Improvement of thermoplasticity for s‐BPDA/PDA by copolymerization and blend with novel asymmetric BPDA‐based polyimides

Asymmetric biphenyl type polyimides (PI) derived from 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA) and p‐phenylenediamine (PDA) or 4,4′‐oxydianiline (ODA) show higher T_gs, and much better thermoplasticity than the corresponding isomeric PIs from symmetric 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA). In addition, a‐BPDA‐derived PIs are completely amorphous owing to their bent chain structures and highly distorted conformations, whereas the PIs from s‐BPDA are semicrystalline. a‐BPDA‐derived PIs possessing these properties or the a‐BPDA monomer were used as a flexible blend component or a comonomer to improve the insufficient thermoplasticity of semirigid s‐BPDA/PDA homo polymer. The blends composed of s‐BPDA/PDA (80%) with a‐BPDA‐derived PIs (20%), as well as the s‐BPDA/PDA‐based copolymer containing 20% a‐BPDA, showed a certain extent of thermoplasticity above the T_gs without causing a decrease in T_g. In addition, these blends and copolymer provided comparatively low thermal expansion coefficient (ca. 18 ppm). The improved film properties for the blends are related to good blend miscibility. On the other hand, when s‐BPDA/ODA was used as a flexible matrix polymer instead of a‐BPDA‐derived PIs, the 80/20 blend film annealed at 400°C exhibited no prominent softening at the T_g. This result arises from annealing‐induced crystallization of the flexible s‐BPDA/ODA component. Thus, these results revealed that a‐BPDA‐derived PIs are promising candidates as matrix polymers for semirigid s‐BPDA/PDA for the present purpose. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2499–2511, 1999     

Fixed crosslink formation and viscoelasticity of polystyrene networks

The crosslinking formation in the 8/92 mol % random copolymer of ethynyl- styrene and styrene is clarified quantitatively from the IR spectrum analysis on the basis of the thermally homogeneous reaction of ethynylstyrenes between the chains. The viscoelastic properties of the crosslinked polystyrene, CL-P(ESt/St), are investigated based on the temperature and frequency dependencies of the dynamic Young modulus. The relaxation spectrum of CL-P(ESt/St) drops deeply like the Wedge type with a slope of −½ in the glass transition region, and became a plateau without a terminal zone in the rubbery elasticity region. The effects of the ethynyl crosslinked junctions for the micro-Brownian motions of the segments in the strand are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3319–3327, 1999     

Cyclodextrin gels which have a temperature responsiveness

β-Cyclodextrin (CD) gels crosslinked by epichlorohydrin (CD-gel) were modified with poly(N-isopropylacrylamide) (PIPA; M_n 4900) chains. The CD residue in the gel associated with 8-anilino-1-naphthalenesulfonic acid (ANS) more strongly than the free PIPA-carrying CD. The van't Hoff plot for complexation of ANS with the gel drifted largely from linear relationship above the coil-globule transition temperature of individual PIPA chains. Furthermore, a relatively more significant temperature effect on the stereoselective adsorption of phenylalanine to the CD gel was observed by the modification with PIPA chains. These results imply that the ability of the CD-gel–PIPA conjugate to form inclusion complex could be skillfully controlled by temperature. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1535–1541, 1997     

Synthesis of gels by means of Michael addition reaction of multi-functional acetoacetate and diacrylate compounds and their application to ionic conductive gels

Michael-addition reactions of multi-functional acetoacetate, meso-erythritol tetraacetoacetate (ETAA), trimethylolpropane triacetoacetate (TPTAA), and diacrylate compounds, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, or poly(ethylene glycol) diacrylate (PEGDA), in dimethyl sulfoxide have successfully yielded the corresponding gels in the presence of 1,8-diazabicyclo[5.5.0]undecane-7-ene as a catalyst at room temperature. The gel formation rates of the reaction systems with TPTAA were higher than those with ETAA. The gels prepared with the alkyl diacrylate compounds or low molecular weight PEGDA showed higher Young's modulus in compression test. The ETAA-PEGDA gels were also prepared in propylene carbonate containing Li ion or in an ionic liquid. These gels showed good ionic conductivity with conductivity value as high as 2.26 and 2.38 mS/cm at room temperature for the Li ion and ionic liquid containing systems respectively.     

One-Step Simultaneous Synthesis of Circularly Polarized Luminescent Multiple Helicenes Using a Chrysene Framework

A series of multiple helicenes was simultaneously synthesized in one step by intramolecular cyclization of a single chrysene derivative containing two 2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the aryl pendants. The electrophile-induced double cyclization with or without aryl migrations proceeded efficiently under acidic conditions to afford annulative π-extension of the chrysene units and produced quadruple (QH- 2 ), triple (TH- 2 ), and double (DH- 2 ) helicenes containing [4]- and/or [5]helicene frameworks with dynamic and/or static helicene chirality in one step. Three multiple helicenes’ structures were determined by X-ray crystallography and/or density functional theory calculations. The multiple TH- 2 and DH- 2 helicenes were separated into enantiomers because of the stable one and two [5]helicene moieties, respectively, and showed intense circular dichroism and circularly polarized luminescence. Although QH- 2 , which comprises four [4]helicene subunits, was not resolved into enantiomers, the TH- 2 enantiomers were further separated into a pair of diastereomers at low temperature resulting from their substituted [4]helicene chirality.     

Thermal analysis of cesium hafnium chloride using DSC–TG under vacuum,nitrogen atmosphere,and in enclosed system

Journal of Thermal Analysis and Calorimetry - This paper reports on the preparation of undoped cesium hafnium chloride (Cs2HfCl6) and study of its thermal properties. The Cs2HfCl6 is considered,...     

Efficient light-harvesting,energy migration,and charge transfer by nanographene-based nonfullerene small-molecule acceptors exhibiting unusually long excited-state lifetime in the film state

Electron-acceptor small-molecules possessing a long exciton lifetime and a narrow energy band gap, opposing the energy gap law, are highly desirable for high-performance organic photovoltaics (OPVs) by realizing their efficient light-harvesting ability (LH), exciton diffusion (ED), and charge transfer (CT). Toward this goal, we designed an acceptor–donor–acceptor (A–D–A) type nonfullerene acceptor (NFA), TACIC, having an electron-donating, self-assembling two-dimensional (2D) nanographene unit, thienoazacoronene, at the center with electron-withdrawing groups at both ends. The TACIC film exhibited a narrow band gap (1.59 eV) with excellent LH. Surprisingly, the TACIC film showed an extremely long exciton lifetime (1.59 ns), suppressing undesirable nonradiative decay by its unique self-assembling behavior. When combined with a conjugated polymer donor, PBDB-T, slow ED and CT were observed (60 ps) with the excitation of TACIC owing to the large TACIC domain sizes. Nevertheless, the unusually high efficiencies of ED and CT (96% in total) were achieved by the long TACIC exciton lifetime. Additionally, unusual energy transfer (EnT) from the excited PBDB-T to TACIC was seen, demonstrating its dual LH role. The OPV device with PBDB-T and TACIC showed a high incident photon-to-current efficiency (IPCE) exceeding 70% at up to 710 nm and a power conversion efficiency of ∼10%. This result will open up avenues for a rational strategy of OPVs where LH, ED, and CT from the acceptor side as well as LH, EnT, ED, and CT from the donor side can be better designed by using 2D nanographene as a promising building block for high-performance A–D–A type NFAs.

A nonfullerene acceptor, TACIC, showed efficient light-harvesting, exciton diffusion, and charge transfer.     

Selective Formation of a Mixed-Valence State from Linearly Bridged Oligo(aromatic diamines): Drastic Structural Change into a Folded Columnar Stack for Half-filled Polycations

A method to obtain an organic mixed-valence state with long-range delocalization is proposed, which enables the selective generation of half-filled (n/2-charged) polycations from linearly bridged oligomers with n electron-donating units. When π-extended phenylenediamine units are connected by meta-xylylene-type spacers, the resulting oligomers adopt non-folded structures in the neutral state owing to the non-conjugating and flexible nature of the spacer, whereas the structure shows a drastic change into a one-dimensional columnar stack upon oxidation to the corresponding half-filled polycations. Although they are nano-sized discrete molecules, they can mimic the electronic structure of crystalline organic conductors in a mixed-valence state. The key for the oligomer design is adoption of the best-matched spacer that facilitates formation of the singly charged pimer in the dichromophoric system whereas the corresponding doubly charged π-dimer is disfavored.