Upscaling single unit monomer insertion to synthesize discrete oligomers

Installing a Single Monomer within Acrylic Polymers Using Photoredox Catalysis

Incorporating exactly one monomer at a defined position during a chain polymerization is exceptionally challenging due to the statistical nature of monomer addition. Herein, photoinduced electron/energy transfer (PET) enables the incorporation of exactly one vinyl ether into polyacrylates synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Near-quantitative addition (>96%) of a single vinyl ether is achieved while retaining >99% of the thiocarbonylthio chain ends. Kinetic studies reveal that performing the reactions at 2 °C limits unwanted chain breaking events. Finally, the syntheses of diblock copolymers are reported where molecular weights and dispersities are well-controlled on either side of the vinyl ether. Overall, this report introduces an approach to access acrylic copolymers containing exactly one chemical handle at a defined position, enabling novel macromolecular architectures to probe structure-function properties, introduce sites for de/reconstruction, store information, etc.

Step-growth polymerization by the RAFT process

Reversible Addition-Fragmentation Chain Transfer (RAFT) step-growth polymerization is an emerging method that synergistically combines the benefits of RAFT polymerization (functional group and user-friendly nature) and step-growth polymerization (versatility of the polymer backbone). This new polymerization method is generally achieved by using bifunctional reagents of monomer and Chain Transfer Agent (CTA), that efficiently yield Single Monomer Unit Insertion (SUMI) adducts under stoichiometrically balanced conditions. This review covers a brief history of the RAFT-SUMI process and its transformation into RAFT step-growth polymerization, followed by a comprehensive discussion of various RAFT step-growth systems. Furthermore, characterizing the molecular weight evolution of step-growth polymerization is elaborated based on the Flory model. Finally, a formula is introduced to describe the efficiency of the RAFT-SUMI process, assuming rapid chain transfer equilibrium. Examples of reported RAFT step-growth and SUMI systems are then categorized based on the driving force.

Main-Chain Fluoropolymers with Alternating Sequence Control via Light-Driven Reversible-Deactivation Copolymerization in Batch and Flow

Polymers with regulated alternating structures are attractive in practical applications, particularly for main-chain fluoropolymers. We for the first time enabled controlled fluoropolymer synthesis with alternating sequence regulation using a novel fluorinated xanthate agent via a light-driven process, which achieved on-demand copolymerization of chlorotrifluoroethylene and vinyl esters/amides under both batch and flow conditions at ambient pressure. This method creates a facile access to fluoropolymers with a broad fraction range of alternating units, low dispersities and high chain-end fidelity. Moreover, a two-step photo-flow platform was established to streamline the in-situ chain-extension toward unprecedented block copolymers continuously from fluoroethylene. Influences of structural control were illustrated with thermal and surface properties. We anticipate that this work will promote advanced material engineering with customized fluoropolymers.

Photomediated RAFT step-growth polymerization with maleimide monomers

Photomediated RAFT step-growth polymerization was performed with and without the presence of a photocatalyst using a trithiocarbonate-based CTA and a maleimide monomer.

PET-RAFT single unit monomer insertion of β-methylstyrene derivatives: RAFT degradation and reaction selectivity

Reversible addition-fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) of β-methylstyrene derivatives into diverse RAFT agents presented fast reaction kinetics, but significant degradation of the SUMI products occurred due to a hydrogen abstraction reaction. Fortunately, such degradation can be suppressed through appropriate design of initial RAFT agents attributed to effective chain transfer and selective photoactivation.

Reversible-Addition Fragmentation Chain Transfer Step-Growth Polymerization

Reversible-addition fragmentation chain transfer (RAFT) polymerization has been widely explored since its discovery due to its structural precision, versatility, and efficiency. However, the lack of tunability of the polymer backbone limits some applications. Herein, we synergistically combine RAFT and step-growth polymerization mechanisms, by employing a highly selective insertion process of a single monomer with a RAFT agent, to achieve RAFT step-growth polymerization. A unique feature of the RAFT step-growth polymers is that each backbone repeat unit bears a pendant RAFT agent, which can subsequently graft side chains in a second polymerization step and afford molecular brush polymers. Enabled by cleavable backbone functionality, we demonstrate transformation of the resulting brushlike polymers into linear chains of uniform size upon a stimulus.

Regulation of tectonic sequences in chain-folding-directed monodisperse isomeric oligomers precisely tailored by Ugi-hydrosilylation orthogonal cycles

Monodisperse discrete oligomers with a tailored sequence of linkages within their backbones, which has been defined as a tectonic sequence, were precisely constructed through Ugi-4CRs coupled to hydrosilylation orthogonal cycles.

How does the single unit monomer insertion technique promote kinetic analysis of activation and initiation in photo-RAFT processes?

The single unit monomer insertion technique provides a simple platform for the kinetic investigation of early stage of photo-RAFT process that comprises photo-activation of initial RAFT agents and addition of RAFT leaving radicals to the monomers.

Sequence-regulated vinyl polymers via iterative atom transfer radical additions and acyclic diene metathesis polymerization

Iterative ATRAs and ADMET polymerization enabled the synthesis of sequence-regulated vinyl polymers without statistical distribution of monomer compositions and sequences.

PISA: construction of self-organized and self-assembled functional vesicular structures

PISA reaction networks alone, integrated with other networks, or designing properties into the amphiphiles confer functionalities to the supramolecular assemblies.

Photoregulated reversible addition–fragmentation chain transfer (RAFT) polymerization

Different strategies on photoregulated RAFT polymerization are developed. This minireview summarizes recent advances in photoregulated RAFT polymerization and its applications.

Sequential and alternating RAFT single unit monomer insertion: model trimers as the guide for discrete oligomer synthesis

A complete set of model trimers and their synthetic kinetics are established to guide the synthesis of diverse sequence-defined polymers.

Precise control of single unit monomer radical addition with a bulky tertiary methacrylate monomer toward sequence-defined oligo- or poly(methacrylate)s via the iterative process

Iterative single unit monomer radical addition with a bulky tertiary methacrylate monomer, adamantyl and isopropyl pendant methacrylate (IPAMA), under ATRP conditions was studied in detail toward the syntheses of sequence-defined oligo- or poly(methacrylate)s in higher yields.

Flow mediated metal-free PET-RAFT polymerisation for upscaled and consistent polymer production

A slug flow process has been utilised in conjunction with metal-free photopolymerisation to produce well-defined polymers with outstanding consistency.