THERMALLY STIMULATED CURRENT AND DSC STUDIES OF THE BROADENED GLASS-TRANSITION IN LIQUID-CRYSTALLINE POLYMERS

被引:34
作者
SAUER, BB [1 ]
BECKERBAUER, R [1 ]
WANG, LX [1 ]
机构
[1] SCIMED LIFE SYST INC,MAPLE GROVE,MN 55369
关键词
THERMALLY STIMULATED CURRENTS; LIQUID CRYSTAL POLYMERS; GLASS TRANSITION;
D O I
10.1002/polb.1993.090311219
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
The high sensitivity of the thermally stimulated current, thermal sampling (TS) method is emphasized in a study of the breadth of the glass transition in several liquid-crystalline polymers (LCPs). Differential scanning calorimetry (DSC) was performed on all samples to further quantify the glass transition regions. For ''random'' copolyester LCPs with widely varying degrees of crystallinity, including highly amorphous samples, very broad glass transition regions were observed. One semicrystalline alternating copolyester and a series of semicrystalline azomethine LCPs were studied as examples of structurally regular polymers. These exhibited relatively sharp glass transitions more comparable to ordinary isotropic amorphous or semicrystalline polymers. The broad glass transitions in the random copolyesters are attributed to structural heterogeneity of the chains. In one example of a moderate-crystallinity random copolyester LCP (Vectra), glass transitions ranging up to ca. 150-degrees-C in breadth were determined by the thermal sampling (TS) method and DSC. In other lower crystallinity copolyester LOPs, the main glass transition temperature as determined by DSC was comparable to that determined by TSC although cooperative relaxations of a minor fraction of the overall relaxing species were detected well below the main T(g), by the TS method and not by DSC. Rapid quenches from the isotropic melt to an isotropic glass were possible with one LCP. The anisotropic and isotropic glassy states for this LCP were found to have the same breadth of the glass transition as was determined by the TS method, although TSC and DSC show that T(g) is shifted downward by ca. 15-degrees-C in the anisotropic glass as compared to the isotropic glass. (C) 1993 John Wiley & Sons, Inc.
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页码:1861 / 1872
页数:12
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