Showing papers on "Ionic polymerization published in 2018"

Homoleptic Rare-Earth Aryloxide Based Lewis Pairs for Polymerization of Conjugated Polar Alkenes

Abstract: An efficient Lewis pair polymerization of conjugated polar alkenes utilizing simple, homoleptic rare-earth aryloxides with a combination of phosphines and N-heterocyclic carbenes was developed. The polymerizations were found to be active for Lewis acids across the full range of rare-earth metals, and the catalytic activities were observed to be dependent on the ionic radii of the rare-earth metals and the steric and electronic profiles of the Lewis bases. For the methyl methacrylate polymerization, a syndiotactic polymer was produced with an rr value of up to 85%. This rare-earth Lewis pair polymerization system was also found to be effective on more challenging acrylates and acrylamide monomers, such as tert-butyl methacrylate, furfuryl methacrylate, and N,N-dimethylacrylamide. In the case of furfuryl methacrylate, the polymerization proceeded in a controlled manner with a high initiation efficiency. FLP-type addition was confirmed as the initiating step by stoichiometric reactions producing the zwitteri...

Electro-Controlled Living Cationic Polymerization.

Abstract: Cationic polymerizations have long been industrialized; however, stimulus-regulated cationic polymerization remains to be developed. An electrochemically controlled living cationic polymerization is presented for the first time. In the presence of external potential and organic-based electrocatalyst, a series of monomers can be polymerized under a cationic chain-transfer mechanism. The resulting polymers exhibit well-defined molecular mass, narrow dispersity, and good chain-end fidelity. By controlling the external potential to switch the electrocatalyst between its oxidized and reduced states, ON/OFF polymerization can be achieved. This method is a versatile way to a large range of monomers, including vinyl ether-type and p-substituted styrene-type monomers. Given the sustainability feature and broad interest of electrochemical synthetic techniques, we envisaged that this method would lead a new direction of external regulated living ionic polymerization.

Iron-based electrochemically mediated atom transfer radical polymerization with tunable catalytic activity

Abstract: An iron-based electrochemically mediated atom transfer radical polymerization (eATRP) system with tunable catalytic activity was developed by adjusting the supporting electrolyte formula. Kinetic behaviors of the systems using four typical supporting electrolytes (namely, TBABr, TBAPF6, TBACl and TBABF4) were investigated. The type of anions was found to significantly affect the polymerization kinetics. TBAPF6 system proceeded with a considerable polymerization rate, whereas TBABr system showed better controllability. Importantly, the effect of supporting electrolyte on eATRP kinetics (mainly on ATRP equilibrium) was confirmed through kinetic modeling. Furthermore, the effect of catalyst loading using TBAPF6 as supporting electrolyte was also studied, and the results showed an uncontrolled polymerization for catalyst loading lower than 500 ppm. When hybrid supporting electrolyte (TBAPF6/TBABr) was used to tune catalytic activity, the polymerization slows down and the dispersity decreases with the increase in TBABr ratio. Polymers with a narrow molecular weight distribution (dispersity index<1.5) were obtained using 100% TBABr under 100 ppm catalyst. Besides, experimental attempt to improve the controllability by adding halogen donors was made, whereas the halogen donors just prolonged the induction period and no improvement was achieved. As a whole, a deeper understanding of kinetic studies is obtained by these controlled trials. This article is protected by copyright. All rights reserved.

4-Styrenesulfonyl-(2-methyl)aziridine: The First Bivalent Aziridine-Monomer for Anionic and Radical Polymerization

Abstract: 4-Styrenesulfonyl-(2-methyl)aziridine (StMAz), the first orthogonal aziridine monomer, for both anionic ring-opening and radical polymerization is presented Both polymerization pathways are accessible without using protective groups Aza-anionic ring-opening polymerization (A-AROP) of StMAz and other methyl-aziridine derivatives provide multifunctional polyaziridines Molecular weights between 3000 and 13 000 g mol−1 are obtained with low molecular weight dispersities (Ð = 11) The amount of vinyl groups in linear polyaziridines from A-AROP depends on the monomer/comonomer ratio The vinyl groups of P(StMAz)- homo- or copolymers are entirely convertible by thiol-ene addition This allows modification with multiple functional groups Free radical polymerization of StMAz leads to polyalkylenes with aziridine side groups, which are known to be efficiently addressable via nucleophiles Polysulfonamides still belong to a rather new class of polymers accessible by anionic polymerization Enlarging the scope of postpolymerization modifications on polyaziridines/-sulfonamides is important for further macromolecular architectures The aziridine and the vinyl group are combined to develop the first orthogonal monomer for aza-anionic polymerization and radical polymerization

Metal-Catalyzed Group-Transfer Polymerization: A Versatile Tool for Tailor-Made Functional (Co)Polymers

Abstract: Accommodating the increasing demand for tailor-made polymers is a major goal in polymer chemistry. Therefore, the investigation of polymerization techniques, which allow the precise synthesis of macromolecules is of exceptional interest. Ionic or controlled radical polymerization are capable living-type methods for the generation of uniform polymers. However, even these approaches reach their limits in certain issues. In the last decades, group-transfer polymerization (GTP) and especially metal-catalyzed GTP have proven to give access to a plethora of tailor-made homo- and copolymers based on α,β-unsaturated monomers. Thereby, GTP has established its potential in the development of functional and smart polymers. This concept article highlights the most significant progress in metal-catalyzed GTP with a focus on functional (co)polymers including different polymeric architectures and microstructures.

Difluoroboranyl derivatives as efficient panchromatic photoinitiators in radical polymerization reactions

Abstract: Photoinitiating systems based on BF2 derivatives and tetramethylammonium phenyltriethylborate salt were tested in photopolymerization reactions through the photo-DSC method. The good rates of TMPTA polymerization and final monomer conversion were obtained for tested system. The effect of the type of heterocycle on their properties was revealed. The excited state processes, investigated by nanosecond flash photolysis, lie on a fast excited state photoinitiated cleavage leading to reactive species. A triplet state is observed for investigated derivatives.

Hydrocarbon-Soluble Piperazine-Containing Dilithium Anionic Initiator for High Cis-1,4 Isoprene Polymerization

Abstract: The synthesis of 1,4-bis[4-(1-phenylethenyl)benzyl] piperazine and subsequent reaction with sec-butyllithium enables a novel piperazine-containing difunctional organolithium initiator for the living anionic polymerization of isoprene. Piperazine provides a polar unit within the difunctional initiator, promoting ion dissociation and miscibility with hydrocarbon solvents, and enabling the formation of well-defined polyisoprene homopolymers with predictable molecular weights and controlled microstructure. In situ Fourier transform infrared spectroscopy monitors the dilithium initiator formation and the anionic polymerization of isoprene, revealing kinetic insight into this synthetic method. Furthermore, sequential monomer addition with styrene affords poly(styrene-block-isoprene-block-styrene) triblock copolymers with controlled molecular weights and narrow polydispersities. This novel initiator facilitates the synthesis of thermoplastic elastomers with desired cis-1,4 microstructure in polydienes.

Ionic Polymerization in Ionic Liquids

Abstract: Ionic liquids have emerged as a new class of solvents for ionic polymerization due to their low volatility, chemical stability, high conductivity, wide electrochemical window. The advantages and limitations of application of ionic liquids as solvents for ionic polymerization processes are critically discussed in this chapter. The field of cationic polymerization in ionic liquid has undergone rapid growth in recent years. The most important types of cationic monomers, such as styrene and its derivatives, vinyl ethers and isobutylene have been polymerized in ionic liquids; even undergo living polymerization. Corresponding elementary reactions of cationic polymerization in ionic liquids were proposed. Methyl methacrylate and styrene can undergo anionic polymerization in ionic liquids. However, ionic liquids seem unsuitable solvents for anionic polymerization.

On Surface Polymerization With Amines

Abstract: The formation of porous covalent organic frameworks (COFs) on metal surfaces has potential application in the field of heterogeneous catalysis. The use of polymerization reactions involving amines is particularly attractive as it leads to polymers with functional groups in the pore walls. This functionality can directly provide hydrogen bonding sites or can be utilized to synthetically graft more complex functionality onto the pore walls. Amine polymerization to form surface confined COFs has been reported under ultrahigh vacuum conditions as well as at the gas–solid and liquid–solid interfaces. Most studies have focused on less reactive surfaces. The factors influencing the surface chemistry of these systems will be discussed, and approaches will be described which target the formation of high-quality sCOFs on metals which have higher catalytic activity.