Martin Pulst, Yury Golitsyn, Christian Schneemann, Paweł Ruda, Detlef Reichert, and Jörg Kressler
Faculty of Natural Sciences II, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 4, D-06120 Halle (Saale), Germany
While many traditional schematic models show the crystalline polymer chains aligned parallel to the lamella thickness Lc recent sophisticated studies on poly(ethylene) show that the crystalline polymer chains are tilted at an angle φ to the lamella thickness .
Here, we investigate the chain tilt of poly(ethylene oxide) (PEO) by the means of mid-chain defects using wide-angle X-ray scattering and solid state 13C MAS cross polarization NMR spectroscopy. At low temperatures, one polymer chain of PEO9-meta-PEO9 and PEO11-TR-PEO11 [2-4] containing a 1,3-disubstituted benzene and a 1,4-disubstituted 1,2,3-triazole defect in central position of the polymer chain, respectively, form crystals and the other PEO chain as well as the defect remain amorphous. The aromatic defects of these two polymers can be incorporated into the crystalline lamellae upon heating below Tm and the corresponding structure models confirm that the amorphous PEO chains exit the tilted lamellae at a preordained angle. Thus, the chain tilt angle φ can directly be calculated from the bent angle ξ between the amorphous and crystalline PEO chains, which is given by the substitution patterns of the aromatic mid-chain units and a tilt angle range between 36° ≤ φ ≤ 60° is determined. Furthermore, our studies on PEO9-para-PEO9 containing a 1,4-disubstituted benzene mid-chain defect confirm that also linear unbent PEO chains form tilted lamellae.
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