Showing papers by "En-Tang Kang published in 1995"

Surface modification of polyimide films by graft copolymerization

Abstract: Surface modifications of polyimide (PI) films by Ar-plasma, O2-plasma, and O3 pretreatment and by near-UV light-induced graft copolymerization with water-soluable monomers, such as acrylamide (AAm), acrylic acid (AAc), and sodium salt of 4-styrenesulfonic acid (NaSS), have been carried out. The angle-resolved x-ray photoelectron spectroscopy (XPS) results show that surface pretreatment results in the formation of peroxide species on the polymer film surfaces and leads to a substantial enhancement of the density of surface graft. The XPS results further suggest that in the case where substantial grafting has taken place, the grafted polymer either forms a surface layer uniformly intermixed with the substrate chains, or a graft-rich surface layer in the case of sterically hindered migration of the graft. The resulting surface structures are further supported by dynamic water contact angle measurements. These surface structures are probably associated with the thermoset character of PI, as they differ from the stratified microstructures observed on most thermoplastic films after surface modification by graft copolymerization with hydrophilic monomers. © 1995 John Wiley & Sons, Inc.

Protonation of polyaniline by surface-functionalized polymer substrates

Abstract: The protonation of solution-coated emeraldine (EM) base by sulfonic and carboxylic acid groups on surface-functionalized low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), poly(ethylene terephthalate) (PET), and polytetrafluoroethylene (PTFE) films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and conductivity measurements. Surface functionalizations were achieved by sulfonation (for LDPE, HDPE, PP, and PET), by hydrolysis (for PET), and by near-UV-light-induced surface graft copolymerization with the Na salt of styrene sulfonic acid and acrylic acid (for all substrates). The efficiency of surface functionalization by graft copolymerization is substantially enhanced for substrates pretreated with O3 or Ar plasma. Protonation levels of 50% can be readily achieved for EM coated on sulfonic acid, but not carboxylic acid, functionalized surfaces. The extent of protonation, however, is also dependent on the microstructures of the modified substrate surfaces. In all cases, charge transfer interactions between the EM layer and the functionalized substrates readily result in good adhesion of the electroactive polymer on the polymer substrates to give rise to conductive surface structures. © 1995 John Wiley & Sons, Inc.

Polymerization of o -Trimethylsilylphenylacetylene Initiated by a Tungsten Carbene Complex

Abstract: The polymerization of o-trimethylsilylphenylacetylene (o-Me3SiPA) initiated by tungsten carbene complex (I) was investigated under various conditions. Both a larger molar mass and larger yield of polymer were obtained in CCl4 and CHCl3 and in the presence of a Lewis acid such as AlCl3. The higher the temperature and the lower the initiator concentration, the larger was the molar mass of the polymer. The molar mass increases with concentration of cocatalyst SnCl4 and shows a maximum value for a ratio [SnCl4]/[I] =1. Moreover, when a solution of tungsten carbene complex in CCl4 was irradiated with UV light, the molar mass was remarkably enhanced. Kinetic orders and apparent rate constants were determined by gas chromatography. According to thermogravimetric results for poly(o-Me3SiPA), there is no significant interaction between the polymer and oxygen below 260°C. Above 260°C, the loss of mass in the presence of oxygen follows a two-step process. X-Ray diffraction measurements show that poly(o-Me3SiPA) has an amorphous structure.

Spectroscopic studies of the effects of salt addition in the protonation and deprotonation of emeraldine films

Abstract: Emeraldine base films were treated with HClO4 solutions of various concentrations, with and without the addition of NaClO4. The protonation of the films was studied using angle-resolved x-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) absorption spectroscopy, and ultraviolet (UV)-visible absorption spectroscopy. The protonation level can be substantially increased by the presence of salt if sufficient time is allowed for the anions to migrate into the bulk of the film. Conversely, in the partial deprotonation of emeraldine salt films, a higher retention of anions is observed in the presence of salt, even though the effect is not as pronounced as in the protonation process. © 1995 John Wiley & Sons, Inc.