Photoluminescent polymer cubosomes prepared by RAFT-mediated polymerization-induced self-assembly

Abstract

Polymer assemblies with photoluminescent properties are of increasing interest for biomedical applications, ranging from biosensing and bioimaging to biotracking. However, the preparation of these nano/micro-objects often requires multistep polymer synthesis and a tedious self-assembly process. Herein, we demonstrate the preparation of photoluminescent polymer assemblies with a wide range of morphologies, from simple spherical micelles, worm-like micelles, and vesicles, to rarely achieved microparticles with inverse mesophases such as spongosomes and cubosomes, via an efficient RAFT-mediated polymerization-induced self-assembly (RAFT-PISA) process. To access the polymer assemblies with photoluminescent properties, an aggregation-induced emission (AIE) active monomer (TPE) was copolymerized with 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl acrylate (TBA) in a RAFT-PISA process with poly(N,N-dimethylacrylamide) (PDMA) as the stabilizer block. It was found that the conversion of TBA is highly dependent on the addition ratio of TPE. When the TPE ratio increased to 5 mol% of the total monomer, phase-separation induced by the incompatibility between different components of polymers led to the production of highly sought-after multiphase morphologies such as “colloidal polymers” and phase-separated vesicles, but the morphological evolution terminated at the stage of the spongosome. The reduction of the TPE ratio to 1–2 mol% allows the successful production of photoluminescent cubosomes and hexosomes, capable of emitting blue light upon illumination with light of wavelengths 365–405 nm as confirmed by fluorescence spectroscopy, confocal laser scanning microscopy (CLSM) and digital photographs taken under UV light. Overall, this study is expected to greatly expand the utility of RAFT-PISA by providing facile access to photoluminescent polymer assemblies with a diverse range of morphologies, especially those containing inverse mesophases.