Inside Block Copolymer Micelles—Tracing Interfacial Influences on Crosslinking Efficiency in Nanoscale Confined Spaces

Abstract

AbstractRecently, several studies have demonstrated the excellent capabilities of tip‐enhanced Raman spectroscopyfor in‐depth investigations of structural properties of matter with unprecedented resolution and chemical specificity. These capabilities are utilized here to study the internal structure of core‐crosslinked micelles, which are formed by self‐assembly of the diblock terpolymer poly(ethylene oxide)‐block‐poly(furfuryl glycidylether‐co‐tert‐butylglycidyl ether). Supplementing force–volume atomic force microscopy experiments address additionally the nanomechanical properties. Particularly, TERS enables investigating the underlying principles influencing the homogeneity and efficiency of the Diels–Alder core‐crosslinking process in the confined hydrophobic core. While the central core region is homogenously crosslinked, a breakdown of the crosslinking reaction is observed in the core–corona interfacial region. The results corroborate that a strong crosslinking efficiency is directly correlated to the formation of a mixed zone of the glycidyl ether and PEO corona blocks reaching ≈5 nm into the core region. Concomitantly a strong exclusion of the encapsulated bismaleimide crosslinker from the interfacial region is observed. It is conceivable that a changed structure, chemical composition and altered nanomechanical properties of this interfacial region may also influence the crosslinking efficiency across the entire core region by a modification of the solubility of the crosslinker in the interfacial core‐corona region.