Dimensionally and thermally stable polymer,containing disordered graphitic structure and adamantane

In an attempt to develop a low‐k interlayer dielectric, adamantane‐diphenyldiethynyl moiety containing oligomer is prepared. Oligomerization of 1,3,5,7‐tetrakis[3/4‐ethynylphenyl]adamantane ( 4 ) is accomplished by a Glaser–Hay oxidative coupling with 1,3,5‐triethynylbenzene and phenylacetylene end‐capping agent. The CHCl₃ soluble oligomer is then thermally treated by step‐curing at 200, 300, 380, and 450 °C for 30 min at each temperature under nitrogen flow to render a shiny void‐free black polymer. TGA analysis indicates that the polymer is stable under nitrogen up to 500 °C with a marginal decomposition up to 800 °C. Solid‐state ¹³C NMR, Raman scattering, and FTIR are used to characterize the structure of the polymer. The polymer consists of amorphous carbon networks with the adamantane moieties and nanosized graphitic regions (clusters), which are generated from the thermal crosslinking of the diphenyldiethynyl units. It shows a remarkably low linear coefficient of thermal expansion (～25 ppm/°C), presumably due to the presence of the disordered graphitic structure. Its high density (～1.21 g/cm³), refractive index (～1.80 at 632 nm), and Young's modulus (～17.0 GPa) are also consistent with the interpretation. This study reveals important details about the effect of microscopic structure on the macroscopic properties of the highly crosslinked polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6909–6925, 2006     

Alternating copolymer of thiophene andN‐(phenylethynyl)pyrrole. New π‐conjugated alternating five‐membered ring copolymer and its packing structure

An alternating copolymer, Copoly‐1 , of thiophene and N‐(phenylethynyl)pyrrole was prepared by palladium‐catalyzed polycondensation. Powder X‐ray diffraction (XRD) analysis indicated that Copoly‐1 formed a stacked packing structure with doubly‐running polymer main chains. Optical data support the molecular and packing structures of Copoly‐1 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2219–2224, 2005     

Supramolecular architectures with ladder and lamellar topologies using metal-ligand coordination units via C–H···Cl and O–H···Cl hydrogen bonding

New Mn^II/Cu^II/Zn^II complexes [(L¹)MnCl₂] (1), [(L²)CuCl₂]·0.5H₂O (2) and [(L²)ZnCl(H₂O)][ClO₄] (3), containing (2-pyridyl)alkylamine ligands, N-methyl-N,N-bis(2-pyridylmethyl)amine (L¹) and methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine (L²), have been prepared and characterized, including X-ray crystallography. The most striking feature of the structures of these complexes is the formation of molecular ladder and lamellar topology through the crystal packing arrangement, determined by both strong O–H···Cl and weak (however, multiple) C–H···Cl hydrogen-bonding interactions, to maintain the neutral/cationic metal-ligand coordination units linked to each other. In 3, additional secondary interactions are observed involving coordinated solvent and the counter-ion. The results presented here demonstrate that (i) the choice of organic ligands to provide flexibility and inherent potential to participate in hydrogen-bonding interactions, (ii) the coordination geometry preferences of metal ions, (iii) the number of metal-bound chloride ion and (iv) the presence of solvent/counter-anion have a great influence on supramolecular network topology.     

Multiaxial mechanical behavior of aramid fibers and identification of skin/core structure from single fiber transverse compression testing

The transverse and longitudinal mechanical properties of aramid fibers like Kevlar? 29 (K29) fibers are strongly linked to their highly oriented structure. Mechanical characterization at the single fiber scale is challenging especially when the diameter is as small as 15 µm. Longitudinal tensile tests on single K29 fibers and single fiber transverse compression test (SFTCT) have been developed. Our approach consists of coupling morphological observations and mechanical experiments with SFTCT analysis by comparing analytical solutions and finite element modeling. New insights on the analysis of the transverse direction response are highlighted. Systematic loading/unloading compression tests enable to experimentally determine a transverse elastic limit. Taking account of the strong anisotropy of the fiber, the transverse mechanical response sheds light on a skin/core architecture. More importantly, results suggest that the skin of the fiber, typically representing a shell of one micrometer in thickness, has a transverse apparent modulus of 0.2 GPa. That is around more than fifteen times lower than the transverse modulus of 3.0 GPa in the core. By comparison, the measured longitudinal modulus is about 84 GPa. The stress distribution in the fiber is explored and the critical areas for damage initiation are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 374–384     

Photovoltaic devices using semiconducting polymers containing head‐to‐tail‐structured bithiophene,pyrene, and benzothiadiazole derivatives

An alternating copolymer composed of heal‐to‐tail‐structured 3,4′‐dihexyl‐2,2′‐bithiophene (DHBT) and pyrene units [poly(DHBT‐alt‐PYR)] was synthesized using a Stille coupling reaction for use in photovoltaic devices as a p‐type donor. For the reduction of the bandgap energy of poly(DHBT‐alt‐PYR), 4,7‐bis(3′‐hexyl‐2,2′‐bithiophen‐5‐yl)benzo[c][1,2,5]thiadiazole (BHBTBT) units were introduced into the polymer. Poly(DHBT‐co‐PYR‐co‐BHBTBT)s were synthesized using the same polymerization reaction. The synthesized polymers were soluble in common organic solvents and formed smooth thin films after spin casting. The optical bandgap energies of the polymers were obtained from the onset absorption wavelengths. The measured optical bandgap energy of poly(DHBT‐alt‐PYR) was 2.47 eV. As the BHBTBT content in the ter‐polymers increased, the optical bandgap energies of the resulting polymers decreased. The bandgap energies of poly(50DHBT‐co‐40PYR‐co‐10BHBTBT) and poly(50DHBT‐co‐20PYR‐co‐30BHBTBT) were 1.84 and 1.73 eV, respectively. Photovoltaic devices were fabricated with a typical sandwich structure of ITO/PEDOT:PSS/active layer/LiF/Al using the polymers as electron donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester as the electron acceptor. The device using poly(50DHBT‐co‐20PYR‐co‐30BHBTBT) showed the best performance among the fabricated devices, with an open‐circuit voltage, short‐circuit current, fill factor, and maximum power conversion efficiency of 0.68 V, 5.54 mA/cm², 0.35, and 1.31%, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

APICOPHILICITY AND RING-STRAIN IN FIVE-COORDINATE PHOSPHORANES

Abstract

In order to dicuss mechanism in organophosphorus chemistry a number of assumptions have to be made. Among them are: (a) that substitutions at tetrahedral phosphorus proceed via five-coordinate intermediates; (b) these intermediates are trigonal bipyramidal; (c) they are formed by apical attack and decompose by apical loss; and (d) if sufficiently long-lived, they may undergo permutational isomerization, that is the ligands may alter their relative dispositions round the phosphorus, before going on to products or back to reactants.

Assuming that the course of a given substitution is dictated primarily by thermodynamic considerations, in order to understand the course of that substitution one needs to know how to assess the relative stabilities of the four isomeric tbps (trigonal bipyramids) that can be formed initially and of the others that could be formed by subsequent isomerization, the barriers to those isomerizations, and the relative rates of the various product-forming steps. We have concentrated on the first of these factors and this lecture describes our attempts to provide the necessary data.

The energy difference between two isomeric tbps can be analyzed in terms of changes in the relative apicophilicities¹ of the groups occupying apical positions, changes in ring-strain as small rings move between apical-equatorial and diequatorial positions, and changes in steric strain. I shall consider each of these in turn. Ligand subset symmetry may also have to be taken into account.^1,2     

A ladder conjugated polymer transducer for solid-contact Cu2+-selective electrodes

In recent years, there has been a pronounced interest in solid-contact ion-selective electrodes （SC-ISEs）, with emphasis on the use of conducting polymers as ion-to-electron transducer. In this work, a ladder conjugated polymer, thieno[3,2-b]thiophene （LCPT）, was investigated in fabricating Cu2＋-selective electrodes for the first time. The resulting electrodes were characterized by electrochemical impedance spectroscopy （EIS）, chronopotentiometry, and the water layer test. Results proved that the active LCPT facilitates the ion-to-electron transduction, and avoids the detrimental aqueous layer formed at the interface of SC-ISEs.     

Analysis of diverse direct arylation polymerization (DArP) conditions toward the efficient synthesis of polymers converging with stille polymers in organic solar cells

Despite the emergence of direct arylation polymerization (DArP) as an alternative method to traditional cross‐coupling routes like Stille polymerization, the exploration of DArP polymers in practical applications like polymer solar cells (PSCs) is limited. DArP polymers tend to have a reputation for being marginally inferior to Stille counterparts due to the increased presence of defects that result from unwanted side reactions in direct arylation, such as unselective C‐H bond activation and homocoupling. We report ten DArP protocols across the three major classes of DArP to generate poly[(2,5‐bis(2‐hexyldecyloxy)phenylene)‐alt‐(4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT). Through evaluation of the method and resulting photophysical and electronic properties, we show not all DArP methods are suitable for generating device‐quality alternating copolymers. When DArP PPDTBT was synthesized in superheated THF with Cs₂CO₃, neodecanoic acid, and P(o‐anisyl)₃, it generated polymers of exceptional quality that performed comparably to Stille counterparts in both roll coated ITO‐free and spin‐coated ITO devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2907–2918     

Regioregular poly(3‐alkanoylthiophene): Synthesis and electrochemical,photophysical, charge transport,and photovoltaic properties

Head‐to‐tail regioregular poly(3‐heptanoylthiophene) (PHOT) was synthesized by Ni‐catalyzed polycondensation of the 2,2‐dimethyl‐1,3‐propanediol‐protected Grignard monomer followed by deprotection. Cyclic voltammetric (CV) study demonstrates that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of PHOT are 0.5 eV lower in energy than those of the head‐to‐tail poly(3‐hexylthiophene) (HT‐P3HT). Their optical band gaps are essentially the same. Incomplete photoluminescence (PL) quenching was observed in thin films of the 1:1 blend of PHOT and HT‐P3HT. PHOT displayed a glass transition at ～269 °C and decomposed at ～300 °C according to differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Wide‐angle X‐ray diffraction (WAXD) study showed that PHOT exists in a not highly ordered state in solid films especially in the π‐stacking direction. Only p‐channel activity was observed in field‐effect transistors (FETs) for PHOT. The hole mobility was on the order of 10^?4 cm² V^?1 s^?1. Photovoltaic devices with an active layer of 1:1 blend of PHOT and PC₇₁BM had a power conversion efficiency (PCE) of ～0.5%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010