Kumada Catalyst-transfer Polycondensation Research Articles

Controlled Synthesis of an Alternating Donor-Acceptor Conjugated Polymer via Kumada Catalyst-Transfer Polycondensation.

Kumada catalyst-transfer polycondensation was used to synthesize poly(5,6-difluorobenzotriazole-alt-4-hexylthiophene) (PFBTzHT), an alternating donor-acceptor conjugated polymer, in a controlled manner. Through a series of kinetic studies, a linear relationship between the monomer conversion and the molecular weight of the resulting polymer was observed while maintaining narrow polydispersities (Đs ≤ 1.4). Moreover, the Mn displayed a linear relationship with the initial monomer-to-catalyst feed ratio, and polymers with Mns up to 25 kDa were successfully synthesized. All-conjugated block copolymers containing segments of PFBTzHT and poly(3-hexylthiophene) (P3HT) were also obtained in various compositions (30-70% P3HT) via sequential monomer addition in a single vessel.

The Synthesis of Poly(thiophene-co-fluorene) Gradient Copolymers

The copolymerization of thiophene and fluorene starting from a mixture of the two monomers is investigated. It is shown that these monomers are incapable of copolymerizing using a Kumada catalyst transfer polycondensation. However, when the Pd(RuPhos) protocol is used, this copolymerization is enabled and gradient copolymers are obtained. Consequently, this protocol is applied to the synthesis of a series of six polymers with varying monomer feeds, and the properties of these gradient copolymers are investigated. This new class of materials, which was previously inaccessible using other catalysts, shows unique properties compared with the block copolymer analogues.

Controlled synthesis of high molecular weight poly(3-hexylthiophene)s via Kumada catalyst transfer polycondensation with Ni(IPr)(acac)2 as the catalyst.

The controlled synthesis of poly(3-hexylthiophene)s (P3HTs) with number-average molecular weights (Mns) up to 350 kg mol(-1) has been realized with Ni(IPr)(acac)2 as the catalyst.

Kumada catalyst transfer polycondensation for controlled synthesis of polyfluorenes using 1,3-bis(diarylphosphino)propanes as ligands

The moderately hindered catalyst Ni(acac)2/L2 outperformed other catalysts, affording PF8s with Mn up to 91.1 in a controlled manner.

Effects of catalyst loading amount on the synthesis of poly(3-hexylthiophene) via externally initiated Kumada catalyst-transfer polycondensation

A series of model polymerization are carried out via the one-pot externally initiated Kumada catalyst-transfer polycondensation (KCTP) of 2-bromo-5-chloromagnesium thiophene monomers, and the excess amount of initiators or catalysts are found no need to be isolated during the polycondensation process. Especially, the impacts of the nickel catalyst loading variation on regioregularity (rr), yield, molecular weight (M n), polydispersity (PDI) and initiation efficiency of poly(3-hexylthiophene) (P3HT) are systematically investigated. The 1H NMR, size-exclusion chromatography (SEC), and MALDI-TOF mass spectroscopy results indicated that an excess amount of catalyst does not influence yield, rr, M n, and PDI of P3HT, nor the initiation efficiency. However, the PDI of the product is broad, and the M n and rr values decreased in the absence of 1,3-bis (diphenylphosphino)propane (dppp). It can be concluded that the in-situ KCTP polymerization of P3HT is a practical and effective process. These results are especially valuable for the synthesis of all-conjugated block copolymers where macroinitiators are used.

Synthesis of TiO2-poly(3-hexylthiophene) hybrid particles through surface-initiated Kumada catalyst-transfer polycondensation.

TiO2/conjugated polymers are promising materials in solar energy conversion where efficient photoinduced charge transfers are required. Here, a "grafting-from" approach for the synthesis of TiO2 nanoparticles supported with conjugated polymer brushes is presented. Poly(3-hexylthiophene) (P3HT), a benchmark material for organic electronics, was selectively grown from TiO2 nanoparticles by surface-initiated Kumada catalyst-transfer polycondensation. The grafting of the polymer onto the surface of the TiO2 nanoparticles by this method was demonstrated by (1)H and (13)C solid-state NMR, X-ray photoelectron spectrometry, thermogravimetric analysis, transmission electron microscopy, and UV-visible spectroscopy. Sedimentation tests in tetrahydrofuran revealed improved dispersion stability for the TiO2@P3HT hybrid material. Films were produced by solvent casting, and the quality of the dispersion of the modified TiO2 nanoparticles was evaluated by atomic force microscopy. The dispersion of the P3HT-coated TiO2 NPs in the P3HT matrix was found to be homogeneous, and the fibrillar structure of the P3HT matrix was maintained which is favorable for charge transport. Fluorescence quenching measurements on these hybrid materials in CHCl3 indicated improved photoinduced electron-transfer efficiency. All in all, better physicochemical properties for P3HT/TiO2 hybrid material were reached via the surface-initiated "grafted-from" approach compared to the "grafting-onto" approach.

Fully Conjugated Graft Copolymers Comprising a P-Type Donor–Acceptor Backbone and Poly(3-hexylthiophene) Side Chains Synthesized Via a “Graft Through” Approach

A series of fully conjugated graft copolymers containing poly(3-hexylthiophene) (P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole (CbzDPP) donor–acceptor backbone were synthesized via a graft through Suzuki polymerization. The macromonomers were formed by externally initiating P3HT growth from a boronic ester-functionalized carbazole via Kumada catalyst transfer polycondensation. Subsequently, this macromonomer was copolymerized with a DPP monomer via a graft through Suzuki polymerization to yield the final graft copolymers. The graft copolymers exhibit optical and electronic properties of both P3HT and the CbzDPP polymers independently due to the break in conjugation between the carbazole unit and P3HT chain. Moreover, these properties reflect the relative proportion of P3HT and CbzDPP polymers; shorter P3HT chain lengths lead to graft copolymers that possess more CbzDPP character and vice versa. The macromonomers were characterized by gel permeation chromatography, mass spectrometry, and UV...

Nickel Catalyst with a Hybrid P, N Ligand for Kumada Catalyst Transfer Polycondensation of Sterically Hindered Thiophenes.

A highly active nickel catalyst with a hybrid P,N ligand is successfully used for the first time for the polymerization of a thiophene monomer with sterically very demanding side groups. The performance of this catalyst is by far not achievable with commercially available standard catalysts. Polythiophenes with special side chain patterns can thus be made with predetermined molecular weight, low dispersity, and high regioregularity, which enable the preparation of various large crystalline superstructures for the investigation of anisotropic optoelectronic properties in the absence of π-π interactions.

Synthesis of All-Conjugated ABA and AB-type Donor-Acceptor Block Copolymers and Their Application in All-Polymer Solar Cells

ABSTRACTIn this work, we report the synthesis of all-conjugated donor-acceptor block copolymers via a externally initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized by KCTP initiated by Ni(COD)2 activated PNDI complexes. Therefore, a series of ABA (P3HTs were initiated from both ends of PNDI) and AB-type (P3HT was initiated from one end of PNDI) block copolymers were successfully synthesized. Before fabrication of all-polymer solar cells, the morphologies and crystalline behaviors of the block copolymers were extensively investigated as a function of thermal annealing and the main chain composition of PNDI block. As a control, the crystalline behaviors of the physical blends of P3HT and PNDIs were also reported. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active component or as surfactants. A PCE of 0.11 % with Voc=0.46 V, Jsc=0.50 mA/cm2, and FF=0.46 was recorded by using the donor-acceptor all-conjugated block copolymer as the single active component.

Poly(3-hexylthiophene) Molecular Bottlebrushes via Ring-Opening Metathesis Polymerization: Macromolecular Architecture Enhanced Aggregation.

We report a facile synthetic strategy based on a grafting through approach to prepare well-defined molecular bottlebrushes composed of regioregular poly(3-hexylthiophene) (rr-P3HT) as the conjugated polymeric side chain. To this end, the exo-norbornenyl-functionalized P3HT macromonomer was synthesized by Kumada catalyst transfer polycondensation (KCTP) followed by postpolymerization modifications, and the resulting conjugated macromonomer was successfully polymerized by ring-opening metathesis polymerization (ROMP) in a controlled manner. The P3HT molecular bottlebrushes display an unprecedented strong physical aggregation upon drying during recovery, as verified by several analyses of the solution and solid states. This remarkably strong aggregation behavior is attributed to a significant enhancement in the number of π-π interactions between grafted P3HT side chains, brought about due to the bottlebrush architecture. This behavior is qualitatively supported by coarse-grained molecular dynamics simulations.

Synthesis of All-Conjugated Donor-Acceptor-Donor ABA-Type Triblock Copolymers via Kumada Catalyst-Transfer Polycondensation.

A novel initiator, N,N'-bis(2-decyltetradecyl)-2,6-dibromonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-Br2), was found effective in the Kumada catalyst-transfer polycondensation (KCTP) for the synthesis of regioregular poly(3-hexylthiophene) (P3HT). In addition, a two-step method of synthesizing all-conjugated triblock copolymers comprised of both n-type and p-type blocks was proposed. With a 10:9 feed molar ratio of NDI-Br2 to 2,5-bis(trimethylstannyl)thiophene, an n-type macroinitiator (PNDITh-Br2) was prepared via the Stille coupling reaction. Two outer P3HT blocks were then emanated via KCTP initiated by PNDITh-Br2 to produce all-conjugated ABA-type triblock copolymers. The size exclusion chromatography (SEC) curves of all the triblock copolymers showed narrow distribution, with the lowest polydispersity index (PDI) of 1.15. Moreover, the molecular weight of the block copolymer was found to be independent of the amount of Ni catalyst, while it can be tailored by the feed molar ratio of the thiophene monomer to PNDITh-Br2. The transmission electron microscopy (TEM) images and grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns of the block copolymer thin film revealed a well-defined lamellar structure and two distinguished crystalline domains, where the P3HT layer was in the range of 10-20 nm and presented an edge-on rich alignment.

Synthesis and Characterization of All-Conjugated Graft Copolymers Comprised of n-Type or p-Type Backbones and Poly(3-hexylthiophene) Side Chains

All-conjugated graft copolymers containing poly(3-hexylthiophene) (P3HT) side chains and both of p-type and n-type backbones that are connected with all π-conjugated linkages were synthesized via a two-step method involving the Stille coupling reaction and Kumada catalyst-transfer polycondensation (KCTP). A series of naphthalene diimide copolymers with different compositions of 3-(4′-chloro-3′-tolyl)thiophene (CTT) units (PNDICTT) were designed as n-type backbones, while the poly(3-(4′-chloro-3′-tolyl)thiophene-alt-thiophene) (PCTT) was designed as a p-type backbone which were converted into n-type or p-type macroinitiators, and P3HT side chains were then in situ grafted from the macroinitiators via an externally initiated KCTP at room temperature. By using this newly developed two-step method for the synthesis of all-conjugated graft copolymers, the number of P3HT side chains in the graft copolymers can be simply controlled by varying the composition of the CTT units in PNDICTT. Meanwhile, the chain leng...

Synthesis of poly[(4,4′-(dihexyl)dithieno(3,2-b;2′,3′-d)silole)] and copolymerization with 3-hexylthiophene: new semiconducting materials with extended optical absorption

The synthesis of poly[(4,4′-(dihexyl)dithieno(3,2-b;2′,3′-d)silole)] has been carried out through Kumada catalyst transfer polycondensation and its copolymerization with 3-hexylthiophene (3HT) leads to well-defined diblock copolymers in terms of molecular characteristics. These copolymers show a wider absorption window than P3HT, which is of potential interest for photovoltaic applications.

Synthesis of Poly(3-Hexylthiophene) with High Molecular Weight and Small Polydispersity

Regioregular head-tail poly(3-hexylthiophenes) (HT-P3HT) with a controlled high molecular weight and a small polydispersity have been synthesized via an improved Kumada catalyst-transfer polycondensation (KCTP) by using the new-prepared hexylmagnesium bromide as the Grignard reagent. As the amount of nickel catalyst dichloro[1,3-diphenylphosphinopropane] nickel (Ni(dppp)Cl2) was 0.5% mol of the amount of monomer 2,5-dibromo-3-hexylthiophene (DBHT) we can obtain a HT-P3HT with a high molecular weight Mn (38 449) and a small polydspersity (1.18). By using of LiCl as a co-catalyst, the regioregularity of the P3HT with high molecular weight (40 270) is maintained and the PDI (1.03) is smaller than that of the P3HT polymerized in the absence of LiCl but the conversion ratio of the monomer is promoted. The HT-P3HT with high molecular weight and small polydispersity will be an attractive candidate applied in solar cells.

Surface-Initiated Poly(3-methylthiophene) as a Hole-Transport Layer for Polymer Solar Cells with High Performance

In this work, uniform poly(3-methylthiophene) (P3MT) films are fabricated on indium-tin oxide (ITO) surfaces using surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) from surface-bound arylnickel(II) bromide initiators. The P3MT interfacial layer is covalently bound to the ITO surface, thereby preventing possible delamination during the processing of additional layers. These surface-bound P3MT layers successfully serve as the hole-transport layer for solution-processed bulk heterojunction polymer solar cells. Efficiencies greater than 5% have been achieved on devices based on doped thin P3MT interfacial layers. Moreover, because of the excellent stability of the covalently immobilized P3MT on ITO substrates, devices based on reused P3MT/ITO substrates extracted from old devices exhibit efficiencies similar to those of the original devices.

Palladium‐Mediated Surface‐Initiated Kumada Catalyst Polycondensation: A Facile Route Towards Oriented Conjugated Polymers

Palladium-mediated surface-initiated Kumada catalyst transfer polycondensation is used to generate poly(3-methyl thiophene) films with controlled thickness up to 100 nm. The palladium initiator density is measured using cyclic voltammetry and a ferrocene-capping agent, where the surface density is found to be 55% (1.1 × 10(14) molecules per cm(2)). UV-Vis spectroscopy and AFM show increased aggregation in palladium-initiated films due to the higher grafting density of palladium initiators on the surface. The anisotropy of the P3MT films is determined using polarized UV-Vis spectroscopy, which indicates a degree of orientation perpendicular to the substrate. Evidence that palladium can maintain π-complexation even at elevated temperatures, is also shown through the exclusive intramolecular coupling of both a phenyl and thiophene-based magnesium bromide with different dihaloarenes.

On the Role of Disproportionation Energy in Kumada Catalyst-Transfer Polycondensation.

Kumada catalyst-transfer polycondensation (KCTP) is an effective method for the controlled polymerization of conjugated polymers. Nevertheless, side reactions leading to early termination and unwanted chain coupling cause deviations from the target molecular weight, along with increasing polydispersity and end group variation. The departure from the KCTP cycle stems from a disproportionation reaction that leads to experimentally observed side products. The disproportionation energies for a series of nickel-based initiators containing bidentate phosphino attendant ligands were computed using density functional theory at the B3LYP/DZP level. The initiator was found to be less favorable toward disproportionation by 0.5 kcal mol-1 when ligated by 1,3-bis(diphenylphosphino)propane (dppp) rather than 1,2-bis(diphenylphosphino)ethane (dppe). Trends in disproportionation energy (Edisp) with a variety of bidentate phosphine ligands match experimental observations of decreased polymerization control. Theoretical Edisp values can thus be used to predict the likelihood of disproportionation in cross-coupling reactions and, therefore, aid in catalyst design.

Controlled Synthesis of Polyfluorenes via Kumada Catalyst Transfer Polycondensation with Ni(acac)2/dppp as the Catalyst

A new catalyst system, i.e., nickel acetylacetonate/1,3-bis(diphenylphosphino)propane (Ni(acac)2/dppp), was explored to catalyze the Kumada catalyst transfer polycondensation (KCTP) of three fluorene monomers with different substituents at 9-position. The “living” nature of the polymerization was confirmed by polymerization kinetic studies, “monomer addition” experiment and block copolymerizations. As a result, poly(9,9-dioctylfluorene)s (PF8s) with the number-average molecular weights (Mns) in the range 2.8–62.2 kDa and polydispersity indices (PDIs) of ∼1.20 were successfully synthesized in a controlled manner. The syntheses of fluorene-fluorene and fluorene-thiophene diblock copolymers with Mns up to 46 kDa were also demonstrated. A complex, i.e. Ni(dppp)(acac)2, with an octahedral coordination geometry was isolated and confirmed by X-ray crystallographic analysis. The polymerization experiments indicated that the in situ formed Ni(dppp)(acac)2 should be the active catalyst. To the best of our knowledge, this is the first report on the controlled synthesis of polyfluorenes (PFs) via KCTP.

Surface-Initiated Synthesis of Conjugated Microporous Polymers: Chain-Growth Kumada Catalyst-Transfer Polycondensation at Work.

Most of conjugated microporous polymers (CMPs) prepared to date are poorly processable, intractable solids. The immobilization of CMPs onto various surfaces is strongly desirable for many applications, such as for gas storage and separation, heterogeneous catalysis, and so forth. However, the preparation of thin porous films remains a challenging task. This Letter reports Ni-catalyzed surface-initiated Kumada catalyst-transfer polycondensation of a tetrafunctional thiophene-based (AB) 2-monomer from organosilica microparticles leading to microparticles covered by thin-film (∼30 nm) layers of the CMP. A sample of unbound CMP was also prepared by a bulk polymerization of the same monomer. Thus-obtained CMP possesses a relatively high specific surface area of 463 m2 g-1. The porosity of the immobilized polymer is somewhat lower with a specific surface area of 123 m2 g-1.

On the Role of Single Regiodefects and Polydispersity in Regioregular Poly(3-hexylthiophene): Defect Distribution, Synthesis of Defect-Free Chains, and a Simple Model for the Determination of Crystallinity

Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl(2) as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl(2)-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well.