Lower critical ordering transition of poly(ethylene oxide)-block-poly(2- vinylpyridine)

A new diblock copolymer exhibiting the unconventional lower critical ordering transition (LCOT) behavior was investigated. The system is composed of a poly (ethylene oxide) (PEO) and a poly(2-vinylpyridine) (P2VP) block. The PEO-b-P2VP samples were synthesized by sequential anionic polymerization of 2-vinylpyridine and ethylene oxide. The number-average molecular weights (M _n) of both blocks in the symmetric diblock were ca. 40 000, which prescribed the volume fraction of PEO (f_PEO) as 0.49. The M _n of PEO and P2VP blocks in the asymmetric diblock were 20 000 and 100 000, respectively, and the corresponding fPEO was 0.16. The thermally induced phase transition of PEO-b-P2VP was detected by the temperature-dependent SAXS measurement. The intensity of this peak grew with increasing temperature, and a second-order peak was discernible above 160°C, signaling the formation of a microphase-separated lamellar morphology.