Radical Ring-Opening Single Unit Monomer Insertion: An Approach to Degradable and Biocompatible Sequence-Defined Oligomers

Pyrazole carbodithiolate-driven iterative RAFT single-additions

In this Communication, we comprehensively investigated substituent effects relevant to iterative reversible activation fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) reactions. Through the use of the pyrazole carbodithiolate (PCDT) "Z-group" as the chain transfer component in RAFT SUMI, we show the importance of "Z-group" effects and its interplay with "R-group" (the carbon-centred radical precursor) effects. We also expanded the scope of RAFT SUMI to new monomer types and sequences thereof. As such, the C-S bond dissocation/reformation steps were found to be crucial factors in SUMI, and it was found that general substituent effects must be wholistically examined for every step of this reaction. This stands in contrast with conventional knowledge of RAFT polymerisation, where the main consideration is often centred around the propagation stage, i.e., the key C-C bond formation step. Indeed, contrary to SUMI, the latter characteristic was observed in the analogous alternating copolymerisation.

Development of Sequence-Controlled, Degradable, and Cytocompatible Oligomers with Explicit Fragmentation Pathways

Sequence-defined and degradable polymers can mimic biopolymers, such as peptides and DNA, to undertake life-supporting functions in a chemical way. The design and development of well-structured oligomers/polymers is the most concern for the public, even to further uncover their degradation process illustrating the degraded products and their properties. However, seldom investigation has been reported on the aforementioned aspects. In this work, the alternating photo-reversible addition-fragmentation chain-transfer (photo-RAFT) single unit monomer insertion (SUMI) of different N-substituted maleimides and thermal radical ring-opening SUMI of a cyclic ketene acetal monomer (i.e., 5,6-benzo-2-methylene-1,3-dioxepane (BMDO)) is adopted, to produce two degradable pentamers owing to the conversion of the exo-methylene group of BMDO into ester bonds along the main chains of the prepared products. Moreover, the possible degraded approach of pentamers is studied by combining high-resolution mass spectrometry (HRMS) and liquid chromatography-mass spectrometry (LC-MS) for the first time. This work also sheds light on the precise structures and cytotoxicity of SUMI products and their degraded compounds, proposing a detailed and credible outlook for biomedical applications.

Cationic Single-Unit Monomer Insertion (cSUMI): From Discrete Oligomers to the α-/ω-End and In-Chain Sequence-Regulated Polymers

Single-unit monomer insertion (SUMI) has become an important strategy for the synthesis of sequence-controlled vinyl polymers due to its strong versatility and high efficiency. However, all reported SUMI processes are based on a free-radical mechanism, resulting in a limited number of monomer types being applicable to SUMI or a limited number of sequences of structural units that SUMI can synthesize. Herein, we developed a novel SUMI based on a cationic mechanism (cSUMI), which operates through a degenerative (similar to radical SUMI) but cationic chain transfer process. By optimizing the chain transfer agent (CTA) and monomer pairs, a high-efficiency cSUMI was achieved for vinyl ether and styrene monomers. Based on this reaction, a range of discrete oligomers containing vinyl ether and styrene moieties, and even α-/ω-end and in-chain sequence-regulated polymers were synthesized, most of which cannot be achieved by radical SUMI. In addition, we explored the application of these sequence-regulated polymers in the preparation of miktoarm star polymers, delivery of photosensitizers, and solubilization of fluorescence probes. The development of SUMI with a new mechanism will certainly broaden the scope of structures and sequences in precise vinyl-based polymers.

Rational design of a multi-in-one heterofunctional agent for versatile topological transformation of multisite multisegmented polystyrenes

A “seven-in-one” initiating, coupling and stimuli-labile agent is designed to achieve topological transformations with reduced, similar and enhanced molar masses.