Thermoresponsive Amphiphilic Block Copolymers Research Articles

Bilayer-domain formation of thermoresponsive amphiphilic block copolymers in hybrid liposomes for synthetic molecular channels

Maltopentaose-b-PPO copolymer can be incorporated into phospholipid membranes and form bilayer-domains, where they act as synthetic molecular channels.

Association of the Thermodynamics with the Functionality of Thermoresponsive Chimeric Nanosystems.

Stimuli-responsive nanosystems are an emerging technology in the field of therapy and are very promising for various applications, including targeted drug delivery. In this chapter, our scope is to integrate two different methodologies, namely differential scanning calorimetry (DSC) and dynamic light scattering (DLS), in order to rationally approach the functional behavior of thermoresponsive chimeric/mixed liposomes and interpret their thermoresponsiveness on a thermodynamic basis. In particular, chimeric bilayers comprised of the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and two different-in-composition thermoresponsive amphiphilic block copolymers poly(N-isopropylacrylamide)-b-poly(lauryl acrylate) (PNIPAM-b-PLA) 1 or 2 were built by a conventional evaporation technique, followed by DSC, and chimeric liposomes of DPPC and PNIPAM-b-PLA 1 were developed and studied by DLS, after preparation and after a simple heating protocol. The results from both methodologies indicate the composition- and concentration-dependent lyotropic effect of the foreign copolymer molecule on the properties and functionality of the lipidic membrane.

Novel poly(3-hydroxy butyrate) macro RAFT agent. Synthesis and characterization of thermoresponsive block copolymers

A novel reversible addition fragmentation transfer (RAFT) agent based on the poly-3-hydroxy butyrate (PHB) with three hydroxyl groups (PHB-R2) and thermoresponsive amphiphilic block copolymers derived from N-isopropyl acryl amide (NIPAM) are described. Hydroxylated PHB is obtained by the reaction between PHB and diethanol amine (DEA) to prepare hydroxylated PHB (PHB-DEA). It is then reacted with a RAFT agent, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT). Hydroxyl ends of the hydroxylated PHB are capped with carboxylic acid end of the trithiocarbonate. The block copolymers obtained by the polymerization of NIPAM initiated by PHB-R2 were characterized by 1H NMR and physicochemical techniques. PHB content in the obtained block copolymers is varying between 14 and 45 wt%. The thermo-responsive PHB-PNIPAM block copolymers show the lower critical solution temperature (LCST) 28 and 30 °C while LCST of the pure PNIPAM is 32 °C.

Preparation of photochromic liquid core nanocapsules based on theoretical design

Photochromic materials have attracted considerable attention for their practical applications in optoelectronic devices. In this study, we developed the photochromic liquid core nanocapsules by polymerization of oil-in-water (O/W) nanoemulsion monomer droplets on the basis of Hansen solubility parameters. The thermoresponsive amphiphilic block copolymers (POEGMAm-b-PStn and POEGMAm-b-PMMAn) were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization of hydrophilic oligo(ethylene glycol) methyl ether methacrylate and hydrophobic styrene or MMA. The O/W nanoemulsion methyl methacrylate (MMA) droplets, dissolving dipropylene glycol methyl-n-propyl ether (DPMNP) and (E)-3-(adamantan-2-ylidene)-4-[1-(2,5-dimethyl-3-furyl) ethylidene]dihydro-2,5furandione (Aberchrome 670) as a core liquid and a photochromic dye, respectively, were obtained through the phase inversion temperature emulsification technique using POEGMAm-b-PStn as a surfactant. As theoretically predicted in terms of the spreading coefficients, the DPMNP solution of Aberchrome 670 was successfully encapsulated by coacervation of the crosslinked PMMA condensed phase. Aberchrome 670 dissolved in a liquid core was found to photoisomerize twice as fast as that dispersed in the solid polymer matrices.

Synthesis of star thermoresponsive amphiphilic block copolymer nano-assemblies and the effect of topology on their thermoresponse

Well-defined multi-arm star thermoresponsive block copolymer nano-assemblies of [poly(N-isopropylacrylamide)-block-polystyrene]n [(PNIPAM-b-PS)n] with n = 1, 2, 3 and 4 arms were synthesized by RAFT dispersion polymerization via polymerization-induced self-assembly.

アルコキシアミン骨格を連結点にもつ両親媒性ブロック共重合体ミセルの感熱応答性

本研究では，異種ブロック鎖間の連結点にアルコキシアミン骨格をもつ両親媒性のポリアクリル酸-b-ポリメタクリル酸メチル(PAA-b-PMMA)を双頭型の開始剤を用いて合成し，PAA-b-PMMAが水中で形成するミセルの感熱応答性について検討を行った．小角X線散乱(SAXS)および動的光散乱(DLS)測定から，PAA-b-PMMAは室温で半径が20 nm程度の球状のミセルを形成していることがわかった．一方，このPAA-b-PMMAミセル溶液を90°Cで12時間熱処理を行うと，水に不溶の成分が生成した．SAXS測定から，回転半径7.5 nmのポリアクリル酸が分子状分散していることがわかった．また，GPC測定から，水に不溶の成分はPAA-b-PMMAから解離したPMMAであった．ここから，熱処理を行うことによりPAA-b-PMMAの連結点が解離するためにミセルが崩壊し，PMMAが水層から放出されることがわかった．

Novel Structural Changes during Temperature-Induced Self-Assembling and Gelation of PLGA-PEG-PLGA Triblock Copolymer in Aqueous Solutions.

The thermoresponsive amphiphilic block copolymer poly(d,l-lactic acid-co-glycolic acid)-block-poly(ethylene glycol)-block-poly(d,l-lactic acid-co-glycolic acid) (PLGA-PEGn -PLGA), which exhibits a reversible temperature-induced sol-gel transition at higher polymer concentrations in aqueous solution has attached a great deal of interest because of its potential in biomedical applications. In the present work, the length of the hydrophobic PLGA blocks is kept constant, whereas the length of the hydrophilic PEG block is altered and this variation has a pronounced impact on the phase behavior of the aqueous samples and the structure of the polymer. A short PEG block promotes gelation at a low temperature, whereas a longer PEG block shifts the gelation point to higher temperature. By using a combination of turbidity, rheology, and small angle neutron scattering (SANS) methods, the authors have revealed dramatic temperature effects. In dilute solution, the SANS experiments expose asymmetric ellipsoid structures for the copolymer with the short PEG-spacer, whereas spherical core-shell structure is observed for the polymer with long PEG-spacer. In the semidilute concentration regime, SANS measurements disclose similar profiles for the two copolymers. In a broad temperature interval, the transition from spherical core-shell micelles to cylindrical structure and packing of cylinders is observed.

Fine-tuning thermoresponsive functional poly(ε-caprolactone)s to enhance micelle stability and drug loading.

Block copolymers synthesized by the ring-opening polymerization of γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-ε-caprolactone (ME3CL), γ-2-methoxyethoxy-ε-caprolactone (ME1CL), and ε-caprolactone (CL) are reported. Previously, diblock copolymers of PME3CL-b-PME1CL displayed excellent thermoresponsive tunability (31-43 °C) and self-assembled into micelles with moderate thermodynamic stability. In this report, two strategies are employed to enhance thermodynamic stability of PME3CL/PME1CL-type block copolymer micelles while maintaining their attractive thermoresponsive qualities: modification of the end group position and alteration of hydrophobic block composition by using both ME1CL and CL. These new thermoresponsive amphiphilic block copolymers showed lower critical micelle concentration (CMC) values by one order of magnitude and formed thermodynamically stable micelles. Furthermore they demonstrated good biocompatibility and up to 4.97 wt% doxorubicin loading, more than double the amount loaded into the PME3CL-type polymeric micelles previously reported.

Ultraviolet light-breakable and tunable thermoresponsive amphiphilic block copolymer: from self-assembly, disassembly to re-self-assembly

Novel ultraviolet (UV) light-breakable and tunable thermoresponsive amphiphilic block copolymers were synthesized by atom transfer radical polymerization (ATRP). These amphiphilic copolymers can self-assemble into micelles in water. The lower critical solution temperature (LCST) and size of the micelles were adjusted by altering the ratio of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA). Upon UV light irradiation, 2-nitrobenzyl moieties were detached from polymer chains and the micelles were dissociated. When the solutions were heated above LCST, the micelles can be re-self-assembled. Investigation revealed that the Nile red molecules which were encapsulated in micelles can be controllably released through changing temperature and undergoing UV light irradiation of micelle solutions.

MADIX Thermoresponsive Amphiphilic Block Copolymers as Stimulable Emulsion Stabilizers

A series of Macromolecular Design by Interchange of Xanthates (MADIX)-derived amphiphilic block copolymers exhibiting lower critical solution temperature behaviour was synthesized and evaluated as silicone oil-in-water emulsion co-stabilizers. It was demonstrated that the cloud point of the block copolymer is mainly controlled by the chemical composition of the N-isopropylacrylamide-based hydrophilic block. The reversible stabilization and destabilization phenomena of the silicone emulsions occurred at a temperature equal to the cloud point of the block copolymer taken alone.

Synthesis and characterization of thermoresponsive amphiphilic block copolymers incorporating a poly(ethylene oxide‐stat‐propylene oxide) block

AbstractAmphiphilic BuO‐(PEO‐stat‐PPO)‐block‐PLA‐OH diblock and MeO‐PEO‐block‐(PEO‐stat‐PPO)‐block‐PLA‐OH triblock copolymers incorporating thermoresponsive poly(ethylene oxide‐stat‐propylene oxide) (PEO‐stat‐PPO) blocks were prepared by ring‐opening polymerization of lactide (LA) initiated by macroinitiators formed from treating BuO‐(PEO‐stat‐PPO)‐OH and MeO‐PEO‐block‐(PEO‐stat‐PPO)‐OH with AlEt3. MeO‐PEO‐block‐(PEO‐stat‐PPO)‐OH was prepared by coupling MeO‐PEO‐OH and HO‐(PEO‐stat‐PPO)‐OH, followed by chromatographic purification. The cloud points of 0.2% aqueous solutions are between 36 and 46 °C for the diblock copolymers that contain a 50 wt % EO thermoresponsive block and 78 °C for the triblock copolymer that contains a 75 wt % EO thermoresponsive block. Variable temperature 1H NMR spectra recorded on D2O solutions of the diblock copolymers display no PLA resonances below the cloud point and fairly sharp PLA resonances above the cloud point, suggesting that desolvation of the thermoresponsive block increases the miscibility of the two blocks. Preliminary characterization of the micelles formed in aqueous solutions of BuO‐(PEO‐stat‐PPO)‐block‐PLA‐OH conducted using laser scanning confocal microscopy and pulsed gradient spin echo NMR point to significant changes in the size of the micellar aggregates as a function of temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5156–5167, 2005

A Simple Approach to Micro-Patterned Surfaces by Breath Figures with Internal Structure Using Thermoresponsive Amphiphilic Block Copolymers

Employing amphiphilic block copolymers in a casting process to obtain honeycomb-structured films via breath figures leads to a suborder of these porous films. A thermoresponsive block copolymer, polystyrene-block-poly(N-isopropyl acrylamide), was synthesized and used to test the arrangement of both blocks within the honeycomb-structured films. Contact angle measurements reveal that the surface of these films has a different composition compared to the structure of the pores. The pores were found to be enriched in hydrophilic sequences showing stimuli-responsive behavior, whereas the surface reacts like a typical hydrophobic porous film.