Abstract
Here we report the dual light- and thermo-responsive behavior of well-defined rod-coil block copolymers composed of an azobenzene unit, 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA). Azobenzene-containing rigid rod blocks prepared by chain growth condensation polymerization of the azobenzene containing monomer were used as a macroinitiator of atom transfer radical polymerization (ATRP) after attaching an α-bromoisobutyryl group as an end group. Synthesis of well-defined rod-coil block copolymers with different coil block lengths was achieved by copolymerization of MEO2MA and OEGMA monomers. The synthesized polymers exhibited amphiphilic properties and polymeric micelles were formed in aqueous solution. The light-responsive behaviors of azobenzene moieties, photoisomerization by irradiation of light, and thermo-responsive behaviors of P(MEO2MA-co-OEGMA) coil blocks, aggregation by increment of temperature over lower critical solution temperature, were investigated. A dual stimuli-responsive behavior of the rod-coil block copolymers was observed when exposed to light and heat.
Highlights
Self-assembly of block copolymers consisting of two immiscible polymer chains has received considerable attentions owing to their ability to form well-defined structures composed of polymeric materials [1,2]
To construct complicated systems with precise control, syntheses of well-defined polymers is required through controlled polymerization techniques such as chain-growth condensation polymerization (CGCP) [7,8] and atom transfer radical polymerization (ATRP) [9,10]
The Poly(arylene ether azobenzene) (PAEAz) rod block with a narrow molecular weight distribution was synthesized by CGCP according to the reported procedure [42]
Summary
Self-assembly of block copolymers consisting of two immiscible polymer chains has received considerable attentions owing to their ability to form well-defined structures composed of polymeric materials [1,2]. The light-responsive behavior of azobenzene moieties incorporated into polymer chains have been known to induce reversible modulation of their mechanical, morphological and polar properties by irradiation of light [19,20,21]. Another readily available physical stimulus is heat, and thermo-responsive polymers have been extensively investigated because of their relation to biotechnology and nanotechnology [22,23]. A uniform thermal profile compared with PNIPAM was reported [28] Polymers containing the both light-responsive moieties and thermo-responsive moieties are expected to exhibit dual stimuli-responsive behaviors against change of temperature and irradiation of light [29,30]. The self-assembly behavior of the prepared polymers in aqueous solution was investigated to demonstrate dual stimuli-responsive behavior of the rod-coil block copolymers
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