Ring-opening Copolymerization Research Articles

Schiff‐Base Aluminum Complexes as Bifunctional Catalysts for the Selective Ring‐Opening Co‐Polymerization of Cyclohexene Oxide and Succinic Anhydride

The ring‐opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is emerging as a powerful method for the synthesis of polyesters with innovative structures and properties. In this work, a series of dialkyl‐aluminum complexes stabilized by Schiff‐base ligands with different functional side arms (pyridine, amine, or phosphine) and different substituents on the phenoxy moieties have been synthetized and tested as catalysts in the ROCOP of cyclohexene oxide (CHO) and succinic anhydride (SA). The selectivity of the catalysts in the ROCOP was significatively depending on the nature of the pendant arm and/ or of the substituents of the ligand framework. The complexes designed to have a dynamic coordination sphere in which the side arms simulate the role of a neutral cocatalyst favored the desired selectivity, giving poly(CHO‐alt‐SA) with narrow dispersity and negligible ether linkage. NMR investigations and DFT calculations rationalized the observed behavior.

Choline Halide-Based Deep Eutectic Solvents as Biocompatible Catalysts for the Alternating Copolymerization of Epoxides and Cyclic Anhydrides.

Aliphatic polyesters have received considerable attention in recent years due to their biodegradability and biocompatible, mechanical, and thermal properties that can make them a suitable alternative to today's commercialized polymers. The ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a route to synthesize a diverse array of polyesters that could be useful in many applications. However, the catalysts used rarely consider biocompatible catalysts in the case that any are left in the polymer. To the best of our knowledge, we report the first example of using deep eutectic solvents (DESs) as biocompatible catalysts for this target ROCOP with polymerization activity for at least six diverse monomer pairs. Choline halide salts are active for this polymerization, with dried salts showing polymerization slower than that of those conducted in air. Hydrogen bonding with water is hypothesized to enhance the rate-determining step of epoxide ring opening. While the presence of water improves the rate of polymerization, it also acts as a chain transfer agent, leading to smaller molar mass polymers than intended. Combining the choline halide salts with urea or ethylene glycol hydrogen bond donors in air led to DES catalysts that reacted similarly to the salts exposed to air. However, when generating these DESs in air-free conditions, they showed similar rates of polymerization without a drop in polymer molar mass. The hydrogen bonding provided by urea and ethylene glycol seems to promote the rate increase without serving as a chain transfer agent. Results reported herein display the promising potential of biocompatible catalyst systems for this ROCOP process as well as introducing the use of hydrogen bonding to enhance polymerization rates.

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.

Insights into the Distinct Behaviors between Bifunctional and Binary Organoborane Catalysts through Terpolymerization of Epoxide, CO2, and Anhydride.

Alkyl borane compounds-mediated polymerizations have expanded to Lewis pair polymerization, free radical polymerization, ionic ring-opening polymerization, and polyhomologation. The bifunctional organoborane catalysts that contain the Lewis acid and ammonium or phosphonium salt in one molecule have demonstrated superior catalytic performance for ring-opening polymerization of epoxides and ring-opening copolymerization of epoxides and CO2 than their two-component analogues, i.e., the blend of organoborane and ammonium or phosphonium salt. To explore the origin of the differences of the one-component and two-component organoborane catalysts, here we conducted a systematic investigation on the catalytic performances of these two kinds of organoborane catalysts via terpolymerization of epoxide, carbon dioxide and anhydride. The resultant terpolymers produced independently by bifunctional and binary organoborane catalyst exhibited distinct microstructures, where a series of gradient polyester-polycarbonate terpolymers with varying polyester content were afforded using the bifunctional catalyst, while tapering diblock terpolymers were obtained using the binary system. The bifunctional catalyst enhances the competitiveness of CO2 insertion than anhydride, which leads to the premature incorporation of CO2 into the polymer chains and ultimately results in the formation of gradient terpolymers. DFT calculations revealed the role of electrostatic interaction and charge distribution caused by intramolecular synergistic effect for bifunctional organoborane catalyst.

A Sacrificial Linker in Biodegradable Polyesters for Accelerated Photoinduced Degradation, Monitored by Continuous Atline SEC Analysis.

Polymeric materials that undergo photoinduced degradation have wide application in fields such as controlled release. Most methods for photoinduced degradation rely on the UV or near-UV region of the electromagnetic spectrum; however, use of the deeply penetrating and benign wavelengths of visible light offers a multitude of advantages. Here we report a lactone monomer for ring-opening copolymerizations to introduce a sacrificial linker into a polymer backbone which can be cleaved by reactive oxygen species which are produced by a photocatalyst under visible light irradiation. We find that copolymers of this material readily degrade under visible light. We followed polymer degradation using a continuous flow size exclusion chromatography system, the components of which are described herein.

Organobase-Catalyzed Ring-Opening Copolymerization of Cyclic Anhydrides and Oxetanes: Establishment and Application in Block Copolymer Synthesis

Organobase-Catalyzed Ring-Opening Copolymerization of Cyclic Anhydrides and Oxetanes: Establishment and Application in Block Copolymer Synthesis

Quantifying CO2 Insertion Equilibria for Low-Pressure Propene Oxide and Carbon Dioxide Ring Opening Copolymerization Catalysts.

While outstanding catalysts are known for the ring-opening copolymerization (ROCOP) of CO2 and propene oxide (PO), few are reported at low CO2 pressure. Here, a new series of Co(III)M(I) heterodinuclear catalysts are compared. The Co(III)K(I) complex shows the best activity (TOF = 1728 h-1) and selectivity (>90% polymer, >99% CO2) and is highly effective at low pressures (<10 bar). CO2 insertion is a prerate determining chemical equilibrium step. At low pressures, the concentration of the active catalyst depends on CO2 pressure; above 12 bar, its concentration is saturated, and rates are independent of pressure, allowing the equilibrium constant to be quantified for the first time (Keq = 1.27 M-1). A unified rate law, applicable under all operating conditions, is presented. As proof of potential, published data for leading literature catalysts are reinterpreted and the CO2 equilibrium constants estimated, showing that this unified rate law applies to other systems.

Visible light-induced photo-radical ring-opening copolymerization of thionolactone and acrylates

Radical ring-opening (co)polymerization (RROP) provides an accessible method for synthesizing main chain degradable vinyl polymers. Although the applications of reversible deactivation radical polymerization (RDRP) into RROP have been reported, the use of photo-mediated RDRP methods has received less attention than the thermal process. Here, photo-RROP of the thionolactone dibenzo [c,e]-oxepine-5(7H)-thione (DOT) and methyl acrylate (MA) was studied using photo-iniferter (PI) reversible addition-fragmentation (chain) transfer (RAFT) polymerization at ambient temperature without external radical initiators or photocatalysts. Despite the occurrence of some side reactions including desulfurization-oxygenation and O–S isomerization of DOT promoted by photoexcited thiocarbonyl groups, polymers with thioester linkages in the backbone were prepared, which degraded in the presence of amines and bleach.

Ring Opening Copolymerization of Epoxides with CO2 and Organic Anhydrides Promoted by Dinuclear [OSSO]‐type Metal Complexes

AbstractThe ternary copolymerization of a series of cyclic anhydrides with epoxides and carbon dioxide using dinuclear [OSSO]‐type chromium (III),1, and ‐iron(III), 2, complexes (0.1 mol %) in combination with (bis(triphenylphosphine)iminium chloride) (PPNCl, 0.5–1.0 mol with respect to catalyst) as co‐catalyst is reported in this study. The results have yielded copolymers with polyester and polycarbonate segments with high molecular weights and narrow dispersity. The catalytic systems 1–2/PPNCl were tested in the copolymerization of different epoxides, such as propylene oxide (PO), cyclohexene oxide (CHO), and vinylcyclohexene oxide (VCHO), with a variety of cyclic anhydrides, such as phthalic (PA), diglycolic (DGA) and succinic (SA), with CO2 pressure of 20 bar, temperature range of 45–80 °C in 24 h. Anhydride reaction, affording the polyester segments, exceeded the conversion of 99 % in all the explored cases. On the other hand, in the case of epoxide copolymerization with CO2, for the propylene oxide (PO) reaction, the selectivity towards polypropylene carbonate (PPC) without polyether linkage consistently was &gt;99 %. For the terpolymerization of PO, CO2 and diglycolic anhydride (DGA), a notable epoxide conversion of 86 %, selectively to polycarbonate, with TOF value as high as 36 h−1, was achieved.

PH/GSH-responsive diselenide-containing micelle via backbone ketoxime cross-links for efficient drug delivery and controlled release

Stimulus-responsive polymers are promising drug delivery systems for cancer therapy. However, low drug loading and drug leakage of polymeric carriers remain challenges. Here, a crosslinked diselenide-containing micelle was developed with pH/GSH dual responsiveness. Polyesters with multiple diselenide bonds and pendant ketone groups were synthesized by the ring-opening copolymerization of three cyclic monomers (diselenide-containing macrocyclic carbonate, 2-oxepane-1,5-dione, and 1,3-dioxan-2-one). The crosslinked polyester was obtained by the oxime click reaction of pendant ketone groups with hydroxylamine and then self-assembled into crosslinked micelle. This crosslinked micelle remained stable for 14 days, and responded to disassembly under the condition of pH = 5.0 and 10 mM glutathione (GSH). When the crosslinked micelle was loaded with the chemotherapeutic drug DOX, which possessed an active ketone group, the encapsulation efficiency of the crosslinked micelle increased to 91.36 %. The cumulative DOX release reached approximately 45 % under pH = 5.0 and 10 mM GSH. Importantly, the crosslinked diselenide-containing micelle could be taken up in MCF-7 breast cancer cells, responding to the tumor microenvironment and releasing encapsulated DOX. This crosslinked diselenide-containing micelle with pH/GSH dual responsiveness was proven to be a stable and efficient carrier with a promising application.

High Molar Mass Polycarbonates as Closed-Loop Recyclable Thermoplastics.

Using carbon dioxide (CO2) to make recyclable thermoplastics could reduce greenhouse gas emissions associated with polymer manufacturing. CO2/cyclic epoxide ring-opening copolymerization (ROCOP) allows for >30 wt % of the polycarbonate to derive from CO2; so far, the field has largely focused on oligocarbonates. In contrast, efficient catalysts for high molar mass polycarbonates are underinvestigated, and the resulting thermoplastic structure-property relationships, processing, and recycling need to be elucidated. This work describes a new organometallic Mg(II)Co(II) catalyst that combines high productivity, low loading tolerance, and the highest polymerization control to yield polycarbonates with number average molecular weight (Mn) values from 4 to 130 kg mol-1, with narrow, monomodal distributions. It is used in the ROCOP of CO2 with bicyclic epoxides to produce a series of samples, each with Mn > 100 kg mol-1, of poly(cyclohexene carbonate) (PCHC), poly(vinyl-cyclohexene carbonate) (PvCHC), poly(ethyl-cyclohexene carbonate) (PeCHC, by hydrogenation of PvCHC), and poly(cyclopentene carbonate) (PCPC). All these materials are amorphous thermoplastics, with high glass transition temperatures (85 < Tg < 126 °C, by differential scanning calorimetry) and high thermal stability (Td > 260 °C). The cyclic ring substituents mediate the materials' chain entanglements, viscosity, and glass transition temperatures. Specifically, PCPC was found to have 10× lower entanglement molecular weight (Me)n and 100× lower zero-shear viscosity compared to those of PCHC, showing potential as a future thermoplastic. All these high molecular weight polymers are fully recyclable, either by reprocessing or by using the Mg(II)Co(II) catalyst for highly selective depolymerizations to epoxides and CO2. PCPC shows the fastest depolymerization rates, achieving an activity of 2500 h-1 and >99% selectivity for cyclopentene oxide and CO2.

Phosphorus-containing stereocontrolled polyhydroxyalkanoates by yttrium-mediated ring-opening copolymerization of β-lactones

Poly(3-hydroxybutyrate) (PHB) polymers functionalized with pendent diphenyl-phosphinate moieties were prepared by the simultaneous ring-opening copolymerization (ROCOP) of racemic or enantiopure β-butyrolactone (rac- or (S)-BPLMe, respectively) with racemic-(4-oxooxetan-2-yl)methyl diphenylphosphinate (rac-BPLOP). The reactions were mediated by yttrium catalysts which tunable ancillary structure enabled preparing copolymers containing syndio-enriched (Pr up to 0.84; Pr is the probability of racemic linkage), atactic (Pr ∼ 0.50) and highly isotactic (Pr < 0.06) poly(BPLMe) (P(BPLMe), aka PHB for polyhydroxybutyrate) segments, starting from rac-BPLMe or (S)-BPLMe, respectively, as assessed by detailed NMR analyses of the copolymer samples. The amount of BPLOP incorporated within the P[(BPLMe)x-co-(BPLOP)y] samples were in line with the initial comonomer loadings (1.8–8.1 mol% vs. 2–10 mol%). The ROCOP was rather well-controlled affording linear α-isopropoxy, ω-crotonyl telechelic and cyclic random copolymers with Mn,NMR up to 15,000 g.mol−1 and ÐM = 1.34–1.95. Detailed MALDI and high-resolution ESI mass spectrometric analyses evidenced the formation of three major series of macromolecules, namely the cyclic one and two linear ones end-capped with an α-isoproxy and either an ω-hydroxy or a ω-crotonate groups; for each of these series, the populations containing y = 0, 1 or 2 BPLOP repeating units were unambiguously distinguished. The thermal characteristics of the P[(BPLMe)x-co-(BPLOP)y] copolymers were investigated by DSC and TGA, revealing in comparison to those of the parent PHB homopolymers, tunable features as a function of their molar mass, tacticity and BPLOP content.

Stereocomplexed Functional and Statistical Poly(lactide-carbonate)s via a Simple Organocatalytic System.

The stereocomplexation of polylactide (PLA) has been widely relied upon to develop degradable, sustainable materials with increased strength and improved material properties in comparison to stereopure PLA. However, forming functionalized copolymers of PLA while retaining high crystallinity remains elusive. Herein, the controlled ring-opening copolymerization (ROCOP) of lactide (LA) and functionalized cyclic carbonate monomers is undertaken. The produced polymers are shown to remain crystalline up to 25 mol % carbonate content and are efficiently stereocomplexed with homopolymer PLA and copolymers of opposite chirality. Polymers with alkene and alkyne pendent handles are shown to undergo efficient derivatization with thiol-ene click chemistry, which would allow both the covalent conjugation of therapeutic moieties and tuning of material properties.

Alternating ring‐opening copolymerization of cyclic anhydrides and epoxides by zeolitic imidazolate framework‐67: A promising approach

The ring opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is one of the most important ways to synthesize polyesters both in industrial and academic fields. Herein, the zeolitic imidazolate framework‐67 (ZIF‐67) was used as a heterogeneous catalyst for the ROCOP of epoxides and cyclic anhydrides without co‐catalyst and initiator. Notably, the obtained polyesters with alternate structures were proved by the 1H NMR spectrum and FTIR spectrum, which indicate the ROCOP is alternatively copolymerized. Kinetic study of the ROCOP of cyclohexene oxide (CHO) and phthalic anhydride (PA) shows that the polymerization reaction is first‐order kinetics. The apparent activation energy (Ea) of the ROCOP of CHO and PA catalyzed by ZIF‐67 was found to be about 104.4 KJ/mol. A possible mechanism of ROCOP of CHO and PA is that the metal Co coordinates with the oxygen atom on the monomer to weaken the C‐O bond thereby opening the ring structure and initiating the copolymerization reaction. In this study, a new system for the copolymerization of epoxide and anhydride catalyzed by heterogeneous catalysts was discovered, which has important guiding significance.

Functional and Degradable Polyester-co-polyethers from CO2, Butadiene, and Epoxides.

Carbon dioxide (CO2), as a renewable and nontoxic C1 feedstock, has been recognized as an ideal comonomer to prepare sustainable materials. In this regard, substantial focus has been dedicated to the ring-opening copolymerization of CO2 and epoxides, which results in the creation of aliphatic polycarbonates in most cases. Here, we report an unprecedented strategy to synthesize functional and degradable polyester-co-polyethers from CO2, butadiene, and epoxides via a CO2/butadiene-derived δ-valerolactone intermediate (EVP). Utilizing a chromium salen complex as the catalyst, the copolymerization of EVP and epoxides was successfully achieved to produce CO2/butadiene/epoxide terpolymers. The obtained polyester-co-polyethers with varied 39-93 mol % EVP content (equal to 18-28 wt % CO2 incorporation) show high thermal stability, tunable glass-transition temperatures, on-demand functionality, and good chemical degradability. This method extends the potential to access functional CO2-based polymers.

Metalloporphyrin catalyzed self-switchable terpolymerization of propene oxide, phthalic anhydride and lactide for one-pot prepare block copolyesters

The copolymerization of polylactic acid with other monomers or polymers can enhance its performance and expand its range of applications. In this work, a range of metalloporphyrin catalysts featuring diverse substituents and metal coordination centers were synthesized and employed in conjunction with co-catalyst bis(triphenylphosphoranylidene) ammonium chloride (PPNCl) for the terpolymerization of phthalic anhydride (PA), propylene oxide (PO), and lactide (LA) ester without the use of initiators. The catalytic activity of the porphyrin ligand is significantly influenced by its substituents and different metal centers. Under optimal conditions, catalyst TOMePP-CoCl exhibits the most outstanding reactivity among all catalysts. In particular, this terpolymerization is a one-pot self-switching polymerization catalyzed by the metalloporphyrin/PPNCl system. PA selectively undergoes ring-opening copolymerization with PO first, while LA remains inert until PA totally consumed. Through continuous feeding experiments, a multiblock copolymer with fine structure controllability was successfully synthesized, which has been verified by DOSY NMR analysis.

Ring‐opening polymerization of l‐lactide in the presence of α‐hydroxy‐γ‐butyrolactone

AbstractAmong the polymer families, aliphatic polyesters stand out from this category thanks to their degradable and biocompatible properties. In particular, the γ‐lactones differ from other lactones by yielding polyesters that can be depolymerized back to the monomer and offer the advantage of counting various biobased monomers. As an example, α‐hydroxy‐γ‐butyrolactone (HBL) is a hydroxy‐functionalized monomer that can be obtained by a biological synthetic route from glucose. In this article, the ring‐opening copolymerization (ROCP) of HBL and l‐lactide (LLA) using t‐BuP4 as catalyst is investigated. The copolymerizations were conducted within a temperature range of 5–100°C, affording monomer conversions exceeding 80%. The characterization of the copolyesters revealed a branched structure consisting of different HBL patterns, including cyclic, linear, and branched motives. Performing a kinetic study of the copolymerization at room temperature provided a deeper understanding of the mechanism. By modulating the reaction parameters, copolymers of low molar masses with an HBL content of up to 33% were synthesized. High molar mass LLA/HBL‐based copolyesters, with up to 290,000 g/mol, were synthesized by a straightforward chain coupling reaction with a diisocyanate.

Self-switchable terpolymerization of cyclic anhydrides, epoxides and lactide catalyzed by C2v-symmetric cobaltoporphyrins

The urgency for biodegradable plastics free from crude oil-based chemicals is currently paramount. These materials should be easily recyclable and capable of undergoing degradation at the end of their useful life. Herein, a series of C2v-symmetric cobaltoporphyrins featuring different substituents were synthesized, and evaluated for their catalytic performance in the self-switchable terpolymerization of epoxides, cyclic anhydrides and lactide in coordination with a co-catalyst bis(triphenylphosphoranylidene) ammonium chloride (PPNCl), under initiator-free conditions. These cobaltoporphyrin homogeneous catalysts exhibit promising chemical selectivity in the multicomponent copolymerization, resulting in kinetic differentiation between the ring-opening copolymerization of epoxides with cyclic anhydrides and the ring-opening polymerization of lactide. Lactide only participates in polymerization after complete conversion of cyclic anhydrides, leading to sequence-regulated block copolyesters. The substituents on the porphyrin ligand have significant influence on its catalytic activity. Among all catalysts tested, DOMePP-CoCl exhibited the most outstanding reactivity under optimal conditions. Furthermore, by utilizing different cyclic anhydrides and epoxide monomers, the DOMePP-CoCl/PPNCl catalytic system still exhibited excellent reaction activity, allowing for the high-yielding and high-selectivity transformation into corresponding multiblock copolyesters.

Highly Active Aggregate Catalysts for the Synthesis of High-Molecular-Weight Polyesters via Copolymerization of Epoxides and Cyclic Anhydrides

Although the ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a promising route to polyesters, the efficient production of high molecular weight (Mn) polyesters remains a great challenge. Herein,...

A direct comparison between ring-opening copolymerization and polycondensation to produce polyesters using poly(ethylene succinate) as an example

A direct comparison between ROCOP and polycondensation to produce polyesters was made using PES, by evaluating the monomer preprocessing, polymerization technique, post-processing, and the properties of the produced polyesters.