A Catalyst Platform for Unique Cationic (Co)Polymerization in Aqueous Emulsion

Synthesis of block copolymer with cis-1,4-polybutadiene and isotactic-rich polystyrene using α-diimine nickel catalysts

A series of styrene-butadiene di-block copolymers with high cis-1,4 unit content (greater than 92%) polybutadiene (PB) and isotactic-rich polystyrene (PS) (mmmm > 65%) was synthesized using α-diimine nickel catalysts (Ni-diimine). Four different Ni-diimine catalysts were synthesized via a complexing reaction between nickel (II) naphthenate and laboratory-made α-diimine ligands L1, L2, L3 and L4, which have different steric volume structures. The results indicate that the Ni-diimine catalyst prepared using the L4 ligand with a higher steric volume can effectively initiate the block polymerization of butadiene and styrene, and the resulting polymer has distinguished cis-1,4 structure unit PB and high isotactic-selective PS block. Differential scanning calorimetry and electrochemical performance tests show that these block copolymers with cis-1,4-regulated and isotactic-selective polymerization have advantages in terms of high-temperature and low-temperature resistance as well as corrosion resistance. Therefore, these copolymers are expected to be widely used in some harsh industrial environments.

Organic Chemistry and Synthesis Rely More and More upon Catalysts

A few months before the COVID-19 pandemic, Pierre Vogel and Kendall N. Houk published with a new textbook Wiley-VCH, “Organic Chemistry: Theory, Reactivity, and Mechanisms in Modern Synthesis”, with a foreword from the late Roberts H. Grubbs. The book demonstrates how catalytic processes dominate all fields of modern organic chemistry and synthesis, and how invention combines thermodynamics, kinetics, spectroscopy, quantum mechanics, and thermochemical data libraries. Here, the authors present a few case studies that should be of interest to teachers, practitioners of organic and organometallic chemistry, and the engineers of molecules. The Vogel–Houk book is both textbook and reference manual; it provides a modern way to think about chemical reactivity and a powerful toolbox to inventors of new reactions and new procedures.

Characterization and mechanism study of aqueous cationic polymerization of p-methylstyrene

Aqueous cationic polymerization has attracted considerable interest as a novel polymerization technique, because it conforms to the “green chemistry” trend and challenges the concept of traditional cationic polymerization. In this paper, a CumOH/B(C₆F₅)₃/Et₂O system was used to initiate the aqueous polymerization of p-methylstyrene through suspension and emulsion methods. Several types of surfactants were used, including the cationic surfactant CTAB, non-ionic surfactant NP-40, and anionic surfactant SDBS, and the influences of initiator concentration and temperature on polymerization were investigated. Consistent with previous literature, initiator activity was positively correlated with temperature unlike in traditional cationic polymerization. Gaussian 09W simulation software was used to calculate and optimize changes in the bond lengths and angles of B(C₆F₅)₃ after ether was added to the system. The addition of ether increased the polarity of B(C₆F₅)₃, rendering it soluble in water. ¹H-NMR was used in identifying the main chain and terminal structures of the polymer, and the mechanism of p-methylstyrene aqueous phase cationic polymerization was proposed.

The co-initiator B(C₆F₅)₃ first complexed with ether. Then the complex deprives the OH⁻ of CumOH at the water–oil interface, and initiates the polymerization of p-methylstyrene at the interface.

Surfactant-mediated thioglycosylation of 1-hydroxy sugars in water

Thioglycosides are an important class of sugars, since they can be used as non-ionic biosurfactants, biomimetic glycosides, and building blocks for carbohydrate synthesis. Previously, Brønsted- or Lewis-acid-catalyzed dehydrative glycosylations between a 1-hydroxy sugar and a thiol have been reported to yield open-chain dithioacetal sugars as the major products instead of the desired thioglycosides. These dithioacetal sugars are by-products derived from the endocyclic bond cleavage of the thioglycosides. Herein, we report dehydrative glycosylation in water mediated by a Brønsted acid-surfactant combined catalyst (BASC). Glycosylations between 1-hydroxy furanosyl/pyranosyl sugars and primary, secondary, and tertiary aliphatic/aromatic thiols in the presence of dodecyl benzenesulfonic acid (DBSA) provided the thioglycoside products in moderate to good yields. Microwave irradiation led to improvements in the yields and a shortening of the reaction time. Remarkably, open-chain dithioacetal sugars were not detected in the DBSA-mediated glycosylations in water. This method is a simple, convenient, and rapid approach to produce a library of thioglycosides without the requirement of anhydrous conditions. Moreover, this work also provides an excellent example of complementary reactivity profiles of glycosylation in organic solvents and water.

On the limitations of cationic polymerization of vinyl monomers in aqueous dispersed media

We investigate the effects of chain transfer to monomer and chain transfer to water on the molecular weight of polymers obtained by cationic polymerization in aqueous dispersed media.

Synthesis of butadiene/isoprene–styrene di-block copolymer with high cis-1,4 unit content based on a neodymium phosphate ester

A novel two-step synthesis strategy based on a liquid neodymium phosphate ester (Nd(P₅₀₇)₃) catalyst was used to synthesize diene-styrene di-block copolymers with high cis-1,4 unit content, such as butadiene–styrene (PB-b-PS), isoprene–styrene (PI-b-PS), and so on. The strategy not only makes full use of the high cis-1,4 stereo-selectivity of the rare earth catalyst to conjugated dienes, but also adjusts the electron cloud density of the catalytic active center by introducing triphenyl phosphine (PPh₃). Thus, the catalytic activity of the neodymium-based catalyst center toward styrene has been largely improved, and a series of PB/PI-b-PSs with high cis-1,4 unit content (98.3 and 98.1% respectively), narrow molecular weight distribution and controllable block ratio were successfully synthesized. Herein, molecular weight (M_n), molecular weight distribution (M_w/M_n) and microstructure of the block polymers were characterized using SEC-MALLS, FT-IR, ¹H NMR, ¹³C NMR and DSC. The DSC curve of a PB-b-PS with 98.3% cis-1,4 unit and 18.6% polystyrene content shows a T_g of −103.1 °C, which means it has relatively excellent mechanical properties at lower temperature. The results show that these PB/PI-b-PS materials have good application prospects in harsh low temperature environments.

A novel synthesis strategy of butadiene/isoprene–styrene di-block copolymer with high cis-1,4 content was explored based on a neodymium phosphate catalyst, by adjusting the electron cloud density of the catalytic active center via triphenyl phosphine.

Lewis acid-surfactant complex catalyzed polymerization in aqueous dispersed media: cationic or radical polymerization?

Evidence is presented that shows Lewis acid-surfactant complex catalyzed polymerization proceeds via a radical, not a cationic, mechanism.

A novel synthetic strategy for styrene-butadiene-styrene tri-block copolymer with high cis-1,4 units via changing catalytic active centres

A styrene-butadiene-styrene tri-block copolymer (SBS) with a high cis-1,4 unit content (greater than 97%) was synthesized by a novel synthetic strategy based on changing the catalytic active centres using n-butyllithium and a nickel-based catalyst. Firstly, styrene was polymerized via anionic polymerization using butyllithium as the initiator (Li, activity centre Li) at 50°C. The obtained alkylated macroinitiator (PSLi) was aged with nickel naphthenate (Ni) and boron trifluoride etherate (B) to prepare a second reactive centre (Ni-F), which was used to initiate the polymerization of butadiene (Bd). Finally, triphenyl phosphine (PPh3) was added to adjust the electron density of the third active centre (P-Ni-F), and styrene monomer was added again to synthesize the second polystyrene block to obtain SBS. The polymerization technique presented here is simple and has an efficient initiation effect due to the high initiation activities for the different monomers. It also exhibits excellent control over the stereo-structure of the butadiene segments in the prepared copolymers, and the SBS polymers with high cis-1,4 unit content were easily achieved.

A New Strategy for the Synthesis of Hydroxyl Terminated Polystyrene-b-Polybutadiene-b-Polystyrene Triblock Copolymer with High Cis-1, 4 Content

This work reports the preparation of a hydroxyl terminated polystyrene-b-polybutadiene-b-polystyrene triblock copolymer (SBS) with high cis-1, 4 content via a novel nickel catalyst, [η³-Ni(CH₂CHCHCH₂OOCH₃)][BPh^F₄]. FT-IR, ¹H-NMR, and ¹³C NMR indicated that the polybutadiene segment of the copolymer contains greater than 90% cis-1, 4 structure, indicating achievement of the objective. Toward the functionalization goal, a hydroxyl group was successfully introduced at the end of the triblock copolymer (HO–SBS–OH). The results of gel permeation chromatography (GPC) revealed that the polymer is indeed a triblock copolymer, with no traces of homopolymer. Differential scanning calorimetry (DSC) showed that HO–SBS–OH synthesized using the novel catalyst had a lower glass transition temperature (T_g) than HO–SBS–OH synthesized with an alkyl lithium catalyst. Therefore, the polymer synthesized via the novel catalyst contains high cis-1,4 content and displays excellent low-temperature mechanical properties.

Characteristics and Mechanism of Vinyl Ether Cationic Polymerization in Aqueous Media Initiated by Alcohol/B(C₆F₅)₃/Et₂O

Aqueous cationic polymerizations of vinyl ethers (isobutyl vinyl ether (IBVE), 2-chloroethyl vinyl ether (CEVE), and n-butyl vinyl ether (n-BVE)) were performed for the first time by a CumOH/B(C₆F₅)₃/Et₂O initiating system in an air atmosphere. The polymerization proceeded in a reproducible manner through the careful design of experimental conditions (adding initiator, co-solvents, and surfactant or decreasing the reaction temperature), and the polymerization characteristics were systematically tested and compared in the suspension and emulsion. The significant difference with traditional cationic polymerization is that the polymerization rate in aqueous media using B(C₆F₅)₃/Et₂O as a co-initiator decreases when the temperature is lowered. The polymerization sites are located on the monomer/water surface. Density functional theory (DFT) was applied to investigate the competition between H₂O and alcohol combined with B(C₆F₅)₃ for providing a theoretical basis. The effectiveness of the proposed mechanism for the aqueous cationic polymerization of vinyl ethers using CumOH/B(C₆F₅)₃/Et₂O was confirmed.

A New Synthesis Strategy on Styrene-Butadiene Di-Block Copolymer Containing High cis-1,4 Unit Via Transfer of Anionic to Coordination Polymerization

A novel synthesis strategy on styrene-butadiene di-block copolymer (PS-b-PB) with high cis-1,4 unit content was developed, based on a transfer technique from anionic to coordination polymerization. Firstly, the styrene monomer was initiated by n-butyllithium (Li) utilizing anionic polymerization at 50 °C, which resulted in a macromolecular alkylating initiator (PSLi). Secondly, PSLi was aged with nickel naphthenate (Ni) and boron trifluoride etherate (B) for obtaining a complex catalyst system (Ni/PSLi/B). Then, Ni/PSLi/B was applied to initiate the butadiene (Bd) polymerization. Following this new strategy, a series of PS-b-PBs were successfully synthesized. The experimental results indicated that under the molar ratio combination of [Li]/[Ni] = 5 and [B]/[Li] = 1, styrene-butadiene di-block copolymers could be easily achieved with high cis-1,4 unit content (>97%) and controlled molecular weight as well as narrow molecular weight distribution (Mw/Mn < 1.5). Furthermore, the copolymer's block ratio could also be effectively controlled by controlling the two components' monomer feed ratio.

Aqueous cationic homo- and co-polymerizations of β-myrcene and styrene: a green route toward terpene-based rubbery polymers

A green and cost-efficient approach for the synthesis of bio-based poly(β-myrcene) and poly(β-myrcene-co-styrene) via emulsion cationic polymerization is developed.

Nucleophile-initiated anionic polymerization of zwitterionic monomers derived from vinylpyridines in aqueous media under ambient aerobic conditions

Anionic polymerization of vinylpyridine based zwitterionic monomers using nucleophile initiators under natural conditions and DFT calculations for such polymerization are reported here.

Carbocationic polymerization of isoprene using cumyl initiators: progress in understanding side reactions

The cationic polymerization of isoprene using cumyl chloride/B(C₆F₅)₃ and cumyl ether/TiCl₄ systems was investigated in dichloromethane or in dichloromethane/methylcyclohexane mixtures varying the polymerization conditions.