Controlled synthesis of water-compatible molecularly imprinted polymer microspheres with ultrathin hydrophilic polymer shells via surface-initiated reversible addition-fragmentation chain transfer polymerization

Abstract

The first controlled synthesis of pure water-compatible molecularly imprinted polymer (MIP) microspheres with ultrathin hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) shells (including both PHEMA brushes and lightly crosslinked PHEMA hydrogel layer) via surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization is described. The presence of ultrathin hydrophilic polymer shells on the MIP microspheres was confirmed by SEM, FT-IR, fluorescent labeling treatment, contact angle studies, and water dispersion stability test, and some quantitative information including the thickness of the grafted hydrophilic polymer layers as well as the molecular weights and polydispersities of the grafted polymer brushes and their grafting densities was provided. The facile surface-grafting of both PHEMA brushes and PHEMA hydrogel layer on the MIP microspheres proved to be highly efficient for improving their surface hydrophilicity and suppressing the hydrophobically driven nonspecific interactions between the MIPs and template molecules, leading to MIPs with pure water-compatible binding properties. The findings presented here not only prove the general applicability of the controlled hydrophilic polymer brushes-grafting approach in obtaining pure water-compatible MIPs, but also largely extend the scope of this versatile surface-grafting approach through the controlled surface-grafting of hydrophilic polymer hydrogel layer onto the MIPs. Moreover, the significant effect of the chain length of the grafted polymer brushes and the presence of crosslinking in the grafted polymer shells on the surface hydrophilicity and water-compatibility of the MIP microspheres was also demonstrated for the first time, which is of great importance for the rational design of water-compatible MIPs by using this controlled surface-grafting approach.