Well-Defined Star-Shaped Rod−Coil Diblock Copolymers as a New Class of Unimolecular Micelles: Encapsulation of Guests and Thermoresponsive Phase Transition

Abstract

A series of star-shaped rod-coil diblock copolymers composed of poly(arylene ether sulfone) (PAES) as a core, and poly[2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate] [poly(MEO 2 MA-co-OEGMA)] as a shell was synthesized by combination of chain-growth condensation polymerization (CGCP) and atom transfer radical polymerization (ATRP). In the presence of 4-arm initiator (1), CGCP of 4-fluoro-4 0 -hydroxydiphenyl sulfone potassium salt (2) via nucleophilic aromatic substitution (S N Ar) reaction yielded a well-defined star-shaped polymer with four fluorine end groups (C5-F and C8-F). Transformation of the fluorine groups into ATRP initiating sites produced a macroinitiator having four bromine groups (C5-Br and C8-Br). In the presence of the macroinitiator, random copolymerization of MEO 2 MA and OEGMA via ATRP formed thermoresponsive shell blocks to produce a desired star-shaped PAES-b-poly(MEO 2 MA-co-OEGMA) block copolymer with various block lengths. Dynamic light scattering (DLS) of the star-shaped diblock copolymers in aqueous solutions revealed that hydrodynamic diameters (D h ) of the polymers decreases significantly by addition of Nile Red due to the transition from polymeric aggregates to unimolecular micelles. Fluorescence spectroscopy confirmed that the polymers behave as unimolecular micelles in the encapsulation of Nile Red, but another transition into multimolecular polymer micelles was observed by UV/vis spectroscopy when the excess amount of Nile Red was used. Turbidity measurements of the polymer solutions indicated that unimolecular micellar state was necessary to exhibit lower critical solution temperature (LCST) if the shell length was relatively short compared to the core size. Macroscopic aggregation was observed above LCST, and removal of encapsulated guests from water was demonstrated by simple filtration.

Thermo‐Switchable Materials Prepared Using the OEGMA‐Platform

“…Several groups reported for example the synthesis of amphiphilic block copolymers composed of a hydrophobic segment and an OEGMA-based thermoresponsive hydrophilic segment. [63][64][65] Below the LCST of the hydrophilic block, these macromolecules form micelles in water. However, above LCST, the micellar aggregates precipitate in water, thus allowing fi ltration and recycling or eventually the formation of larger superstructures.…”

“…However, above LCST, the micellar aggregates precipitate in water, thus allowing fi ltration and recycling or eventually the formation of larger superstructures. [ 65 ] Alternatively, double hydrophilic block copolymers containing a permanently hydrophilic segment and a thermoresponsive POEGMA segment have been also described. [66][67][68][69] These macromolecules are fully soluble in water below LCST but micellize at higher temperatures due to the aqueous precipitation of the POEGMA blocks.…”

Temperature-responsive self-assembly of star block copolymers with poly(ionic liquid) segments

“…In particular, interest in the design and synthesis of star block copolymers with stimuli-responsive segments has increased because the chain architecture (topology) of block copolymers affects their self-assembling behavior and stimuli-responsive properties. [29][30][31][32][33][34][35] Herein, we report the controlled synthesis of novel star block copolymers with poly(N-vinylimidazolium salt) as a poly(ionic liquid) segment and poly(NIPAAm) as a thermoresponsive segment by RAFT polymerization. In addition to the comonomer composition and chain length of each segment, the branched structure and location of the thermoresponsive segment affected the stimuliresponsive properties and assembled structure of the material.…”

Synthesis and Self-Assembly Behavior of Temperature Responsive 2-Hydroxy-3-Isopropoxypropyl Hydroxyethyl Cellulose

“…以 Nile Red 为探针, 通过荧光光谱仪(Hitachi F 7000, Japan)来测定 Nile Red 增溶行为及其增溶胶束的 温度响应性, Nile Red-HIPEC 胶束水溶液的制备: 使用 微量进样器吸取一定量 Nile Red 的乙酸乙酯溶液(50 mg/L)于 10 mL 的容量瓶中, 将乙酸乙酯吹干, 加入一 定浓度的 HIPEC 水溶液, 放入超声中震荡, 使其溶解并 静置过夜 [23,24] .…”