7,7,8,-p-quinodimethanes with bulky aryloxy groups such as benzyloxy (1a), pentafluorobenzyloxy (1b), and both benzyloxy and pentafluorobenzyloxy (1c) were synthesized. We investigated effects of these bulky groups on thermal solid-state polymerization reactivities on the basis of crystal structures of 1a−1c. Thermal polymerizations gave 1,6-trans-type stereoregular polymers in quantitative yields in 1 day at 110°C for 1a, 1 day at 150°C for 1b, and 6 days at 110°C for 1c. Their initial crystal shapes were retained in appearance during polymerization to yield solid bundle assemblies of their polymeric chains. X-ray single-crystal structure analysis indicates that their crystals adopt molecular arrangements suitable for one-dimensional polymerization with the 1,6-trans-type addition along one crystallographic axis. Such arrangements led to expansion polymerization of 1b and contraction one of 1c. The resulting stereoregular polymers form less ordered bundle assemblies than those prepared by the conventional topochemical polymerization. In this manner, the bulky aryloxy groups enabled us to observe a close relation between the molecular assembly modes and the polymerization behaviors, providing the first example for proving diversity of thermal solid-state polymerizations.