Monomer sequence determination in the living anionic copolymerization of styrene and asymmetric bi-functionalized 1,1-diphenylethylene derivatives

Due to their distinct steric hindrance, 1,1-diphenylethylene (DPE) and its derivatives cannot homopolymerize via living anionic polymerization and thus are advantageous for investigating the sequence structure of the corresponding copolymers. The substitution of functional groups on the benzene rings of DPE derivatives can be used to adjust the reactivity ratios for the copolymerization of styrene and the DPE derivatives. Two types of DPE derivatives, DPE-SiH/OMe and DPE-SiH/NMe2, were designed and prepared in this work. An electron withdrawing substituent and an electron donating substituent are simultaneously present at the para positions of the two phenyl rings of DPE. These derivatives were copolymerized with styrene under Schlenk conditions via living anionic polymerization. The statistical in-chain functionalized copolymers were prepared, and the corresponding average reactivity ratios were 1.42 for DPE-SiH/OMe and 1.79 for DPE-SiH/NMe2. Additionally, a time sampling strategy under high vacuum conditions was used during the copolymerization of the two systems (styrene with DPE-SiH/OMe and styrene with DPE-SiH/NMe2) with [MS]0/[MD]0 = 4. The propagation rate constants and statistical sequence structures were analyzed by 1H NMR spectroscopy, SEC and MALDI-TOF MS, and the average sequential arrangements of the corresponding copolymers were determined. The critical conditions for preparing copolymers with alternating structures were determined and implemented, and the monomer unit ratios were both nearly 1 : 1.