Well-Ordered Nanoporous ABA Copolymer Thin Films via Solvent Vapor Annealing, Homopolymer Blending, and Selective Etching of ABAC Tetrablock Terpolymers

Solvent vapor annealing treatments are used to control the orientation of nanostructures produced in thin films of a poly­(styrene)-<i>block</i>-poly­(isoprene)-<i>block-</i>poly­(styrene)-<i>block</i>-poly­((±)-lactide) (PS–PI–PS–PLA) and its blends with PLA homopolymer. The PS–PI–PS–PLA tetrablock terpolymer, previously determined to adopt a core­(PLA)–shell­(PS) cylindrical morphology in the bulk, gave perpendicular alignment of PLA cylinders over a limited range of thicknesses using a mixed solvent environment of tetrahydrofuran and acetone. On the other hand, perpendicular alignment was achieved regardless of film thickness by inclusion of 5 wt % homopolymer PLA in the PS–PI–PS–PLA tetrablock. Tapping mode atomic force microscopy (AFM) was used to visualize film surface morphologies. Subsequent reactive ion etching (RIE) and basic hydrolysis of PLA produced 15 nm pores in a PS–PI–PS triblock thin film matrix. Nanoporosity was confirmed by scanning electron microscopy (SEM) images and the vertical continuity of pores was confirmed by cross-sectional SEM analysis

Ultrafiltration Membranes with a Thin Poly(styrene)‑<i>b</i>‑poly(isoprene) Selective Layer

Ultrafiltration membranes with an 80 nm thick block polymer derived selective layer containing 20 nm cylindrical pores were prepared by removing poly­(lactide) (PLA) from a poly­(styrene)-<i>b</i>-poly­(isoprene)-<i>b</i>-poly­(lactide) (PS-PI-PLA) film onto a microporous polymer support. The block polymer film adopted a core­(PLA)-shell­(PI) cylindrical morphology in which vertically-oriented PLA cylinders were degraded to leave PI-lined channels in a PS matrix. Thanks to the combination of PS and PI in the nanoporous matrix, chemical cross-linking was not needed to provide mechanical stability in the thin film. The membranes showed a hydraulic flux of 165 L m^–2 h^–1 bar^–1 and were able to size-discriminate poly­(ethylene oxide) (PEO) solutes in agreement with theoretical predictions

An ADMET Route to Low-Band-Gap Poly(3-hexadecylthienylene vinylene): A Systematic Study of Molecular Weight on Photovoltaic Performance

The effect of molecular weight on organic photovoltaic device performance is investigated for a series of low-band-gap (ca. 1.65 eV) poly­(3-hexadecylthienylene vinylene)­s (C16-PTVs) prepared by acyclic diene metathesis (ADMET) polymerization. By utilizing monomers of varying cis:trans (<i>Z</i>:<i>E</i>) content, seven C16-PTVs were prepared with a number-average molecular weight range of 6–30 kg/mol. Polymers were characterized by size-exclusion chromatography, ¹H NMR spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, wide-angle X-ray scattering, and differential scanning calorimetry. C16-PTVs were integrated into bulk-heterojunction (BHJ) solar cells with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), and conversion efficiency was found to increase with increasing molecular weight. This observation is attributable to an increase in polymer aggregation in the solid state and a corresponding increase in hole mobility. Finally, phase behavior and morphology of the C16-PTV:PCBM active layers were investigated by differential scanning calorimetry and atomic force microscopy, respectively