IONIC CONDUCTIVITY OF EPOXY NETWORK/POLYETHYLENE GLYCOL- LITHIUM PERCHLORATE COMPLEX IPN SYSTEM

In an attempt to prepare a polymeric solid electrolyte with both high ionic conductivity at ambient temperature and adequate mechanical strength, an ionic conducting IPN composed of bisphenol A epoxy resin/polyethylene glycol containing LiClO_4 was synthesized. The dependence of conductivity was investigated as a function of salt content, composition and temperature. It has been revealed that a maximum of conductivity appeared when EO/Li=25, where EO denotes the—(CH_2CH_2O)-unit in polyethylene glycol, and that the temperature dependence of conductivity followed VTF equation, suggesting that the motion of ionic carriers resulted from the segmental motion of the polymer. When glycerol epoxy resin was used instead of bisphenol A epoxy, the ambient temperature (25℃) conductivity could somewhat further be raised up to 3×10~(-5) S/cm.     

HEAT SHRINKING BEHAVIOUR OF γ-RADIATION CROSSLINKED POLYETHYLENE

Heat shrinking material of γ-radiation erosslinked polyethylene is widely used for various application in industry. In this study, DSC, TMA, WAXD and density measurement techniques were used to investigate the influence of MI and thermal history of LDPE on the effectiveness of network formation. Based on the results of heat stretching and heat shrinkage tests, it is found that the formation of a network as perfect as possible is indispensable to the irradiated material if good heat shrinkage property is desired. To this end, quenching technique and polyethylene with appropriate MI must be used so that an effective radiation effect will be obtained with a minimum amount of radiation dose. In spite of that the mechanical property of the irradiated polyethylene in the rubbery state is basically in agreement with the classical expression of the theory of high elasticity, only about 90% shrinkage can be reached. Besides, the heat shrinkage temperature T_s and the % shrinkage Sare both related to the radiation dose.     

EQUILIBRIUM HEAT OF FUSION OF POLYTETRAFLUOROETHYLENE

The reliability of the values of equilibrium heat of fusion, △H_m, of polytetrafluoroethylene (PTFE)reported in the literature and the inadequacy of the generally accepted value of 13 .7 or 14.6 cal/gwere discussed. Through extrapolating linear plot of △H_m vs. V_(sp) of the thermally aged PTFE virginas-polymerized samples prepared in accord with ASTM D 1457-81a, △H_m~o=79.6J/g (19.0 cal/g)and V_(sp) (specific volume of amorphous PTFE at 23℃)=0.480 cm~3/g (or ρ_a=2 .08g/cm~3) were ob-tained. The heats of fusion, △H_m, of the thermally aged and γ-irradiated samples are different irrespec-tive of the same V_(sp) value for both samples. A qualitative explanation of this phenomenon was givenbased on the H_v patterns of SALS and Kawai's model.     

MECHANICAL RELAXATION TIME OF A TWO-COMPONENT EPOXY NETWORKLiClO_4 POLYMER ELECTROLYTE

The mechanical relaxation time of a two-component epoxy network-LiClO_4 system as a polymer electrolyte was investigated. The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG), wherein LiCIO_4 was incorporated and acts as both the ionic carrier and the curing catalyst. As the relaxation time is informative to the segmental mobility, which is known to be essential for ionic conductivity, the average relaxation times of the specimens were determined through master curve construction. Experimental results showed that the salt concentration, molecular weight of PEG in DGEPEG and DGEPEG/TGEG ratio have profound effect on the relaxation time of the specimen. Among these factors , the former reinforces the network chains, leading to lengthen the relaxation time, whereas the latter two are in favour of the chain flexibility and show an opposite effect. The findings was rationalized in terms of the free volume concept.     

STUDY ON FACTORS AFFECTING ROOM TEMPERATURE TRANSITION OF POLYTETRAFLUOROETHYLENE

In the X-ray diffiaction intensity distribution diagram of PTFE, three diffraction peaks exist inthe range of Bragg angle 30--45°, which are very sensitive to the Crystal trausition at room temperature.At 15℃, the crystal is triclinic and the "small spikes" along with the main peaks appear on the dif-fraction scans due to the distortion of the unit cell, while at 23℃, distortion no longer exists, "smallspikes" disappear completely. When the temperature is raised to 34℃, the hexagonal crystal fur-ther randomizes and the peak at Bragg angle 42°vanishes. We assigned correctly Miller index (108) tothis peak and used 2θ=30--45°region ("sensitive region") as a criterion to characterize qualita-tively the crystal transition. It has been found that some factors such as γ-irradiation, cold press-ing, drawing, calendering and copolymerization which are usually encountered in the fabrication orapplication of PTFE articles have profound effect on the crystal transition as evidenced by X-raydiffraction patterns and DSC thermograms. The information obtained in the present work isbeneficial to the use of PTFE articles.