Traceless switch organocatalysis enables multiblock ring-opening copolymerizations of lactones, carbonates, and lactides: by a one plus one approach in one pot

A switch of organocatalysis from cationic to base/conjugate-acid bifunctional mechanisms made ring-opening copolymerizations of lactones/carbonates to lactides success.

Macromolecular Design via an Organocatalytic, Monomer-Specific and Temperature-Dependent "On/Off Switch". High Precision Synthesis of Polyester/Polycarbonate Multiblock Copolymers

The employment of a monomer-specific "on/off switch" was used to synthesize a nine-block copolymer with a predetermined molecular weight and narrow distribution (Đ = 1.26) in only 2.5 h. The monomers consisted of a six-membered cyclic carbonate (i.e., 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC)) and ε-caprolactone (εCL), which were catalyzed by 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD). The dependence of polymerization rate with temperature was different for the two monomers. Under similar reaction conditions, the ratio of the apparent rate constant of AOMEC and εCL [kpapp(AOMEC)/kpapp(εCL)] changes from 400 at T = -40 °C to 50 at T = 30 °C and 10 at T = 100 °C. Therefore, by decreasing the copolymerization temperature from 30 °C to -40 °C, the conversion of εCL can be switched "off", and by increasing the temperature to 30 °C, the conversion of εCL can be switched "on" again. The addition of AOMEC at T = -40 °C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of εCL along with a simultaneous temperature change leads to the formation of multiblock copolymers. This result provides a new straightforward synthetic route to degradable multiblock copolymers, yielding new interesting materials with endless structural possibilities.

Robust formation of biodegradable polymersomes by direct hydration

A mild, robust and fast method to form nano-sized biodegradable polymersomes is described.

Selective O-acyl ring-opening of β-butyrolactone catalyzed by trifluoromethane sulfonic acid: application to the preparation of well-defined block copolymers

HOTf catalyzes ring-opening of β-butyrolactone selectively via O-acyl bond cleavage, enabling efficient copolymerization.