Depth-gradient and photoinitiator-free photocrosslinking of poly(ethylene oxide)

Poly(ethylene oxide) (PEO) films are photocrosslinked by continuous UV irradiation without photoinitiators. Maximum gel fraction and swelling of the photocrosslinked PEO films reach up to about 38.8% and 2824%, respectively. From NMR analysis, the photocrosslinking mechanism of PEO can be attributed to recombination between methine radicals, which are generated from the polymer chain by hydrogen abstraction. However, the relatively low degree of crosslinking is attributed to more facile photooxidation of the generated radicals and concomitant photo-scission of the crosslinks. Depth-gradient crosslinked structure can be formed by inherent UV absorption and successive photoscission of the crosslinked polymer surface, which can be made uniform by adjusting UV energy. The photocrosslinked PEO shows the higher glass transition temperature as much as 7.3°C coupled with significantly enhanced storage modulus and thermal stability. The lower crystallinity causes by the reduced recrystallizability of the crosslinked polymer chains in melt. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012