Substituent Regulation of Alternating Crystalline Copolymers Synthesized via Carbanionic Copolymerization-Induced Crystallization

We previously developed a method called carbanionic copolymerization-induced crystallization (CCPIC) to prepare alternating crystalline copolymers by adjusting the copolymer composition rather than by increasing the content of a certain stereochemical structure. In this work, eight new alternating crystalline copolymers were developed by regulating the substituent structure of conjugated dienes used in CCPIC. These types of conjugated dienes can achieve alternating growth with 1,1-diphenylethylene (DPE) and its derivatives (9-methylene-9H-thioxanthene, MTAE; 9,9-dimethyl-10-methylene-9,10-dihydroanthracene, MMAE) under neat conditions. When the substituents at the 2- or 3-position of the dienes change from 2-H/3-H (butadiene, BD) to 2-cyclopentyl/3-CH₃ (2-cyclopentyl-3-methyl-1,3-butadiene, MCPBD) and 2-cyclohexyl/3-CH₃ (2-cyclohexyl-3-methyl-1,3-butadiene, MCHBD) with greater steric hindrance, the alternating copolymers DPE/MTAE/MMAE-alt-MCPBD/MCHBD exhibit crystallization characteristics. DPE (without a bridge structure)-alt-MCPBD/MCHBD exhibits low crystallinity, and the crystallinity of MMAE (with a bridge structure containing two methyl substituents)-alt-MCPBD/MCHBD decreases with the increase in the size of the substituents. This indicates that the structure of DPE and its derivatives affects the aggregation structure of these alternating polymers. Interestingly, DPE and its derivatives (MTAE and MMAE) do not have chiral carbon atoms or stereoisomers in their polymer chains. The amorphous-to-crystalline transition of the polymer was achieved by changing the substituent structure of the dienes and DPE derivatives used in alternating copolymerization. Therefore, the crystallization of these crystalline polymers in CCPIC can be attributed to the steric hindrance effect brought about by the comonomer structure rather than just the stereoregularity of the monomer units in the chain.