Ligand For Atom Transfer Radical Polymerization Research Articles

Structural, molecular and thermal properties of cardanol based monomers and polymers synthesized via atom transfer radical polymerization (ATRP)

Cardanol, a byproduct of the cashew processing industry, has been widely studied feeedstock for sustainable monomers and polymers. In this article, the Atom Transfer Radical Polymerization (ATRP) of three radically polymerizable monomers, namely, cardanyl acrylate (CA), hydrogenated cardanyl acrylate (PA) and hydrogenated cardanyl methacrylate (PMA), was studied. The monomers as well as the polymers were structurally characterized and studied by differential scanning calorimetry (DSC) to understad their thermal behavior. The PA monomer showed melting (Tm) at 35 °C and crsytallization (Tc) at −3.27 °C. The synthesized polymer shows Tm of 16.5 °C and the Tc increased to 7.2 °C. In PMA monomer, the Tm was observed at 15.21 °C and Tc at −11 °C and the correponding values for the polymer decreasing to 1 °C and −18 °C, respectively. The coressponding transitions of CA monomer and its polymer were broad and less defined. The homopoymerization of CA and PMA yielded good conversions but the PA polymer yield was low under identical conditions, probably due to the higher monomer crystallinity of PA. The effect of different ATRP ligands, viz, pentamethyldiethylenetriamine (PMDETA) and bipyridine (dNbpy), on the conversion, molecular weight and polydispersity was also investigated.

Computational design of next generation atom transfer radical polymerization ligands

Computational studies show that the activity of ATRP catalysts can be dramatically improved using quinuclidine bridgehead ligands.

Rational Design of Highly Activating Ligands for Cu-Based Atom Transfer Radical Polymerization.

Atom transfer radical polymerization (ATRP) is the most commonly utilized technique in controlled radical polymerization. However, the identification of more active catalysts could further increase its scope, both for polymerization and small-molecule synthesis more generally. To this end, a series of novel ligands were designed on the basis of two strategies: replacing nitrogen-based ligands with their phosphorus equivalents and rigidifying the ligand cap of nitrogen-based ligands so as to enforce short Cu-cap distances. Each ligand was assessed using accurate computational chemistry, which was used to compute the thermodynamics and, in selected cases, kinetics of an ATRP reaction with a model methyl methacrylate propagating radical. In principle, the use of phosphorus ligand caps was found to be a powerful strategy for increasing catalyst activity. Unfortunately, in practice, speciation issues sacrificed much of their advantage. In contrast, cap rigidification increases the activity of nitrogen-based ligands, well beyond existing ATRP ligands such as TPMANMe2. The effectiveness of these ligands was further demonstrated for hard-to-activate initiating systems based on ethylene, vinyl chloride, and vinyl acetate polymerization. Several of these improved ligands are synthetically accessible, with rigid piperidine or quinuclidine analogues of TPMANMe2 possessing improved thermodynamic and kinetic activity by 2 to 3 orders of magnitude.

Synthesis, structural and magnetic characterization of a copper(II) complex of 2,6-di(1H-imidazol-2-yl)pyridine and its application in copper-mediated polymerization catalysis

The 2,6-di(1H-imidazol-2-yl)pyridine (H2dimpy) ligand is synthesized and suggested as an alternative ligand for copper mediated catalysis. A Cu(II) complex was obtained with this ligand and characterized via ESI-MS, FT-IR, UV–vis and the structure was confirmed by single crystal XRD. The crystal showed the [Cu2(H2dimpy)2(μ-Cl)2](PF6)2·2H2O dimeric complex, in which Cu(II) is in a distorted square-pyramidal geometry (τ=0.301). Ferromagnetic coupling with J=-11.1cm−1 was confirmed by experiment and corroborated by density functional calculations. In order to evaluate the applicability of H2dimpy in atom transfer radical polymerization (ATRP), polystyrene was produced in DMF solution at low polydispersity (1.3) while maintaining the livingness of the polymer chain. The good performance of the H2dimpy compared to a standard ligand for ATRP (5,5′-dimethyl-2,2′-dipyridyl) indicates that it is suitable for this reaction.

Exploring Self-Condensing Vinyl Polymerization of Inimers in Microemulsion To Regulate the Structures of Hyperbranched Polymers

A synthetic method was successfully developed to produce structurally defined hyperbranched polymers using confined micellar space in microemulsion to regulate atom transfer radical polymerization (ATRP) of inimers. Systematic exploration of experimental variables, including five methacrylate-based inimer species, two ATRP ligands, and varied amounts of inimers and catalysts, produced a series of hyperbranched polymers that encompassed a broad range of molecular weights (Mn = 194–1301 kg/mol), high degrees of branching (DB = 0.26–0.41), and narrow molecular weight distribution (Mw/Mn = 1.1–1.7). The ATRP of inimers in the microemulsion media showed a fast polymerization rate with quantitative conversion of methacrylate groups within 0.5 h. At high conversion, there was essentially one hyperbranched polymer per discrete latex particle, whose dimension (hydrodynamic diameter Dh = 10.95–20.13 nm in water) and uniformity directly determined the molecular weight and polydispersity of the hyperbranched polymer. The DB of hyperbranched polymers was quantitatively determined using inverse gated 13C NMR spectroscopy, and its value was affected by several parameters, all related to the effective amount of copper catalysts in the polymerization loci for dynamic ATRP exchange reactions. The use of inimers and ligands that showed high copper complex solubility and a high feed ratio of copper to inimer could increase the concentration of copper catalyst in the discrete particles and consequently the DB value. Within the investigation, the polymerization of inimer 3 using 4,4′-dinonyl-2,2′-dipyridyl (dNbpy) as ligand produced hyperbranched polymers with the highest DB = 0.41 due to the high solubility of Cu(II)/(dNbpy)2 in inimer 3. When acetal group as a linker was incorporated into the inimer, the produced hyperbranched polymers exhibited complete degradation in acidic environment, indicating potential utility in biomedical applications.

Enantiomer-Selective Radical Polymerization of Bis(4-vinylbenzoate)s with Chiral Atom Transfer Radical Polymerization Initiating Systems

We report a series of cyclopolymerizations of bis(4-vinylbenzoate) monomers through an atom transfer radical polymerization (ATRP) using chiral ligands. Cyclized polymers showing chiroptical properties were produced by polymerization of the racemic bifunctional monomer, rac-2,4-pentanediyl bis(4-vinylbenzoate) (rac-1), and enantiomerically unbalanced bifunctional monomers were recovered, providing substantial evidence for the enantiomer-selective polymerization of rac-1 mediated through the ATRP with chiral ligands. A comparison between the enantiomerically pure monomers, (2R,4R)-2,4-pentanediyl bis(4-vinylbenzoate) (RR-1) and (2S,4S)-2,4-pentanediyl bis(4-vinylbenzoate) (SS-1), revealed a drastic discrepancy in the rates of their homopolymerizations during the ATRP. The enantiomeric copolymerization of RR-1 and SS-1 indicated that the monomer reactivity ratio of RR-1 was higher than that of SS-1 for the ATRP with chiral ligands. The results of both homopolymerizations and copolymerizations clearly demonstrate the propensity for incorporation of the RR-1 enantiomer and thus the enantiomer-selective polymerization in this system. The monomer-structural effects on the enantiomer-selectivity were examined, and it was concluded that the chirality in the monomer is also essential for the enantiomer-selective polymerization as well as the chiral ligands for ATRP. Finally, the viability of the cyclopolymerization in the enantiomer-selective polymerization was proved using mono(4-vinylbenzoate) monomers incapable of cyclizing through the polymerization.

Copper Triflate as a Catalyst in Atom Transfer Radical Polymerization of Styrene and Methyl Acrylate

The use of copper triflate complexes as catalysts for atom transfer radical polymerization (ATRP) of styrene and methyl acrylate (MA) is presented. The ability to start with Cu(OTf)2 catalyst precursors allows for a simple experimental setup without catalyst oxidation. Reduction with copper(0) powder occurs quickly in most cases to form the copper(I) catalysts. The traditional bipyridine-based ATRP ligands were less efficient for styrene polymerization, but for methyl acrylate polymerization resulted in faster polymerizations relative to the CuBr analogues. The methylated triamine ligand was used for the Cu(OTf)2/Cu0 system and also yielded good results for the polymerization of styrene (Mw/Mn = 1.10). This catalyst gave a rapid polymerization of MA with low polydispersities (Mw/Mn = 1.15) even at high conversions. The Cu(OTf) complexes are more active than their CuBr counterpart; however, this may be detrimental to having a controlled polymerization. In the case of styrene, it is possible that radical ge...