Stimuli-responsive Diblock Copolymer Research Articles

PH and ionic strength triggered destabilization of biocompatible stable water-in-oil-in-water (W/O/W) emulsions

The design of biocompatible multiple emulsions is an important challenge in the field of controlled delivery systems for protecting and delivering compounds encapsulated and protected in the innermost phase. In this paper, we use biocompatible water – Miglyol®812 water-in-oil-in-water (W/O/W) emulsions stabilized by a stimuli-responsive diblock copolymer consisting of poly(dimethylsiloxane) (PDMS) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to design an easy-to-process new delivery W/O/W system. Such emulsions are formed in a single emulsification step. They present a high encapsulation yield and are shown to be stable over months. As such, the encapsulation of a hydrophilic dye (Alexa fluor) in the innermost water phase is successfully demonstrated over months. These emulsions are stimulable either by a shift in pH level or in ionic strength. The former destabilizes the multiple emulsion and leads to a simple one while the latter partly maintains the multiple character. Eventually both stimulations are effective in the dye release and molecular mechanisms are proposed for explaining the observed two-stage kinetics of release. Triggered release of a hydrophilic dye encapsulated in a biocompatible W/O/W emulsion, formed by one-step mixing and stabilized by a single block copolymer using pH and ionic strength ( I ) stimuli. Oil phases appear in blue, dye-loaded aqueous phases appear in red and dye-free aqueous phases appear in black.

Functional nanoporous materials from boronate-containing stimuli-responsive diblock copolymers

Functional nanoporous polymeric materials have been prepared from novel polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer precursors containing a reversible boronate ester junction between both blocks.

Synthesis and aggregation behaviour of thermo-responsive-b-poly(ionic liquid) diblock copolymers in aqueous solution

Stimuli-responsive di-block copolymers viz. poly(N-isopropylacrylamide)m-block-poly(butyl-3-vinylimidazolium bromide)n [abbreviated as PNIPAMm-b-PBVIBn m = 50 and 100, n = 54 and 115] were synthesized using RAFT (Reversible addition−fragmentation chain-transfer) polymerization. Gel permeation chromatography (GPC) and nuclear magnetic resonance (1H NMR) spectroscopy were used to characterize the block copolymer. Turbidity data shows that the lower critical solution temperature (LCST) of PNIPAM is independent of the molecular weight. No LCST behavior was estimated for PBVIB58 in an aqueous media. The addition of 2.75 M NaCl brings LCST of PBVIB58 to room temperature. The cloud point temperature (CPT) of both the block copolymers increases with an increase in the degree of polymerization of PBVIB. Scattering techniques confirm the molecular state of all the homopolymers at 28 °C in the dissolved condition. With an increase in temperature and the presence of sodium chloride (NaCl), both the copolymers remain as aggregates with PNIPAM as a core and PBVIB as a shell. The reverse structure is formed via the addition of 10 mM sodium dodecyl sulfate (SDS) into PNIPAM100-b-PBVIB54 solution.

Surface-Grafted Stimuli-Responsive Block Copolymer Brushes for the Thermo-, Photo- and pH-Sensitive Release of Dye Molecules

We present a general approach for using surface-grafted stimuli-responsive diblock copolymer brushes as stimuli-sensitive and controllable release systems. Surface-initiated ATRP was used to grow sequentially a first block serving as an inner reservoir for loading and a second block that acts as a stimuli-responsive outer layer controlling the closure or opening of the brush in water. We show that the release kinetics of loaded model dyes (hydrophobic or hydrophilic) could be controlled by the second block switchable between the collapsed and extended brush chain states in response to temperature or pH change or exposure to light. On the one hand, diblock copolymer brushes of polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) and poly(N,N′-dimethylacrylamide)-b-poly(N-isopropylacrylamide) (PDMA-b-PNIPAM) were synthesized to demonstrate the thermosensitive release of dyes based on the LCST-determined solubility switching between swollen and collapsed PNIPAM chains. On the other hand, a diblock copolym...

Mesoscopic Simulations of Morphological Transitions of Stimuli-Responsive Diblock Copolymer Brushes

Using coarse-grained DPD simulations, we study the morphology of AB diblock copolymer brushes in selective solvents which are good for the anchored A blocks but poor (of varying degrees measured by the distance from the Θ-point, τB) for B blocks. Choosing appropriate polymer compositions given by the fraction of B blocks, fB, we find transitions between spherical and cylindrical micelles as well as inverted morphologies (perforated layer). We discuss the phase diagram in the fB−τB parameter space and analyze characteristic quantities of the structures obtained such as domain size, periodic spacing and brush height. The internal structure of the uniform (lamellar) structure is investigated in detail. The simulation results are compared with theoretical predictions and experimental observations.

Synthesis and characterization of well-defined thermo- and light-responsive diblock copolymers by atom transfer radical polymerization and click chemistry

We synthesized a series of well-defined, stimuli-responsive diblock copolymers composed of poly(N-isopropylacrylamide) and poly(6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate) by atom transfer radical polymerization and click chemistry. The diblock copolymers were then characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography. When the azobenzene content reached 4.5 mol%, the diblock copolymer became insoluble in water. The aqueous solutions of the polymers exhibited a lower critical solution temperature (LCST) that depended on the amount of incorporated azobenzene. Higher LCSTs were observed after UV irradiation, with a maximum difference of 4.1 °C for the copolymer containing 1.4 mol% azobenzene groups. The photochemical properties of the polymer were also studied by UV-vis spectroscopy.

Reversible gold “locked” synthetic vesicles derived from stimuli-responsive diblock copolymers

Polymersomes derived from a RAFT-generated, thermally responsive diblock copolymer, P(DMAEMA165-b-NIPAM435), were shell cross-linked by in situ gold nanoparticle formation. The cross-linking was subsequently reversed by the addition of the thiols capable of inducing a ligand exchange on the surface of the gold nanoparticle.

Tuning Nanostructure Morphology and Gold Nanoparticle “Locking” of Multi-Responsive Amphiphilic Diblock Copolymers † Paper No. 138 in a series on Water Soluble Polymers.

Reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to prepare multiresponsive, self-assembling amphiphilic poly[(N,N-dimethylaminoethyl methacrylate)x-b-(N-isopropylacrylamide)y] (DMAEMAx-b-NIPAMy). Controlling block lengths, solution pH, and NaCl concentration to elicit changes in the hydrophilic mass fraction resulted in specific morphological changes upon thermally induced assembly. At y = 102 (68 wt % DMAEMA), DMAEMA165-b-NIPAM102 copolymers self-assemble into simple core−shell micelles (58 nm). Increasing y to 202 (48 wt % DMAEMA) leads to a mixture of spherical micelles (78 nm) and worm-like micelles (D = 50−100 nm, L = 400−500 nm). Further increasing y to 435 (36 wt % DMAEMA) produces vesicular structures (179 nm). Significantly, reversible assembly of these nanostructures from the present stimuli-responsive diblock copolymers can be accomplished directly in aqueous media without the necessity of dialysis or manipulation with cosolvents. Additionally, the associated...

Synthesis of Surface-Initiated Stimuli-Responsive Diblock Copolymer Brushes Utilizing a Combination of ATRP and RAFT Polymerization Techniques

The synthesis of diblock copolymer brushes, including poly(styrene) (PSty)-b-PSty, PSty-b-poly(acrylic acid), PSty-b-poly(N-isopropylacrylamide), and poly(methyl acrylate)-b-poly(N,N-(dimethylamino)ethyl acrylate), was achieved utilizing a combination of surface-mediated atom transfer radical polymerization (ATRP) and reversible addition−fragmentation chain transfer (RAFT) polymerization techniques. Conversion of bromine end groups of homopolymer brushes formed by ATRP via a modified atom transfer addition reaction to a RAFT agent and diblock extension via RAFT polymerization allowed the direct formation of well-defined stimuli-responsive diblock copolymer brushes. The addition of sacrificial initiator and/or chain transfer agent permitted formation of well-defined diblock copolymer brushes and free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Ellipsometry, contact angle measurements...

Stimuli-Responsive Diblock Copolymers by Living Cationic Polymerization: Precision Synthesis and Highly Sensitive Physical Gelation

Stimuli-responsive diblock copolymers with a thermosensitive segment and a hydrophilic segment have been synthesized via sequential living cationic copolymerization, which involves a poly(vinyl ether) with oxyethylene pendants exhibiting LCST-type phase separation in water and a poly(hydroxyethyl vinyl ether) segment. Highly sensitive and reversible thermally induced micelle formation and/or physical gelation were observed with such diblock copolymers. For example, the flow behavior of an aqueous solution of a diblock copolymer varied from Newtonian to non-Newtonian and plastic flow within a very narrow temperature range. TEM and SANS studies showed that the observed change in viscosity was due to the formation of a macrolattice with body-centered-cubic symmetry of spherical micelles in aqueous solution. The critical temperature of micelle formation and/or physical gelation could be varied by altering the combination of two segments in the diblock copolymer. On the basis of these results, several systems incorporating various patterns of physical gelation behavior have been developed, and a strategy for constructing stimuli-responsive systems with block copolymers was established.

高分子ミセルＩＩ リビングカチオン重合による刺激応答性ジブロックコポリマーの合成 感熱応答ミセル化およびゲル化

高分子ミセルＩＩ リビングカチオン重合による刺激応答性ジブロックコポリマーの合成 感熱応答ミセル化およびゲル化