Development of amphiphilic multi-star polymers with highly grafted pyrene connectors as unimolecular encapsulation devices

Abstract

Complex and hierarchically structured unimolecular polymeric architectures provide unique opportunities for self-assembly, encapsulation, segregation and recognition. Herein, we report the synthesis of unimolecular anisotropic and amphiphilic multi-star architectures consisting of multiple discrete core cross-linked star (CCS) polymers covalently tethered together through highly grafted polymeric connectors. These multi-star architectures, referred to as di-star and tri-star polymers, were prepared via a combination of atom transfer radical polymerisation (ATRP) and a copper-catalysed azide-alkyne cycloaddition (CuAAC) grafting-to approach. Initially, poly(tert-butyl methacrylate) (PtBMA)-based multi-star polymers with polyalkyne linear connectors were prepared via ATRP and the arm-first approach. Following isolation of the individual di-star and tri-star polymers, an azido-pyrene derivative was grafted onto the connectors via click chemistry with grafting efficiencies of 88 and 84%, respectively. Subsequently, hydrolysis of the PtBMA star arms provided amphiphilic poly(methacrylic acid) (PMAA)-based multi-stars with pyrene grafted connectors. The ability of the unimolecular di-star polymer to sequester and stabilise hydrophobic guests in aqueous solutions via π–π stacking interactions was investigated through the encapsulation of the anticancer drug pirarubicin. UV measurements provided loading capabilities of ca. 135 molecules of pirarubicin per di-star polymer (ca. 12 wt%).