三醋酸纤维素
结晶度
单斜晶系
结晶学
固态核磁共振
纤维素
单晶
衍射
化学
聚合物
晶体结构
X射线晶体学
碳-13核磁共振
Crystal(编程语言)
材料科学
有机化学
核磁共振
程序设计语言
物理
光学
计算机科学
作者
Pawel Sikorski,Masahisa Wada,Laurent Heux,Hiroyuki Shintani,Bjørn T. Stokke
出处
期刊:Macromolecules
[American Chemical Society]
日期:2004-05-20
卷期号:37 (12): 4547-4553
被引量:39
摘要
Highly crystalline samples of cellulose triacetate (CTA) were prepared from cellulose I by heterogeneous acetylation in an equal amount mixture of acetic anhydride and toluene. Highly crystalline and oriented films of cellulose I from green alga Cladophora sp. was used as a starting material. Prepared samples were studied by FT-IR, solid-state 13C NMR, and X-ray diffraction. Spectroscopic data indicate a complete degree of acetylation. In the solid-state 13C NMR spectrum, each carbon atom appears only as a single resonance, indicating that the asymmetric unit in the CTA I crystal includes only a single chemical repeat unit. This behavior is in contrast with the currently accepted crystal structure of CTA I, in which the unit cell includes two parallel polymer chains. In the fiber X-ray diffraction, prepared samples show high crystallinity and good orientation. A new unit cell is proposed, and the crystalline structure was refined using molecular modeling. Possible conformations of the acetate side chains are also considered. The proposed models include a single polymer chain in a 21 helical conformation placed in a monoclinic unit cell with a = 0.5939 nm, b = 1.1431 nm, c = 1.046 nm, and γ = 95.4°. Agreement between observed and predicted diffraction intensities, compared both by visual methods and in terms of the crystallographic reliability index R, is good with R = 0.22.
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