Chain-Growth Condensation Polymerization of Propargyl Electrophiles Enabled by Copper Catalysis

In the pursuit of creating macromolecules with controlled molecular weight, sequence, and end groups, condensation polymerization remains an underexploited synthetic tool because of its intrinsic step-growth nature. Introducing chain-growth pathways into condensation polymerization calls for highly efficient chemistries that effect the challenging differentiation between functional groups of the same type present in monomers and polymers. Here, we address this challenge by a catalyst bifurcation strategy that enables a copper-catalyzed chain-growth condensation polymerization. Using a copper(I) arylacetylide as an initiator/precatalyst along with a phosphine ligand, polydiynes of controllable molecular weights and end groups are synthesized from readily available propargyl carbonates, including a block copolymer. This method provides a new chain-growth access to functional acetylenic polymers, a class of useful materials that have been obtained essentially by step-growth methods to date. This work demonstrates the power of dual-role transition metal catalysis in accomplishing unusual selectivity in organic synthesis.