Gradient Structure‐Induced Temperature Responsiveness in Styrene/Methyl Methacrylate Gradient Copolymers Micelles

Abstract

In this work, micelles are formed by gradient copolymer of styrene and methyl methacrylate in acetone-water mixture and their temperature responsiveness is investigated in a narrow range near room temperature. Three different kinds of structural transitions could be induced by temperature: unimers to micelle transition, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles. In addition, a model analysis on the interface of gradient copolymer micelle is made to better understand these phenomena. It is found that both position and composition of the interface could alter in response to the change in temperature. According to the experiments and model analysis, it is proposed that temperature responsiveness might be an intrinsic and universal property of gradient copolymer micelles, which only originates from the gradient structure.

Asymmetric Copolymers: Synthesis, Properties, and Applications of Gradient and Other Partially Segregated Copolymers

“…He and co‐workers observed three types of structural transition in solutions of temperature‐responsive poly(St‐ co ‐MMA) gradient copolymers: unimers to micelles, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles . Similar transitions could be obtained by decreasing the solvent quality using various acetone/water mixtures ( Figure ) …”

“…This may be achieved by varying the solvent composition, [157][158][159] pH, [7,56,160] or temperature. [105,123,128,161,162] Where block copolymers undergo sharp transitions between dissolved and aggregated species, asymmetric copolymers undergo continuous evolution with changing solvent conditions, as polymer segments of different compositions react differently. In pH-responsive asymmetric copolymers, the sharper the gradient profile, the lower the pH required to trigger the conformational change and the narrower the pH range needed to complete the transition.…”

“…Similarly to block copolymers, the self‐assembly of asymmetric copolymers may be induced by changing the solvent quality such that one component becomes insoluble. This may be achieved by varying the solvent composition, pH, or temperature . Where block copolymers undergo sharp transitions between dissolved and aggregated species, asymmetric copolymers undergo continuous evolution with changing solvent conditions, as polymer segments of different compositions react differently.…”

Facile Synthesis of CO2‐Responsive Nano‐Objects: Batch versus Semi‐Batch RAFT Copolymerization

“…[27][28][29][30][31] In particular, amphiphilic gradient copolymers consisting of hydrophobic and hydrophilic units exhibit unusual self-assembly behavior and stimuli-responsive properties compared with corresponding statistical or block copolymers. [32][33][34][35] For instance, Boyer and co-workers applied the semi-batch polymerization process to 2-hydroxypropyl methacrylate (HPMA) and oligo(ethylene glycol)methyl ether methacrylate (OEGMA 300 ) monomer pairs. More interestingly, the amphiphilic gradient copolymers poly(OEGMA 300 -grad-HPMA) presented unusual self-assembly behavior and thermo-responsive properties, exhibiting a sphere-to-worm morphological transition with the temperature increase.…”

Synthesis of gradient copolysiloxanes by simultaneous copolymerization of cyclotrisiloxanes and mechanism for kinetics inverse between anionic and cationic ring‐opening polymerization

“…However, in recent years, gradient copolymers of different siloxane units have gradually produced extensive concern because of their potential unique properties which are significantly different compared with the properties of block and random copolymers . Gradient copolymers are a novel class of polymers that exhibit a gradual change in composition along the chain . They can potentially be used as polymer blend compatibilizers, surfactants, and environment‐sensitive materials …”