Methods for the preparation of narrow-distribution ROMP polycyclopentene are developed to suppress the rate of acyclic metathesis: reaction between the active metal-carbene chain end and an acyclic olefin in the reaction medium. In particular, we investigate interchain metathesis, which generates linear polymers with “scrambled” chain lengths, and we demonstrate the formation of ring polymers by intrachain backbiting and quantify their content in the reaction product. By controlling the relative rates of propagation versus these side reactions, we prepare ROMP polycyclopentene with low dispersity to substantially higher molecular weights than have been reported previously. Polymerization kinetics are quantitatively described by a kinetic model, which accounts for the reversible binding of added trimethylphosphine to the active chain end.

Colloids with internally structured geometries have shown great promise in applications ranging from biosensors to optics to drug delivery, where the internal particle structure is paramount to performance. The growing demand for such nanomaterials necessitates the development of a scalable processing platform for their production. Flash nanoprecipitation (FNP), a rapid and inherently scalable colloid precipitation technology, is used to prepare internally structured colloids from blends of block copolymers and homopolymers. As revealed by a combination of experiments and simulations, colloids prepared from different molecular weight diblock copolymers adopt either an ordered lamellar morphology consisting of concentric shells or a disordered lamellar morphology when chain dynamics are sufficiently slow to prevent defect annealing during solvent exchange. Blends of homopolymer and block copolymer in the feed stream generate more complex internally structured colloids, such as those with hierarchically structured Janus and patchy morphologies, due to additional phase separation and kinetic trapping effects. The ability of the FNP process to generate such a wide range of morphologies using a simple and scalable setup provides a pathway to manufacturing internally structured colloids on an industrial scale.

Comtinuous-wave ͑cw͒ operation of organometallic vapor phase epitaxy-grown In 0.4 Ga 0.6 As 0.995 N 0.005 quantum well ͑QW͒ lasers has been realized, at a room-temperature near-threshold emission wavelength of 1.295 m, with a threshold-current density of 220 A/cm 2 for 2000 m cavity-length (L cav) devices. A threshold current density of only 615 A/cm 2 was achieved for cw operation at a temperature of 100°C, with an emission wavelength of 1.331 m. A maximum cw-output power of 1.8 W was obtained for InGaAsN QW lasers with cavity lengths of 1000 and 2000 m, at a heat-sink temperature of 20°C.

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The thermodynamic interaction strengths between linear polyethylene (PE) and members of a family of hydrogenated polynorbornenes prepared by ring-opening metathesis polymerization can be tuned across a wide range via the choice of substituent appended to the polynorbornene backbone at the 5-position. Isopropyl and certain n-alkyl groups yield polynorbornenes that are highly miscible with PE, capable of producing symmetric diblock copolymers with homogeneous melts at molecular weights in excess of 100 kg/mol. In contrast, phenyl-substituted polynorbornenes are quite immiscible with PE, exhibiting microphase separation in the melt at diblock molecular weights as low as 10 kg/mol. Interaction strengths within this series of polymers do not quantitatively obey regular mixing; entropic contributions to the mixing energy arising from mismatches in free volume and chain stiffness cannot account for the observed deviations. Instead, the interactions can be satisfactorily described by an empirical mixing rule of the form X = (Δγ)1.5, where X is the interaction energy density and γ is a pure-component quantity, operationally analogous to a solubility parameter, with a distinct value for each polymer. These empirical γ parameters are obtained by regression against the entire set of experimental pair interaction energies.