This Article describes a simple two-step synthesis of comb block copolymers with molecular weights exceeding 1,000,000 g mol(-1) and their assembly into ordered morphologies in the solid state. This work is exciting because these polymers assembled into morphologies with domain sizes exceeding 100 nm and, in some examples, 200 nm without the use of additives. These materials reflected selected wavelengths of visible light, and these wavelengths could be affected by swelling with methylene chloride vapor. A comparison between the structures of comb block copolymers and linear block copolymers is presented with a discussion of important parameters affecting their assembly in the solid state. This Article will first describe the synthesis of comb block copolymers using ring opening metathesis polymerization and atom transfer radical polymerization and their subsequent characterization. The comb block copolymers, backbone polymers, and polystyrene arms were all characterized independent of each other and had low polydispersities. The comb block copolymers were assembled by dissolving in methylene chloride and allowing the solvent to evaporate. After thermal annealing, the polymers were characterized by scanning electron and optical microscopy. These polymers assembled into spherical, lamellar, and cylindrical arrays with domain sizes from 132 to 258 nm. This work extends the molecular architectures of polymers that can be assembled in the solid state, the molecular weights of block copolymers that were assembled, and the domain sizes that can be realized without the use of additives.

This article reports the synthesis of comb block copolymers with backbones from exo-norbornene esters via ring-opening metathesis polymerizations (ROMP) and arms composed of polystyrene and polylactide. These polymers represent an exciting new architecture of polymers that have applications in the fabrication of photonic materials and nanofluidic systems. The living polymerization of block copolymers by ROMP with degrees of polymerization up to 2000 units and polydispersities less than 1.2 are described. This result is important as it extends the range of block copolymers that can be synthesized by ROMP to include those with high molecular weights. Comb block copolymers were grown from these block copolymers as they displayed initiators for the ring-opening polymerization of lactide and the atom transfer radical polymerization of styrene. Comb block copolymers with polystyrene and polylactide arms were synthesized with molecular weights up to 63 000 000 g mol -1 . The polystyrene arms had narrow polydispersities and molecular weights in excess of 10 000 g mol -1 ; this result showed that the polymerization of styrene was well controlled. The sizes and shapes of these comb polymers were characterized by multiangle laser light scattering and scanning probe microscopy and demonstrated that some of these polymers were shaped as rigid rods with lengths in excess of 300 nm. To demonstrate their potential as photonic materials, an example of a comb block copolymer was assembled in the solid state with domain sizes exceeding 100 nm and characterized by scanning electron microscopy.

Backbone Polymer Synthesis and Characterization. The backbone block copolymers were synthesized by ROMP according to our previously reported procedure (JACS, 2007, 10551-10560). The backbone polymers were characterized by size exclusion chromatography with a flow rate of 1 mL min -1 with chloroform as the mobile phase. A Waters 515 HPLC pump and two columns (styragel HMW7 and HMW7 or HR4 and HR5E) were used. The detectors were a multi-angle laser light scattering detector (Wyatt DAWN EOS), a quasi elastic light scattering detector (Wyatt QELS), and a refractive index detector (Wyatt Optilab DPS). The absolute molecular weights were found and compared to the predicted molecular weights based on the monomer to catalyst loadings and assuming consumption of all monomer. The results are shown in Table 1.

Electrically conductive hydrogel composites consisting of oligo(polyethylene glycol) fumarate (OPF) and polypyrrole (PPy) were developed for applications in nerve regeneration. OPF-PPy scaffolds were synthesized using three different anions: naphthalene-2-sulfonic acid sodium salt (NSA), dodecylbenzenesulfonic acid sodium salt (DBSA), and dioctyl sulfosuccinate sodium salt (DOSS). Scaffolds were characterized by ATR-FTIR, XPS, AFM, dynamic mechanical analysis, electrical resistivity measurements, and swelling experiments. OPF-PPy scaffolds were shown to consist of up to 25 mol% polypyrrole with a compressive modulus ranging from 265 to 323 kPa and a sheet resistance ranging from 6 to 30 × 103 Ohms/square. In vitro studies using PC12 cells showed OPF-PPy materials had no cytotoxicity and PC12 cells showed distinctly better cell attachment and an increase in the percent of neurite bearing cells on OPF-PPy materials compared to OPF. The neurite lengths of PC12 cells were significantly higher on OPF-PPyNSA and OPF-PPyDBSA. These results show that electrically conductive OPF-PPy hydrogels are promising candidates for future applications in nerve regeneration.