Living Group Transfer Polymerization of Renewable α-Methylene-γ-butyrolactones Using Al(C6F5)3 Catalyst

An Arbitrarily Regulated Monomer Sequence in Multi-Block Copolymer Synthesis by Frustrated Lewis Pairs

Rapid access to sequence-controlled multi-block copolymers (multi-BCPs) remains as a challenging task in the polymer synthesis. Here we employ a Lewis pair (LP) composed of organophosphorus superbase and bulky organoaluminum to effectively copolymerize the mixture of methacrylate, cyclic acrylate, and two acrylates, into well-defined di-, tri-, tetra- and even a hepta-BCP in one-pot one-step manner. The combined livingness, dual-initiation and CSC feature of Lewis pair polymerization enable us to achieve not only a trihexaconta-BCP with the highest record in 8 steps by using four-component monomer mixture as building blocks, but also the arbitrarily-regulated monomer sequence in multi-BCP, simply by changing the composition and adding order of the monomer mixtures, thus demonstrating the powerful capability of our strategy in improving the efficiency and enriching the composition of multi-BCP synthesis.

Zinc-Mediated Allylation-Lactonization One-Pot Reaction to Methylene Butyrolactones: Renewable Monomers for Sustainable Acrylic Polymers with Closed-Loop Recyclability

Despite biomass-derived methylene butyrolactone monomers having great potential in substituting the petroleum-based methacrylates for synthesizing the sustainable acrylic polymers, the possible industrial production of these cyclic monomers is unfortunately not practical due to moderate overall yields and harsh reaction conditions or a time-consuming multistep process. Here we report a convenient and effective synthetic approach to a series of biomass-derived methylene butyrolactone monomers via a zinc-mediated allylation-lactonization one-pot reaction of biorenewable aldehydes with ethyl 2-(bromomethyl)acrylate. Under simple room-temperature sonication conditions, near-quantitative conversions (>90%) can be accomplished within 5-30 min, providing pure products with high isolated yields of 70-80%. Their efficient polymerizations with a high degree of control and complete chemoselectivity were enabled by the judiciously chosen Lewis pair catalyst based on methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) [MeAl(BHT)₂] Lewis acid and 3-diisopropyl-4,5-dimethylimidazol-2-ylidene (I ⁱ Pr) Lewis base, affording new poly(methylene butyrolactone)s with high thermal stability and thermal properties tuned in a wide range as well as pendant vinyl groups for postfunctionalization. Through the development of an effective depolymerization setup (370-390 °C, ca. 100 mTorr, 1 h, a muffle furnace), thermal depolymerizations of these polymers have been achieved with monomer recovery up to 99.8%, thus successfully constructing sustainable acrylic polymers with closed-loop recyclability.

Sustainable Approach for Synthesis and Completely Recycle of Cyclic CO2-based Polycarbonates

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics. Polycarbonates derived from the copolymerization of CO₂ and epoxides have attracted much attention since they can enable CO₂-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO₂-based polycarbonates have been reported and typically degraded to cyclic carbonates. Here we synthesize a homogeneous dinuclear methyl zinc catalyst ((BDI-ZnMe)₂, 1) to rapidly copolymerize meso-CHO and CO₂ into poly(cyclohexene carbonate) (PCHC) with an unprecedentedly cyclic structure. Moreover, in the presence of trace amounts of water, a heterogeneous multi-nuclear zinc catalyst ((BDI-(ZnMe₂·xH₂O))_n, 2) is prepared and shows up to 99% selectivity towards the degradation of PCHC back to meso-CHO and CO₂. This strategy not only achieves the first case of cyclic CO₂-based polycarbonate but also realizes the complete chemical recycling of PCHC back to its monomers, representing closed-loop recycling of CO₂-based polycarbonates.

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics.

Dual-initiating and living frustrated Lewis pairs: expeditious synthesis of biobased thermoplastic elastomers

Biobased poly(γ-methyl-α-methylene-γ-butyrolactone) (PMMBL), an acrylic polymer bearing a cyclic lactone ring, has attracted increasing interest because it not only is biorenewable but also exhibits superior properties to petroleum-based linear analog poly(methyl methacrylate) (PMMA). However, such property enhancement has been limited to resistance to heat and solvent, and mechanically both types of polymers are equally brittle. Here we report the expeditious synthesis of well-defined PMMBL-based ABA tri-block copolymers (tri-BCPs)-enabled by dual-initiating and living frustrated Lewis pairs (FLPs)-which are thermoplastic elastomers showing much superior mechanical properties, especially at high working temperatures (80-130 °C), to those of PMMA-based tri-BCPs. The FLPs consist of a bulky organoaluminum Lewis acid and a series of newly designed bis(imino)phosphine superbases bridged by an alkyl linker, which promote living polymerization of MMBL. Uniquely, such bisphosphine superbases initiate the chain growth from both P-sites concurrently, enabling the accelerated synthesis of tri-BCPs in a one-pot, two-step procedure. The results from mechanistic studies, including the single crystal structure of the dually initiated active species, detailed polymerizations, and kinetic studies confirm the livingness of the polymerization and support the proposed polymerization mechanism featuring the dual initiation and subsequent chain growth from both P-sites of the superbase di-initiator.

Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts

The history of silyl cations has all the makings of a drama but with a happy ending. Being considered reactive intermediates impossible to isolate in the condensed phase for decades, their actual characterization in solution and later in solid state did only fuel the discussion about their existence and initially created a lot of controversy. This perception has completely changed today, and silyl cations and their donor-stabilized congeners are now widely accepted compounds with promising use in synthetic chemistry. This review provides a comprehensive summary of the fundamental facts and principles of the chemistry of silyl cations, including reliable ways of their preparation as well as their physical and chemical properties. The striking features of silyl cations are their enormous electrophilicity and as such reactivity as super Lewis acids as well as fluorophilicity. Known applications rely on silyl cations as reactants, stoichiometric reagents, and promoters where the reaction success is based on their steady regeneration over the course of the reaction. Silyl cations can even be discrete catalysts, thereby opening the next chapter of their way into the toolbox of synthetic methodology.

Living polymerization of naturally renewable butyrolactone-based vinylidenes mediated by a frustrated Lewis pair

The frustrated Lewis pair composed of an organophosphorus(iii) superbase and a bulky organoaluminum Lewis acid promoted the living/controlled polymerization of naturally renewable butyrolactone-based vinylidenes.

Synthesis and Reactivity of Fluorinated Triaryl Aluminum Complexes

The addition of the Grignard 3,4,5-Ar^FMgBr to aluminum(III) chloride in ether generates the novel triarylalane Al(3,4,5-Ar^F)₃·OEt₂. Attempts to synthesize this alane via transmetalation from the parent borane with trimethylaluminum gave a dimeric structure with bridging methyl groups, a product of partial transmetalation. On the other hand, the novel alane Al(2,3,4-Ar^F)₃ was synthesized from the parent borane and trimethylaluminum. Interestingly, the solid-state structure of Al(2,3,4-Ar^F)₃ shows an extended chain structure resulting from neighboring Al···F contacts. Al(3,4,5-Ar^F)₃·OEt₂ was then found to be an effective catalyst for the hydroboration of carbonyls, imines, and alkynes with pinacolborane.

The addition of the Grignard 3,4,5-Ar^FMgBr to aluminum(III) chloride in ether generates the novel triarylalane Al(3,4,5-Ar^F)₃·OEt₂. Attempts to synthesize this alane via transmetalation from the parent borane with trimethylaluminum gave a dimeric structure with bridging methyl groups; a product of partial transmetalation. On the other hand, the novel alane Al(2,3,4-Ar^F)₃ was synthesized from the parent borane and trimethylaluminum. Al(3,4,5-Ar^F)₃·OEt₂ was then found to be an effective catalyst for the hydroboration of carbonyls, imines and alkynes with pinacolborane.

MPV reduction of ethyl levulinate to γ-valerolactone by the biomass-derived chitosan-supported Zr catalyst

Biomass-derived chitosan-supported Zr catalyst with dual acid–base properties exhibits highly efficient performance towards MPV reduction of ethyl levulinate to γ-valerolactone.

High chemical recyclability of vinyl lactone acrylic bioplastics

Biomass-derived vinyl lactone acrylic bioplastics not only exhibit higher thermostability but also depolymerize more selectively to monomers with higher yield and purity compared to their petroleum-based vinyl ester acrylic counterpart.

Lewis pairs polymerization of polar vinyl monomers

The globally increasing demands for polymer materials stimulate the significantly intense attention focused on the Lewis pair polymerization (LPP) of various polar vinyl monomers catalyzed by Lewis pairs (LPs) composed of Lewis acid (LA) and Lewis base (LB). According to the degree of interaction between LA and LB, LPs could be divided into classical Lewis adduct (CLA), interacting Lewis pair (ILP) and frustrated Lewis pair (FLP). Regulation of the Lewis basicity, Lewis acidity, and steric effects of these LPs has a significant impact on the polymer chain initiation, propagation and termination as well as chain transfer reaction during polymerization. Compared with other polymerization strategies, LPP has shown several unique advantages towards the polymerization of polar vinyl monomers such as high activity, control or livingness, mild conditions, and complete chemo- or regioselectivity. We will comprehensively review the recent advances achieved in the LPP of polar vinyl monomers according to the classification of the employed LPs based on different LAs, by highlighting the key polymerization results, polymerization mechanisms as well as the currently unmet challenges and the future research directions of LPP chemistry.

Chemoselective and living/controlled polymerization of polar divinyl monomers by N-heterocyclic olefin based classical and frustrated Lewis pairs

Chemoselective and living/controlled polymerization of polar divinyl monomers by N-heterocyclic olefin based classical and frustrated Lewis pairs.

Living polymerization of acrylamides catalysed by N-heterocyclic olefin-based Lewis pairs

Living/controlled polymerization of acrylamides achieved by a Lewis pair composed of an N-heterocyclic olefin as a Lewis base and triphenylaluminum as a Lewis acid.

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.