Anionic polymerization of MMA and renewable methylene butyrolactones by resorbable potassium salts

Three resorbable potassium salts of hydride (K[H]), enolate Me₂C?C(OⁱPr)OK (K[E]), and allyl K[1,3‐(SiMe₃)₂C₃H₃] (K[A]) have been investigated for controlled anionic polymerization of methyl methacrylate (MMA) and its cyclic analogs, naturally renewable methylene butyrolactones including α‐methylene‐γ‐butyrolactone (MBL) and γ‐methyl‐α‐methylene‐γ‐butyrolactone (MMBL). When used alone at ambient temperature in toluene, these salts exhibit no (K[H]) to low (K[A]) to modest (K[E]) polymerization activity. Mixing of K[H] and Al(C₆F₅)₃ leads to the formation of an “ate” complex, K⁺[HAl(C₆F₅)₃]^?, which has been structurally characterized by X‐ray diffraction; this complex has a high polymerization activity producing atactic PMMA, but addition of another equiv of Al(C₆F₅)₃ further enhances both the rate and the efficiency of the polymerization, now producing syndiotactic PMMA with a narrow molecular weight (MW) distribution of 1.04. The K[H]/2Al(C₆F₅)₃ system also exhibits high activity for polymerization of (M)MBL. In sharp contrast, addition of Al(C₆F₅)₃ to K[A] shuts down the polymerization at various temperatures. The most active, controlled, and syndioselective polymerization system in this series is K[E]/2Al(C₆F₅)₃. Accordingly, the polymerization control and kinetics of this most effective system have been examined in more detail. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chain transfer to aluminium in MAO-activated metallocene-catalyzed polymerization reactions

Chemical trapping of metal-bound oligomeric chains during the MAO-activated, metallocene-catalyzed polymerization of ethylene identify the two observed chain-bearing species to be alkylzirconocenium species and higher alkyl aluminiums, consistent with a proposed mechanism.     

ansa-Rare-earth-metal catalysts for rapid and stereoselective polymerization of renewable methylene methylbutyrolactones

Two ansa-half-sandwich rare-earth-metal (REM) dialkyl complexes supported by an ethylene-bridged fluorenyl (Flu)-N-heterocyclic carbene (NHC) ligand, [M{C(2)H(4)(η(5)-Flu-κ(1)-NHC)}(CH(2)SiMe(3))(2)] (M=Y, 1; Lu, 2), and a chiral ansa-sandwich samarocene incorporating a C(2) ligand, [Sm(η(5)-C(12)H(8))(2)(thf)(2)] (3), have been investigated for the coordination-addition polymerization of renewable methylene butyrolactones, α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone ((γ)MMBL). Both ansa-half-sandwich complexes 1 and 2 exhibit exceptional activity for the polymerization of (γ)MMBL at room temperature in dimethylformamide (DMF); with a 0.25 mol% catalyst loading, quantitative monomer conversion can be achieved under 1 min, giving a high turn-over frequency (TOF) of 24,000 h(-1). This TOF value represents a rate enhancement, by a factor of 8, 22, or 2400, over the polymerizations by unbridged samarocene [Sm(Cp*)(2)(thf)(2)] (Cp*=η(5) -pentamethylcyclopentadienyl), by bridged ansa-samarocene 3 with C(2) ligation, or by the corresponding REM trialkyls without the ansa-Flu-NHC ligation, respectively. Complexes 1 and 2 are also highly active for the polymerization of β-methyl-α-methylene-γ-butyrolactone ((β)MMBL), realizing the first example of the metal-mediated coordination polymerization of this monomer and its copolymerization with (γ)MMBL. More remarkably, the resulting P(β)MMBL homopolymer is highly stereoregular (91% mm) and exhibits a high T(g) of 290 °C. In sharp contrast, catalysts 1 and 2 have poor activity and efficiency in the polymerization of the parent MBL or the acyclic analog methyl methacrylate. Polymerization and kinetic studies using the most active catalyst (1) of the series have uncovered characteristics of its (γ)MMBL polymerization and yielded a unimolecular propagation mechanism. A surprising chain-initiation pathway for the polymerization in DMF by 1 has been revealed, and catalytic polymerization in the presence of an organoacid has also been examined.     

Review: Lanthanide coordination chemistry: from old concepts to coordination polymers

Because of their remarkable and unmatched optical and magnetic properties, the lanthanides are under the limelight when it comes to high technology. These elements are used in strategic applications such as optical glasses and lasers, telecommunications, lighting and displays, magnetic materials, hard-disk drives, security inks and counterfeiting tags, catalysis, biosciences, and medicine, to name but a few. Long considered as minor actors in transition metal chemistry, they have now gained respect from coordination chemists who insert them into sophisticated functional and polyfunctional molecules and materials. This mini review focuses on trivalent lanthanide ions and first summarizes their basic properties. Then some classical aspects of their coordination chemistry are discussed, followed by macrocyclic chemistry, supramolecular chemistry, and self-assembly processes. The last part of this contribution deals with coordination polymers and hybrid materials including potential applications.     

Controlled polymerization of an AB2 monomer using a chloromethylarene as comonomer: branched polymers from activated methylene compounds

Hyperbranched and branched polymers were synthesized by one-pot reaction of the AB₂ monomer 4-(4′-chloromethylbenzyloxy)phenylacetonitrile (1 ). The polymerization of 1 was controlled by adding a chloromethylarene (A₁ comonomer) such as methoxybenzyl chloride and by adding TBAC (tetrabutylammonium chloride). Copolymerization of 1 with A₂ comonomers, bis(chloromethyl)arenes, gives the corresponding copolymers.     

Stereoselectivity of the cyclooctene ring-opening polymerization

The stereoselectivity of the cyclooctene ring-opening polymerization in the presence of the tungsten hexachloride–tetraisobutylalumoxane (TBAO) catalyst system has been studied. The reaction conditions have been established in which the polymer chain isomerization is reduced to a minimum. Under these conditions the stereoselectivity is determined by an individual act of the monomer molecule insertion. The dependence of stereoselectivity on monomer concentration, number of active sites, and temperature has been investigated. The results obtained suggest that the cyclooctene polymerization is selective in favor of the geometrical configuration of the starting cycloolefin (the “retention” effect) by analogy with the previously reported metathesis of acyclic olefins. Considerations which support the idea that cis and trans units are reproduced by the same type of active sites are discussed. The experimental evidence indicates that in this case the stereoselectivity is determined by the difference in kinetics of two reaction paths of the monomer molecule insertion that lead to the formation of cis and trans units.     

From coordination complexes to coordination polymers through self-assembly

Metal ion coordination in metallo-supramolecular assemblies offers the opportunity to fabricate and study devices and materials that are equally important for fundamental research and new technologies. Metal ions embedded in a specific ligand field offer diverse thermodynamic, kinetic, chemical, physical and structural properties that make these systems promising candidates for active components in functional materials. In particular, dynamic coordination polymers offer exciting opportunities to provide materials with responsive properties. In addition, this approach allows to incorporate the well known properties of metal complexes in polymeric architectures. This review highlights the improvements and the possible applications based on metallo-supramolecular systems with an emphasis on materials science. Examples for new materials such as molecular magnets, coordination polymers as carrier package as well as molecular electronics are featured in this article.     

Synthesis of methylene butyrolactone polymers from itaconic acid

Herein, we report the transformation of β‐monomethyl itaconate, an inexpensive and biorenewable alternative to petroleum feedstocks, to the high‐value monomer α‐methylene‐γ,γ‐dimethyl‐γ‐butyrolactone (Me₂MBL) through a selective addition strategy. This strategy is also applied to the synthesis of α‐methylene‐γ‐butyrolactone (MBL, tulipalin A), a monomer that can be polymerized to give materials with desirable properties (high decomposition temperature, glass transition temperature, and refractive index). Subsequent polymerization of both Me₂MBL and MBL through reversible addition‐fragmentation chain‐transfer polymerization generates well‐defined poly(Me₂MBL) and poly(MBL) (PMBL). Physical characterization of poly(Me₂MBL) shows good physical properties comparable with known PMBL materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2730–2737     

Dinuclear silylium-enolate bifunctional active species: remarkable activity and stereoselectivity toward polymerization of methacrylate and renewable methylene butyrolactone monomers

Novel dinuclear silylium-enolate active species, consisting of an electrophilic silylium catalyst site and a nucleophilic silicon enolate initiating site that are covalently linked as single molecules, and their unique polymerization characteristics and kinetics are reported. Such unimolecular, bifunctional propagating species are conveniently generated from activation of ethyl- and oxo-bridged disilicon enolate (i.e., disilyl ketene acetal, di-SKA) compounds with [Ph(3)C][B(C(6)F(5))(4)]. Both the ethyl- and oxo-bridged dinuclear species are much more active for the polymerization of methyl methacrylate (MMA) than the mononuclear SKA-based active species, exhibiting an approximate rate enhancement by a factor of 12 and 44, respectively. The oxo-bridged silylium-enolate species is considerably more active and controlled than the ethyl-bridged one, with their differences being even more pronounced in polymerizing a renewable monomer, γ-methyl-α-methylene-γ-butyrolactone. The polymerization by the oxo-bridged silylium-enolate active species follows first-order kinetics in both monomer and silylium catalyst concentrations, indicating a unimolecular propagation mechanism which involves an intramolecular delivery of the polymeric enolate nucleophile to the monomer activated by the silylium ion electrophile being placed in proximity in the same catalyst molecule. Highly stereoregular poly(methyl methacrylate) (PMMA), with a syndiotacticity up to 92% rr, can be produced in quantitative yield using the oxo-bridged propagator at low temperature.     

Supramolecular polymerization from polypeptide-grafted comb polymers

The helical and tubular structures self-assembled from proteins have inspired scientists to design synthetic building blocks that can be "polymerized" into supramolecular polymers through coordinated noncovalent interactions. However, cooperative supramolecular polymerization from large, synthetic macromolecules remains a challenge because of the difficulty of controlling the structure and interactions of macromolecular monomers. Herein we report the synthesis of polypeptide-grafted comb polymers and the use of their tunable secondary interactions in solution to achieve controlled supramolecular polymerization. The resulting tubular supramolecular structures, with external diameters of hundreds of nanometers and lengths of tens of micrometers, are stable and resemble to some extent biological superstructures assembled from proteins. This study shows that highly specific intermolecular interactions between macromolecular monomers can enable the cooperative growth of supramolecular polymers. The general applicability of this strategy was demonstrated by carrying out supramolecular polymerization from gold nanoparticles grafted with the same polypeptides on the surface.     

Novel triazole-bridged cadmium coordination polymers varying from zero- to three-dimensionality

Cadmium salts with different triazole ligands have led to a series of novel triazole-cadmium compounds varying from zero- to three-dimensionality. [Cd(2)(deatrz)(2)(H(2)O)Br(4)] (1) (deatrz = 3,5-diethyl-4-amino-1,2,4-triazole) is a zero-dimensional complex which uses a triazole ligand together with micro-OH(2) as bridges to form a 1D chain via hydrogen-bonding contacts. [[Cd(3)(deatrz)(2)Cl(6)(H(2)O)(2)].2H(2)O](n) (2), [[Cd(dmtrz)Cl(2)].1.5H(2)O](n)(3) (dmtrz = 3,5-dimethyl-1,2,4-triazole), and [[Cd(3)(deatrz)(4)Cl(2)(SCN)(4)].2H(2)O](n)(4) are polymeric 1D chains. 2 and 4 were constructed via trinuclear cadmium units bridged by triazole ligands and chloride atoms, while 3 consists of micro(2)-Cl, micro(3)-Cl, and triazole bridges, cross-linked by hydrogen bonding to give a 3D framework. [[Cd(3)(dmatrz)(4)(SCN)(6)]](n)(5) (dmatrz = 3,5-dimethyl-4-amino-1,2,4-triazole) shows a two-dimensional structure whose fundamental units are trinuclear metal cations bridged via triazole ligands. The complex [[Cd(dmtrz)(SCN)(2)]](n)(6) is the first three-dimensional example in N1,N2-didentate-bridged triazole-metal compounds. Six complexes exhibit six types of bridging modes of N1,N2-triazole in combination with single-atom bridges. 2, 4, and 5 are the unprecedented examples of polymeric chains and planes constructed via trinuclear metal ion clusters, whereas 3 is the first example of the micro(3)-Cl bridging mode in triazole-metal complexes. We have briefly discussed the variety of dimensionalities based on the tuning of different organic ligands and anions.     

Bio-based benzoxazine from renewable L-tyrosine: Synthesis,polymerization, and properties

Developing thermosets derived from renewable sources is of great importance. In this work, a fully bio-based benzoxazine monomer, 3,6-bis((3-(furan-2-ylmethyl)-3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)methyl)piperazine-2,5-dione (TCDPF), is conveniently synthesized from L-tyrosine cyclic dipeptide (TCDP), furfurylamine and paraformaldehyde. The chemical structure of TCDPF is confirmed by nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy (FT-IR) techniques. The curing behavior of TCDPF is investigated by differential scanning calorimetry and in situ FT-IR techniques. After temperature-programmed curing, the thermomechanical property and thermal stability of the resulting TCDPF polymer (PTCDPF) are evaluated by dynamic mechanical analysis and thermogravimetric analysis techniques, respectively. It is found that PTCDPF have excellent comprehensive performance such as high glass transition temperature (T_g = 322 °C), high thermal degradation temperature (T_5% = 342 °C, T_10% = 395 °C in N₂ atmosphere), and high char yield (CY = 51.3% at 800 °C in N₂ atmosphere). The results demonstrate that L-tyrosine is a promising bio-based raw material for preparing high performance polybenzoxazines.     

Networking of calixcrowns: from heteronuclear endo/exocyclic coordination polymers to a photoluminescence switch

Solvato-PL switching and shrinking-and-opening process: we present two CuI coordination polymers of calix[4]-bis-monothiacrown (L) obtained in the absence (1) and presence (2) of KI. The structures show not only very unusual CuI-based network arrangements but also unique reversible photolunimescence switching behavior induced by removal of coordinated solvent. Furthermore, upon inclusion of K+ ions the crown ring shrinks leading to "opening" of opposite aromatic rings in the host calixarene unit, rare behavior for this class of compound.     

Engineering with metallo-supramolecular polymers: linear coordination polymers and networks

Here we demonstrate the synthesis of telechelics with different spacer units and different numbers of metal-complexing units, like α-methoxy-ω-(2,2′:6′,2″-terpyrid-4′-yl)-poly(ethylenoxide)₇₈ ( 1 ), bis(2,2′:6′,2″-terpyrid-4′-yl) di(ethylene glycol) ( 2 ), bis(2,2′:6′,2″-terpyrid-4′-yl)-poly(ethylene oxide)₁₈₀ ( 3 ) and tris[(2,2′:6′,2″-terpyrid-4′-yl)-oligo (ethylenoxy-)_3.33]glycerin ( 4 ) utilizing 4-chloro-2,2′:6′,2″-terpyridine. The complexation behaviour of a variety of metal-salts towards the telechelics was studied and different supramolecular architectures were investigated, such as symmetric polymeric complexes and linear coordination polymers. Furthermore, attempts have been undertaken to prepare metallo-supramolecular cross-linked systems.     

C2-symmetric ansa-metallocene catalysts for propene polymerization: Stereoselectivity and enantioselectivity

Important similarities between the new homogeneous catalysts for 1-alkene polymerization based on C₂-symmetric ansa-metallocenes of the 4th column and their heterogeneous Ziegler–Natta predecessors are unquestionable; in particular, the factors leading to the remarkable enantioselectivity of both catalyst classes have been proved to be strictly analogous. In the case of metallocene catalysts, however, an insidious side reaction of chain epimerization, unnoticed for a relatively long time, can undermine the stereoselectivity of the polymerization process; this recent finding and its mechanistic implications are discussed in the present paper.