Cascade Alternating Metathesis Cyclopolymerization of Diynes and Dihydrofuran

Abstract

Ruthenium alkoxymethylidene complexes have recently come into view as competent species for metathesis copolymerization reactions when coupled with appropriate comonomer targets. Here, we explore the ability of Fischer-type carbenes to participate in cascade alternating metathesis cyclopolymerization (CAMC) through facile terminal alkyne addition. The combination of diyne monomers and an equal feed ratio of low-strain dihydrofuran leads to a controlled chain-growth copolymerization with high degrees of alternation (>97% alternating diads) and produces degradable polymer materials with low dispersities and targetable molecular weights. When combined with enyne monomers, this method is amenable to the synthesis of alternating diblock copolymers that can be fully degraded to short oligomer fragments under aqueous acidic conditions. This work furthers the potential for the generation of functional metathesis materials via Fischer-type ruthenium alkylidenes.

Figure 1.

(A) Synthetic design for CAMC using enyne and cyclic enol ethers. (B) Diyne monomers for metathesis polymerization. (C) New synthetic design for CAMC using diyne and cyclic enol ethers.

Figure 2.

¹H NMR for polymers: a. polyM1, b. polyM1/DHF (1/1.2, 0.1 M of M1, RT), and c. polyDHF.

Figure 3.

(A) SEC chromatogram of P4 at different targeted degrees of polymerization (DP) and (B) linear correlation of ln([M4]₀/[M4]) with time.

Figure 4.

(A) Synthesis of diblock P4₁₀-b-PE1₁₃₅ through sequential monomer addition and (B) SEC chromatogram of the first block and chain-extension.

Figure 5.

Degradation of P4 in acidic condition in 2 hours.