Substituent\nRegulation of Alternating Crystalline\nCopolymers Synthesized via Carbanionic Copolymerization-Induced Crystallization

We previously developed a method called carbanionic copolymerization-induced\ncrystallization (CCPIC) to prepare alternating crystalline copolymers\nby adjusting the copolymer composition rather than by increasing the\ncontent of a certain stereochemical structure. In this work, eight\nnew alternating crystalline copolymers were developed by regulating\nthe substituent structure of conjugated dienes used in CCPIC. These\ntypes of conjugated dienes can achieve alternating growth with 1,1-diphenylethylene\n(DPE) and its derivatives (9-methylene-9H-thioxanthene, MTAE; 9,9-dimethyl-10-methylene-9,10-dihydroanthracene,\nMMAE) under neat conditions. When the substituents at the 2- or 3-position\nof the dienes change from 2-H/3-H (butadiene, BD) to 2-cyclopentyl/3-CH<sub>3</sub> (2-cyclopentyl-3-methyl-1,3-butadiene, MCPBD) and 2-cyclohexyl/3-CH<sub>3</sub> (2-cyclohexyl-3-methyl-1,3-butadiene, MCHBD) with greater\nsteric hindrance, the alternating copolymers DPE/MTAE/MMAE-<i>alt</i>-MCPBD/MCHBD exhibit crystallization characteristics.\nDPE (without a bridge structure)-<i>alt</i>-MCPBD/MCHBD\nexhibits low crystallinity, and the crystallinity of MMAE (with a\nbridge structure containing two methyl substituents)-<i>alt</i>-MCPBD/MCHBD decreases with the increase in the size of the substituents.\nThis indicates that the structure of DPE and its derivatives affects\nthe aggregation structure of these alternating polymers. Interestingly,\nDPE and its derivatives (MTAE and MMAE) do not have chiral carbon\natoms or stereoisomers in their polymer chains. The amorphous-to-crystalline\ntransition of the polymer was achieved by changing the substituent\nstructure of the dienes and DPE derivatives used in alternating copolymerization.\nTherefore, the crystallization of these crystalline polymers in CCPIC\ncan be attributed to the steric hindrance effect brought about by\nthe comonomer structure rather than just the stereoregularity of the\nmonomer units in the chain.