Polycondensation in confined nanopores toward the selective formation of narrowly dispersed linear polyesters

Abstract

The synthesis of linear polymers with both ends conserved is severely impeded due to the inevitable macrocyclization in step-growth polymerization (SGP). Indeed, macrocyclic polymers are considered as the ultimate destination of polycondensations for AB or A₂ + B₂ monomer combinations. Here, we present a new strategy to limit the macrocyclization process towards the selective formation of linear polyesters in the polycondensations of ω-hydroxyaliphatic acid and the combinations of dicarboxylic acids and diols. By embedding the catalyst (sulfonic acid) in dendritic mesoporous silica nanoparticles (DMSNs), the polyesterifications were ushered to exclusively take place in the confined nanopores of DMSNs. The distribution of the α,ω-ends in different positions in the bundle of polyesters limited the end-to-end cyclization, leading to the selective chain extension especially in the high molecular weight region. NMR, GPC and MALDI-TOF results show that while the polyesters obtained in homogeneous polycondensation or with a nonporous heterogeneous catalyst were mainly with cyclic structures, the selective formation of linear polyesters was found in the confined nanopores of DMSNs. This finding contradicts the general sense that confined geometries are in favor of macrocyclization and provides a new understanding to manipulate the polymerization process towards the control of cyclic and linear topologies.