Direct ATRP of Methacrylic Acid with Iron-Porphyrin Based Catalysts

An iron porphyrin catalyst, derived from the active center of proteins such as horseradish peroxidase and hemoglobin, was successfully used for the atom transfer radical polymerizations (ATRP) of methacrylic acid. ATRP of methacrylic acid and other acidic monomers is challenging due to Cu complexation by carboxylates, protonation of the ligand, and displacement of the halogen chain end. A robust mesohemin-based catalyst provided controlled ATRP of methacrylic acid, yielding poly­(methacrylic acid) with <i>M</i>_n ≥ 20000 and dispersity <i>Đ</i> < 1.5. Retention of halogen chain end was confirmed by successful chain extension of a poly­(methacrylic acid)–Br macroinitiator

Kinetics of Fe–Mesohemin–(MPEG₅₀₀)₂‑Mediated RDRP in Aqueous Solution

A speciation analysis for Fe–mesohemin–(MPEG₅₀₀)₂-mediated reversible-deactivation radical polymerization (RDRP) in aqueous solution was carried out by a combination of visible (vis) and ⁵⁷Fe Mössbauer spectroscopy. The results were used within kinetic studies of ATRP and OMRP reactions via highly time-resolved EPR spectroscopy. ATRP control was effective with the rate coefficient for deactivation clearly exceeding the one for formation of organometallic species. Deactivation rate coefficients increase by more than 1 order of magnitude in passing from polymerization in 30 to 90 wt % H₂O. Media with water contents of and above 70 wt % are well suited for controlled ATRP. The Fe–mesohemin catalyst provides an exceptionally high ATRP equilibrium constant even at ambient temperature, which approaches the one of highly active Cu catalysts

Stackable, Covalently Fused Gels: Repair and Composite Formation

Combining modeling and experiment, we created multilayered gels where each layer was “stacked” on top of the other and covalently interconnected to form mechanically robust materials, which could integrate the properties of the individual layers. In this process, a solution of new initiator, monomer, and cross-linkers was introduced on top of the first gel, and these new components then underwent living (co)­polymerization to form the subsequent layer. We simulated this process using dissipative particle dynamics (DPD) to isolate factors that affect the formation and binding of chemically identical gel as well as incompatible layers. Analysis indicates that the covalent bond formation between the different layers is primarily due to reactive chain-ends, rather than residual cross-linkers. In the complementary experiments, we synthesized multilayered gels using either free radical (FRP) or atom transfer radical polymerizations (ATRP) methods. Polymerization results demonstrated that chemically identical materials preserved their structural integrity independent of the polymerization method. For gels encompassing incompatible layers, the contribution of reactive chain-ends plays a particularly important role in the integrity of the material, as indicated by the more mechanically robust systems prepared by ATRP. These studies point to a new approach for combining chemically distinct components into one coherent, multifunctional material as well as an effective method for repairing severed gels

ATRP under Biologically Relevant Conditions: Grafting from a Protein

Atom transfer radical polymerization (ATRP) methods were developed in water-based media, to grow polymers from proteins under biologically relevant conditions. These conditions gave good control over the resulting polymers, while still preserving the protein’s native structure. Several reaction parameters, such as ligand structure, halide species, and initiation mode were optimized in water and PBS buffer to yield well-defined polymers grown from bovine serum albumin (BSA), functionalized with cleavable ATRP initiators (I). The CuCl complex with ligand 2,2′-bipyridyne (bpy) provides the best conditions for the polymerization of oligo­(ethylene oxide) methacrylate (OEOMA) in water at 30 °C under normal ATRP conditions (I/CuCl/CuCl₂/bpy = 1/1/9/22), while the CuBr/bpy complex gave better performance in PBS. Activators generated by electron transfer (AGET) ATRP gave well-controlled polymerization of OEOMA at 30 °C with the ligand tris­(2-pyridylmethyl)­amine (TPMA), (I/CuBr₂/TPMA = 1/10/11). The AGET ATRP reactions required slow feeding of a very small amount of ascorbic acid into the aqueous reaction medium or buffer. The reaction conditions developed were used to create a smart, thermoresponsive, protein–polymer hybrid

Biocompatible Polymeric Analogues of DMSO Prepared by Atom Transfer Radical Polymerization

The synthesis of a sulfoxide-based water-soluble polymer, poly­(2-(methylsulfinyl)­ethyl acrylate) (polyMSEA), a polymeric analogue of DMSO, by atom transfer radical polymerization (ATRP) is reported. Well-defined linear polymers were synthesized using relatively low amounts of copper catalyst (1000 or 100 ppm). Two types of star polymers were synthesized by either an “arm-first” approach or a “core-first” approach using a biodegradable β-cyclodextrin core. The glass transition temperatures of both the linear polymer (16 °C) and star polymer (32 °C) were determined by differential scanning calorimetry (DSC). The lower critical solution temperature (LCST) of poly­(MSEA) was estimated to be ca. 140 °C by extrapolating the LCST of a series of copolymers with NIPAM. Cytotoxicity tests revealed that both the linear and star polymers have low toxicity, even at concentrations up to 3 mg/mL