Construction of temperature responsive hybrid crosslinked self-assemblies based on PEG-b-P(MMA-co-MPMA)-b-PNIPAAm triblock copolymer: ATRP synthesis and thermoinduced association behavior

A novel amphiphilic thermosensitive poly(ethylene glycol) ₄₅-b-poly(methyl methacrylate₄₆-co-3-(trimethoxysilyl) propyl methacrylate)₂-b-poly(N-isopropylacrylamide)₄₂₉ (PEG₄₅-b-P(MMA₄₆-co-MPMA₂)-b-PNIPAAm ₄₂₉) triblock copolymer was synthesized via consecutive atom transfer radical polymerization techniques. The thermoinduced association behavior of the resulting triblock copolymers in aqueous medium was further investigated in detail by ¹H NMR, transmission electron microscopy, and dynamic light scattering. The results showed that at the temperature (25 °C) below the LCST, PEG₄₅-b-P(MMA₄₆-co-MPMA₂)-b-PNIPAAm ₄₂₉ triblock copolymers self-assembled into the core crosslinked micelles with the hydrophobic P(MMA-co-MPMA) block constructing a dense core, protected by the mixed soluble PEG and PNIPAAm chains acting as a hydrophilic shell simultaneously. With an increase in temperature, the resulting core-shell micelles converted into a new type of micelles with the hydrophilic PEG chains stretching out from the hydrophobic core through the collapsed PNIPAAm shell. On the other hand, at the temperature (40 °C) above the LCST, such triblock copolymers formed the crosslinked vesicles with the hydrophobic PNIPAAm and P(MMA-co-MPMA) blocks constructing a membrane core and the soluble PEG chains building the hydrophilic lumen and the shell. On further decreasing the temperature, the resulting vesicles underwent transformation from the shrunken to the expanded status, leading to the formation of swollen vesicles with enlarged size. This study is believed to present the first formation of two types of hybrid crosslinked self-assemblies by thermoinduced regulation.