Living anionic copolymerization of DPE derivatives containing alkynyl with controlled kinetic behaviors and monomer sequence

Abstract

Alkyne functional group plays a significant and versatile role in the post-polymerization modifications to prepare advanced materials. We found an inevitable side reaction, specifically a coupling reaction between poly(styryl)lithiums and alkynes protected with trimethylsilyl groups, when alkyne-contained 1,1-diphenylethylene (DPE) derivative was incorporated into a polymer chain through living anionic polymerization (LAP) method in the previous study. Herein, we redesigned the structure of alkynyl-functionalized DPE derivative by introducing more bulky protecting group (i.e. 1-phenyl-1′-[4-[2-(triisopropylsilyl)ethynyl]phenyl]ethylene, DPE-TPSE), and found that this strategy is effective for restraining the side reaction through investigating the end-capping reaction. However, the phenomenon of multi peaks in SEC is still existed in the copolymerization with scant feeding of DPE-TPSE, which was revealed by Kinetic Monte Carlo simulation and can be attributed to excessively low cross-over of P-DPE-Li to P-St-Li for high reactivity of DPE-TPSE. Further, this unexpected phenomenon was completely eliminated by introducing another electron-donating methoxyl group into the DPE structure (i.e. 1-(4-methyloxyphenyl)-1′-[4-[2-(triisopropylsilyl)ethynyl]phenyl]ethylene, DPE-OTPSE) and the in situ1H NMR method was applied to precisely analyze the kinetics and sequence for the copolymerization with DPE-OTPSE. The apparent kinetic constants for DPE-OTPSE and St (KOTPSE and KSt) are calculated to be 4.35 × 10-4 min−1 and 3.15 × 10-4 min−1, respectively, and the rSt is calculated to be 0.27, which indicates the sequence of DPE-OTPSE units in chain presents gradient feature.