Rong-Ho Lee

Phosphorus-containing epoxy for flame retardant. III: Using phosphorylated diamines as curing agents

Two phosphorus-containing diamine compounds, bis(4-aminophenoxy)-phenyl phosphine oxide and bis(3-aminophenyl)phenyl phosphine oxide, were synthesized for use as curing agents of epoxy resins. Phosphorylated epoxy resins were obtained by curing Epon 828 and Eponex 1510 with these two diamine agents. For raising the phosphorus contents of the resulting epoxy resins, the phosphorus-containing epoxy, bis(glycidyloxy)phenyl phosphine oxide (BGPPO), was also used. These two diamine agents showed similar reactivity toward epoxies. Their reactivities were higher than DDS and lower than DDM. High char yields in TGA evaluation were found for all the phosphorylated epoxy resins, implying their high flame retardancy. The excellent flame-retardant properties of these phosphorylated epoxy resins were also demonstrated by the high limiting oxygen index (LOI) values of 33 to 51.

Single-Layered Graphene Oxide Nanosheet/Polyaniline Hybrids Fabricated Through Direct Molecular Exfoliation

In this study, we used direct molecular exfoliation for the rapid, facile, large-scale fabrication of single-layered graphene oxide nanosheets (GOSs). Using macromolecular polyaniline (PANI) as a layered space enlarger, we readily and rapidly synthesized individual GOSs at room temperature through the in situ polymerization of aniline on the 2D GOS platform. The chemically modified GOS platelets formed unique 2D-layered GOS/PANI hybrids, with the PANI nanorods embedded between the GO interlayers and extended over the GO surface. X-ray diffraction revealed that intergallery expansion occurred in the GO basal spacing after the PANI nanorods had anchored and grown onto the surface of the GO layer. Transparent folding GOSs were, therefore, observed in transmission electron microscopy images. GOS/PANI nanohybrids possessing high conductivities and large work functions have the potential for application as electrode materials in optoelectronic devices. Our dispersion/exfoliation methodology is a facile means of preparing individual GOS platelets with high throughput, potentially expanding the applicability of nanographene oxide materials.

Novel polythiophene derivatives functionalized with conjugated side-chain pendants comprising triphenylamine/carbazole moieties for photovoltaic cell applications†

We synthesized a series of polythiophenes (PTs) featuring 2-ethylhexyl-substituted terthiophene (T) or quaterthiophene (BT) as the conjugated unit in the polymer backbone with pendant conjugated tert-butyl-substituted triphenylamine (tTPA)- or carbazole (tCz)-containing moieties as side chains, namely PTtTPA, PBTtTPA, PTtCz and PBTtCz. Incorporating T and BT moieties into the polymer backbone and attaching tTPA or tCz units promoted efficient conjugation within the extended conjugated frameworks of the polymers, resulting in lower band-gap energies and red-shifting of the maximal UV-Vis absorption wavelength. The higher electron-donating ability of tTPA resulted in broader absorption bands and lower band-gap energies of PTtTPA and PBTtTPA as compared with PTtCz and PBTtCz. Incorporation of the T and BT moieties into the polymer backbone enhanced the compatibility of PT and the fullerene derivative by reducing the side-chain density of PT, thus providing sufficient free volume for efficient incorporation of [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) into the polymer chains. Polymer solar cells (PSCs) were fabricated by spin-coating a blend of each PT with the fullerene derivative (PC61BM) as a composite film-type photoactive layer; PBTtTPA/PC61BM-based PSCs showed superior photovoltaic (PV) performance to PTtTPA/PC61BM-based PSCs in terms of conjugation and absorption band broadness. However, PBTtCz/PC61BM-based PSCs showed inferior PV performance to PTtCz/PC61BM-based PSCs. The lower HOMO level led to a higher open-circuit voltage (Voc; 0.74 V) and larger photo-energy conversion efficiency (η; 2.77%) of PTtCz/PC61BM-based PSCs.

Sequential self-repetitive reaction toward wholly aromatic polyimides with highly stable optical nonlinearity

A sequential self-repetitive reaction (SSRR) based on carbodiimide (CDI) chemistry was utilized for preparing a high-yield wholly aromatic polyimide. The polyimide was synthesized with 4,4′-methylene-diphenylisocyanate (MDI) and a di(acid-ester) compound which was derived from the ring-opening reaction of 3,3′,4,4′-oxydiphthalic dianhydride (ODPA) at room temperature by the addition of equimolar methanol. Poly-CDI was first synthesized from MDI. The di(acid-ester) compound was then reacted with poly-CDI to form poly(N-acylurea). After curing process, N-acylurea moiety was converted to di(ester-amide) structure viaSSRR and further subjected to a ring-closure reaction to form the wholly aromatic polyimide with a Tg of 247 °C. This approach was further taken to prepare thermally stable nonlinear optical (NLO) materials. Similarly a diimide-diacid containing chromophore was reacted with poly-CDI to obtain an intermediate, poly(N-acylurea). The poly(N-acylurea) with the ester side groups would exhibit excellent organosolubility, which enabled the fabrication of high quality optical thin films. After in situ poling and curing processes, N-acylurea moiety was converted to di(ester-amide) structure viaSSRR and further subjected to a ring-closure reaction to form the wholly aromatic NLO polyimide with an electro-optical coefficient, r33 of 25 pm/V (830 nm). Excellent temporal stability at elevated temperatures (200 °C) and a waveguide optical loss of 2.5 dB cm−1 at 1310 nm were also obtained.

Dielectric study of a ferroelectric side-chain liquid crystalline polysiloxane with a broad temperature range of the chiral smectic C phase: 2. Doping effect of a non-linear optically active dye

Abstract Dielectric relaxation behaviour of the guest-host mixture of a ferroelectric side chain liquid crystalline polymer (FLCP) and a nonlinear optical (NLO) dye has been investigated with broadband dielectric relaxation spectroscopy. The liquid crystal (LC) phases of these guest-host materials were characterized with the differential scanning calorimeter, optical polarizing microscopy, and X-ray diffractometer. No phase separation is observed when the doping level of the NLO dye is below 10 wt%. The doping of the NLO dye into the FLCP results in the significant increase of the relaxation intensity and frequency of the Goldstone mode in the chiral smectic C phase ( S C ∗ ). Moreover, the NLO dye has high relaxation intensity in the LC phase for such guest-host material. On the other hand, the occurrence of phase separation is observed when the doping level of the NLO dye is 30% by weight. The phase separation results in the reduction of the relaxation intensity for both the Goldstone mode of the FLCP and molecular motion of the NLO dye. The relationship between the thermal dynamic behaviour and the environment around molecules for such NLO active guest-host material was discussed in great detail.

Dielectric study of ferroelectric side‐chain liquid crystalline polysiloxanes with broad temperature ranges of the chiral smectic C phase 1. Structure dependence of dielectric relaxation

The dielectric behavior of a series of ferroelectric side-chain liquid crystalline polysiloxanes containing 1–3 oligooxyethylene units as spacers, and 4-(S)-2-methyl-1-butyl[[[(4-hydroxy-biphenyl-4′-yl)]carbonyl]oxy] benzoate or 4-(S)-2-methyl-1-butyl[[(4-hydroxy-biphenyl-4′-yl)carbonyl]oxy]-3-fluoro benzoate side groups was studied by broadband dielectric spectroscopy. The increase of the spacer length, and incorporation of a strong dipole moment fluoro-substituent into the mesogenic group, resulted in a decrease of the relaxation activation energy and an increase in the intensity of the relaxation. Moreover, the relaxation peak of the Goldstone mode has only been observed for the FLCP with a lateral fluoro-substituent. The relationship between the thermal dynamic behavior and chemical structure is discussed in detail. Furthermore, analysis of the dielectric relaxation behavior of these FLCPs showed that the molecular relaxations could be described by the Cole-Cole equation.

Enhanced shape memory performance of polyurethanes via the incorporation of organic or inorganic networks

A diol compound with a reactive azetidine-2,4-dione group was prepared and introduced as a side chain moiety of poly(e-caprolactone) (PCL) based polyurethane (PU). The PUs with reactive pendants were crosslinked by 1,6-diaminohexane, or modified by an alkoxysilane (3-aminopropyltriethoxysilane, APTS) followed by a sol–gel reaction to bring about crosslinked PUs for shape memory applications. Thermal and mechanical properties of the crosslinked PUs are strongly dependent on the chemical structure of the interchain-linker between the polymer chains. Higher tensile strengths would be achieved for the PU samples crosslinked with alkoxysilanes in comparison with the ones crosslinked with an aliphatic diamine, while higher values of elongation at break were observed for the latter. As compared to the PCL based linear and side-chain PUs, much better shape memory performance was observed as the PU sample was crosslinked with the aliphatic diamine, or by the sol–gel reaction of alkoxysilanes, particularly the latter. Higher shape retention (91%) and recovery (99%) ratios were observed for the CPU samples with inorganic networks. By introducing the chemically crosslinked structures, the deformed PU samples completely recovered their original shape in less than 10 seconds without any deficiency during shape recovery measurements.

Solution processable star-shaped molecules with a triazine core and branching thienylenevinylenes for bulk heterojunction solar cells†

Two new star-shaped A–π–D molecules with triazine as a core and an acceptor unit, thienylenevinylene as the π bridge, and tert-butyl-substituted triphenylamine (tTPA)- or carbazole (tCz) as the end group and donor units of TTVTPA and TTVCz were synthesized for their application as donor materials in solution processed bulk heterojunction organic solar cells (OSCs). The charge transfer was convergent from peripheral groups to the central core along the conjugated branches in these star-shaped molecules (SSMs). TTVTPA and TTVCz are soluble in common organic solvents. Excellent thermal stability was observed for TTVTPA and TTVCz. OSCs were fabricated by spin-coating a blend of each SSM with the fullerene derivatives (PC61BM or PC71BM) as a composite film-type photoactive layer. The PV properties of the TTVTPA/fullerene derivative based OSCs were considerably better than those of the TTVCz/fullerene derivative blend based OSCs. A power conversion efficiency of 2.48%, a short-circuit current density of 10.57 mA cm−2, an open-circuit voltage of 0.69 V, and a fill factor of 0.34 were observed for the OSC based on the active layer of TTVTPA/PC71BM (1 : 7, w/w).

Adjustable bioadhesive control of PEGylated hyperbranch brushes on polystyrene microplate interface for the improved sensitivity of human blood typing.

A PEGylated 96-well polystyrene (PS) microplate was first introduced for applications in high-throughput screening for selective blood typing to minimize the risks in blood transfusions. Herein, we present a hemocompatible PS 96-well microplate with adjustable PEGylated hyperbranch brush coverage prepared by ozone pretreated activation and thermally induced surface PEGylation. The grafting properties, hydration capacity, and blood compatibility of the PEGylated hyperbrush immobilized PS surfaces in human blood were illustrated by the combined chemical and physical properties of the surface, and the dependence of the specific absorption of human plasma fibrinogen onto the PEGylated surfaces on the grafting density was analyzed by monoclonal antibodies. The surface coverage of PEGylated brushes plays a major role in the bioadhesive properties of modified PS microplates, which in turn control the level of agglutination sensitivity in blood typing. The bioadhesive resistance toward proteins, platelets, and erythrocytes in human whole blood showed a correlation to the controlled hydration properties of the PEGylated hyperbrush-modified surfaces. Therefore, we suggested that the surface coverage of PEGylated hyperbrushes on PS surfaces can increase the sensitivity of cross-matching blood agglutination by up to 16-fold compared to that of the conventional 96-well virgin PS due to the regulated biorecognition of hematocrit and antibodies of the PEGylated hyperbrush-modified surfaces.

Orderly arranged NLO materials on exfoliated layered templates based on dendrons with alternating moieties at the periphery

Nonlinear optical dendrons with alternating terminal groups of the stearyl group (C18) and chromophore were prepared through a convergent approach. These chromophore-containing dendrons were used as the intercalating agents for montmorillonite via an ion-exchange process. An orderly exfoliated morphology is obtained by mixing the dendritic structure intercalated layered silicates with a polyimide. As a result, optical nonlinearity, i.e. the Pockels effect was observed for these nanocomposites without resorting to the poling process. EO coefficients of 9–22 pm V−1 were achieved despite that relatively low NLO densities were present in the nanocomposites, particularly for the samples comprising the dendrons with alternating moieties. In addition, the hedging effects of the stearyl group on the self-alignment behavior, electro-optical (EO) coefficient and temporal stability of the dendron-intercalated montmorillonite/polyimide nanocomposites were also investigated.