Study on liquid-liquid transition of chlorinated butyl rubber by positron annihilation lifetime spectroscopy

The existence of liquid-liquid transition (T-ll) above the glass transition (T-g) in amorphous polymers remains a controversial topic. In this letter, positron annihilation lifetime spectroscopy was used to detect T-ll in cured and uncured chlorinated butyl rubber. It is found that the temperature spectra of orthopositronium lifetime and free-volume fraction of both samples clearly demonstrate two inflection points around -70 and -10 degrees C, corresponding to T-g and T-ll, respectively, while the orthopositronium intensity decreases at the transition regions, which may imply molecular cooperativity. Moreover, two equations should be adopted to describe the development of free-volume fraction after T-g. (c) 2006 American Institute of Physics.