On Thiol‐Ene Radical Coupling Reaction when Synthesis of ABCL₂Type Heteroarm Star Copolymer Containing PDPA Arm

Abstract

In this paper, we designed novel ABCL 2 -type heteroarm star copolymers, where A, B and C are poly(ε-caprolactone) (PCL), poly(2-(diisopropylamino) ethyl methacrylate) (PDPA) and poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC) arms, respectively, and L is 4-([2,2':6',2''-terpyridine]-4'-yl) phenyl (Tpyp) ligand group. In the final synthesis step, thiol-ene radical coupling was used to link PMPC chain onto PCL/PDPA copolymer to form a heteroarm star copolymer. However, it was found that the presence of the PDPA block with tertiary amine moieties led the thiol-ene radical coupling not to be achieved easily in common conditions. Herein we focus on investigating the photoinitiated thiol-ene coupling reaction. Finally, we achieve the reaction via selecting appropriate solvent. It is expected that the exploration can broaden application of thiol-ene radical reaction in synthesis of polymer architectures.

A Robust Strategy for Photoinitiated Macromolecular Thiol‐Ene Radical Coupling Reaction with High‐Efficiency Based on a RAFT‐Generated Thiol‐Terminated PDPA Reactant

“…[ 7 ] Thus, PCL(‐Pene) 2 ‐OH (Scheme 1b) was first obtained via the esterification of @(‐Pene) 2 (‐OH) 2 with PCL‐COOH, which was prepared by ring‐opening polymerization (ROP) of ε ‐caprolactone (CL) according to previous methods reported. [ 4,39,40 ] The structures of PCL(‐Pene) 2 ‐OH and its precursors were confirmed by 1 H NMR spectra, and 1 H NMR spectra and GPC traces of typical PCL‐COOH and PCL(‐Pene) 2 ‐OH are shown in Figures S8–S10, Supporting Information. The resonances of the characteristic groups of the obtained polymers were marked in Figures S8 and S9, Supporting Information, and their structure data were summarized in Table S1, Supporting Information.…”

“…The formation of thiolates prevented thiol groups to be translated into the thiyl radials. [ 4,8–10 ] In the case of our current experiments, if the presence of the DPA units had only made a thiol group be changed into the thiolate, the addition of glacial acetic acid solvent should have made the thiolate recover into the thiol and the subsequent thiol‐ene coupling should have enabled to occur robustly. But it was not the case.…”

“…Our recent works are paid on the incorporation of ligand DOI: 10.1002/macp.202200321 groups to a miktoarm star copolymer for constructing novel self-assembly unit and further exploration of its possible novel selfassembly morphologies. [3,4] However, the construction of a miktoarm star copolymer usually involves multi-step reactions, and in most cases, it needs to combine several diverse reaction technologies , [3][4][5] compared with that of a homoarm star polymer. Therefore, a robust, efficient, and facile reaction strategy is required for the precise construction of a macromolecular architecture.…”

“…[16,17] There are few reports on examples of photoinitiated thiol-ene radical coupling reaction in constructing macromolecules containing amine moieties like poly (2-(diisopropylamino) ethyl methacrylate) (PDPA). [4] On the one hand, an amine reagent itself may be involved in photoreaction; [5,23,24] and on the other hand, amine moieties can create an alkaline environment, which may retard the thiol-ene radical coupling reaction. [4,8,25] However, an amine macromolecule like PDPA is a class of important pH-responsive ones and exhibits good application in the medical field.…”

“…[4] On the one hand, an amine reagent itself may be involved in photoreaction; [5,23,24] and on the other hand, amine moieties can create an alkaline environment, which may retard the thiol-ene radical coupling reaction. [4,8,25] However, an amine macromolecule like PDPA is a class of important pH-responsive ones and exhibits good application in the medical field. [26][27][28][29] Thus, exploration of an appropriate condition for photoinitiated thiol-ene radical reaction in the presence of this type of amine macromolecular building block is also indispensable, which enables enriching strategies of polymer synthesis and enlarges the application scope of the photoinitiated thiol-ene radical coupling reaction.…”