Twofold Helical Polymerization: Thermal Solid-State Polymerization of 7‑Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone Methides

7-Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone methides bearing 2′-haloethoxy groups such as 2′-fluoroethoxy (1a), 2′-chloroethoxy (1b), 2′-bromoethoxy (1c), and 2′-iodoethoxy (1d) were synthesized. The halogen atoms of the haloalkoxy group in the quinone methide skeleton greatly affected their crystal structures, which belong to space group P21/c for 1a, P21/a for 1b, and P-1 for 1c and 1d. The thermal solid-state polymerizations in vacuo at 60 or 80 °C gave amorphous polymers with regular head-to-tail configuration and proceeded with retention of the crystal shapes in appearance. Relations between the molecular assembly modes and the polymerization modes indicate that 21 (2-fold) assemblies of 1b are able to undergo 21 helical polymerization with handedness.