Shi-Min Shau

Flame retardant epoxy polymers based on all phosphorus-containing components

A phosphorus-containing epoxy resin, bis(3-t-butyl-4-glycidyloxyphenyl-2,4-di-t-butylphenyl)resorcinol diphosphate, was synthesized and subsequently cured with non-phosphorus containing amines, and/or novel phosphorus-containing aromatic or polyoxyalkylene amines. Chemical structures of these materials were characterized with FTIR, NMR, elemental analysis, and amine titration. The introduction of soft –P–O– linkage, polyoxyalkyene, or hard aromatic group into the backbones of the synthesized phosphorus-containing amines provides epoxy polymers with high phosphorus contents and tailored flexibility. Thermal analysis of differential scanning calorimeter and thermal gravimetric analysis (TGA) reveals that these resulted epoxy polymers possess moderate Tgs and thermal stability. Furthermore, high char yields in TGA analysis and high limited oxygen index values indicate that these phosphorus-containing epoxy polymers possess excellent flame retardant properties.

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.

Individual graphene oxide platelets through direct molecular exfoliation with globular amphiphilic hyperbranched polymers

In this study, we used a solution process, involving direct molecular exfoliation of graphite oxide (GO) stacked layers, to obtain individual graphene oxide platelets (GOPs) through amphiphilic hyperbranched polymers (HPs). The HPs, based on poly(amic acid) and polyimide with terminal amino functionalities, were obtained through a facile “A2 + B3” synthesis; gel permeation chromatography of the HPs revealed molecular weights of 5000–8200 g mol−1 with a distribution of polydispersity between 2.0 and 4.2. Next, we inserted these globular HPs into the interlayer spaces of GO to prepare a series of GO/HP nanohybrids possessing intercalated and exfoliated morphologies. The intercalation processes featured a critical transition point at which a dramatic enlargement occurred to the interlayer spacing, depending on the content of the bulky embedded HPs. From transmission electron microscopy images, we observed transparent folding of the GOPs; powder X-ray diffraction analysis revealed individual nanosheets with well-defined diffraction patterns. Incorporating the bulky three-dimensional globular structure into the layered GO significantly influenced the solution exfoliation, allowing us to examine the intercalating behavior of GO intergallery. This solution-phase methodology, through direct HP molecular exfoliation, provides the way toward obtaining individual nanosheets, opening up opportunities for platelet-like nanographene oxide materials in many technological applications.

Thermal stability of poly(oxyalkylene)amine-grafted polypropylene copolymers

Abstract The thermal and thermo-oxidative degradation of a family of amphiphilic copolymers consisting of a polypropylene (PP) backbone and several poly(oxyethylene) /poly(oxypropylene) (POE/POP) pendants were investigated by using a thermal gravimetric analysis (TGA). Their relative stability was correlated to the chemical structures with respect to the POE versus POP in pendants and the terminal functionalities. In comparing the starting amines, molecular weight (Mw) and the types of polymer backbone were the main controlling factors for thermal stability in nitrogen, while the terminal amine contributed most to the thermo-oxidative stability in air. In the amine-grafted PP copolymers, the functional groups including the tethered amine, quaternary amine and sodium salt complexes significantly stabilized the PP copolymers, particularly in oxidative condition. The following trends of relative stability in air were observed: PP-g-MA/EDA>PP-g-MA/DAP ≫ PP-g-MA/ED2001 ≫ PP-g-MA/M2070=PP-g-MA/D2000>ED2001>D2000=PEG2000>PPG2000; PP-g-MA/Na+>PP-g-MA. Under the condition of helium gas and at 550°C, the representative PP-g-MA/ED2001 copolymer was pyrolyzed into fragments of olefins/dienes from PP backbone as well as vinyl ethers from POE pendants, as observed by GC/mass spectroscopy. Reaction pathways for degradation and the controlling factors for the thermal and thermooxidative stability of these functionalized PP copolymers are discussed.

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.

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.