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Poly(3-hexylthiophene) formed gels and showed liquid crystalline structures at high concentrations. The absorption properties of poly(3-hexylthiophene) showed dramatic changes during gelation, which is an indication of strong intermolecular π-electronic coupling of the ordered self-assembled poly(3-hexylthiophene) gels. The effect of conformational transitions on the photovoltaic properties of solution-processed poly(3-hexylthiophene)/fullerene blends has been studied in this Article. It is shown that the photovoltaic performance is strongly affected by gelation, which alters the morphology of the photoactive layer. Device optimization yields solar cells with a power conversion efficiency of 3.78% under standard test conditions (AM 1.5, 100 mW/cm2).

Three novel 2-trifluoromethyl-activated bisfluoro monomers have been synthesized successfully using a Suzuki-coupling reaction of 4-fluoro-3-trifluoromethyl phenyl boronic acid with 4,4 '-dibromo-p-terphenyls with varied phenyl substitution on the middle phenylene ring. Three monomers were converted to a series of phenyl substituted poly(arylene ether)s by nucleophilic displacement of the fluorine atoms on the terminal benzene ring, with several bisphenols. The polymers obtained by displacement of the fluorine atoms exhibit weight-average molecular weight up to 1.44 10 5 g/mol in GPC. Thermal analysis studies indicated that these polymers did not show melting endotherms but did show ultrahigh glass-transition temperature (Tg) values up to 332 °C in differential scanning calorimetry (DSC) and outstanding thermal stability up to 671 °C for 5% weight loss in TGA under nitrogen atmosphere. The polymers are soluble in a wide range of organic solvents: tetrahydrofuran (THF), chloroform (CHCl3), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimeth- ylformamide (DMF), toluene, etc., and are insoluble in dimethyl sulfoxide (DMSO) and acetone at room temperature. Transparent and flexible films were easily prepared by solution casting from a chloroform solution of each of the polymers. The UV absorption spectra of thin films showed no absorption in the visible light region of the spectrum, suggesting a good application to optical transparent materials in the visible light region of the spectrum.

The grain structure in lamellar block copolymer samples undergoing a disorder-to-order transition was studied by a combination of depolarized light scattering (DPLS) and transmission electron microscopy (TEM). The 4-fold symmetry of the DPLS profiles indicated the presence of anisotropic grains. A pattern recognition algorithm for analyzing the TEM micrographs of samples partially filled with anisotropic, ordered grains was developed. The volume fractions of sample occupied by ordered grains determined from light scattering and electron microscopy are in reasonable agreement. Both methods indicate that, on average, the characteristic length of the grains in the direction perpendicular to the lamellar planes was a factor of 2 larger than that in the plane of the lamellae. The absolute magnitudes of grain sizes determined by light scattering are about 50% larger than those determined by microscopy.

A combination of in situ birefringence and depolarized light-scattering experiments was used to study the formation of an ordered cylindrical microstructure in a polystyrene-block-polyisoprene copolymer melt under a shear flow field. We demonstrate that our sample forms an imperfect “single crystal” with a fraction of the cylinders aligned in the flow direction. The aligned regions of the sample coexist with randomly oriented grains. The birefringence experiments enable the characterization of the aligned regions while the depolarized light-scattering experiments enable the characterization of the randomly oriented grains. A model for depolarized light scattering from such samples was developed. It was shown that the usual scattering formulas for grains embedded in an isotropic matrix are applicable provided one recognizes that the scattering vector, q, has transverse (qT) and longitudinal (qL) components even in the small angle scattering limit (qL is the component of q in the propagation direction). Thi...

An investigation of the morphological behavior of a series of graft copolymers having multiple regularly spaced, tetrafunctional branch points has been carried out. The behavior of these materials, comprised of polyisoprene backbones with two polystyrene arms grafted to the backbone at each branch point, is shown to be effectively modeled by considering the behavior of smaller, architectural subunits based on the local environment of each junction point (constituting block copolymer). Morphological behavior was characterized using TEM and SAXS. Well-ordered cylindrical and lamellar morphologies were observed. Several samples appear to form cylindrical domains in disordered arrangements. Samples predicted to form spheres form instead a microphase-separated “mesh” morphology. Lamellar grain size and shape were also investigated, and lamellar grain orientation correlation lengths were determined. These measurements show a decrease in grain size with increasing number of branch points per molecule. They also ...

The objective of this paper is to identify the molecular parameters that govern ordering kinetics in a diblock copolymer melt. Experimental data on the ordering kinetics were obtained by time-resolved depolarized light scattering after the sample was quenched from the disordered to the ordered state. The ordered state consisted of cylinders arranged on a hexagonal lattice. During the early stages of the disorder-to-order transition, a dilute suspension of ordered grains grow by invading the surrounding, disordered phase. A time-dependent Ginzburg−Landau model was used to relate the growth rate of these grains to molecular parameters. The growth rate is predicted to be proportional to the quench depth and chain radius of gyration and inversely proportional to the molecular relaxation time. Independent estimates of these parameters were obtained from small angle neutron scattering and rheological measurements. The experimentally determined grain growth rates are in good agreement with theoretical prediction...

Ordering kinetics after quenching a block copolymer melt from the disordered state to the ordered state were studied by time-resolved, depolarized light scattering. A theoretical framework for rela...