Interface cross-linked polymeric micelles with mixed coronal chains prepared by RAFT polymerization at the interface

Abstract

Poly(ethylene glycol-block-2-hydroxyethyl methacrylate-block-tert-butyl acrylate) (PEG-b-PHEMA-b-PtBA) triblock copolymer was synthesized by the sequential atom transfer radical polymerization (ATRP) of HEMA and tBA using an ATRP initiator terminated PEG (PEG-Br) as the macroinitiator. Azide groups were introduced to the short mid-blocks by reactions of the triblock copolymer with 2-bromoisobutyryl bromide and sodium azide. In aqueous solution, the triblock copolymer self-assembled into micelles with azide groups at the interfaces. Reactive polymeric micelles with reversible addition–fragmentation chain transfer agents (RAFT CTAs) at the interfaces were prepared by a click cross-linking reaction between dialkynetrithiocarbonate and the azide groups. FT-IR, ¹H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to characterize the interface cross-linked (ICL) micelles and the grafting of the RAFT CTAs to the interfaces. Polymeric micelles with PEG–poly(N-isopropylacrylamide) (PNIPAM) mixed coronal chains were prepared by the in situ RAFT polymerization of NIPAM at the interfaces. The TEM results demonstrate that the mixed coronal chains have nano-sized phase separation on the surfaces of the micelles. The use of the polymeric micelles as particulate emulsifiers was also investigated in this research. These ICL micelles with mixed coronal chains produce relatively fine 1-undecanol-in-water (o/w) emulsions compared to emulsions stabilized by the PEG homopolymer under the same conditions.