Marta Horecha

“Hairy” Poly(3-hexylthiophene) Particles Prepared via Surface-Initiated Kumada Catalyst-Transfer Polycondensation

Herein, we present a new paradigm in the engineering of nanostructured hybrids between conjugated polymer and inorganic materials via a chain-growth surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) from particles. Poly(3-hexylthiophene), P3HT, a benchmark material for organic electronics, was selectively grown by SI-KCTP from (nano)particles bearing surface-immobilized Ni catalysts supported by bidentate phosphorus ligands, that resulted in hairy (nano)particles with end-tethered P3HT chains. Densely grafted P3HT chains exhibit strongly altered optical properties compared to the untethered counterparts (red shift and vibronic fine structure in absorption and fluorescence spectra), as a result of efficient planarization and chain-aggregation. These effects are observed in solvents that are normally recognized as good solvents for P3HT (e.g., tetrahydrofurane). We attribute this to strong interchain interactions within densely grafted P3HT chains, which can be tuned by changing the surface curvature (or size) of the supporting particle. The hairy P3HT nanoparticles were successfully applied in bulk heterojunction solar cells.

Grafting of Polyfluorene by Surface‐Initiated Suzuki Polycondensation

Graft work: The first surface-initiated and site-specific palladium-catalyzed Suzuki polycondensation that allows selective grafting and patterning of semiconducting and emissive poly[9,9-bis(2-ethylhexyl)fluorene] (1) at room temperature is developed (see scheme). The patterning is demonstrated by AFM (see image).

Surface Engineering Using Kumada Catalyst-Transfer Polycondensation (KCTP): Preparation and Structuring of Poly(3-hexylthiophene)-Based Graft Copolymer Brushes

Poly(4-vinylpyridine)-block-poly(4-iodo-styrene), P4VP-b-PS(I), block copolymers obtained by iodination of readily available P4VP-b-PS block copolymers strongly adhere to variety of polar substrates including Si wafers, glasses, or metal oxide surfaces by a polar P4VP block, forming polymer brushes of moderately stretched PS(I) chains. Kumada catalyst-transfer polycondensation (KCTP) from the P4VP-b-PS(I) brushes results into planar brushes of the graft copolymer in which relatively short ( approximately 10 nm) poly(3-hexylthiophene), P3HT, grafts emanate from the surface-tethered PS(I) chains. Grafting of the P3HT leads to significant stretching of the PS(I) backbone as a result of increased excluded volume interactions. Specific adsorption of the P4VP block to polar surfaces was utilized in this work to pattern the P4VP(25)-b-PS(I)(350) brush. The microscopically structured P4VP(25)-b-PS(I)(350) brush was converted into the respectively patterned P4VP-PS(I)-g-P3HT one using KCTP. We also demonstrated that KCTP from functional block copolymers is an attractive option for nanostructuring with polymer brushes. P4VP(75)-b-PS(I)(313) micelles obtained in selective solvent for the PS(I) block form a quasi-ordered hexagonal array on Si wafer. The P4VP(75)-b-PS(I)(313) monolayer preserves the characteristic quasi-regular arrangement of the micelles even after extensive rinsing with various solvents. Although the grafting of P3HT from the nanopatterned P4VP(75)-b-PS(I)(313) brush destroys the initial order, the particulate morphology in the resulting film is preserved. We believe that the developed method to structured brushes of conductive polymers can be further exploited in novel stimuli-responsive materials, optoectronic devices, and sensors.

Ordered surface structures from PNIPAM-based loosely packed microgel particles

On-surface self-assembly of several types of microgels prepared via the precipitation polymerization of (N-isopropylacrylamide) (NIPAM) with N,N′-methylenebisacrylamide (MBA), acrylic acid or acrylamide as comonomers is investigated with the aim to establish the main factors that govern the formation of periodic loosely packed (PLP) two-dimensional arrays. A core–shell structure is detected for all microgels, with the thickest shells being observed for the microgels containing acrylic acid or acrylamide. The main factor driving the formation of PLP arrays and determining the microgel separation is found to be the presence of large low-density shells around the highly cross-linked cores of the microgels. This key observation of our experiments has been explained by the developed theoretical model that proves to adequately describe the experimental findings. The size of microgel dry-state “footprints” can be reduced by making use of plasma-etching. The periodic microgel arrays are used as masks for the preparation of patterns of reactive silanes with controllable separation between the patterned features. Sputtering of gold onto the periodic microgel arrays followed by washing out the microgels in ultrasonic bath is proven to be an efficient way of preparing perforated gold films with PLP holes.

Polymer microcapsules loaded with Ag nanocatalyst as active microreactors

We report on the fabrication of a new complex catalytic system composed of silica-supported silver nanoparticles (AgNP) encapsulated inside polymer microcapsules (MC)s. The silver nanocatalyst itself was obtained by reduction of silver salt in the presence of SiO2 particles acting as AgNP carriers, to provide a complex Ag/SiO2 catalyst with the Ag surface completely free of capping agents. Ag/SiO2 particles were enclosed inside the interior of polymer microcapsules. Due to the presence of the hydrophobic shell on the MC surface, catalytic reactions become feasible in an organic solvent environment. On the other hand, the hydrophilic nature of the MC interior forces the water-soluble reactants to concentrate inside the capsules which act as microreactors. Based on the example of catalytically driven reduction of 4-nitrophenol we demonstrate that encapsulated Ag/SiO2 particles possess enhanced catalytic activity as compared to the catalyst being freely dispersed in reaction medium.

Cyclopolymerization-derived block-copolymers of 4,4-bis(octyloxymethyl)-1,6-heptadiyne with 4,4- dipropargyl malonodinitrile for use in photovoltaics

The synthesis of AB-type block copolymers of 4,4-bis(octyloxymethyl)-1,6-heptadiyne (M1) and dipropargyl malonodinitrile (M2) via metathesis-based cyclopolymerization using well-defined molybdenum- and ruthenium-based initiators is described. While backbiting reactions were observed in the case where polymerizations were triggered by [Ru(NCO)2(IMesH2)(CH-2-(2-PrO)–C6H4] (I2) and [Ru(NCO)2(3-Br-Py)2(IMesH2)(CHPh)] (I3), (IMesH2 = 1,3-dimesitylimidazolin-2-ylidene, 3-Br-Py = 3-bromopyridine), the use of RuCl2(Py)2(IMesH2)(CHPh) (I1) in THF allowed for the synthesis of poly(M1) without any backbiting, though with a broad PDI. Block copolymers, i.e. poly(M1)-b-poly(M2), could be prepared in a living manner without any backbiting by the use of the Mo-based Schrock-type initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OCH(CH3)2)2 (I4) and THF as solvent. Poly(M1)-b-poly(M2) was characterized by UV and fluorescence spectroscopy and used for the construction of a photovoltaic device.

Hydrophobically Covered Hydrogels: Preparation Approaches and Possible Applications

This article overviews methods for preparation of micrometer-sized particles having hydrogel core and hydrophobic shell. It demonstrates that water-in-oil inverse suspension polymerization is a versatile method for one-step synthesis of either non-hollow spherical hydrogel particles or hollow capsules, depending on the nature of the gel-forming polymer. It further shows that rather thin hydrophobic shell provides a good stability of the particles in organic solvents while still does not preclude swellability of the hydrophilic core with water and small water-soluble molecules. A stepwise approach for fabrication of the core-shell hydrogel particles is also described which assumes preparation of hydrogel particles as the first step, their arrangement on surfaces followed by growing of the hydrophobic shell. Two methods for preparation of the hydrophobic shell were explored. The first one assumes free-radical polymerization of the polyisoprene from adsorbed hydrogel particles while the second one implies electrostatically-driven adsorption of polyisoprene latex particles onto oppositely charged hydrogels. Thus-obtained core-shell particles were used in fabrication of switchable coatings.