Crystallization and melting of highly monodisperse poly(ethylene-oxide)

We present a quantitative study of the crystallization and melting behaviours of highly monodisperse PEO oligomers, and compare to previous studies. Through evaporative purification, we were able to isolate low molecular weight PEO oligomers that are much more monodisperse than the as-purchased material (as measured by mass spectrometry). Crystal structure, crystal growth rate and melting temperatures were characterized. Melting temperatures of isolated fractions were described by the Gibbs-Thomson relation. We show that during crystallization the isolated fractions are able to form crystal lamellae not only with extended chains, but also with once-folded chains. This chain folding is unexpected for polymers with such short chain lengths. We use these samples to investigate the effects of polydispersity on crystal formation and chain folding, and discuss both qualitative and quantitative differences from previous studies on similar but more polydisperse small chains.