5 research outputs found
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><sub>n</sub> ≥ 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–(MPEG<sub>500</sub>)<sub>2</sub>‑Mediated RDRP in Aqueous Solution
A speciation
analysis for Fe–mesohemin–(MPEG<sub>500</sub>)<sub>2</sub>-mediated reversible-deactivation radical polymerization
(RDRP) in aqueous solution was carried out by a combination of visible
(vis) and <sup>57</sup>Fe 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 % H<sub>2</sub>O. 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/CuCl<sub>2</sub>/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/CuBr<sub>2</sub>/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