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

The existence of liquid-liquid transition (Tll) above the glass transition (Tg) in amorphous polymers remains a controversial topic. In this letter, positron annihilation lifetime spectroscopy was used to detect Tll 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°C, corresponding to Tg and Tll, 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 Tg.