Organocatalytic Ring-opening Polymerization Research Articles

Versatile Preparation of Branched Polylactides by Low-Temperature, Organocatalytic Ring-Opening Polymerization in N-Methylpyrrolidone and Their Surface Degradation Behavior.

We describe how the organocatalytic, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-based lactide ring-opening polymerization can be effectively performed in a very polar solvent, N-methylpyrrolidone (NMP). Due to a low ceiling temperature, this “living” mechanism has been unreported to date, but we here demonstrate that through a combination of low temperature and repeated monomer additions (starve-fed process), this mechanism enables the generation of a plethora of multifunctional homo- and (stereo)block-poly(lactide)s (PLAs) with exquisite control of the molecular weight dispersity (typically Đ < 1.1) and topology (from linear through 4-, 6-, or 8-armed stars and up to ∼140 armed combs). They are scarcely obtainable or inaccessible through more classical synthetic methods due to the poor solubility of multifunctional initiators (polyols) in most organic solvents and monomer melts. In these precisely designed structures, branching significantly altered the nature of the materials’ hydrolytic degradation, allowing them to acquire a pronounced surface character (as opposed to the bulk degradation of linear polymers). Finally, we have assessed the amenability of this method to in situ block copolymerization by using the tacticity of PLLA blocks in PLLA-b-PDLLA versus PDLLA-b-PLLA (L-LA polymerized before or after DL-LA) as a sensitive method to detect (stereochemical) defects.

Polyphosphonate-Based Macromolecular RAFT-CTA Enables the Synthesis of Well-Defined Block Copolymers Using Vinyl Monomers.

Reversible addition-fragmentation chain transfer (RAFT) polymerization has become a straightforward approach to block copolymers using a wide variety of functional vinyl monomers. Polyphosphoester (PPE) macroinitiators from ring-opening polymerization (ROP) of their corresponding cyclic phosphoesters have been previously prepared for atom transfer radical polymerization; however, to date, these biodegradable macroinitiators for RAFT polymerization have not been reported. Herein, a macromolecular RAFT-chain transfer agent (CTA) based on poly(ethyl ethylene phosphonate) was prepared by the organocatalytic ROP of 2-ethyl-2-oxo-1,3,2-dioxaphospholane using 2-cyano-5-hydroxypentan-2-yl dodecyl trithiocarbonate as the initiator and 1,8-diazabycyclo[5.4.0]undec-7-ene as the catalyst. Precise macro-CTAs of degrees of polymerization (DPn) from 34 to 70 with Đ ≤ 1.10 were prepared and used in the dioxane solution RAFT polymerization of acrylamide, acrylates, methacrylates, and 2-vinylpyridine to yield a library of well-defined block copolymers. Additionally, the PPE-based macro RAFT-CTA was used as a nonionic surfactant in a typical aqueous emulsion polymerization of styrene to produce well-defined nanoparticles with the hydrophilic PPEs on their surface as the stabilizing agent. This general protocol allowed the combination of polyphosphoesters with RAFT polymerization.

Hybrid Block Copolymer Synthesis by Merging Photoiniferter and Organocatalytic Ring-Opening Polymerizations.

Access to block copolymers from monomers that do not polymerize via a common mechanism requires initiation from a multifunctional species that allows orthogonal polymerization chemistries. We disclose a strategy to provide well-defined polyacrylamido-b-polyether block copolymers by a one-pot combination of photoiniferter polymerization and organocatalytic ring-opening polymerization (ROP) using a hydroxy-functionalized trithiocarbonate photoiniferter as the dual initiator at ambient temperature. Our results reveal good compatibility between the two polymerization systems and highlight that they can be performed in arbitrary order or simultaneously with good retention of the thiocarbonylthio functionality. We also demonstrate selective temporal control over the photoiniferter polymerization during concurrent ROP. We harnessed the efficiency of combining these polymerization systems to provide tailor-made block copolymers from chemically distinct monomers.

Polyether-Based Block Co(ter)polymers as Multifunctional Lubricant Additives

A series of polyether-based diblock copolymers were synthesized by sequential organocatalytic ring-opening polymerization (ROP) of either hexene oxide (HO) or octene oxide (OO) as the first monomer with propylene oxide (PO) as the second monomer. In addition, one triblock terpolymer of OO, PO, and styrene oxide (SO) was synthesized following the same method. The ROP was catalyzed by triethyl borane (TEB)/(phosphazene base t-BuP2) with eicosanol as the initiator. The resulting co(ter)polymers have a low polydispersity index and good solubility in hydrocarbon-based oils and are metal-free. By blending polyoctene oxide (POO) and polyhexene oxide (PHO) homopolymers with a Group II base oil (AramcoPrima 230) (2.5 to 5.0 wt %), the viscosity index (VI) increased from 100 to 160, and the thermal stability enhanced up to 50 °C. By using diblock copolymers, POO-block-poly(propylene oxide) (POO-b-PPO) and PHO-block-PPO (PHO-b-PPO), instead of the homopolymers, the VI and the thermal stability are almost the same, but the oil exhibits superior lubrication performance, with friction and wear decreasing up to 46 and 86%, respectively. The addition of the PSO block to the POO-b-PPO chain (POO-b-PPO-b-PSO) further improves the thermal stability but worsens the rheological and tribological properties (i.e., VI, friction, and wear) of lubricating oils.

Precise Synthesis of Linear Polysiloxanes End-Functionalized with Alkynylsilyl Groups by Organocatalytic Ring-Opening Polymerization of Cyclotrisiloxanes

Precise Synthesis of Linear Polysiloxanes End-Functionalized with Alkynylsilyl Groups by Organocatalytic Ring-Opening Polymerization of Cyclotrisiloxanes

Precise Synthesis of Side-Chain-Functionalized Linear Polysiloxanes by Organocatalytic Ring-Opening Polymerization of Monofunctional Cyclotrisiloxanes

Precise Synthesis of Side-Chain-Functionalized Linear Polysiloxanes by Organocatalytic Ring-Opening Polymerization of Monofunctional Cyclotrisiloxanes

Effects of Hydrophobicity on Antimicrobial Activity, Selectivity, and Functional Mechanism of Guanidinium-Functionalized Polymers.

In this study, a series of guanidinium-functionalized polycarbonate random co-polymers is prepared from organocatalytic ring-opening polymerization to investigate the effect of the hydrophobic side chain (ethyl, propyl, isopropyl, benzyl, and hexyl) on their antimicrobial activity and selectivity. Although the polymers exhibit similar minimum inhibitory concentrations, the more hydrophobic polymers exhibit a faster rate of bacteria elimination. At higher percentage content (20 mol%), polymers with more hydrophobic side chains suffer from poor selectivity due to their high hemolytic activity. The highly hydrophobic co-polymer, containing the hydrophobic hexyl-functionalized cyclic carbonate, kills bacteria via a membrane-disruptive mechanism. Micelle formation leads to a lower extent of membrane disruption. This study unravels the effects of hydrophobic side chains on the activities of the polymers and their killing mechanism, providing insights into the design of new antimicrobial polymers.

Grafting polysulfonamide from cellulose paper through organocatalytic ring-opening polymerization of N-sulfonyl aziridines

A facile and effective “grafting from” method by ROP of N-sulfonyl aziridines toward cellulose-g-polysulfonamides has been developed for efficient oil/water separation. The cellulose paper was initially succinylated to transform the hydroxyl to carboxyl acid groups, which act as the initiating sites for the ring-opening copolymerization of fluorescent 2-methyl-1-dansylaziridine and 2-methyl-1-tosylaziridine (TsMAz) towards the grafted cellulose. Both steps are catalyzed by the same compound, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD). The grafted polysulfonamide ratio was up to 136 wt%, and the surface contact angle up to 147°. A one-pot tandem strategy was applied to produce the grafted cellulose paper with a grafting ratio ranging from 96 to 150 % and a contact angle over 127°. The modified cellulose paper material showed promising properties for efficient oil/water separations.

Organocatalyzed Ring-Opening Polymerization of Cyclic Lysine Derivative: Sustainable Access to Cationic Poly(ε-lysine) Mimics

Poly(e-lysine) has broad applications and is dominantly produced via fermentation. Our group successfully realized the chemosynthesis of poly(e-lysine) through ring-opening polymerization (ROP) of a 2,5-dimethylpyrrole-protected cyclic lysine monomer, but the complete removal of the protecting group suffers from a prolonged time and low yield. Herein, we have developed organocatalyzed ROP of a dimethyl-protected cyclic lysine that avoids the tedious deprotection procedures to prepare cationic poly(e-lysine) mimics with quaternary ammonium groups in high yields. Such poly(e-lysine) mimics not only exhibit potent antimicrobial activities but also demonstrate good biocompatibility and have no significant hemolytic activities. The antimicrobial activities of poly(e-lysine) mimics were ∼80.0% at a concentration of 100 μg/mL in comparison to 76.0% of the poly(e-lysine) control. In brief, our research provides a novel class of functional mimics of poly(e-lysine) and opens up new avenues for designing and furnishing poly(amino acid) mimetics for biological functions and applications.

Recent Advances in Organocatalytic Ring-opening Polymerization

As compared with widely used polyolefin materials, aliphatic polyesters have been primarily used in electronics, packaging, and biomedicine owing to its unique biocompatibility and degradability. At present, ring-opening polymerization (ROP) of lactone is the main method to synthesize polyesters. Two types of catalysts, including metal-based catalysts and organocatalysts, were most researched today. However, metal-based catalysts lead to polymer materials with metal residues, which limits its properties and applications. As a result, organocatalysts have received great attention. In this review, the progress of organocatalytic ring-opening polymerization in the past decades was systematically summarized. The potential challenges and development directions in this field are also discussed.

Methoxy-Functionalized Glycerol-Based Aliphatic Polycarbonate: Organocatalytic Synthesis, Blood Compatibility, and Hydrolytic Property.

Polymers that are biocompatible and degradable are desired for tissue engineering approaches in the treatment of vascular diseases, especially for those involving small-diameter blood vessels. Herein, we report the compatibility of a newly developed glycerol-based aliphatic polycarbonate possessing simple methoxy side groups, named poly(5-methoxy-1,3-dioxan-2-one) (PMDO), with blood cells and plasma proteins as well as its susceptibility to hydrolysis. As a consequence of the organocatalytic ring-opening polymerization (ROP) of a methoxy-functionalized cyclic carbonate derived from glycerol, PMDO with a sufficiently high molecular weight (Mn 14 kg/mol) and a narrow distribution (D̵M 1.12) was obtained for evaluation as a bulk biomaterial. This study demonstrates for the first time the organocatalytic ROP of a glycerol-based cyclic carbonate in a controlled manner. Compared with the clinically applied aliphatic polycarbonate poly(trimethylene carbonate) (PTMC), PMDO inhibits platelet adhesion by 33% and denaturation of fibrinogen by 23%. Although the wettability of PMDO based on water contact angle was almost comparable to those of PTMC and poly(ethylene terephthalate), the reason for the inhibited platelet adhesion and protein denaturation appeared to be related to the presence of specific hydrated water formed in the hydrated polymer. The improved hydration of PMDO also enhanced the susceptibility to hydrolysis, with PMDO demonstrating a slightly higher hydrolytic property than PTMC. This simple glycerol-based aliphatic polycarbonate has the following benefits: bio-based characteristics of glycerol and improved blood compatibility and hydrolytic biodegradability stemming from moderate hydration of the methoxy side groups.

Elucidating the anticancer activities of guanidinium-functionalized amphiphilic random copolymers by varying the structure and composition in the hydrophobic monomer.

Rationale: Use of traditional anticancer chemotherapeutics has been hindered by the multifactorial nature of multi-drug resistance (MDR) development and metastasis. Recently, cationic polycarbonates were reported as novel unconventional anticancer agents that mitigated MDR and inhibited metastasis. The aim of this study is to explore structure-anticancer activity relationship. Specifically, a series of cationic guanidinium-based random copolymers of varying hydrophobicity was synthesized with a narrow polydispersity (Ð = 1.12-1.27) via organocatalytic ring-opening polymerization (OROP) of functional cyclic carbonate monomers, and evaluated for anticancer activity, killing kinetics, degradability and functional mechanism.Methods: Linear, branched and aromatic hydrophobic side chain units, such as ethyl, benzyl, butyl, isobutyl and hexyl moieties were explored as comonomer units for modulating anticancer activity. As hydrophobicity/hydrophilicity balance of the polymers determines their anticancer efficacy, the feed ratio between the two monomers was varied to tune their hydrophobicity.Results: Notably, incorporating the hexyl moiety greatly enhanced anticancer efficiency and killing kinetics on cancer cells. Degradation studies showed that the polymers degraded completely within 4-6 days. Flow cytometry and lactate dehydrogenase (LDH) release analyses demonstrated that anticancer mechanism of the copolymers containing a hydrophobic co-monomer was concentration dependent, apoptosis at IC50, and both apoptosis and necrosis at 2 × IC50. In contrast, the homopolymer without a hydrophobic comonomer killed cancer cells predominantly via apoptotic mechanism.Conclusion: The hydrophobicity of the polymers played an important role in anticancer efficacy, killing kinetics and anticancer mechanism. This study provides valuable insights into designing novel anticancer agents utilizing polymers.

Organocatalytic ring-opening polymerization of thionolactones: anything O can do, S can do better

Organocatalysts facilitate the synthesis of polythionolactones; oxidative crosslinking yields a degradable polymer foam.

Visible light-regulated organocatalytic ring-opening polymerization of lactones by harnessing excited state acidity

A metal-free ring-opening polymerization of lactones has been developed using PyOH as a photocatalyst under visible light mediation.

Synthesis of Sustainable Polyesters via Organocatalytic Ring-Opening Polymerization of O-carboxyanhydrides: Advances and Perspectives.

Sustainable polyesters can be furnished via ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs). Various catalysts, especially metal-based catalysts, are devised to achieve controlled ROP of OCAs. In the following mini review, the recent progress on the organocatalytic ROP of OCAs, including the usage of thiourea-based bifunctional single-molecule organocatalysts for eliminating epimerization in OCAs polymerization is summarized. Moreover, the future development of the organocatalytic ROP of OCAs for the synthesis of sustainable polyesters will be discussed.

Synthesis of PCL–PEG–PCL Triblock Copolymer via Organocatalytic Ring-Opening Polymerization and Its Application as an Injectable Hydrogel—An Interdisciplinary Learning Trial

Biocompatible and biodegradable block copolymers composed of poly(ethylene glycol) (PEG) and aliphatic polyester are a class of promising biomaterials. Herein, a teaching experiment was designed to furnish undergraduates with a reliable method to synthesize an amphiphilic poly(e-caprolactone)-PEG-poly(e-caprolactone) (PCL–PEG–PCL) triblock copolymer via ring-opening polymerization of e-caprolactone using PEG as the macroinitiator and diphenyl phosphate as the green organocatalyst; the concentrated solution of synthetic polymer in water was then demonstrated as an injectable thermogel with a sol–gel transition upon heating. Ten students serving as volunteers successfully synthesized PCL–PEG–PCL copolymer, and then analyzed their specimens using various techniques including proton-nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry, and X-ray diffraction and learned the principles of instruments. Finally, students prepared an aqueous polymer solution, and observed its interesting spontaneous physical gelation upon heating via the tube-inverting approach and dynamic rheological analysis. The experimental features captured the students’ attention and made them more enthusiastic participants. This newly designed teaching experiment afforded senior undergraduates an excellent opportunity to consolidate basic concepts and principles in books with practical experimental sessions in the field of polymer chemistry, analytical chemistry, and materials science.

Organocatalytic Synthesis of Alkyne-Functional Aliphatic Polycarbonates via Ring-Opening Polymerization of an Eight-Membered-N-Cyclic Carbonate.

The synthesis of well-defined propargyl-functional aliphatic polycarbonates is achieved via the organocatalytic ring-opening polymerization of prop-2-yn-1-yl 2-oxo-1,3,6-dioxazocane-6-carboxylate (P-8NC) using a wide variety of commercially available or readily made, shelf-stable organocatalysts. The resulting homopolymers show low dispersities and end-group fidelity, with the versatility of the system being demonstrated by the synthesis of telechelic copolymers and block copolymers with molar mass up to 40kDa.

Organocatalyzed ring opening polymerization of lactide from the surface of cellulose nanofibrils

The surface initiated ring opening polymerization (SI-ROP) of cellulose nanofibers (CNF) with rac-Lactide under mild conditions using N,N-dimethyl aminopyridine (DMAP) was investigated. The influence of catalyst amount, monomer-to-initiator (cellulose surface –OH groups) ratio, temperature, and cellulose preconditioning (lyophilization vs solvent exchange) were studied to determine the best SI-ROP conditions, and to understand the effect of the parameters on grafting efficiency. The fibers modified after lyophilization had a PLA content comparable to those obtained with traditional metal catalysts (e.g. tin-(II)ethylhexanoate). Starting from a stable dispersion of CNF in dichloromethane obtained through solvent-exchange showed better results at low catalyst amounts. Furthermore, DMAP was readily removed from the products whereas metal catalysts can be hard to remove from the final material, potentially shortening the material lifespan and making it unfit for some applications. Therefore, the use of an easily removable and more efficient organocatalyst can be considered a good alternative to metal catalysts.

Organocatalytic Ring-Opening Polymerization Toward Poly(γ-amide-ε-caprolactone)s with Tunable Lower Critical Solution Temperatures

γ-Amide-e-caprolactones including 7-oxo-N-propyloxepane-4-carboxamide (NNCL), N-isopropyl-7-oxooxepane-4-carboxamide (NICL), N,N-diethyl-7-oxooxepane-4-carboxamide (DECL), and 5-(pyrrolidine-1-carb...

Preparation of Degradable Polymenthide and Its Elastomers from Biobased Menthide via Organocatalyzed Ring-opening Polymerization and UV Curing

Development of degradable polyester elastomers plays an important role in the applications of soft mateirals. Noncrystalline polymenthides (PMs) from menthol derived lactone monomers are excellent soft segments for preparing degradable polyester elastomers. By using cyclic trimeric phosphazene base (CTPB) as an organocatalyst, we successfully synthesized PMs with different molecular weights (8.2 kDa to 100.7 kDa) in high yields via ring-opening polymerization (ROP) of menthide. When a CTPB/urea binary catalytic system was adopted, the polymerizations proceeded in a more controlled manner. Using glycerol as initiator, star shaped PMs with well-defined structure were synthesized and subsequently end-capped by acrylate. UV irradiation of the terminal acrylate groups in the star-shaped PMs resulted in formation of chemically cross-linked polyester elastomers without heat or other stimuli. The obtained polyester elastomers exhibit matched modulus (3.8–5.5 MPa), tensile strength (0.56–0.68 MPa), and strain at break (280%–320%) with soft body tissues, displaying great potential in biomedical applications.