Stereoregular Oligomers of Methyl Methacrylate. V. X-Ray Single Crystal Analysis of Isotactic Pentamer and Syndiotactic Tetramer

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Abstract
Stereostructures of the isotactic pentamer (meso-meso-meso-meso isomer) and the syndiotactic tetramer (racemo-racemo-meso isomer) of MMA were determined by x-ray single crystal analysis. The mmmm-pentamer and the rrm-tetramer were isolated by HPLC from the oligomer mixtures prepared with t-C4H9MgBr and with t-C4H9Li/(C2H5)3Al in toluene, respectively. The melting point of the mmmm-pentamer was 59.0–60.0°C, which was lower than that of the rrm-tetramer (99.4–100.2°C). Monoclinic crystals of the mmmm-pentamer and the rrm-tetramer grown from heptane solution belonged to the space groups P21/n and P21, respectively. The conformation of the main chain (t-C4H9-(C‒C)n‒H) of the mmmm-pentamer was ttttttgtg and that of the rrm-tetramer was ttttttg.