Synthesis of a sequence-controlled in-chain alkynyl/tertiary amino dual-functionalized terpolymer via living anionic polymerization

Abstract

The alkynyl-functionalized 1,1-diphenylethylene (DPE) derivative DPE-yne was incorporated into a polymer chain through living anionic polymerization (LAP). An unanticipated coupling reaction occurred and could be restrained by extra feeding of DPE derivatives. Investigating the mechanism of the side coupling indicated that excess P-SLi coupled with the DPE-yne units in the chain when the feed of DPE-yne was insufficient. Although the use of excess DPE-yne can effectively restrain the side coupling during the copolymerization, these conditions afford only an alternating polymer sequence. For the diversity of sequence structure and multi-functionalization, another DPE derivative, DPE-NMe₂, was introduced into the polymerization, and the use of an appropriate amount of DPE-NMe₂ effectively inhibited the side coupling. Additionally, two functional groups (alkynes and amines) can be incorporated into polymer chains, and their sequence distribution was investigated. The in situ¹H NMR method was applied to monitor the chain propagation during the terpolymerization in real time. The in situ¹H NMR results showed that the entire sequence is a gradient structure with compositional drift from a predominant St-(DPE-yne) fraction initially to a St-(DPE-NMe₂) fraction finally, and the sequence between them is a gradual transition fraction. Consistent with the special sequence distribution in the polymer chain, the terpolymerization kinetic was investigated, and the apparent kinetic constants for each monomer were obtained. The corresponding reactivity ratios (r_St) were also calculated. The r_St-Dyne and r_St-Dnme were simulated as 0.08 and 5.8 during the terpolymerization, respectively. The terpolymerization investigated here not only inhibited the side coupling reaction but also allowed the introduction of a third functional monomer; moreover, its sequence structure shows potentially novel and intriguing properties that could further the applications of functionalized polymers.