Nuclear Magnetic Resonance Study of Poly(oxymethylene)

Hikichi, Kunio; Tsutsumi, Atsushi; Oda, Jun’ichi; Kaneko, Motozo

doi:10.1295/polymj.6.56

Cited by 2 publications

(1 citation statement)

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“…The decrease of the second moment of POM by the thermal lattice expansion has been calculated to be 0.5 Oe 2 between -197°C and 20°C. 7 Therefore, the gradual narrowing is due to molecular motions in the crystal.…”

Section: Resultsmentioning

confidence: 99%

NMR Studies on Poly(oxymethylene) Crystals. II.

Shibata

Iwayanagi

1978

Polym J

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ABSTRACT:The anisotropy of NMR spectrum for poly(oxymethylene) obtained by Tray induced solid-state polymerization of tetraoxane was investigated as a function of the alignment angle of needle-like crystals with respect to a static magnetic field. On the basis of second moment calculations with the Gaussian-type distribution of oscillation amplitude assumed, the narrowing of the spectrum was attributed more to the rather complicated oscillations (the longitudinal oscillation along the helix axis in addition to the rotational oscillation around the helix axis of amplitude 9° at 20°C) than to the simple rotational oscillation around the helix axis. These complicated osciiiations in poly(oxymethylene) crystal occur even at low temperatures and the amplitude of oscillation increases with increasing temperature. These results are in close agreement with those of the X-ray study of the atomic fluctuations by Chiba, et at.KEY WORDS Poly(oxymethylene) I NMR I Molecular Motion I Anisotropy I Solid-State Polymerization I Tetraoxane I Poly(oxymethylene) (POM) obtained from trioxane and tetraoxane single crystals by r-ray induced solid-state polymerization 1 is known to be composed of highly oriented and extended 95 helix molecules with few chain folds and to be almost completely crystalline. 2 ' 3 POM obtained from the needle-like crystal of trioxane or tetraoxane is also a needle-like crystal, the long axis of which coincides with the helix axis of molecule. 1 The anisotropy of the broad-line NMR for an aligned sample of POM obtained from trioxane was reported in a previous paper. 4 However that POM crystal contained a subcrystal in the amount of about 20%, and its c-axis (the helix axis) inclined at an angle of 76° 7' to the main crystal. 1 ' 6 Chatani, et a/., 3 reported that POM obtained from tetraoxane by solid-state polymerization at above lOOoC contained no subcrystal. Therefore, the needle-like crystal polymerized from tetraoxane is well suited for studying NMR anisotropy and molecular motion within the crystal.The molecular motion in POM crystal was investigated by the authors 4 rotational oscillation around the helix axis with the amplitude of 42° at 20°C took place in the crystalline chain, the authors found the upper limit of the oscillation amplitude to be 30° and that the molecular motion is not restricted simply to rotational oscillation around the helix axis. In this study, the anisotropy of the NMR absorption spectrum of POM polymerized from tetraoxane is investigated and molecular motion in the crystal is discussed. EXPERIMENTAL POM specimens used in this study are as follows. 1. Delrin 150X annealed for 9 hr at 154°C in vacuo. The mobile fraction Fm was 27% at 20°C.2. The needle-like crystal obtained from trioxane by solid-state polymerization. Fm was 2% at 20°C.3. The needle-like crystal obtained from tetraoxane by solid-state polymerization. F m was less than 1 % at 20°C. The condition of the polymerization for trioxane was described in a preceding paper.< The polymerization of tetraoxane was performe...

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Section: Resultsmentioning

confidence: 99%