Ultra‐High‐Molecular‐Weight Polymers Produced by the Immortal Phosphine‐Based Catalyst System

Bai, Yun; He, Julong; Zhang, Yuetao

doi:10.1002/anie.201811946

Cited by 83 publications

(63 citation statements)

References 76 publications

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“…Forreaction conditions, see Table 1, entries 3-5. Lewis pair polymerization (LPP), [33,34] as recently reviewed by Chen, [35] for which also NHO-derived examples exist. [36,37] Hence,atriple role is proposed for Mg(HMDS) 2 .F irstly, activation of the epoxide enables zwitterion formation and efficient propagation.…”

Section: Angewandte Chemiementioning

confidence: 99%

Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers

2019

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Ad ual catalytic setup based on N-heterocyclic olefins (NHOs) and magnesium bis(hexamethyldisilazide) (Mg(HMDS) 2 )w as used to prepare poly(propylene oxide) with amolar mass (M n ) > 500 000 gmol À1 ,insome cases even > 10 6 gmol À1 ,a sd etermined by GPC/light scattering.T his is achieved by combining the rapid polymerization characteristics of az witterionic,L ewis pair type mechanism with the efficient epoxidea ctivation by the Mg II species.T ransfer-tomonomer,t raditionally frustrating attempts at synthesizing polyethers with ahigh degree of polymerization, is practically removed as al imiting factor by this approach.N MR and MALDI-ToF MS experiments reveal key aspects of the proposed mechanism, wherebyt he polymerization is initiated via nucleophilic attackbythe NHO on the activated monomer, generating az witterionic species.T his strategy can also be extended to other epoxides,i ncluding functionalized monomers.Itremains am ajor challenge to prepare high-molar-mass polyethers via ring-opening polymerization (ROP) of substituted epoxides such as propylene oxide (PO). [1] Transfer reactions (Scheme 1) pose the main difficulty in this context, most blatantly so for simple metal alkoxide catalysts. [2] Here, the anionic polymerization is not only impractically slow,but molecular weights are also severely capped (typically < 10 000 gmol À1 )a nd control over the end groups is limited. Application of crown ethers or phosphazene-type bases accelerates the reaction, but this still entails significant or even increased transfer rates. [3,4] In this regard, the application of organocatalysts was as ignificant improvement;e mployment of N-heterocyclic carbenes (NHCs) as demonstrated by Taton [5] and, later,ofN-heterocyclic olefins (NHOs) by some of us [6,7] enabled the well-controlled preparation of poly-(propylene oxide) (PPO) with designed end groups and highly defined molecular weight distribution (down to M 1.03). [7] While convenient as well as metal-and solvent-free,t hese methods still displayed limitations;P PO with M n > 12.000 gmol À1 was not reported in these cases.P erhaps tellingly,t he few studies describing the preparation of truly high-molecular-weight PPO resort to dual catalytic,c ooperative setups.E legant work by Carlotti, Deffieux, [8,9] and Coates [10] can be understood as early examples for this concept (M n up to 150 000 gmol À1 ). Very recently ad ual catalytic approach using phosphazenes and triethylborane was used to prepare PPO with M n up to 200 000 gmol À1 . [11,12] In the following,i tw ill be detailed how zwitterionic polymerization, am echanism well established in organopolymerization chemistry, [13][14][15][16] and the monomer-activating Lewis acidity of Mg II combine to provide apowerful tool for the generation of polyethers with exceptionally high molecular weight.NHOs (Scheme 1), which are identical to the so-called deoxy-Breslow intermediates frequently encountered in NHC catalysis, [17] possess an electron-rich, polar olefinic bond. [18][19][20] Them esomeric structure suggests...

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Section: Angewandte Chemiementioning

confidence: 99%

Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers

2019

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“…Considering the high activity, control and livingness feature of LPP, we envisioned the LPP should enable us to synthesize ultrahigh molecular weight (UHMW) polymer. In 2018, we synthesized a series of strong organophosphorus superbase, imidazolin-2ylidenamino substituted phosphines (IAPs), and employed them to combine with different organoaluminum LAs for polymerization of MMA at room temperature [64]. Among the examined LPs, (BHT) Al i Bu 2 /IAP3 exhibited the best polymerization performance, achieving near quantitative monomer conversion at high polymerization rate for all polymerizations with MMA to IAP3 ratio ranging from 400 to 20,000 and furnishing PMMA with medium to UHMW (M n up to 1,927 kg/mol) and narrow MWD (Ð < 1.10).…”

Section: Al-based Lpsmentioning

confidence: 99%

Lewis pairs polymerization of polar vinyl monomers

Zhao

Zhang

2019

Science Bulletin

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“…18 However, most studies reported the vinyl-addition polymerization (VAP) of MBL through Michael-type addition across the exocyclic double bond to produce P(MBL)VAP (Scheme 1a, pathway a), which is not fully degradable or recyclable. [18][19][20][21][22][23] The selective ROP of MBL to produce recyclable polyesters is even more challenging compared to the ROP of γBL due to the competing polymerization between the highly reactive exocyclic double bond and the low-strained five membered lactone ring. To the best of our knowledge, the only selective ROP of MBL was exemplified by Chen et al by utilizing La[N(SiMe3)2]3 or yttrium based catalysts.…”

Section: Introductionmentioning

confidence: 99%

Chemoselective Ring-Opening Polymerization of Bio-Renewable α-Methylene-γ-Butyrolactone via an Organophosphazene/urea Binary Synergistic Catalytic System Toward a Sustainable Polyester

Shen

Xiong²,

Y³

et al. 2020

Preprint

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Despite the great potential of bio-renewable a-methylene-<a></a><a></a><a>g-butyrolactone</a> (MBL) to produce functional recyclable polyester, the ring-opening polymerization (ROP) of MBL remains as a challenge due to the competing polymerization of the highly reactive exocyclic double bond and the low strained five membered ring. In this contribution, we present the first organocatalytic chemoselective ROP of MBL to exclusively produce recyclable unsaturated polyester by utilizing a phosphazene base/urea binary catalyst. We show that delicate chemoselectivity can be realized by controlling the temperature and using selected urea catalysts. Experimental and theoretical calculations provide mechanistic insights and indicate that the kinetically controlled ROP pathway is favored by using urea with stronger acidity at low temperatures.

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Ultra‐High‐Molecular‐Weight Polymers Produced by the Immortal Phosphine‐Based Catalyst System

Cited by 83 publications

References 76 publications

Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers

Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers

Lewis pairs polymerization of polar vinyl monomers

Chemoselective Ring-Opening Polymerization of Bio-Renewable α-Methylene-γ-Butyrolactone via an Organophosphazene/urea Binary Synergistic Catalytic System Toward a Sustainable Polyester

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