Synthesizing a Trefoil Knotted Block Copolymer via Ring-Expansion Strategy

A synthetic trefoil knotted poly(ε-caprolatone)-block-poly(l-lactide) (TK-PLA-b-PCL) is synthesized via a ring-expansion strategy from a trefoil knotted tin (Sn) initiator. Ring-closing reaction between the bis-copper(I) templated phenanthroline complex and dibutyldimethoxytin results in a templated trefoil knotted initiator. The bis-copper(I) templated trefoil knotted poly(l-lactide) (TK-PLA) can be synthesized by ring-opening polymerization of l-lactide monomer, and decomplexation reaction of the templated TK-PLA will result in a geniune TK-PLA without constraint from the copper template. Subsequent insertion of ε-caprolactone in the bis-copper(I) templated TK-PLA forms the templated trefoil knotted block copolymer, i.e., TK-PLA-b-PCL, and the copper-free TK-PLA-b-PCL can be obtained by decomplexation reaction. Both TK-PLA and TK-PLA-b-PCL are analyzed by the ¹H NMR, FT-IR, UV-vis, DLS, and GPC.