Design and use of organic nanoparticles prepared from star-shaped polymers with reactive end groups.

Star-shaped poly(isobornyl acrylate) (PiBA) was prepared by atom transfer radical polymerization (ATRP) using multifunctional initiators. The optimal ATRP conditions were determined to minimize star-star coupling and to preserve high end group functionality (>90%). Star-shaped PiBA with a narrow polydispersity index was synthesized with 4, 6, and 12 arms and of varying molecular weight (10,000 to 100,000 g x mol(-1)) using 4 equiv of a Cu(I)Br/PMDETA catalyst system in acetone. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis, NMR spectroscopy, and size exclusion chromatography (SEC) confirmed their controlled synthesis. The bromine end group of each arm was then transformed to a reactive end group by a nucleophilic substitution with methacrylic acid or cinnamic acid (conversion >90%). These reactive star polymers were used to prepare PiBA nanoparticles by intramolecular polymerization of the end groups. The successful preparation of this new type of organic nanoparticles on a multigram scale was proven by NMR spectroscopy and SEC. Subsequently, they have been used as additives for linear, rubbery poly(n-butyl acrylate). Rheology measurements indicated that the viscoelastic properties of the resulting materials can be fine-tuned by changing the amount of incorporated nanoparticles (1-20 wt %), as a result of the entanglements between the nanoparticles and the linear polymers.

Synthesis of multi(metallo)porphyrin dendrimers through nucleophilic aromatic substitution on meso-pyrimidinyl substituted porphyrins.

A convergent synthetic strategy toward novel all-porphyrin dendrimers, which can be regarded as synthetic model systems of the natural photosynthetic light-harvesting antennae, was successfully explored. The dendron propagation, based on nucleophilic aromatic substitution reactions on a meso-dichloropyrimidinyl substituted porphyrin AB2 monomer, was carried out up to the second-generation dendron, and the used approach was proven to be compatible with the stepwise introduction of different metals in the successive generations. Three different metals (Pt, Zn, and Ni) could be introduced in the second-generation heptaporphyrin dendron. By applying analogous meso-dichloropyrimidinyl substituted porphyrin cores, novel multiporphyrin dendrimers were obtained.