Organic Spirocyclic Initiators for the Ring-Expansion Polymerization of β-Lactones

We report spirocyclic imidazolidines derived from N-heterocyclic carbenes and β-lactones. These spirocycles are initiators for the zwitterionic ring-expansion polymerization of β-lactones to generate cyclic polyesters of well-defined molecular weight. The zwitterionic strategy based on the equilibrium between the zwitterionic intermediates and spiro macrocyclics enables the controlled synthesis of cyclic poly(β-lactone)

Organic Spirocyclic Initiators for the Ring-Expansion Polymerization of β-Lactones

We report spirocyclic imidazolidines derived from N-heterocyclic carbenes and β-lactones. These spirocycles are initiators for the zwitterionic ring-expansion polymerization of β-lactones to generate cyclic polyesters of well-defined molecular weight. The zwitterionic strategy based on the equilibrium between the zwitterionic intermediates and spiro macrocyclics enables the controlled synthesis of cyclic poly(β-lactone)

Group Transfer Polymerization of Acrylates Catalyzed by N-Heterocyclic Carbenes

Group transfer polymerization (GTP) is an effective method for the synthesis of poly(methyl methacrylate) (pMMA) with controlled molecular weights and narrow polydispersities. Silyl ketene acetals initiate the polymerization of methyl methacrylate in the presence of either nucleophilic or Lewis acid catalysts. We report the use of N-heterocyclic carbenes (NHCs) as neutral nucleophilic catalysts for GTP of methyl methacrylate (MMA) and tert-butyl acrylate (TBA). For MMA, polymer molecular weights increase linearly with conversion and are predictable over a range of [M]0/[I]0 ratios. Polydispersities trend downward with conversion and approach 1.2 at >95% conversion. Significantly, NHCs were also shown to be effective for the controlled GTP of TBA, generating living polymers with predictable molecular weights, narrow molecular weight distributions (Mw/Mn ≤ 1.2), and living chain ends, as illustrated by chain-extension experiments

Broadening the Scope of Functional Groups Accessible in Aliphatic Polycarbonates by the Introduction of RAFT Initiating Sites

Broadening the Scope of Functional Groups Accessible in Aliphatic Polycarbonates by the Introduction of RAFT Initiating Site

Programmable High-Throughput Platform for the Rapid and Scalable Synthesis of Polyester and Polycarbonate Libraries

The critical role of composition, architecture, molecular weight, and molecular weight distribution on the functional properties of macromolecular materials underscores the need for reproducible, robust, scalable, and programmable synthetic methods to generate macromolecules that span a systematic and wide range of structure–property space. Herein, we describe the marriage of tunable and highly active organic catalysts with programmed continuous-flow reactors to rapidly generate libraries of polyester and polycarbonate homopolymers and block copolymers with exquisite efficiency and control. Under continuous-flow conditions, highly controlled polymerizations occur with residence times as low as 6 ms (TOF = 24 000 000 h–1) and can be readily scaled-up to generate polymers at a rate of tens of grams per minute. We describe an in-flow catalyst switch strategy to enable the rapid generation of block copolymer libraries (100 distinct polymers in 9 min) from monomers with drastically different reactivity profiles

Silver(I)−Carbene Complexes/Ionic Liquids: Novel <i>N</i>-Heterocyclic Carbene Delivery Agents for Organocatalytic Transformations

N-Heterocyclic carbene (NHC) complexes with silver were investigated as sources of unsaturated NHC carbene catalysts via thermal decomposition. The NHC complex (1-ethyl-3-methylimidazol-2-ylidene)silver(I) chloride is an ionic liquid, and was found to catalyze the ring-opening polymerization of lactide at elevated temperatures to give narrowly dispersed polylactide of predictable molecular weight. Silver−carbene complexes can also be used for the catalysis of small molecule transesterification reactions. Thermolysis of the silver complexes in the presence of CS2 yielded the zwitterionic CS2 adducts of the carbene, implicating the intermediacy of the free carbene in these reactions

Facile Synthesis of Functionalized Lactones and Organocatalytic Ring-Opening Polymerization

A facile one-step synthesis of functionalized valerolactones was carried out by the conjugate addition of thiols to the α,β-unsaturated valerolactone 5,6-dihydro-2H-pyran-2-one. The resultant 3-mercaptovalerolactones undergo ring-opening polymerization in solution or in the melt to generate polyesters functionalized either with benzyl mercaptans or oligoethylene glycol pendant groups. The copolymerization of the 3-mercaptovalerolactones with ε-caprolactone generates random copolymers

Programmable High-Throughput Platform for the Rapid and Scalable Synthesis of Polyester and Polycarbonate Libraries

The critical role of composition, architecture, molecular weight, and molecular weight distribution on the functional properties of macromolecular materials underscores the need for reproducible, robust, scalable, and programmable synthetic methods to generate macromolecules that span a systematic and wide range of structure–property space. Herein, we describe the marriage of tunable and highly active organic catalysts with programmed continuous-flow reactors to rapidly generate libraries of polyester and polycarbonate homopolymers and block copolymers with exquisite efficiency and control. Under continuous-flow conditions, highly controlled polymerizations occur with residence times as low as 6 ms (TOF = 24 000 000 h–1) and can be readily scaled-up to generate polymers at a rate of tens of grams per minute. We describe an in-flow catalyst switch strategy to enable the rapid generation of block copolymer libraries (100 distinct polymers in 9 min) from monomers with drastically different reactivity profiles

Starlike Block Copolymers with Amphiphilic Arms as Models for Unimolecular Micelles

Starlike Block Copolymers with Amphiphilic Arms as Models for Unimolecular Micelle