Synthesis of Aliphatic Polyamide Dendrimers Based on Facile Convergent Method

A novel and rapid approach for the synthesis of aliphatic polyamide dendrimers, consisting of the 3,4-dialkoxyhydrocinnamamide structure as a repeating unit, has been developed. Aliphatic polyamide dendrons and dendrimers were easily prepared by a convergent approach involving activation of a carboxylic acid at the focal point using (2,3-dihydro-2-thioxo-3-benzoxazolyl)­phosphonate (DBOP) as the activating agent, followed by condensation with an unprotected AB₂ building block. Dumbbell-shaped and star-shaped third generation dendrimers were prepared from the third generation dendron and core molecules containing two or three functional groups. All the above products could be purified only by precipitation, and their structures were confirmed by ¹H NMR, IR, and matrix-assisted laser desorption ionization time-of-flight mass (MALDI–TOF–MS) spectroscopies and elemental analysis

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

A novel initiator, <i>N</i>,<i>N′</i>-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 <i>n</i>-type and <i>p</i>-type blocks was proposed. With a 10:9 feed molar ratio of NDI-Br₂ to 2,5-bis­(trimethylstannyl)­thiophene, an <i>n</i>-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

Nonstoichiometric Stille Coupling Polycondensation for Synthesizing Naphthalene-Diimide-Based π‑Conjugated Polymers

A nonstoichiometric Stille coupling polycondensation was first succeeded between 2,5-bis­(trimethylstannyl)­thiophene (<b>1</b>) and 4,9-dibromo-2,7-bis­(2-decyltetradecyl)­benzo­[<i>lmn</i>]­[3,8]-phenanthroline-1,3,6,8-tetraone (<b>2</b>) with ratios ranging from 1:1 to 1:10. The model reaction using 2-(tributylstannyl)­thiophene (<b>3</b>) and 4,9-dibromo-2,7-bis­(2-hexyl)­benzo­[<i>lmn</i>]­[3,8]-phenanthroline-1,3,6,8-tetraone (<b>4</b>) at a 1:1 molar ratio in the presence of catalytic Pd₂(dba)₃/P­(<i>o</i>-tolyl)₃ indicated that the rate constant of the second substitution reaction (<i>k</i>₂) is 15 times higher than that of the first one (<i>k</i>₁). It was found that the selective intramolecular catalyst transfer was promoted by the naphthalene-diimide (NDI) skeleton. The results also provided a new one-pot symmetrical end-functionalization method to synthesize an NDI-based n-type polymer with NDI groups at both α,ω-chain ends

Triggered Structural Control of Dynamic Covalent Aromatic Polyamides: Effects of Thermal Reorganization Behavior in Solution and Solid States

Thermally rearrangeable aromatic polyamides (TEMPO-PA) and random copolyamides (TEMPO-PA-COOH) incorporating alkoxyamine moieties in the main chain were synthesized, and the effects of thermal reorganization behavior on their solution and solid-state structures were investigated. The hydrodynamic radius in solution decreased as the solution temperature increased because of the dissociation of the alkoxyamine unit. Additionally, the dry density of the thin films decreased as the fabrication temperature increased because of the suppression of polymer aggregation caused by the thermally induced radical crossover reaction. In addition, at the film surface of the random copolyamide containing hydrophobic TEMPO and hydrophilic 3,5-diaminobenzoic acid (DABA) units, the hydrophilicity decreased as the fabrication temperature increased. This is because hydrophobic TEMPO and hydrophilic DABA units tend to be discretely aggregated near the film surface to minimize the surface energy and suppress the hydrogen bonding via a radical crossover reaction during the thin-film fabrication process. The present study clearly shows that both the solution structure and the solid-state molecular aggregation structure of the dynamic covalent polymers can be easily controlled by a thermal trigger, and it provides a new method for controlling the higher-order structure of polymer solutions and solids

Sequentially Different AB Diblock and ABA Triblock Copolymers as P3HT:PCBM Interfacial Compatibilizers for Bulk-Heterojunction Photovoltaics

The P3HT:PCBM (P3HT = poly­(3-hexylthiophene, PCBM = phenyl-C61-butyric acid methyl ester) bulk-heterojunction (BHJ) organic photovoltaic (OPV) cells using the AB diblock and ABA triblock copolymers (A = polystyrene derivative with donor–acceptor units (PTCNE) and B = P3HT) as compatibilizers were fabricated. Under the optimized blend ratio of the block copolymer, the power conversion efficiency (PCE) was enhanced. This PCE enhancement was clearly related to the increased short-circuit current (<i>J</i>_sc) and fill factor (FF). The incident photon to current efficiency (IPCE) measurement suggested that the P3HT crystallinity was improved upon addition of the block copolymers. The increased P3HT crystallinity was consistent with the increased photovoltaic parameters, such as <i>J</i>_sc, FF, and consequently the PCE. The surface energies of these block copolymers suggested their thermodynamically stable location at the interface of P3HT:PCBM, showing the efficient compatibilizing performance, resulting in enlarging and fixing the interfacial area and suppressing the recombination of the generated carriers. Grazing incidence X-ray scattering (GIXS) results confirmed the superior compatibilizing performance of the ABA triblock copolymer when compared to the AB diblock copolymer by the fact that, after blending the ABA triblock copolymer in the P3HT:PCBM system, the enhanced crystallinity of matrix P3HT was observed in the excluded areas of the less-aggregated PCBM domains, changing the P3HT crystalline domain orientation from “edge-on” to “isotropic”. This is, to the best of our knowledge, the first sequential effect (AB vs ABA) of the block copolymers on the compatibilizing performances based on BHJ OPV device systems

Synthesis and Postfunctionalization of Rod–Coil Diblock and Coil–Rod–Coil Triblock Copolymers Composed of Poly(3-hexylthiophene) and Poly(4-(4′‑<i>N</i>,<i>N</i>‑dihexylaminophenylethynyl)styrene) Segments

Poly­(3-hexylthiophene) (P3HT) with a bromobutyl functional group at the ω-chain-end (P3HT-C₄Br) and P3HT with bromobutyl functional groups at the α,ω-chain-ends (BrC₄-P3HT-C₄Br) were synthesized by selecting the appropriate initiators for the Grignard metathesis (GRIM) polymerization. The high end-functionality was confirmed by matrix assisted laser desorption-ionization time-of-flight (MALDI–TOF) mass spectrometry. These polymers were efficiently reacted with the living anionic polymers of 4-(4′-<i>N</i>,<i>N</i>-dihexylaminophenylethynyl)­styrene (DHPS) to yield novel rod–coil diblock and coil–rod–coil triblock copolymers composed of rigid P3HT and flexible poly­(4-(4′-<i>N</i>,<i>N</i>-dihexylaminophenylethynyl)­styrene) (PDHPS) segments. The expected structures of the block copolymers were confirmed by size exclusion chromatography (SEC), proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared (FT-IR) spectroscopies. Furthermore, the side chain alkynes of the PDHPS segments of both P3HT-<i>b</i>-PDHPS and PDHPS-<i>b</i>-P3HT-<i>b</i>-PDHPS were quantitatively functionalized by a [2 + 2] cycloaddition followed by a cycloreversion with tetracyanoethylene (TCNE), producing the corresponding block copolymers with donor–acceptor moieties in the flexible polystyrene segments. The formation of the new chromophores was confirmed by UV–vis spectroscopy and cyclic voltammetry (CV), which revealed strong intramolecular charge-transfer bands and redox activities ascribed to the formed donor–acceptor moieties. The thermal properties and surface morphology of the block copolymers were also evaluated by differential scanning calorimetry (DSC), atomic force microscopy (AFM) observations, and small-angle and wide-angle X-ray scattering (SAXS and WAXS). This is the first report about the development of P3HT-based block copolymers with tunable optoelectronic properties, which was achieved by the combined synthetic techniques of the GRIM polymerization, living anionic polymerization, and click postfunctionalization

Polymer Electrolyte Membranes Based on Multiblock Poly(phenylene ether ketone)s with Pendant Alkylsulfonic Acids: Effects on the Isomeric Configuration and Ion Transport Mechanism

Two structural variations of multiblock poly­(phenylene ether ketone)­s (bSPPEKs) with pendant alkylsulfonic acids were prepared by a polycondensation reaction between oligomeric difluoro and diphenoxide precursors, followed by successive demethylation and sulfonation processes. Two isomers, bis­[4-fluoro-3-(4′-methoxylbenzoyl)]­biphenyl (<i>p</i>-BFMBP) and bis­[5-fluoro-2-(4′-methoxylbenzoyl)]­biphenyl (<i>m</i>-BFMBP), were prepared as the difluoro starting monomers. The corresponding polymer membranes were obtained with good mechanical stability to facilitate the further characterizations. The morphology of bSPPEKs was confirmed by atomic force microscopy, from which the distinct phase separation could be identified with the average hydrophilic domain size of ca. 15–20 nm for the <i>m</i>-bSPPEKs. It is worth noting that both <i>m</i>- and <i>p</i>-bSPPEKs show quite comparable, or even better, ion conduction capacities than commercially available Nafion membrane, especially under low relative humidity conditions (30–50%), suggesting their promising future as polymer electrolyte membrane candidates. Meanwhile, the proton conductivities of all of the <i>m</i>-bSPPEKs were found to be greater than those of the <i>p</i>-bSPPEKs over the entire relative humidity range, indicating better water-retention capacity and lower resistance to the ion transport. In addition, molecular dynamics simulation was employed to extensively explore the structure–property relationship between the two polymers. The length, angle, and torsion distribution results clearly reveal their steric configurations, that is, a longer length and smaller angle in the side chain, together with a smaller torsion angle in the main chain for <i>m</i>-bSPPEKs, which produces slightly more free volume inside the polymer matrix. Analysis of the diffusion coefficients and coordination numbers shows that there is more water clustering around the sulfonic acid groups in the meta-polymers than in the para-polymers

Thermal Diffusivity of Hexagonal Boron Nitride Composites Based on Cross-Linked Liquid Crystalline Polyimides

Hexagonal boron nitride (h-BN) composites with the oriented cross-linked liquid crystalline (LC) polyimide have been developed as high thermally conductive materials. Well-dispersed h-BN composite films were obtained, as observed by scanning electron microscopy. The morphology of the composite films was further investigated in detail by the wide-angle X-ray diffraction. The obtained composite films based on the cross-linked LC polyimide showed that the polymer chains vertically aligned in the direction parallel to the films, while those based on the amorphous polyimide showed an isotropic nature. Moreover, the alignment of the cross-linked LC polyimides was maintained, even after increasing the volume fraction of h-BN. This alignment plays an important role in the effective phonon conduction between h-BN and the matrices. Indeed, the thermal diffusivity in the thickness direction of the composite films based on the LC polyimide measured by a temperature wave analysis method was increased to 0.679 mm² s^–1 at a 30 vol % h-BN loading, which was higher than that based on the amorphous polyimide

Poly(phenylene thioether)s with Fluorene-Based Cardo Structure toward High Transparency, High Refractive Index, and Low Birefringence

To realize high-performance thermoplastic camera lenses for compensating chromatic aberration in which lenses with large and small Abbe numbers were combined, novel poly­(phenylene thioether)­s with a fluorene-based cardo structure were developed with the potential for simultaneously realizing high transparency, a high refractive index, low birefringence, and small Abbe number. Excellent transmittance was observed in all polymer films because the interchain packing was effectively suppressed by the cardo structure (e.g., transmittance was as high as 90% at 400 nm), and furthermore, high refractive index values (1.6553–1.6762) were attained. The polymer with the highest content of cardo structure exhibited a low birefringence of 0.0014. The efficient cancellation of polarization anisotropy between the polymer backbone and the fluorene units directed perpendicular to the polymer backbone contributed to the low birefringence. These results indicate that promising materials for high-performance optical applications can be developed based on the well-suited incorporation of the cardo structure into the polymer backbone

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-<i>alt</i>-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 <i>in situ</i> 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 length of P3HT was controllable by varying the feed molar ratio of the thiophene monomer to CTT unit during the KCTP. The optical and electrochemical properties of the all-conjugated graft copolymers were investigated by UV–vis, cyclic voltammetry (CV), and organic field-effect transistor (OFET) measurements. Moreover, the differential scanning calorimetry (DSC) and grazing incident wide-angle X-ray scattering (GIWAXS) results revealed that there were two distinguished crystalline domains in the thin films of the graft copolymer. The morphology of the graft copolymers was first observed by transmission electron microscopy (TEM), in which there was a microphase separation between the PNDICTT and P3HT domains, and the P3HT domains showed partial nanofibril structures with a width of 10–20 nm