Organic Superbase as an Efficient Catalyst for Group Transfer Polymerization of Methyl Methacrylate

Trimethylsilanol Cleaves Stable Azaylides As Revealed by Unfolding of Robust "Staudinger" Single-Chain Nanoparticles

Herein, we disclose a unique and selective reagent for the cleavage of stable azaylides prepared by the nonhydrolysis Staudinger reaction, enabling the on-demand unfolding of robust single-chain nanoparticles (SCNPs). SCNPs with promising use in catalysis, nanomedicine, and sensing are obtained through intrachain folding of discrete synthetic polymer chains. The unfolding of SCNPs involving reversible interactions triggered by a variety of external stimuli (e.g., pH, temperature, light, and redox potential) or substances (e.g., competitive reagents, solvents, and anions) is well known. Conversely, methods for the unfolding (i.e., intrachain disassembly) of SCNPs with stronger covalent interactions are scarce. We show that trimethylsilanol (Me3SiOH) triggers the efficient unfolding of robust "Staudinger" SCNPs with stable azaylide (-N=P-) moieties as intrachain cross-linking units showing exceptional stability toward water, air, and CS2, a standard reagent for azaylides. As a consequence, Me3SiOH arises as a rare, exceptional, and valuable reagent for the cleavage of stable azaylides prepared by the nonhydrolysis Staudinger reaction.

Group-Transfer Polymerization-Induced Self-Assembly (GTPISA) in Non-polar Media: An Organocatalyzed Route to Block Copolymer Nanoparticles at Room Temperature

Polymerization-induced self-assembly (PISA) enables the synthesis at large scale of a wide variety of functional nanoparticles. However, a large number of works are related to controlled radical polymerization (CRP) methods and are generally undertaken at elevated temperatures (>50 °C). Here is the first report on methacrylate-based nanoparticles fabricated by group transfer polymerization-induced self-assembly (GTPISA) in non-polar media (n-heptane). This GTPISA process is achieved at room temperature (RT) using 1-methoxy-1-(trimethylsiloxy)-2-methylprop-1-ene (MTS) and tetrabutylammonium bis-benzoate (TBABB) as initiator and organic catalyst, respectively. Under these conditions, well-defined metal-free and colorless diblock copolymers are produced with efficient crossover from the non-polar stabilizing poly(lauryl methacrylate) (PLMA) block to the non-soluble poly(benzyl methacrylate) (PBzMA) segment. The resulting PLMA-b-PBzMA block copolymers simultaneously self-assemble into nanostructures of various sizes and morphologies. GTPISA in non-polar solvent proceeds rapidly at RT and avoids the use of sulfur or halogenated compounds or metallic catalysts associated with the implementation of CRP methods, thus expanding the potential of PISA formulations for applications in non-polar environments.

Block Copolymer Synthesis by a Sequential Addition Strategy from the Organocatalytic Group Transfer Polymerization of Methyl Methacrylate to the Ring-Opening Polymerization of Lactide

Sequential block copolymerization involving comonomers belonging to different classes, e.g., a vinyl-type monomer and a heterocycle, is a challenging task in macromolecular chemistry, as corresponding propagating species do not interconvert easily from one to the other by crossover reactions. Here, it is first evidenced that 1-methoxy 2-methyl 1-trimethylsilyloxypropene (MTS), i.e., a silyl ketene acetal (SKA)-containing initiator, can be used in presence of the P₄ -t-Bu phosphazene organic base to control the ring-opening polymerization (ROP) of racemic lactide (rac-LA). The elementary reaction, which rapidly transforms SKA groups into propagating alkoxides, can be leveraged to directly synthesize well-defined poly(methyl methacrylate)-b-polylactide (PMMA-b-PLA) block copolymers. This is achieved using P₄ -t-Bu as the single organic catalyst and MTS as the initiator for the group transfer polymerization (GTP) of methyl methacrylate (MMA), followed by the ROP of rac-LA. Both polymerization methods are implemented under selective and controlled/living conditions at room temperature in THF. This sequential addition strategy further expands the scope of organic catalysis of polymerizations for macromolecular engineering of block copolymers involving propagating species of disparate reactivity. This article is protected by copyright. All rights reserved.

Poly(β-trimethylsilyloxy ester): A Degradable Polymer Based on Retro Mukaiyama Aldol Reaction

We herein report a new type of degradable poly(β-trimethylsilyloxy ester) prepared by the organocatalyzed Mukaiyama aldol polyaddition between bis(silyl ketene acetal)s and dialdehydes. Specifically, the t-Bu-P₄ -catalyzed polyaddition between 1,2-bis[2-methyl-1-(trimethylsiloxy)prop-1-enyloxy]ethane (MTS₂ ) and 4,4'-biphenyldicarboxaldehyde (BPDA) or butane-1,4-diyl bis(4-formylbenzoate) (BDA) can produce poly(β-trimethylsilyloxy ester)s with number-average molar mass greater than 10 kg mol^-1 . For the first time, we find these poly(β-trimethylsilyloxy ester)s are degradable in solution in presence of nucleophiles such as fluoride and cyanide anions. We also find that the degradation behavior of poly(β-trimethylsilyloxy ester)s is highly dependent on the nature of the used catalyst, and the bond scission in polymer is fundamentally rooted in the retro Mukaiyama aldol reaction mechanism. This article is protected by copyright. All rights reserved.

Precision synthesis for well-defined linear and/or architecturally controlled thermoresponsive poly(N-substituted acrylamide)s

We describe the progress in precision polymerizations of specific kinds of N-alkylacrylamides and N,N-dialkylacrylamides to produce polymers showing thermoresponsive properties in aqueous media, which representatively include the reversible-deactivation radical polymerizations...

Synthesis of well-defined di- and triblock acrylic copolymers consisting of hard poly(dicyclopentanyl acrylate) and soft poly(alkyl acrylate) segments by organocatalyzed group transfer polymerization and their glass transition behavior

Well-defined acrylic block copolymers with hard poly(dicyclopentanyl acrylate) and soft poly(n-alkylacrylate) blocks prepared by GTP are observed to undergo microphase separation by rheometry except for the crystallizable poly(n-dodecyl acrylate) series.

Metal-free anionic polymerization of n-hexyl isocyanate catalyzed by phosphazene bases

Metal-free anionic polymerization of n-hexyl isocyanate (HIC) catalyzed by phosphazene bases in THF at −98 °C under 10⁻⁶ Torr was attempted to obtain poly(n-hexyl isocyanate) (PHIC) peptide mimics with a high purity.

Polymerization of Polar Monomers Mediated by Main-Group Lewis Acid-Base Pairs

The development of new or more sustainable, active, efficient, controlled, and selective polymerization reactions or processes continues to be crucial for the synthesis of important polymers or materials with specific structures or functions. In this context, the newly emerged polymerization technique enabled by main-group Lewis pairs (LPs), termed as Lewis pair polymerization (LPP), exploits the synergy and cooperativity between the Lewis acid (LA) and Lewis base (LB) sites of LPs, which can be employed as frustrated Lewis pairs (FLPs), interacting LPs (ILPs), or classical Lewis adducts (CLAs), to effect cooperative monomer activation as well as chain initiation, propagation, termination, and transfer events. Through balancing the Lewis acidity, Lewis basicity, and steric effects of LPs, LPP has shown several unique advantages or intriguing opportunities compared to other polymerization techniques and demonstrated its broad polar monomer scope, high activity, control or livingness, and complete chemo- or regioselectivity, as well as its unique application in materials chemistry. These advances made in LPP are comprehensively reviewed, with the scope of monomers focusing on heteroatom-containing polar monomers, while the polymerizations mediated by main-group LAs and LBs separately that are most relevant to the LPP are also highlighted or updated. Examples of applying the principles of the LPP and LP chemistry as a new platform for advancing materials chemistry are highlighted, and currently unmet challenges in the field of the LPP, and thus the suggested corresponding future research directions, are also presented.

Silyl Ketene Acetals/B(C₆F₅)₃ Lewis Pair-Catalyzed Living Group Transfer Polymerization of Renewable Cyclic Acrylic Monomers

This work reveals the silyl ketene acetal (SKA)/B(C₆F₅)₃ Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in situ NMR monitored reaction of SKA with B(C₆F₅)₃ indicated the formation of Frustrated Lewis Pairs (FLPs), although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C₆F₅)₃-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C₆F₅)₃-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C₆F₅)₃ is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). Moreover, using this method, we have successfully synthesized well-defined PMMBL-b-PMBL, PMMBL-b-PMBL-b-PMMBL and random copolymers with the predicated molecular weights (Mn) and narrow molecular weight distribution (MWD).

Synthesis of block copolymers using end-functionalized polyacetylenes as macroinitiators

A block copolymer consisting of helically twisted polyacetylene and α-helical peptide was successfully synthesized for the first time.

Organocatalyzed Group Transfer Polymerization

In contrast to the conventional group transfer polymerization (GTP) using a catalyst of either an anionic nucleophile or a transition-metal compound, the organocatalyzed GTP has to a great extent improved the living characteristics of the polymerization from the viewpoints of synthesizing structurally well-defined acrylic polymers and constructing defect-free polymer architectures. In this article, we describe the organocatalyzed GTP from a relatively personal perspective to provide our colleagues with a perspicuous and systematic overview on its recent progress as well as a reply to the curiosity of how excellently the organocatalysts have performed in this field. The stated perspectives of this review mainly cover five aspects, in terms of the assessment of the livingness of the polymerization, limit and scope of applicable monomers, mechanistic studies, control of the polymer structure, and a new GTP methodology involving the use of tris(pentafluorophenyl)borane and hydrosilane.

Organopolymerization of naturally occurring Tulipalin B: a hydroxyl-functionalized methylene butyrolactone

Naturally occurring, OH-containing, tri-functional Tulipalin B has been successfully polymerized by N-heterocyclic carbene and phosphazene superbase catalysts into polymers with M_n up to 13.2 kg mol⁻¹.

Synthesis of AB block and A2B2 and A3B3 miktoarm star-shaped copolymers using ω-end-functionalized poly(methyl methacrylate) with a hydroxyl group prepared by organocatalyzed group transfer polymerization

The metal-free synthesis of an AB block copolymer, and A₂B₂ and A₃B₃ type miktoarm star-shaped copolymers consisting of PMMA and PDLA arms was achieved.

Facile synthesis and comparative study of poly(l-lactide) with linear-comb and star-comb architecture

The crystallization ability of PLLA with different chain structures.

Synthesis of end-functionalized poly(methyl methacrylate) by organocatalyzed group transfer polymerization using functional silyl ketene acetals and α-phenylacrylates

The α and ω-end-functionalization of PMMA by organocatalyzed GTP was achieved using functional silyl ketene acetals and α-phenylacrylates.

Organic acids as efficient catalysts for group transfer polymerization of N,N-disubstituted acrylamide with silyl ketene acetal: polymerization mechanism and synthesis of diblock copolymers

The GTP of N,N-disubstituted acrylamide using organic acid and silyl ketene acetal was intensively investigated.

B(C6F5)3-catalyzed group transfer polymerization of alkyl methacrylates with dimethylphenylsilane through in situ formation of silyl ketene acetal by B(C6F5)3-catalyzed 1,4-hydrosilylation of methacrylate monomer

The B(C₆F₅)₃-catalyzed GTP of alkyl methacrylates using hydrosilane has been studied in this study.

Engineering exceptionally strong oxygen superbases with 1,8-diazanaphthalene di-N-oxides

1,8-Diazanaphthalene di-N-oxides show extraordinary oxygen basicity, being almost entirely a consequence of a large strain-induced destabilization in neutral forms.