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(A) Mechanism of the organocatalyzed photoredox cascade polymerization of vinyl cyclopropanes. (B) The linear vs. cyclic repeat unit content could be tuned by changing monomer concentration, LED source, and temperature. Representative examples shown. Labels in part B = conditions: Mn in kDa (Đ) DP. Abbreviations: PC = photocatalyst (N,N-di(2-naphthyl)dihydrophenazine). ISC = inter system crossing. DBMM = diethyl 2-bromo-2-methylmalonate
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Traditionally, most polymerizations rely on simple reactions such as alkene addition, ring-opening, and condensation because they are robust, highly efficient, and selective. These reactions, however, generally only yield a single new C–C or C–O bond during each propagation step. In recent years, novel macromolecules have been prepared with propaga...
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Herein we report the discovery of a new photochemical cascade process through a flow-based strategy for intercepting diradicals generated from simple alkenes. This continuous process delivers a series of unprecedented polycyclic reaction products. Exploring the scope of this novel process revealed that this approach is general and affords a variety...
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... [2,13] The catalytic dehydropolymerization of primary amineÀ boranes, H 3 B · NRH 2 (R = alkyl, principally R=Me) was first described in 2008 using the Ir( t BuÀ POCOP)H 2 catalyst, [14][15][16] and since then a wide variety of catalyst systems have been reported. [13] One current generally accepted mechanism for dehydropolymerization is a cascade-like [17] polymerization, where the metal centre first dehydrogenates amineÀ borane to form a very reactive aminoborane, [11] which then undergoes a nucleophilic head to tail chain-growth polymerization via an amido-end group of the growing chain, likely initiated by a metal hydride or free amine. [18][19][20] Scheme 1A exemplifies this with the H 3 B · NMeH 2 pre-monomer to form Nmethylpolyaminoborane, [H 2 BNMeH] n . ...
The sigma amine−borane complexes [Rh(L1)(η²:η²‐H3B⋅NRH2)][OTf] (L1=2,6‐bis‐[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine, R=Me, Et, ⁿPr) are described, alongside [Rh(L1)(NMeH2)][OTf]. Using R=Me as a pre‐catalyst (1 mol %) the dehydropolymerization of H3B ⋅ NMeH2 gives [H2BNMeH]n selectively. Added NMeH2, or the direct use of [Rh(L1)(NMeH2)][OTf], is required for initiation of catalysis, which is suggested to operate through the formation of a neutral hydride complex, Rh(L1)H. The formation of small (1–5 nm) nanoparticles is observed at the end of catalysis, but studies are ambiguous as to whether the catalysis is solely nanoparticle promoted or if there is a molecular homogeneous component. [Rh(L1)(NMeH2)][OTf] is shown to operate at 0.025 mol % loadings on a 2 g scale of H3B ⋅ NMeH2 to give polyaminoborane [H2BNMeH]n [Mn=30,900 g/mol, Ð=1.8] that can be purified to a low residual [Rh] (6 μg/g). Addition of Na[N(SiMe3)2] to [H2BNMeH]n results in selective depolymerization to form the eee‐isomer of N,N,N‐trimethylcyclotriborazane [H2BNMeH]3: the chemical repurposing of a main‐group polymer.
... Therefore, we turned our attention to light-mediated polymerization techniques, as recent works have demonstrated that they are versatile tools to mediate controlled polymerization following radical, [34][35][36][37][38][39][40][41][42] cationic, [43][44][45][46][47] and metathesis pathways [48][49][50] at ambient temperature ( Figure 1B). [51] In particular, we envisioned that the photoinduced electron/energy transferreversible addition/fragmentation chain transfer (PET-RAFT) polymerization developed by Boyer and coworkers [52][53][54][55][56] could be employed to mediate the radical ringopening cascade copolymerization (rROCCP) [57,58] of the macrocyclic allylic sulfone with acrylates or acrylamides ( Figure 1C). Unlike the polymerization that is thermally initiated by azobisisobutyronitrile (AIBN), which requires high temperatures (80-100°C) to maintain a sufficiently high rate of propagation, PET-RAFT can be performed at mild temperatures, thereby enabling favorable comonomer reactivity ratios in copolymerization. ...
Degradable vinyl polymers by radical ring‐opening polymerization are promising solutions to the challenges caused by non‐degradable vinyl plastics. However, achieving even distributions of labile functional groups in the backbone of degradable vinyl polymers remains challenging. Herein, we report a photocatalytic approach to degradable vinyl random copolymers via radical ring‐opening cascade copolymerization (rROCCP). The rROCCP of macrocyclic allylic sulfones and acrylates or acrylamides mediated by visible light at ambient temperature achieved near‐unity comonomer reactivity ratios over the entire range of the feed compositions. Experimental and computational evidence revealed an unusual reversible inhibition of chain propagation by in situ generated sulfur dioxide (SO2), which was successfully overcome by reducing the solubility of SO2. This study provides a powerful approach to degradable vinyl random copolymers with comparable material properties to non‐degradable vinyl polymers.
... Degradable polymers have also been prepared via the cascade metathesis polymerization of monomers bearing terminal alkynes and cyclic alkenes (also referred to as tandem ring-closing/ring-opening metathesis polymerization or enyne metathesis polymerization) using the third-generation Grubbs catalyst (G3). [42][43][44][45][46] This cascade metathesis polymerization ( Figure 1A)was first developed in our group using monomers that do not yield degradable polymers. [47] Mechanistic studies supported that the catalyst first reacts with the alkyne then undergoes intramolecular ring-closing and ring-opening steps ( Figure 1B). ...
Enyne monomers derived from D‐xylose underwent living cascade polymerizations to prepare new polymers with a ring‐opened sugar and degradable linkage incorporated into every repeat unit of the backbone. Polymerizations were well‐controlled and had living character, which enabled the preparation of high molecular weight polymers with narrow molecular weight dispersity values and a block copolymer. By tuning the type of acid‐sensitive linkage (hemi‐aminal ether, acetal, or ether functional groups), we could change the degradation profile of the polymer and the identity of the resulting degradation products. For instance, the large difference in degradation rates between hemi‐aminal ether and ether‐based polymers enabled the sequential degradation of a block copolymer. Furthermore, we exploited the generation of furan‐based degradation products, from an acetal‐based polymer, to achieve the release of covalently bound reporter molecules upon degradation.
https://authors.elsevier.com/sd/article/S0165-9936(24)00165-1
Cascade metathesis polymerization has been developed as a promising method to synthesize complex but well‐defined polymers from monomers containing multiple reactive functional groups. However, this approach has been limited to the monomers involving simple alkene/alkyne moieties or produced mainly non‐degradable polymers. In this study, we demonstrate a complete cascade ring‐opening/ring‐closing metathesis polymerization (RORCMP) using various tricycloalkenes and two strategies for the efficient degradation. Through rational design of tricycloalkene monomers, the structure and reactivity relationship was explored. For example, tricycloalkenes with trans configuration in the central ring enabled faster and better selective cascade RORCMP than the corresponding cis isomers. Also, a 4‐substituted cyclopentene moiety in the monomers significantly enhanced the overall cascade RORCMP performance, with the maximum turnover number (TON) reaching almost 10,000 and molecular weight up to 170 kg/mol using an amide‐containing monomer. Furthermore, we achieved one‐shot cascade multiple olefin metathesis polymerization using tricycloalkenes and a diacrylate, to produce new highly A,B‐alternating copolymers with full degradability. Lastly, we successfully designed xylose‐based tricycloalkenes to give well‐defined polymers that underwent ultra‐fast and complete degradation under mild conditions.
Cascade metathesis polymerization has been developed as a promising method to synthesize complex but well‐defined polymers from monomers containing multiple reactive functional groups. However, this approach has been limited to the monomers involving simple alkene/alkyne moieties or produced mainly non‐degradable polymers. In this study, we demonstrate a complete cascade ring‐opening/ring‐closing metathesis polymerization (RORCMP) using various tricycloalkenes and two strategies for the efficient degradation. Through rational design of tricycloalkene monomers, the structure and reactivity relationship was explored. For example, tricycloalkenes with trans configuration in the central ring enabled faster and better selective cascade RORCMP than the corresponding cis isomers. Also, a 4‐substituted cyclopentene moiety in the monomers significantly enhanced the overall cascade RORCMP performance, with the maximum turnover number (TON) reaching almost 10,000 and molecular weight up to 170 kg/mol using an amide‐containing monomer. Furthermore, we achieved one‐shot cascade multiple olefin metathesis polymerization using tricycloalkenes and a diacrylate, to produce new highly A,B‐alternating copolymers with full degradability. Lastly, we successfully designed xylose‐based tricycloalkenes to give well‐defined polymers that underwent ultra‐fast and complete degradation under mild conditions.
The ability to extend the polymerizations of thiyl radical propagation to be regulated by existing controlled methods would be highly desirable, yet remained very challenging to achieve because the thiyl radicals still cannot be reversibly controlled by these methods. In this article, we reported a novel strategy that could enable the radical ring‐opening polymerization of macrocyclic allylic sulfides, wherein propagating specie is thiyl radical, to be controlled by reversible addition–fragmentation chain transfer (RAFT) agents. The key to the success of this strategy is the propagating thiyl radical can undergo desulfurization with isocyanide and generate a stabilized alkyl radical for reversible control. Systematic optimization of the reaction conditions allowed good control over the polymerization, leading to the formation of polymers with well‐defined architectures, exemplified by the radical block copolymerization of macrocyclic allylic sulfides and vinyl monomers and the incorporation of sequence‐defined segments into the polymer backbone. This work represents a significant step toward directly enabling the polymerizations of heteroatom‐centered radical propagation to be regulated by existing reversible‐deactivation radical polymerization techniques.
The ability to extend the polymerizations of thiyl radical propagation to be regulated by existing controlled methods would be highly desirable, yet remained very challenging to achieve because the thiyl radicals still cannot be reversibly controlled by these methods. In this article, we reported a novel strategy that could enable the radical ring‐opening polymerization of macrocyclic allylic sulfides, wherein propagating specie is thiyl radical, to be controlled by reversible addition–fragmentation chain transfer (RAFT) agents. The key to the success of this strategy is the propagating thiyl radical can undergo desulfurization with isocyanide and generate a stabilized alkyl radical for reversible control. Systematic optimization of the reaction conditions allowed good control over the polymerization, leading to the formation of polymers with well‐defined architectures, exemplified by the radical block copolymerization of macrocyclic allylic sulfides and vinyl monomers and the incorporation of sequence‐defined segments into the polymer backbone. This work represents a significant step toward directly enabling the polymerizations of heteroatom‐centered radical propagation to be regulated by existing reversible‐deactivation radical polymerization techniques.
