Cross-Linked Nano-Objects Containing Aldehyde Groups: Synthesis via RAFT Dispersion Polymerization and Application

Pure cross-linked spherical micelles, nanowires, and vesicles are successfully fabricated from poly(2-hydroxypropyl methacrylate-b-p-(methacryloxyethoxy)benzaldehyde)s (PHPMA-b-PMAEBAs) through reversible addition-fragmentation chain transfer dispersion polymerization of MAEBA in methanol using PHPMA as a macro-CTA and subsequent cross-linking. The cross-linking reaction is conducted by stirring a mixture of 1,4-butanediamine and the resultant nano-objects in methanol at room temperature. For all polymerizations with feed molar ratios of MAEBA/PHPMA ranging from 75/1 to 240/1, the monomer MAEBA conversions are almost complete, and block copolymers with controlled molecular weight are obtained. The transmission electron microscopy, dynamic light scattering, and gel permeation chromatography results reveal that the following three factors significantly influence the morphology of the nano-objects: the feed molar ratio of MAEBA/PHPMA, the copolymer concentration, and the degree of polymerization of PHPMA. The cross-linked nano-objects are very stable in good solvents, the spheres and nanowires slightly decrease in size after cross-linking, whereas the vesicles slightly increase in size. The cross-linked nano-objects are stable in neutral solutions, but they dissociate in weekly acidic solutions. The loading of 1-pyrenemethylamine (PMA) into the vesicles and the unloading of PMA from the vesicles are studied.