Abstract
A trimer of methyl methacrylate was isolated by HPLC from the oligomer mixture prepared in toluene with t-BuMgBr, and the crystal and molecular structure was determined by single crystal X-ray analysis. A monoclinic crystal of the trimer grown from heptane belonged to the space group P21/n having cell constants a=10.047, b=24.743, c=9.026 Å and β=109.02°. The final R value was 0.050. The configuration of the trimer was proved to be meso-meso. This trimer had been differently assigned to meso-racemo isomer in our previous report [K. Hatada et al., Polym. J., 19, 1325 (1987)]. The conformation in the crystal is ttg+tg+ (as (R,S,R)-isomer) along the main chain skeletal sequence t-Bu-CCCCCC-Hω. However, the more extended state ttttg+ was found to be predominant in solution, from the considerations of the chemical shifts of the methylene protons, 4J-correlation peaks observed in 1H COSY spectrum, and 3J vicinal coupling constants between the methine and methylene protons in the ω-end unit. The chemical shift between the nonequivalent methylene protons in the ω-end unit is larger for racemo-sequence than for meso-sequence, while the opposite is true for in-chain monomeric units.
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Ute, K., Nishimura, T., Matsuura, Y. et al. Stereoregular Oligomers of Methyl Methacrylate: X-Ray Crystal Structure Analysis and 1H NMR Spectrum of the Trimer. Polym J 21, 231–240 (1989). https://doi.org/10.1295/polymj.21.231
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DOI: https://doi.org/10.1295/polymj.21.231
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