ABSTRACT:2-Dimensional X-ray and neutron diffraction patterns have been successfully measured for deuterated and hydrogenated polyoxymethylene (POM) samples obtained by -ray induced solid-state polymerization reaction. More than 700 reflections were collected from the X-ray diffraction data at À150C by utilizing a high-energy synchrotron X-ray beam at SPring-8, Japan, from which the crystal structure of POM has been refined thoroughly including the extraction of hydrogen atomic positions as clearly seen in the difference Fourier synthesis map. As the first trial the nonuniform (9/5) helical model was analyzed with the reliability factor (R factor) 6.9%. The structural analysis was made also using the X-ray reflections of about 400 observed at room temperature (R 8.8%), and the thermal parameters of constituent atoms were compared between the low and high temperatures to discuss the librational thermal motion of the chains. The 2-dimensional neutron diffraction data, collected for the deuterated and hydrogenated POM samples using an imaging plate system specifically built-up for neutron scattering experiment, have allowed us to pick up the D and H atomic positions clearly in the Fourier synthesis maps. Another possible model, (29/16) helix, which was proposed by several researchers, has been also investigated on the basis of the X-ray diffraction data at À150 C. The direct method succeeded in extracting this (29/16) model straightforwardly. The R factor was 8.6%, essentially the same as that of (9/5) helical model. This means that the comparison of the diffraction intensity between the data collected from the full-rotation X-ray diffraction pattern and the intensity calculated for both the (9/5) and (29/16) models cannot be used for the unique determination of the superiority of the model, (9/5) or (29/16) helix. However, we have found the existence of 001 and 002 reflections which give the longer repeating period 55.7 Å . Besides there observed a series of meridional 00l reflections forbidden for (9/5) helical model. These additional evidences support the nonuniform (29/16) helical model as the most plausible chain conformation of POM crystal.

The phenomenon of cocrystallization between the deuterated (D) and hydrogenated (H) species of a series of polyoxymethylene blends with various H/D ratios has been established on the basis of the detailed analysis of thermal and infrared (IR) spectral data. The melting and crystallization temperatures were found to shift continuously toward a higher temperature with an increase in the D content. The IR spectra were found to change remarkably depending on the H/D blend content. Both the thermal and the IR spectral observations definitely indicated the cocrystallization between the H and D chains in the common crystallite. These continuous changes could be interpreted by assuming that the arrays of the H and D chains in crystal lattice are random. Polymer Journal ( Keywords: cocrystallization; deuterated species; DSC; infrared spectra; isotopic blend; polyoxymethylene INTRODUCTION Semicrystalline polymers show complex microstructures or higherorder structures that consist of crystalline and amorphous regions. Control of the higher-order structure may govern the physical properties of the polymers. A better understanding of the formation process is required in order to control the higher-order structure of the polymer and develop new materials with better properties. As the first step, the aggregation state of the molecular chains in the crystallized bulk sample must be determined at the molecular level. As the polymer solid is built up by the complicated aggregation of more or less entangled chains, it is difficult to trace the trajectory of a single particular chain in the bulk sample. The isotopic blend between the deuterated (D) and hydrogenated (H) species is considered one of the most useful methods for studying the behavior of a single chain in the aggregation state on the basis of the difference in the thermal and vibrational characters that are due to the difference in atomic mass. In some cases, the difference in the neutron scattering length is also utilized successfully to distinguish the D and H species. 14,17,18 In such cases of isotopic blends, the cocrystallization must be confirmed to take place between the H and D species in the crystalline lattice. For example, the blends between the H and D species of the various types of polyethylene have been comprehensively studied for clarification of the cocrystallization phenomenon between the H and D species. [1][2][3][4][8][9][10][11]14,[16][17][18][19] In the case of samples that are a blend of H high-density polyethylene and D high-density polyethylene, slow

の総数の 3-4 倍の実測回折点が必要である．(たと えば，等方性温度因子 B を仮定した場合，N 個の原子に 対して決定すべきパラメーター総数は凡そ 4N (つまり * 1 豊田工業大学大学院工学研究科極限材料専攻 (〠 468-8511 名古屋市天白区久方 2-12-1) * 2 茨城大学工学部生体分子機能工学科 (〠 316-8511 日立市 中成沢町 4-12-1) * 3 総合科学研究機構 (CROSS) 東海事業センター (〠 319-1106 茨城県那珂郡東海村白方 162-1) * 4 日本原子力研究開発機構量子ビーム応用部門 (〠 319-1106 茨城県那珂郡東海村白方 2-4) * 5 クラレ (株) くらしき研究センター (〠 710-1801 倉敷市酒 津 2045-1) * 6 名古屋大学大学院工学研究科科学・生物工学専攻 (〠 464-8603 名古屋市千種区不老町) * 7 日本大学文理学部化学科 (〠 156-8550 東京都世田谷区桜 上水 3-25-40)

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