Mixed [2 : 6] hetero-arm star polymers based on Janus POSS with precisely defined arm distribution

Abstract

One important, yet less explored molecular parameter of star polymers is the distribution of arms in three dimensional (3D) space. Herein, we describe the synthesis of a series of mixed [2 : 6] hetero-arm star polymers whose arms are precisely arranged on a cubic scaffold of T₈ polyhedral oligomeric silsesquioxane (POSS). The synthesis begins with regio-isomeric Janus POSS compounds (para-, meta-, and ortho-isomers) with two hydroxylethyl and six vinyl pendant groups. Two poly(ε-caprolactone) (PCL) chains are grown from the hydroxyls by Sn(Oct)₂-mediated ring-opening polymerization. The vinyls are then converted to azides for subsequent “grafting” of six polystyrene (PS) arms onto POSS. The configuration of the final star polymers was thoroughly characterized by NMR, FT-IR, SEC, and MALDI-TOF mass spectrometry. This serves as the first few examples of mixed-arm star polymers with precise distribution of multiple arms, providing an intriguing platform for the study of their self-assembly.