Effect of Methoxy Side Groups on the Crystal Structures of a Series of Syndiotactic Polymethoxystyrenes as Studied by the X‑ray Diffraction Data Analysis

The crystal structures have been elucidated for a series of novel syndiotactic polymethoxystyrenes (OMe-SPSs) having −OCH3 groups at the ortho-, meta-, or para-positions of phenyl rings on the basis of the detailed analyses of the two-dimensional X-ray diffraction patterns of the highly oriented and highly crystalline samples. The ortho-OMe-SPS has a monoclinic-type unit cell of a = 11.60 Å, b = 17.90 Å, c (fiber axis) = 7.72 Å, and β = 99°, in which the two 21 helical chains of TTGG conformation are packed with the space group P1211. The unit cell of the meta-OMe-SPS is of the monoclinic type with a = 16.20 Å, b = 14.39 Å, c (f. a.) = 10.12 Å, and β = 90°. The four all-trans zigzag chains are packed in the cell with the space group P1121. The para-OMe-SPS takes a large monoclinic unit cell of a = 16.80 Å, b = 29.00 Å, c (f. a.) = 10.12 Å, and β = 80°, in which the eight chains of trans-zigzag conformation (TTTT) are packed with P121/c1 space group symmetry. For both of meta- and para-OMe-SPS, the crystal structure is disordered in the chain packing mode and chain conformation. The existence of the OCH3 side groups and their positions have been found to play an important role in the determination of the chain conformation and chain packing mode in comparison with the crystal structures of SPS.