The synthesis of two (2) novel triblock terpolymers of the ABC type and one (1) of the BAC type, where A, B and C are chemically different segments, such as polystyrene (PS), poly(butadiene) (PB1,4) and poly(dimethylsiloxane) (PDMS), is reported; moreover, their corresponding molecular and bulk characterizations were performed. Very low dimensions are evident from the characterization in bulk from transmission electron microscopy studies, verified by small-angle X-ray data, since sub-16 nm domains are evident in all three cases. The self-assembly results justify the assumptions that the high Flory–Huggins parameter, χ, even in low molecular weights, leads to significantly well-ordered structures, despite the complexity of the systems studied. Furthermore, it is the first time that a structure/properties relationship was studied for such systems in bulk, potentially leading to prominent applications in nanotechnology and nanopatterning, for as low as sub-10 nm thin-film manipulations.
We describe the phase behavior of a cylinder-forming block copolymer (BCP)/homopolymer blend and the generation of aligned nanopores by a combination of magnetic field alignment and selective removal of the minority-block-miscible homopolymer. Alignment is achieved by cooling through the order–disorder transition temperature (T odt) in a 6 T field. The system is a blend of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) and poly(ethylene glycol) (PEG). PEG is miscible with P4VP and partitions preferentially into the cylindrical microdomains. Calorimetry and X-ray scattering show that T odt decreases linearly with PEG concentration until the onset of macrophase separation, inferred by PEG crystallization. Beyond this point, T odt is invariant with PEG content. Increasing PEG molar mass decreases the concentration at which macrophase separation is observed. Nanopore formation is confirmed by dye uptake experiments that show a clear dependence of dye uptake on PEG content before removal. We anticipate that this strategy can be extended to other BCP/homopolymer blends to produce nanoporous materials with reliable control of pore alignment and effective pore dimensions.
The systematic optimization of the chemical structure of low-bandgap (LBG) donor-acceptor polymeric semiconductors is a challenging task for which accurate guidelines are yet to be determined. Several different structural and molecular parameters are crucial ingredients for obtaining LBG polymers that simultaneously possess high power conversion efficiencies, good processability in common organic solvents, and enhanced stability in organic photovoltaic devices. In this work, we present an extensive structure-optoelectronic properties-solar cell performance study on the emerging class of diketopyrrolopyrrole-based LBG polymers. In particular, we investigate alkyl side chain positioning by introducing linear alkyl side chains into two different positions (a-and b-), and the distance of the electron rich and electron deficient monomers within the repeat units of the polymer chain. We demonstrate that anchoring linear alkyl side chains to the apositions and introducing fused moieties into the polymer backbone, can be beneficial toward maintaining photocurrents similar to the unsubstituted derivative, and concurrently exhibit better processabiliy in common organic solvents. These results can provide a design rationale towards further optimization of semiconducting polymers. V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 138-146 KEYWORDS: alkyl side chains; conjugated polymers; diketopyrrolopyrrole; donor-acceptor; high performance; low band gap copolymers; nanotechnology; organic solar cells INTRODUCTION Low-bandgap (LBG) semiconducting polymers with bandgaps smaller than 1.4 eV and absorption cut-off in the near infrared (NIR) are of great interest for organic photovoltaics (OPV), organic photodetectors, ambipolar field-effect transistors (FETs) and bio-imaging applications. [1][2][3][4][5] Intense efforts have been devoted to the synthesis of new polymers for such applications, and tremendous progress has been made. Among the various classes of LBG conjugated polymers, diketopyrrolopyrrole (DPP) polymers have attracted considerable attention, today yielding power conversion efficiencies (PCEs) above 8% in polymer solar cells 6-8 and hole and electron mobilities of 17.8 and 6.3 cm 2 V 21 s 21 in FETs. 9,10 Currently,
We report the synthesis of three (3) linear triblock terpolymers, two (2) of the ABC type and one (1) of the BAC type, where A, B and C correspond to three chemically incompatible blocks such as polystyrene (PS), poly(butadiene) of exclusively (~100% vinyl-type) -1,2 microstructure (PB1,2) and poly(dimethylsiloxane) (PDMS) respectively. Living anionic polymerization enabled the synthesis of narrowly dispersed terpolymers with low average molecular weights and different composition ratios, as verified by multiple molecular characterization techniques. To evaluate their self-assembly behavior, transmission electron microscopy and small-angle X-ray scattering experiments were conducted, indicating the effect of asymmetric compositions and interactions as well as inversed segment sequence on the adopted morphologies. Furthermore, post-polymerization chemical modification reactions such as hydroboration and oxidation were carried out on the extremely low molecular weight PB1,2 in all three terpolymer samples. To justify the successful incorporation of –OH groups in the polydiene segments and the preparation of polymeric brushes, various molecular, thermal, and surface analysis measurements were carried out. The synthesis and chemical modification reactions on such triblock terpolymers are performed for the first time to the best of our knowledge and constitute a promising route to design polymers for nanotechnology applications.
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