A series of new PPV-based alternating copolymers containing conjugated and nonconjugated blocks have been synthesized with the objective of raising the glass transition temperature (T g) relative to structures previously obtained. The higher T g was achieved by inserting a more rigid unit in the spacer soft block. The effects of molecular architecture and chromophore substituents on the optical and redox properties of the polymers were investigated. The UV−vis absorption and emission in the solid state were in the range 360−415 and 455−533 nm, respectively. The calculated band gaps using cyclic voltammetry data were in the range 2.41−3.30 eV and were in good agreement with those calculated from the UV−vis spectra edge. The results show that, through a choice of substituents and backbone structure, the emission color and other properties can be systematically varied.

The time dependence of coil−globule collapse in atactic poly(methyl methacrylate) samples having molecular weights 6.5 × 106 and 3.3 × 106 g/mol dissolved in isoamyl acetate and n-butyl chloride were studied by dynamic light scattering. For example, a dilute solution of PMMA (6.5 × 106 g/mol) in isoamyl acetate was quenched from 61 °C (ϑ temperature) to 18.5 °C. As a result, the measured hydrodynamic radius (〈R h〉) was reduced from 42 ± 2 to 15 ± 2 nm. For the cells used in these DLS measurements the thermal equilibration time was found to be about 20 s. The transition from coil to globule in this cell was observed to take place in almost 35 s. We have found the coil-to-globule transition time to be inversely related to the depth of quench (ΔT) of the process. This transition time also increases with increase in molecular weight of the polymer chain.

A series of segmented copolymers containing oxadiazole groups in the conjugated main chain have been synthesized with the objective of raising the electron transport ability. The present copolymers consist of alternating blocks of rigid chromophores containing oxadiazole units together with flexible spacer segments. The effects of chromophore substituents on the optical properties of the copolymers were investigated. Strong solvatochromic effects were observed, indicating intramolecular charge transfer in the excited states. The copolymers not only were used as blue-green electroluminescent materials but also were effective as electron transport/hole blocking layers in polymer light emitting diode architectures as a result of the introduction of electron transporting unit oxadiazole. The quantum efficiency of a single-layer device using PPV was greatly enhanced with the use of a thin film of the oxadiazole copolymer serving as an ETL layer. At 6.8 V, a brightness of 2400 cd/m 2 was achieved with an external quantum efficiency of 0.094%.

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