Der-Jang Liaw

Synthesis and properties of new polyamides and polyimides derived from 2,2'-dimethyl-4,4'-bis(4-aminophenoxy)biphenyl

Abstract In this work, we synthesised a new diamine containing noncoplanar 2,2′-dimethyl-biphenylene and flexible aryl ether units, 2,2′-dimethyl-4,4′-bis(4-aminophenoxy)biphenyl (DBAPB), by nucleophilic substitution of 2,2′-dimethylbiphenyl-4,4′-diol with p -chloronitrobenzene in the presence of K 2 CO 3 , followed by catalytic reduction with hydrazine/PdC system. A series of aromatic polyamides having inherent viscosities of 1.03–1.48 dl g −1 were prepared by direct polycondensation with aromatic dicarboxylic acids using triphenyl phosphite and pyridine as condensing agents. Nearly all of the polymers revealed an amorphous nature and were readily soluble in a variety of organic solvents. These polymer films had a tensile strength ranging from 22 to 65 MPa. The glass transition and melting temperature of these polyamides could be determined by d.s.c. and ranged from 226 to 273°C and 392–438°C, respectively. These polyamides remained fairly stable up to a temperature around or below 400°C. Moreover, 10% mass losses were recorded in the range 467–496°C in nitrogen atmosphere. The new polyimides were synthesised from DBAPB and various aromatic tetracarboxylic dianhydrides by the conventional two-step method which involved ring-opening polyaddition to form poly(amic acid)s and subsequently thermal or chemical cyclodehydration to polyimides. The inherent viscosities of poly(amic acid)s and polyimides were in the range 1.32–2.01 and 0.82–1.10 dl g −1 , respectively. These polyimide films had a tensile strength range of 83–139 MPa. These polyimides had glass transition temperatures between 239 and 303°C. Thermogravimetric analyses demonstrated that almost all polymers were stable up to 450°C, and the 10% mass loss temperatures were recorded in the range 488–534°C in nitrogen.

Effects of polyelectrolyte complexation on the UCST of zwitterionic polymer

Abstract A zwitterionic polymer—poly-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (PDMAPS)—was synthesized and its complexation behaviors with polyanion: poly-2-acrylamido-2-methyl propane sulfonic acid (PAMPS); and polycation: poly-3-acryloylamino propyl trimethyl ammonium chloride (PDMAPAA-Q); or: x , y -ionene bromides ( x =3,6; y =3,4) have been studied. One of the characteristic features of these complexes is that they are soluble, in spite of the abolishment of positive or negative charge of PDMAPS after the complexation and is able to exhibit UCST depending on the concentration and the mixing molar ratio. It was found that PDMAPS–PAMPS complex dramatically increases the viscosity to give a network structure through electrostatic interaction extensively decreasing the UCST, while the PDMAPS–polycation complex first decreases, but then increases the UCST without forming the network. The mechanism of different behaviors of these complexes has been discussed.

Bistable electrical switching and write-once read-many-times memory effect in a donor-acceptor containing polyfluorene derivative and its carbon nanotube composites

A conjugated copolymer of 9,9-didodecylfluorene and 4-triphenylamino-2,6-bis(phenyl)pyridine (F12TPN), containing both electron donor and acceptor moieties, was synthesized via Suzuki coupling polymerization. Polymer memory devices, based on thin films of F12TPN and its carbon nanotube composites, were fabricated. The current density-voltage characteristics of the indium tin oxide (ITO)/F12TPN/Al sandwich structure could be switched from a low conductivity (off) state to a high conductivity (on) state, when operated under negative bias with ITO as the anode. The switch-on voltage of the as-fabricated device was around −2.3V. The on/off state current ratio was about 10. The on/off state current ratio could be enhanced to 105 and the switch-on voltage reduced to about −1.7V by doping the F12TPN layer with about 1wt% of carbon nanotubes. Once the memory devices had been switched on, they could not be erased (switched off) with a reverse bias (positive bias). Thus the memory effect was characteristics of that...

The relative physical and thermal properties of polyurethane elastomers: Effect of chain extenders of bisphenols, diisocyanate, and polyol structures

Polyurethane elastomers based on polyols such as polycaprolactone diol of molar mass 2000 and polytetramethylene glycol of molar mass 2000; diisocyanantes such as diphenyl methane 4,4′ diisocyanate and dicyclohexyl methane 4,4′ diisocyanate; and chain extenders such as bisphenol-A, bisphenol-S,bisphenol-AF, and their brominated derivatives were synthesized. The effects of polyol, diisocyanate, and chain extender on the physical and thermal properties were also studied. The polyurethane elastomers were investigated by X-ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Their limiting oxygen indexes (LOIs), solubilities, tensile strengths, hardnesses, and elongations were also determined. XRD analyses revealed that all of the polyurethanes were semicrystalline. However, the addition of bromine atoms in the polyurethanes markedly decreased their degrees of crystallinity. The brominated polyurethane elastomers have good flame retardancy, as indicated by large LOIs. All of the unbrominated polyurethanes showed good mechanical properties and high thermal stabilities. Polyurethanes based on bisphenol-S had lower solvent resistance caused by the dipolar nature of sulfonyl groups in the polymer chains.

Volatile electrical switching in a functional polyimide containing electron-donor and -acceptor moieties

A solution-processable functional polyimide (PYTPA-PI), containing triphenylamine-substituted diphenylpyridine moieties (PYTPA, electron donors) and phthalimide moieties (PI, electron acceptors), was synthesized. The copolymer exhibits a high glass transition temperature of 342 °C. A switching device, based on a solution-cast thin film of PYTPA-PI sandwiched between an indium-tin oxide (ITO) bottom electrode and an Al top electrode, exhibits two accessible conductivity states and can be switched from the low-conductivity (OFF) state to the high-conductivity (ON) state, with an ON/OFF current ratio of more than 103, at the threshold voltage of about 2.7 V. The ON state is volatile and relaxes readily to the OFF state. However, it can be electrically sustained by a refreshing voltage pulse of 2 V. The ON state can also be reset to the initial OFF state by a reverse bias of −0.9 V. The ability to write, erase, read, and refresh the electrical states fulfills the functionality of a dynamic random access memor...

Synthesis and characterization of novel polyamide‐imides containing noncoplanar 2,2′‐dimethyl‐4,4′‐biphenylene unit

A new diimide-dicarboxylic acid, 2,2′-dimethyl-4,4′-bis(4-trimellitimidophenoxy)biphenyl (DBTPB), containing a noncoplanar 2,2′-dimethyl-4,4′-biphenylene unit was synthesized by the condensation reaction of 2,2′-dimethyl-4,4′-bis(4-minophenoxy)biphenyl (DBAPB) with trimellitic anhydride in glacial acetic acid. A series of new polyamide-imides were prepared by direct polycondensation of DBAPB and various aromatic diamines in N-methyl-2-pyrrolidinone (NMP), using triphenyl phosphite and pyridine as condensing agents. The polymers were produced with high yield and moderate to high inherent viscosities of 0.86–1.33 dL · g−1. Wide-angle X-ray diffractograms revealed that the polymers were amorphous. Most of the polymers exhibited good solubility and could be readily dissolved in various solvents such as NMP, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide, pyridine, cyclohexanone, and tetrahydrofuran. These polyamide-imides had glass-transition temperatures between 224–302 °C and 10% weight loss temperatures in the range of 501–563 °C in nitrogen atmosphere. The tough polymer films, obtained by casting from DMAc solution, had a tensile strength range of 93–115 MPa and a tensile modulus range of 2.0–2.3 GPa.

Synthesis and characterization of new polyamides and polyimides prepared from 2,2-bis[4-(4-aminophenoxy)phenyl]adamantane

In this work, we synthesized a new diamine containing a pendant adamantane group and a flexible aryl ether unit, 2,2-bis[4-(4-aminophenoxy)phenyl]adamantane (BAPA) in three steps starting from 2-adamantanone. A series of new polyamides having inherent viscosities of 0.72-0.90 dL.g -1 were prepared by direct polycondensation with aromatic dicarboxylic acids using triphenyl phosphite and pyridine as condensing agents. All polymers revealed an amorphous nature and were almost readily soluble in a variety of polar solvents. The glass transition temperature of these polyamides range from 254-294°C. The polyamides remain fairly stable up to a temperature around 450°C and lose 10% weight between 490 and 524°C in nitrogen atmosphere. A series of new polyimides were also synthesized from BAPA and various aromatic tetracarboxylic dianhydrides by the conventional two-step method. The inherent viscosities of polyimides were in the range of 0.66-0.77 dL.g -1 . The polyimides are amorphous and have glass transition temperatures between 276 and 310°C. Thermogravimetric analyses demonstrated that almost all polymers are stable up to 450 °C, and the 10% weight loss temperatures were recorded in the range of 515 to 541°C in nitrogen.

Synthesis and characterization of fluorine‐containing polyamides derived from 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane by direct polycondensation

A fluorine-containing diamine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BAPPH) (II), was synthesized in two steps on condensation of 2,2-bis(4-hydroxyphenyl)hexafluoropropane with p-chloronitrobenzene in the presence of potassium carbonate, giving 2,2-bis[4-(4-nitrophenoxy)phenyl]hexafluoropropane (I), followed by reduction with hydrazine monohydrate/Pd—C. Fluorine-containing polyamides and copolyamides having inherent viscosities 0.41–0.88 dL g−1 were prepared by direct polycondensation of BAPPH with various aromatic diacids or with mixed diacids, by triphenyl phosphite and pyridine in N-methyl-2-pyrrolidinone (NMP). The polyamides were examined by elemental analysis, IR spectra, inherent viscosity, x-ray diffraction, solubility, DSC, and TGA. The diffractogram showed that the polyamides were crystalline except IVb, IVc, IVf, and Vc. Almost all polyamides were soluble in polar aprotic solvents. The polymers obtained from BAPPH lost no mass below 350°C, with 10% loss of mass being recorded above 467°C in nitrogen. These aromatic polyamides had glass transition temperatures in the 221–253°C range.

Development of aromatic polyamide membranes for pervaporation and vapor permeation

Abstract The pervaporation and vapor permeation performances of a series of fluorine-containing aromatic polyamide membranes for various alcohol mixtures were investigated. Compared with pervaporation, vapor permeation effectively increases the permselectivity of water. The solubility of alcohol in an aromatic membrane is higher than that of water, but the diffusivity of water across the membrane is higher than that of the alcohols. In addition, the relationship between the polymer structure and pervaporation performance was obtained. It was found that the permeation rate can be increased by the introduction of bulky substituted groups and arylene ether groups into the polymer backbone.

Surface structures and adhesion characteristics of poly(tetrafluoroethylene) films after modification by graft copolymerization

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with acrylic acid (AAc), Na salt of styrenesulfonic acid (NaSS) and N,N-dimethylacrylamide (DMAA). The structure and chemical composition of each copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For each PTFE substrate with a substantial amount of grafting, the hydrophilic graft penetrated or became partially submerged beneath a thin surface layer of dense substrate chains to form a stratified microstructure. This surface microstructure was further confirmed by the water contact angle results. In all cases, the concentration of surface grafted polymer increased with the plasma pretreatment time and monomer concentration. Adhesive-free adhesion studies revealed that the AAc graft copolymerized PTFE surface adhered strongly to another similarly modified surface (homo-interface) or to a DMAA graft copolymeri...