GAS PERMEABILITIES AND PERMSELECTIVITY OF PHOTOCHEMICALLY CROSS-LINKED POLYIMIDES

Photosensitive polyimide BTDA-3MPDA was modified by UV irradiation. The structure of UV-irradiated polyimides was investigated by FTIR and gel fraction measurements. The results showed that longer UV exposure time resulted in a higher extent of crosslinking. The gas permeabilities of hydrogen, oxygen and nitrogen through UV-irradiated polyimides were characterized in a temperature range from 30 degrees C to 90 degrees C. Photocrosslinking resulted in a sharp decline in gas permeability for hydrogen, oxygen, and nitrogen through polyimide in the initial stage of photocrosslinking. Then, as the crosslinked benzophenone percentage amounted to 28-38% for hydrogen, 17-31% for oxygen and 3-28% for nitrogen, the gas permeabilities showed another sharp decline. Gas permselectivity increased significantly with the progress of photocrosslinking, and it can be adjusted in a wide range by controlling the extent of crosslinking. Arrhenius plots of gas permeability for hydrogen and oxygen through UV-irradiated polyimides are straight lines; for nitrogen, however, change in the slope of the straight line is observed and activation energies for hydrogen and oxygen permeation show abrupt increases when crosslinked benzophenone percentage amounts to about 30%. UV-irradiated polyimides with simultaneous high gas permeability and permselectivity make them ideal candidate materials for gas separation. (C) 1995 John Wiley & Sons, Inc.

SYNTHESIS OF CROSS-LINKED 2ND-ORDER NONLINEAR-OPTICAL POLYMERS WITH HIGH T-G

Synthesis and characterization of a diamino dihydroxyl azo compound were reported, The crosslinking reaction process of the diamino dihydroxyl azo compound with the biuret of hexamethylene diisocyanate was studied by FTIR, The glass transition temperatures of crosslinked polymers were measured by DSC, The orientation and oriented stability of crosslinked and poled polymers were studied by UV-Vis spectra.

SYNTHESIS AND CHARACTERIZATION OF CROSS-LINKED 2ND-ORDER NONLINEAR-OPTICAL POLYMER

The present paper reports the synthesis of glycidyl monoether of 4-[(p-nitrophenyl) azo] phenol (GMNA) and crosslinking reaction of GMNA with hexamethylene diisocyanate biuret (HDIB). The Tg of crosslinked polymer was investigated by DSC. The orientation and stability of the poled and crosslinked polymer film were studied by UV-Vis spectra and Maker fringe method.

GAMMA-RADIATION INDUCED CROSS-LINKED PEO-LICLO4 SOLID-ELECTROLYTE SYSTEM

Aimed at raising the room temperature ionic conductivity of PEO-based solid polymer electrolyte and considered that the ionic conduction preferentially occurs in the amorphous phase, we lightly crosslinked the high MW PEO through gamma-irradiation and further suppressed the residual crystallinity by plasticizing with propylene carbonate. By incorporating LiClO4 salt to the above described polymer host, the ambient (25 degrees C) ionic conductivity of the electrolyte system could reach as high as 6.8 X 10(-4) S/cm. As the electrolyte was a crosslinked system, it was mechanically self-supportable. Based on the preliminary results of the electrochemical performance of the secondary lithium battery, assembled by using this kind of solid electrolyte and polyaniline as positive electrode, it is realized that the electrolyte thus prepared is of high expectancy.

RADIATION CROSS-LINKING OF POLYTETRAFLUOROETHYLENE

Polytetrafluoroethylene (PTFE) is considered to be a typical radiation degradative polymer. In this work the polymer was crosslinked by means of radiation at 335 +/- 5-degrees-C under vacuum. Crosslinked PTFE showed a great improvement in high temperature

EFFECTS OF STRUCTURE MULTIPLICITY ON MECHANISM OF RADIATION CROSS-LINKING OF POLYMERS

In an attempt to explore the effects of structural multiplicity of polymers on the mechanism of radiation crosslinking, the adaptability of the Charlesby-Pinner's equation and its various modified versions are examined. It is recognized that both chemical

STRUCTURE AND PROPERTIES OF AB CROSS-LINKED POLYMERS

Hydroxy-terminated oligomers, such as polyester, polyether, or castor oil, were reacted with toluene diisocyanate to form isocyanate-terminated prepolymers, which were then reacted with 2-hydroxyethyl acrylate to obtain vinyl-terminated prepolymer (VTP).

ELECTROOXIDATION OF ASCORBIC-ACID AT THE BIS(4-PYRIDYL) DISULFIDE MODIFIED GOLD ELECTRODE

The electrooxidation of ascorbic acid (AA) at the bis(4-pyridyl)disulfide (PySSPy) modified gold electrode was studied. The results showed that the oxidation process was pH-dependent. It was mainly due to the static interaction between AA and the modified

EFFECT OF HYDROPHOBIC OXIDES ON RADIATION CROSS-LINKING OF LOW-DENSITY POLYETHYLENE

Effect of hydrophobic oxide, containing =Si-CH=CH2 groups, on the radiation crosslinking of low density polyethylene (LDPE) has been studied. It was found that mechanical stability of irradiated LDPE containing improved SiO2 is higher than that of samples containing unimproved SiO2.

MECHANISM OF RADIATION CROSS-LINKING OF POLYMERS AND ITS RELATIONSHIP WITH STRUCTURAL MULTIPLICITY

In an attempt to explore the effect of structural multiplicity of polymers on the mechanism of radiation crosslinking, the adaptability of the Charlesby-Pinner's equation and its various modified versions are examined. It is recognized that both chemical and morphological multiplicity of polymer structure results in the multiplicity of crosslinking mechanism, and that any single equation can only be applicable to a certain step of the whole radiation process.

STUDIES ON RADIATION-INDUCED CROSS-LINKING OF POLYISOBUTYLENE

Polyisobutylene can be crosslinked under irradiation as to be expected by either introducing radiation sensitive groups into its macromolecules or blending with a proper radiation crosslinkable polymer.

STUDIES ON RADIATION CROSS-LINKING OF FLUOROPOLYMERS

The research work on radiation modification of a series of fluoropolymers were performed . The radiation crosslinked fluoropolymers obtain a great improvement in high temperature resistance, high temperature mechanical properties and radiation stability.

RADIATION CROSS-LINKING OF CHLORINATED POLYISOBUTYLENE

The effects of radiation on chlorinated polyisobutylene were studied. It was found that polyisobutylene, which is generally considered to be a typical radiation-degradative polymer, could be crosslinked by gamma-ray irradiation after chlorine had been introduced into its macromolecules. Carbon-chlorine bonds act both as radiation-sensitive groups and reaction species in the radiation process of chlorinated polyisobutylene.

THE EFFECT OF RADIATION-INDUCED CROSS-LINKING ON THE RELAXATION OF TAUT TIE MOLECULES DURING ANNEALING OF DRAWN LDPE

Shrinkage, retractive stress, and infrared dichroism of the drawn low-density polyethylene (LDPE) as-drawn and irradiated by Co-60-ray have been measured under different annealing conditions. The shrinkage and the disorientation of the irradiated sample was undergone more rapidly than that of unirradiated one as the temperature was continuously increased, surpassing a certain value, and a higher degree of shrinkage and disorientation was achieved finally for the irradiated sample when the samples were annealed with free ends. For the samples heated isothermally with fixed ends, the retractive stress went through a maximum and then attenuated to a limited value, and the degree of such a stress attenuation for the unirradiated sample was much more than that for the irradiated sample. These results show that the taut tie molecules (TTMs) in drawn PE can relax by the pulling of chain segments out of crystal blocks that they anchored in at elevated temperatures higher than the a transition and also by the displacing of microfibrils if the samples were annealed with free ends. The cross-links produced by irradiation prohibit the former process. It was further observed that the dependence of the average extinction coefficient of the band at 2016 cm-1 on that of the band at 1894 cm-1 is related to irradiation and annealing conditions, which has also been explained by the relaxation of TTMs and the function of irradiation-induced cross-linking on the relaxation.

RADIATION EFFECTS ON CRYSTALLINE POLYMERS .1. GAMMA-RADIATION-INDUCED CROSS-LINKING AND STRUCTURAL CHARACTERIZATION OF POLYETHYLENE OXIDE

By using WAXD, DSC and gel fraction determination techniques, the mechanism of radiation crosslinking of polyethylene oxide (PEO) was explored, and the dependence of aggregated state on the chemical reaction and physical structure was also discussed. It was found that just like other semi-crystalline polymers, the state of aggregation of the specimen has a profound influence on the radiation effects on PEO. On the contrary, the crystalline structure of the specimen is severely affected with the increase in radiation dose and eventually amorphortized when subjected to an extremely high radiation dose.