Synthesis of monodisperse sequence-defined polymers using protecting-group-free iterative strategies

Abstract

The synthesis of "precision" polymers with finely controlled molecular structures is an important new development in synthetic polymer chemistry. This trend is the logical outcome of the continuing evolution of the field of polymer synthesis. Indeed, during the last few decades, synthetic tools, such as living ionic polymerizations, controlled radical polymerizations, and click chemistry, have revolutionized the synthesis of polymers with controlled architectures such as block, graft, star, brush, hyperbranched or cyclic polymers. These aspects being solved, it is now time for polymer chemists to address more challenging questions such as the design of monodisperse polymers and the control of primary (i.e., comonomer sequences), secondary (i.e., single-chain folding), and tertiary (i.e., single-chain compartmentalization) structures. Here, new synthetic tools have to be developed or imported from other disciplines such as organic chemistry and biochemistry. For instance, solid-phase iterative chemistry, which was initially introduced for the synthesis of oligopeptides and oligonucleotides, is an interesting methodology for preparing monodisperse sequence-defined polymers. However, such approaches are usually time-consuming and request demanding coupling/capping/deprotection steps. Yet, interesting protecting-group-free methodologies have been described in recent years for simplifying and accelerating these processes. These promising new approaches are briefly listed and explained in this article. Protecting-group-free iterative strategies that have been recently reported for the synthesis of monodisperse sequence-defined polymers are described. In such approaches, the monomers are attached one-by-one to a growing chain, which is immobilized on a solid- or soluble support. The uses of protecting-group-free coupling chemistries permit the simplification of these multistep growth processes. These promising concepts are listed and explained herein.