Bromoalkyl ATRP initiator activation by inorganic salts: experiments and computations

The bromoalkyl ATRP initiator EBrPA is activated by many alkali, alkaline-earth and ammonium salts, leading to MMA polymerization, but only the iodides yield a controlled process because of a degenerative transfer mechanism contribution.

Design of hybrid molecular brushes with reversible surface adaptability on exposure to specific solvents

Hybrid molecular brushes (HMBs) are macromolecules made of a linear backbone and polymeric side chains that differ in their chemical nature. The authors developed a new method of synthesis of HMB with chitosan (CHI) backbone. In the first step, chitosan-graft-polylactide (CHI-g-PLA) was synthesized by interfacial ring opening polymerization of lactide initiated from CHI. CHI-g-PLA is characterized for its molecular weight and structure. In the second step, polyvinylpyrrolidone (PNVP) or polyacrylamide (PAAm) is grafted by radical polymerization from the CHI in CHI-g-PLA to form CHI-g-PLA-g-PNVP and CHI-g-PLA-g-PAAm. This results in the formation of HMB, with hydrophobic PLA and hydrophilic PNVP or PAAm side chains grafted to CHI. The chemical structure and thermal behavior of the HMBs are characterized. The morphology of CHI-g-PLA as well as the HMBs is determined using atomic force microscopy (AFM). Both the HMBs tethered to separate surfaces exhibit reversible switching between the hydrophilic and hydrophobic polymers on exposure to specific solvents. This is studied by AFM and water contact angle measurements. Hence, the authors developed a method for synthesis of HMB that can be applied for surface modification.

A sustainable photocontrolled ATRP strategy: facile separation and recycling of a visible-light-mediated catalyst fac-[Ir(ppy)3]

A visible-light-mediated catalyst (fac-[Ir(ppy)₃]) in situ separation and recycling ATRP system for PEG-based water-soluble monomers was constructed.

Photocatalyzed iron-based ATRP of methyl methacrylate using 1,3-dimethyl-2-imidazolidinone as both solvent and ligand

A simple photocatalyzed Fe-based ATRP of MMA was conducted under UV irradiation using the “green” solvent DMI as both the solvent and ligand.

Metal-Free Atom Transfer Radical Polymerization of Methyl Methacrylate with ppm Level of Organic Photocatalyst

It is well known that the recently developed photoinduced metal-free atom transfer radical polymerization (ATRP) has been considered as a promising methodology to completely eliminate transition metal residue in polymers. However, a serious problem needs to be improved, namely, large amount of organic photocatalysts should be used to keep the controllability over molecular weights and molecular weight distributions. In this work, a novel photocatalyst 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) with strong excited state reduction potential is successfully used to mediate a metal-free ATRP of methyl methacrylate just with parts per million (ppm) level usage under irradiation of blue light emitting diode at room temperature, using ethyl α-bromophenyl-acetate as a typical initiator with high initiator efficiency. The polymerization kinetic study, multiple controlled "on-off" light switching cycle regulation, and chain extension experiment confirm the "living"/controlled features of this promising photoinduced metal-free ATRP system with good molecular weight control in the presence of ppm level photocatalyst 4CzIPN.

ICAR ATRP of Acrylonitrile under Ambient and High Pressure

It is well known that well-defined polyacrylonitrile (PAN) with high molecular weight (Mw > 106 g·mol-1) is an excellent precursor for high performance carbon fiber. In this work, a strategy for initiators for a continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) system for acrylonitrile (AN) was firstly established by using CuCl₂·2H₂O as the catalyst and 2,2'-azobis(2-methylpropionitrile) (AIBN) as the thermal initiator in the presence of ppm level catalyst under ambient and high pressure (5 kbar). The effect of catalyst concentration and polymerization temperature on the polymerization behaviors was investigated. It is important that PAN with ultrahigh viscosity and average molecular weight (Mη = 1,034,500 g·mol-1) could be synthesized within 2 h under high pressure.

Iron-Mediated Homogeneous ICAR ATRP of Methyl Methacrylate under ppm Level Organometallic Catalyst Iron(III) Acetylacetonate

Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst residue in products. In order to reduce the amount of catalyst and considering good biocompatibility and low toxicity of the iron catalyst, in this work, we developed a homogeneous polymerization system of initiators for continuous activator regeneration ATRP (ICAR ATRP) with just a ppm level of iron catalyst. Herein, we used oil-soluble iron (III) acetylacetonate (Fe(acac)₃) as the organometallic catalyst, 1,1'-azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh₃) as the ligand, toluene as the solvent and methyl methacrylate (MMA) as the model monomer. The factors related with the polymerization system, such as concentration of Fe(acac)₃ and ACHN and polymerization kinetics, were investigated in detail at 90 °C. It was found that a polymer with an acceptable molecular weight distribution (Mw/Mn = 1.43 at 45.9% of monomer conversion) could be obtained even with 1 ppm of Fe(acac)₃, making it needless to remove the residual metal in the resultant polymers, which makes such an ICAR ATRP process much more industrially attractive. The "living" features of this polymerization system were further confirmed by chain-extension experiment.

Catalyst-free iodine-mediated living radical polymerization under irradiation over a wide visible-light spectral scope

Catalyst-free iodine-mediated photo-induced solution LRP of methyl methacrylates under LED light was successfully established over a wide range of irradiation wavelengths (390–630 nm).

Synthesis of amphiphilic nanoparticles and multi-block hydrophilic copolymers by a facile and effective “living” radical polymerization in water

A convenient and robust approach using MANDC-COOH as the initiator and oxidatively stable Cu(OAc)₂as the catalyst to synthesize amphiphilic nanoparticles and hydrophilic multi-block copolymers was successfully developed in water.

Recent Progress on Transition Metal Catalyst Separation and Recycling in ATRP

Atom transfer radical polymerization (ATRP) is a versatile and robust tool to synthesize a wide spectrum of monomers with various designable structures. However, it usually needs large amounts of transition metal as the catalyst to mediate the equilibrium between the dormant and propagating species. Unfortunately, the catalyst residue may contaminate or color the resultant polymers, which limits its application, especially in biomedical and electronic materials. How to efficiently and economically remove or reduce the catalyst residue from its products is a challenging and encouraging task. Herein, recent advances in catalyst separation and recycling are highlighted with a focus on (1) highly active ppm level transition metal or metal free catalyzed ATRP; (2) post-purification method; (3) various soluble, insoluble, immobilized/soluble, and reversible supported catalyst systems; and (4) liquid-liquid biphasic catalyzed systems, especially thermo-regulated catalysis systems.

Fe(iii)-mediated ICAR ATRP in a p-xylene/PEG-200 biphasic system: facile and highly efficient separation and recycling of an iron catalyst

Iron catalyst separation and recycling was successfully achieved in a liquid/liquid biphasic TPSC-based ICAR ATRP system.

Thermoregulated phase transfer catalysis in aqueous/organic biphasic system: facile and highly efficient ATRP catalyst separation and recycling in situ using typical alkyl halide as initiator

An important development of TRPTC-based ICAR ATRP for metal catalyst separation and recycling in an aqueous/organic biphasic system was achieved with alkyl halide as the initiator for the first time.