Step‐Growth Copolymerization Between an Immobilized Monomer and a Mobile Monomer in Metal–Organic Frameworks

The A–A/B–B step‐growth copolymerization between a monomer immobilized in the crystalline state and a monomer mobile in the solution state is demonstrated. One of the two monomers was immobilized as organic ligands of the metal–organic framework (MOF) and polymerized with the mobile guest monomer, resulting in the formation of linear polymers. The polymerization behavior was completely different from that of the solution polymerizations. In particular, the degrees of polymerization (DP) converged to a specific value depending on the MOF structures. The inevitable termination is caused not by imperfectness of the polymerization reaction, but by the selection of the two polymerization partners among the several adjacent immobilized monomers. This is fully supported by the Monte Carlo simulation on the basis of the polymerization mechanism. Precise immobilization of monomers in the supramolecular assemblies is a promising way for the controlled A–A/B–B step‐growth polymerization. Two types of monomers in different environments were copolymerized in a metal–organic framework (MOF). One of the two monomers was immobilized in the MOF as an organic linker and the other is mobile in the 3D channels of the MOF. The polymerization degree converged to a specific value depending on the MOF structure. Immobilization of monomers regularly in supramolecular assemblies is a promising way for controlling step‐growth copolymerization.