No abstract

Modification of bis(2-pyridylmethyl)octadecylamine (BPMODA), a ligand commonly used in ATRP in aqueous dispersed media, was accomplished through the incorporation of electron-donating substituents, resulting in a new, more powerful ligand, bis[2-(4-methoxy-3,5-dimethyl)pyridylmethyl]octadecylamine (BPMODA*). Cyclic voltammetry (CV) indicated the newly synthesized ligand formed much more reducing, i.e., by an order of magnitude more active ATRP catalyst, as compared to BPMODA. Homogeneous polymerizations under normal ATRP conditions confirmed BPMODA* to accelerate polymerization vs BPMODA, with a retained control over the polymerization. Partition experiments of the ligands demonstrate the hydrophobicity of CuBr2/BPMODA has not been compromised by the EDGs as the majority of CuBr2/BPMODA* remains in the organic phase. Heterogeneous polymerizations conducted over a range of catalyst concentrations (2000–250 ppm) with BPMODA* consistently resulted in polymerizations with increased control throughout the polymerizations.

Poly(methyl acrylate)‐b‐polystyrene with controlled molecular weight distribution of each block was synthesized via activators regenerated by electron transfer atom transfer radical polymerization. Polymers with tunable dispersity, in the range of Mw/Mn 1.32 to 2.0, were achieved by adjusting the concentration of the copper catalyst and reaction temperature, thereby controlling the rate of reversible deactivation reaction as well as the number of monomer units added during each activation cycle. Regardless of the increased dispersity, high chain‐end functionality was retained and the livingness of the macroinitiators was confirmed by chain extension, resulting in diblock copolymers with controlled dispersity in each block. Liquid chromatography under critical conditions was employed to determine if any macroinitiator remained in the final product.

Quality of gradient copolymers is evaluated by atomic force microscopy (AFM) and correlated with molecular weight distribution (MWD) values. ARGET ATRP is employed with decreasing levels of catalyst concentrations to generate copolymers with increasing M¯w/M¯n values. The copolymers are transformed into molecular bottlebrushes to enable imaging and analysis of individual molecules by AFM. The average height (cross-sectional) profile of all bottlebrushes agrees with the instantaneous composition (ICHEMA-TMS ) of the analogous copolymer backbone, as determined by (1) H NMR. The copolymer synthesized with 500 ppm of catalyst exhibits more narrow distributions of both brush height and backbone length when analyzed as a bottlebrush by AFM. Correspondingly, the copolymers synthesized with lower catalyst concentrations yield bottlebrushes with broader height and length distribution. These results establish MWD values as an excellent trait to assess quality within gradient copolymers.

The templated growth of nanoparticles via biological agents, such as peptides, provides an exciting complement to abiotic routes, opening facile means to combine the specificity of biomacromolecules with nanoparticle platforms. The specific role of the peptide sequence, and its state relative to the buffer, is still unclear with respect to the processes underlying nanoparticle formation. By investigation of Au mineralization in two commonly used buffers (sodium borate and (2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES)), the role of the phage-display-identified A3 peptide, and its residues, is examined. In a nonreducing buffer (e.g., borate), mineralization is very slow, suggesting that the tyrosine residue in the A3 motif has at most a minor role in reduction of Au(III). In a buffer with substantial reducing capability (e.g., HEPES), the peptide retards nucleation relative to synthetic additives such as poly(ethylene glycol). Furthermore, it also functions to regulate the concentration of free Au in the growth medium, resulting in a diffusion limited process that yields larger nanoparticles with increased peptide concentration. These roles are consistent with the phage-display process that identified the A3 peptide sequence with respect to its binding strength to metal surfaces and not with regard to a specific reduction capability.