Selective Ring-opening Polymerization Research Articles

Achieving a Rapid and Selective Ring Opening Polymerization of Dimethylcyclosiloxanes via Potassium Silanolate Catalysis: Understanding the Role of Potassium Chelation on Polymerization Rate and Backbiting

Achieving a Rapid and Selective Ring Opening Polymerization of Dimethylcyclosiloxanes via Potassium Silanolate Catalysis: Understanding the Role of Potassium Chelation on Polymerization Rate and Backbiting

Lewis-pair derived activated lactone initiator (ALI) complex for rapid, controlled, bench stable and selective ring-opening polymerization of (macro)lactones

Selective, active, stable, and general catalysts for the controlled ring-opening polymerization of (macro)lactones are central in our pursuit of a more benign material economy. Within, we explore the formation of an activated lactone initiator (ALI) based on ZnEt2-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an air-stable and selective initiator/catalyst, yielding linear polymers with one ß-keto ester and one alcohol end-group. Ring-opening polymerization (ROP) with high activity and control was found for unsubstituted (macro)lactones (ω-pentadecalactone (PDL), hexadecanolide (HDL), δ-valerolactone (δVL), and ε-caprolactone (εCL)) and cyclic carbonate trimethylene carbonate (TMC). A particular focus was placed on studying the ALI for the polymerization of strainless PDL and strained εCL. In contrast, ALI-ROP could not polymerize lactones containing substituents on the terminal carbon, indicative of the coordination insertion features of the polymerization. This work explores selective catalysts with high control, fast kinetics, and superb air stability towards the next generation of greener materials.

Selective ring-opening polymerization of glycidyl esters: a versatile synthetic platform for glycerol-based (co)polyethers

Well-defined (isotactic) linear polyglycerols and glycerol-based copolyethers are obtained by controlled and chemoselective ring-opening (co)polymerizations of glycidyl butyrates.

S-Carboxyanhydrides: Ultrafast and Selective Ring-Opening Polymerizations Towards Well-defined Functionalized Polythioesters.

Aliphatic polythioesters are popular polymers because of their appealing performance such as metal coordination ability, high refractive indices, and biodegradability. One of the most powerful approaches for generating these polymers is the ring-opening polymerization (ROP) of cyclic monomers. However, the synthesis of precisely controlled polythioesters via ROP of thiolactones still faces formidable challenges, including the minimal functional diversity of available thiolactone monomers, as well as inevitable transthioesterification side reactions. Here we introduce a hyperactive class of S-carboxyanhydride (SCA) monomers derived from amino acids that are significantly more reactive than thiolactones for ultrafast and selective ROP. Inclusion of the initiator PPNOBz ([PPN]=bis(triphenylphosphine)-iminium) with chain transfer agent benzoic acid, the polymerizations that can be operated in open vessels reach complete conversion within minutes (1-2 min) at room temperature, yielding polythioesters with predictable molecular weight, low dispersities, retained stereoregularity and chemical recyclability. Most fascinating are the functionalized SCAs that allow the incorporating of functional groups along the polythioester chain and thus finely tune their physicochemical performance. Computational studies were carried out to explore the origins of the distinctive rapidity and exquisite selectivity of the polymerizations, offering mechanistic insight and explaining why high polymerizability of SCA monomer is able to facilitate exquisitely selective ring-opening for enchainment over competing transthioesterification and backbiting reactions.

S‐Carboxyanhydrides: Ultrafast and Selective Ring‐Opening Polymerizations Towards Well‐defined Functionalized Polythioesters

AbstractAliphatic polythioesters are popular polymers because of their appealing performance such as metal coordination ability, high refractive indices, and biodegradability. One of the most powerful approaches for generating these polymers is the ring‐opening polymerization (ROP) of cyclic monomers. However, the synthesis of precisely controlled polythioesters via ROP of thiolactones still faces formidable challenges, including the minimal functional diversity of available thiolactone monomers, as well as inevitable transthioesterification side reactions. Here we introduce a hyperactive class of S‐carboxyanhydride (SCA) monomers derived from amino acids that are significantly more reactive than thiolactones for ultrafast and selective ROP. Inclusion of the initiator PPNOBz ([PPN]=bis(triphenylphosphine)‐iminium) with chain transfer agent benzoic acid, the polymerizations that can be operated in open vessels reach complete conversion within minutes (1–2 min) at room temperature, yielding polythioesters with predictable molecular weight, low dispersities, retained stereoregularity and chemical recyclability. Most fascinating are the functionalized SCAs that allow the incorporating of functional groups along the polythioester chain and thus finely tune their physicochemical performance. Computational studies were carried out to explore the origins of the distinctive rapidity and exquisite selectivity of the polymerizations, offering mechanistic insight and explaining why high polymerizability of SCA monomer is able to facilitate exquisitely selective ring‐opening for enchainment over competing transthioesterification and backbiting reactions.

Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands.

At 0 °C in THF in the presence of Grubbs first generation catalyst, cyclobutene derivatives undergo ROMP readily, whereas norbornene derivatives remain intact. When the substrate contains both cyclobutene and norbornene moieties, the conditions using THF as the solvent at 0 °C offer a useful protocol for the selective ROMP of cyclobutene to give norbornene-appended polycyclobutene. Unsymmetrical ladderphane having polycyclobutene and polynorbornene as two strands is obtained by further ROMP of the norbornene appended polycyclobutene in the presence of Grubbs first generation catalyst in DCM at ambient temperature. Methanolysis of this unsymmetrical ladderphane gives polycyclobutene methyl ester and insoluble polynorbornene-amide-alcohol. The latter is converted into the corresponding soluble acetate. Both polymers are well characterized by spectroscopic means. No norbornene moiety is found to be incorporated into polycyclobutene strand at all. The double bonds in the polycyclobutene strand are mainly in cis configuration (ca 70%), whereas the E/Z ratio for polynorbornene strand is 8:1.

Synergetic Organocatalysis for Eliminating Epimerization in Ring-Opening Polymerizations Enables Synthesis of Stereoregular Isotactic Polyester.

Ring-opening polymerization of O-carboxyanhydrides (OCAs) can furnish polyesters with a diversity of functional groups that are traditionally hard to harvest by polymerization of lactones. Typical ring-opening catalysts are subject to unavoidable racemization of most OCA monomers, which hampers the synthesis of highly isotactic crystalline polymers. Here, we describe an effective bifunctional single-molecule organocatalysis for selective ring-opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields highly isotactic poly(mandelic acid) (PMA) with controlled molecular weights (up to 19.8 kg mol-1). Mixing of the two enantiomers of PMA generates the first example of a crystalline stereocomplex in this area, which displayed distinct Tm values around 150 °C. Remarkably, the bifunctional catalysts are moisture-stable, recyclable, and easy to use, allowing sustainable and scalable synthesis of a stereoregular functional polyester.

Selective Ring-Opening Polymerization of Non-Strained γ-Butyrolactone Catalyzed by A Cyclic Trimeric Phosphazene Base.

A new superbase, the cyclic trimeric phosphazene base (CTPB), was prepared with high yield and purity. In the presence of alcohol, the CTPB serves as a highly efficient organocatalyst for ring-opening polymerization of the "non-polymerizable" γ-butyrolactone to offer well-defined poly(γ-butyrolactone) with high conversions (up to 98 %) at -60 °C. The produced polymers have high molecular weights (up to 22.9 kg mol-1 ) and low polydispersity distributions (1.27-1.50). NMR analysis of initiation process and the structural analysis of resulting polymers by MALDI-TOF suggest a mechanism involving an activating initiator which leads only to linear polymers with BnO/H chain ends.

Chavicol benzoxazine: Ultrahigh Tg biobased thermoset with tunable extended network

A novel biobased benzoxazine monomer containing additional allyl functionality was synthesized using a solventless approach from the reaction of a natural occuring phenol: chavicol, para-phenylene diamine and formaldehyde. The chemical structure of this functionalized benzoxazine monomer was confirmed by 1H NMR and FTIR. Its polymerization was investigated and monitored by DSC showing two well defined exotherms allowing the selective ring-opening polymerization of benzoxazine functions and the preservation of the allyl functionality. The network crosslink density could be further increased via the controlled polymerization of allyl functionalities with a post-cure in order to adjust the thermo-mechanical properties. When both networks were polymerized, the thermoset presented an excellent thermo-mechanical stability with a Tα higher than 350°C as measured by DMTA. This exceptional behavior for a potentially biobased benzoxazine resin will allow the preparation of sustainable high performance biocomposite materials.

Bio-Based Polyketones by Selective Ring-Opening Radical Polymerization of α-Pinene-Derived Pinocarvone.

The most abundant naturally occurring terpene, α-pinene, which cannot be directly polymerized into high polymers by any polymerization method, was quantitatively converted under visible-light irradiation into pinocarvone, which possesses a reactive exo methylene group. The bicyclic vinyl ketone was quantitatively polymerized in fluoroalcohols by selective (99%) ring-opening radical polymerization of the four-membered ring, which results in unique polymers containing chiral six-membered rings with conjugated ketone units in the main chain. These polymers display good thermal properties, optical activities, and contain reactive conjugated ketone units. Reversible addition fragmentation chain transfer (RAFT) polymerization was successfully accomplished by using appropriate trithiocarbonate RAFT agents, enabling the synthesis of thermoplastic elastomers based on controlled macromolecular architectures.

Dual Catalysis for Selective Ring-Opening Polymerization of Lactones: Evolution toward Simplicity.

Much work has been directed to the design of complex single-site catalysts for ring-opening polymerization (ROP) to enhance both activity and selectivity. More simply, however, cooperative effects between Lewis acids and organocatalytic nucleophiles/Lewis bases provide a powerful alternative. In this study we demonstrate that the combination of N-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables the ROP of the macrolactone pentadecalactone in a rapid and efficient manner. Remarkably, regardless of the nature of the nucleophile, the order of activity was observed to be MgX2 ≫ YCl3 ≫ AlCl3 and MgI2 > MgBr2 > MgCl2 in every case. The minimal influence of the organobase on polymerization activity allows for the use of simple and inexpensive precursors. Furthermore, extension of the study to other cyclic (di)ester monomers reveals the choice of Lewis acid to lead to monomer selective ROP activity and hence control over copolymer composition by choice of Lewis acid. This approach could lead to the realization of complex polymer structures with tunable physical properties from simple catalyst combinations.

Readily Accessible and Easily Modifiable Ru-Based Catalysts for Efficient and Z-Selective Ring-Opening Metathesis Polymerization and Ring-Opening/Cross-Metathesis

Rationally designed Ru-based catalysts for efficient Z-selective olefin metathesis are featured. The new complexes contain a dithiolate ligand and can be accessed in a single step from commercially available precursors in 68-82% yield. High efficiency and exceptional Z selectivity (93:7 to >98:2 Z:E) were achieved in ring-opening metathesis polymerization (ROMP) and ring-opening/cross-metathesis (ROCM) processes; the transformations typically proceed at 22 °C and are operationally simple to perform. Complete conversion was observed with catalyst loadings as low as 0.002 mol %, and turnover numbers of up to 43,000 were achieved without rigorous substrate purification or deoxygenation protocols. X-ray data and density functional theory computations provide support for key design features and shed light on mechanistic attributes.

Selective Ring-Opening Polymerization of Glycidyl Methacrylate: Toward the Synthesis of Cross-Linked (Co)polyethers with Thermoresponsive Properties

Selective polymerization of glycidyl methacrylate (GMA), which has two polymerizable functional groups such as epoxide and methacrylate, was achieved by the monomer-activated anionic approach using tetraoctylammonium bromide/triisobutylaluminum initiating system in toluene at 20 °C. Quantitative and controlled synthesis of poly(glycidyl methacrylate ether), up to about 20 000 g/mol, with pendant methacrylate functions, was obtained by ring-opening of the epoxide. The copolymerization of glycidyl methacrylate with glycidyl methyl ether (GME) in similar conditions, the resulting copolyether structures, and their properties were investigated as a function of feed composition. Reactive poly(glycidyl methyl ether-co-glycidyl methacrylate ether)s P(GME-co-GMA) with lower critical solubility temperature depending on the ratio [GME]/[GMA] were prepared and analyzed by NMR spectroscopy and differential scanning calorimetry. Postpolymerization cross-linking reactions of PGMA and random P(GME-co-GMA) copolymers were...

Synthesis and Characterization of Cardo Bisbenzoxazines and their Thermal Polymerization

Bisbenzoxazines of bisphenol-C (BCO) and phenolphthalein (PHO) were synthesized by condensing 0.05 mol bisphenol-C/phenolphthalein, 0.2 mol formaldehyde, and 0.1 mol aniline. Both BCO and PHO were thermally polymerized via ring-opening polymerization. The resultant cross-linked polymers (PBCO and PPHO) were characterized by solubility, Infrared (IR), Nuclear Magnetic Resonance (NMR), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). The bisoxazines and their polymers followed two-step degradation. Both BCO and PHO undergo selective ring-opening polymerization over the temperature range 100–150°C and are thermally stable up to about 250°C. The % residue at 550°C is substantially higher for PHO samples (56–67%) than BCO samples (20–25%), indicating the highly thermally stable nature of PHO. A ring transformation reaction is also supported by DSC. New thermosetting materials may be useful for specific applications to be exploited.

Synthesis of 3-Acetamido-3-deoxy-(1→5)-α-D-ribofuranan by Ring-Opening Polymerization of 1,4-Anhydro-3-azido-α-D-ribopyranose Derivative

A stereoregular 3-acetamido-3-deoxy-(1→5)-α-D-ribofuranan (3AAdRF) was synthesized by the synthetic route starting from selective ring-opening polymerization of 1,4-anhydro-3-azido-2-O-t-butyldimethylsilyl-3-deoxy-α-D-ribopyranose (A3ASR). A3ASR was polymerized by BF3·OEt2 catalyst at low temperature to give 3-azido-2-O-t-butyl-dimethylsilyl-(1→5)-α-D-ribofuranan (3AzSRF) with M̄n of 1.4×104—1.9×104 and [α]D of +249—+266°. 3AzSRF was reduced with NaBH4 in a tetrahydrofuran (THF)–ethanol mixture to afford 3-amino-2-O-t-butyldimethylsilyl-3-deoxy-(1→5)-α-D-ribofuranan (3AmSRF). Acetylation of the amino group in 3AmSRF produced 3-acetamido-ribofuranan derivative (3AAdSRF), and then desilylation of the 3AAdSRF gave 3AAdRF with M̄n ranging from 9.4×103 to 10.5×103 and [α]d of +195°. The structure analysis was performed by 13C and 1H NMR spectroscopy, IR spectroscopy, and optical rotation measurements.

Ring-Opening Polymerization of 1, 4-Anhydro-3-azido-3-deoxy-2-<i>O</i>-(<i>p</i>-substituted benzyl)-α-D-ribopyranoses

A new series of 1, 4-anhydro-3-azido-ribopyranose derivatives was synthesized as functional monomers in order to study effects of the monomer structure on selective ring-opening polymerization behaviors and structures of the resulting polysaccharides. The general formula of the four monomers were written as 1, 4-anhydro-3-azido-3-deoxy-2.O-(p-substituted benzyl)-α-D-ribopyranose (A3A2SBR), in which the substituted group represented methyl (CH3), hydrogen (H), chloro (CI), and bromo (Br) group. The four monomers were synthesized by reaction of 1, 4-anhydro-3-azido-3-deoxy-2-O-acetyl-α-D-ribopyranose with p-substituted benzyl chlorides or bromides. Selective ring-opening polymerization of the monomers was performed by BF3•OEt2 catalyst at -20°_??_40°C to give 3-azido-3-deoxy-2-O-(p-substituted benzyl)-(1→5)-α-D-ribofuranans with _??_n of 1.7×104_??_4.6×104and[α]D20of+180.1_??_+217.2°. Ring-opening polymerization by SbCl5 catalyst at-40°C afforded a polymer composed of a mixture of 1, 5-α-and 1, 5-β-ribofuranosidic units. In the selective ring-opening polymerization by BF3•OEt2 catalyst, _??_n increased and molecular weight distributions _??_n/_??_w became narrower with changing Hammett sigma constant of the p-substituted groups from negative to positive values in following order: methyl (-1.4), hydrogen (0), chloro (+2.4) and bromo (+2.6) groups. It was revealed that the p-substituted groups with different Hammett sigma constants had a regular effect in the ring-opening polymerization.

Synthesis of Sulfated Acetamido Group-Containing Copolyribose by Selective Ring-Opening Polymerization and Chemical Modifications.

Synthesis and sulfation of an acetamido group-containing copolyribose was carried out by a five-step synthetic route. Firstly, selective ring-opening copolymerization of 1, 4-anhydro-3-azido-2-O-t-butyldimethylsilyl (TBDMS)-3-deoxy-α-D-ribopyranose (A3ASR) and 1, 4-anhydro-2, 3-di-O-TBDMS-α-D-ribopyranose (ADSR) with BF3•OEt2 as a catalyst at low temperature produced an azido group-containing copolyribose, i.e., poly [ 3-azido-2-O-TBDMS-3-deoxy-(1→5)-α-ribofuranose-co-2, 3-di-O-TBDMS-(1→5)-α-ribofuranose] [copoly (A3ASR)]. The number-average molecular weight (_??_n) of the azido group-containing copolyriboses was in a range of 1.17×104 to 2.96×104. The specific rotation ([α]20D) increased from +117° to +204° as the mole fractions (%) of azido group-containing units (A3ASR) in the copolymers decreased from 83% to 16%. The reactivity ratios of A3ASR (r1=0.42) and ADSR (r2=1.16) in the ring-opening copolymerizations were estimated according to the Kelen-Tudos method.Then, the azido group in a copoly (3A3ASR-ADSR) (_??_n of 1.11×104 and [α] 20D of +141.6°) was reduced into amino group with NaBH4 in a mixture of THF-ethanol to afford an amino group-containing copolymer, i.e., poly [3-amino-2-O-TBDMS-3-deoxy-(1→5)-α-ribofuranose-co-2, 3-di-O-TBDMS-(1→5)-α-ribofuranose] [copoly (AAmSR-ADSR)], and subsequent acetylation of the amino group with acetyl chloride gave an intermediate acetamido group-containing copolymer, i.e., poly [ 3-acetamido-2-O-TBDMS-3-deoxy-(1→5)-α-ribofuranose-co-2, 3-di-O-TBDMS-(1→5)-α-ribofuranose] [copoly (A3AAdSR-ADSR)], and then de-t-butyldimethylsilylation of the copolymer produced a water-soluble acetamido group-containing copolyribose, i.e., poly [ 3-acetamido-3-deoxy-(1→5)-α-ribofuranose-co-(1→5)-α-ribofuranose] [copoly (A3AAdR-R)] with _??_n of 8.63×103 and [α]20D of +141.0°.Finally, sulfation of the acetamido group-containing copolyribose [copoly (A3AAdR-R)] with a sulfur trioxide-pyridine complex in a mixture of dimethyl sulfoxide (DMSO) and pyridine produced a sulfated acetamido group-containing copolyribose [copoly (SA3AAdR-SR)] with _??_n of 10.68×103 and [α] 20D of + 84.9°. The structures of acetamido group-containing copolymer and its sulfate were determined by 13C NMR. The degree of sulfation (DS=1.2) was measured by elemental analysis.

Synthesis and Anti-HIV Activity of Sulfated Polysaccharides Containing Acetamido Groups.

A series of stereoregular azido group-containing copolymers such as poly [3-azido-2-O-t-butyldimethylsilyl-3-deoxy-(1→5)-α-D-xylofuranose-co-2, 3-di-O-t-butyldimethylsilyl-(1→5)-α-D-ribofuranose] [copoly (A3ASX-ADSR)] were synthesized by selective ring-opening polymerization of 1, 4-anhydro-3-azido-2-O-t-butyldimethylsilyl-3-deoxy-α-D-xylopyranose (A3ASX) and 1, 4-anhydro-2, 3-di-O-t-butyldimethylsilyl-α-D-ribopyranose (ADSR) with BF3•OEt2 catalyst. The number-average molecular weights (_??_n) were in a range of 3.5×104_??_4.2×104. The optical rotations ([α] D) increased from +119°to+143° with increasing mole fraction of the xylofuranosidic units in the copolymers from 30% to 78%.Reduction of the azido group in the copolymer into an amino group, acetylation of the amino group into an acetamido group, and removal of the t-butyldimethylsilyl group afforded poly [3-acetamido-3-deoxy-(1→5)-α-D-xylofuranose-co-(1→5)-α-D-ribofuranose] [copoly (A3AAdX-R)] with _??_n 9.0×103 and [α] D of +150.8°. Sulfation of the 3AAdXF and copoly (A3AAdX-R) produced a sulfated 3-acetamido-3-deoxy-(1→5)-α-D-xylofuranan with _??_n of 17.1×103, and a sulfated poly _??_3-acetamido-3-deoxy-(1→5)-α-D-xylofuranose-co-(1→5)-α-D-ribofuranose_??_ with _??_n of 10.9×103. The degrees of sulfation of homo- and co-polymers were 0.72 and 1.03, respectively. The four kinds of sulfated acetamido group-containing polypentoses exhibited medium-to-high anti-HIV (human immunodeficiency virus) activities in the range of EC50 of from 0.42μg/mL to 62.86μg/mL, while they showed low anticoagulant activities in the range of 0 to 6unit/mg.

Synthesis of 3-Acetamido-3-deoxy-(1→5)-α-d-xylofuranan by Ring-Opening Polymerization of a 1,4-Anhydro-3-azido-α-d-xylopyranose Derivative

A stereoregular 3-acetamido-3-deoxy-(1→5)-α-d-xylofuranan (3AAdXF) was synthesized by the synthetic route starting from selective ring-opening polymerization of 1,4-anhydro-3-azido-2-O-tert-butyldimethylsilyl-3-deoxy-α-d-xylopyranose (A3ASX). First, A3ASX was polymerized by BF3·OEt2 catalyst at −20 to −40 °C to give 3-azido-2-O-tert-butyldimethylsilyl-(1→5)-α-d-xylofuranan (3AzSXF) with M̄n of 11.1 × 104−17.8 × 104 and [α]D of +200−212°. A polymer prepared by SbCl5 catalyst had a mixed structure consisting of 1,5-α- and 1,5-β-xylofuranosidic units. 3AzSXF was reduced with NaBH4 in a THF−ethanol mixture to afford 3-amino-2-O-tert-butyldimethylsilyl-3-deoxy-(1→5)-α-d-xylofuranan (3AmSXF). After 3AmSXF was acetylated at its amino groups to produce a 3-acetamidoxylofuranan derivative (3AAdSXF), desilylation of 3AAdSXF gave 3AAdXF with M̄n of 7.8 × 103 and [α]D of +212°. The structure analysis was performed using 13C and 1H NMR spectroscopies, IR spectroscopy, and optical rotation measurements.

New Vistas in Dehydrocoupling Polymerization of Hydrosilanes: Platinum Complex-Catalyzed Dehydrocoupling of Cyclic and Acyclic Secondary Silanes

Abstract Pt(cod)2 catalyzed dehydrocoupling of acyclic and cyclic secondary silanes R1R2SiH2[R1, R2 = alkyl group; R1 + R2 = (CH2)n(n = 3,4,5); R1 + R2 = o-biphenylene] to afford polysilanes while a (CH3)2Pt(cod)-catalyzed reaction of silacyclobutane (n = 3) resulted in selective ring-opening polymerization.