Synthesis and characterization of poly(ethylene glycol)-b-poly (l-lactide)-b-poly(l-glutamic acid) triblock copolymer

A biodegradable amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(l-glutamic acid) (PEG-b-PLLA-b-PLGA) was obtained by catalytic hydrogenation of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(γ-benzyl-l-glutamic acid) (PEG-b-PLLA-b-PBLGA) synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with amino-terminated MPEG-b-PLLA-NH₂ as a macroinitiator. MPEG-b-PLLA-NH₂ converted from MPEG-b-PLLA-OH first reacted with tert-Butoxycarbonyl-l-phenylalanine (Phe-^NBOC) and dicyclohexylcarbodiimide (DCC) and then deprotected the tert-butoxycarbonyl group. MPEG-b-PLLA-OH was prepared by ROP of l-lactide with monomethoxy poly(ethylene glycol) in the presence of stannous octoate. The triblock copolymer and its diblock precursors were characterized by ¹H NMR, FTIR, GPC and DSA (drop shape analysis) measurements. The lengths of each block polymers could be tailored by molecular design and the ratios of feeding monomers. The triblock polymer PEG-b-PLLA-b-PLGA containing carboxyl groups showed obviously improved hydrophilic properties and could be a good potential candidate as a drug delivery carrier.     

Photophysical properties and self-assembly of triblock copolymer with complexes of positively charged PDMAEMA and oppositely charged chromophores

The self-assembly and photophysical properties of a triblock copolymer with complex mid-block in THF and aqueous solution were investigated in this research. Poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(2-(dimethylamino ethyl methacrylate)-block- poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA–b–PDMAEMA–b–PPEGMA) triblock copolymer was synthesized by subsequent atom transfer radical polymerizations (ATRP) of DMAEMA and PEGMA. The PDMAEMA blocks were quaternized by a reaction with iodomethane. The complex of the positively charged PDMAEMA chain unit and sodium salt of 1-pyrenebutyric acid was prepared by mixing equimolar amount of the two components in THF/water mixture. Transmission electron microscopy and fluorescence technique results show that the triblock copolymer chains self-assemble into micelles in THF at high concentration. The critical aggregation concentration (CAC) of the triblock copolymer in THF determined by fluorescence technique is 6.8 × 10^?5 M. The triblock copolymer was also able to self-assemble into micelles in water. The value of CAC of the triblock copolymer in water is 2.0 × 10^?5 M. The photophysical properties and self-assembly structures of the triblock copolymer in aqueous solutions were influenced by added sodium chloride. After salt addition, a transition of the assembled structures from micelles to hollow structures was observed.     

Thermoresponsive core-shell-corona micelles of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene

Core-shell-corona micelles with a thermoresponsive shell self-assembled by triblock copolymer of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene (PEG₄₅-b-PNIPAM₁₆₈-b-PS₄₆) are studied by ¹H NMR, light scattering and atomic force microscopy. The thermoresponsive triblock copolymer, which has a relatively short hydrophobic PS block, can disperse in water at room temperature to form core-shell-corona micelles with the hydrophobic PS block as core, the thermoresponsive PNIPAM block as shell and the hydrophilic PEG block as corona. At temperature above lower critical solution temperature (LCST) of the PNIPAM block, the PNIPAM chains gradually collapse on the PS core to shrink the size and change the structure of the resultant core-shell-corona micelles with temperature increasing. It is found that there possibly exists an interface between the PNIPAM shell and PEG corona of the core-shell-corona micelles at temperature above LCST of the PNIPAM block.     

The influence of hydrophobic substitution on self-association of poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers in aqueous media

A series of amphiphilic poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers were synthesized by reaction between poly(ethylene oxide)-b-polyglycidol-b-poly(ethylene oxide) precursor copolymer and four n-alkyl isocyanates: ethyl, propyl, butyl and pentyl. After dissolution in water at room temperature the copolymers spontaneously form micelles. The critical micellization concentrations were determined by UV-VIS spectroscopy. The dimensions of the micelles, the aggregation numbers, and in some cases the micellar shape were determined by dynamic and static light scattering in a relatively broad temperature range. Special attention has been paid to the influence of the number of the carbon atoms in the alkyl chains, and respectively, the relative hydrophobicity of the middle block upon the self-association process. Clouding transition was observed for all of the copolymers, the clouding point being dependent upon the length of the alkyl chain.     

Complex micelles with a responsive shell for controlling of enzymatic degradation

Complex polymeric micelles with a PLA core and a mixed PEG/PNIPAM shell were prepared by self-assembly of two block copolymers: poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) and poly(N-isopropylacrylamide)-b-poly(lactic acid) (PNIPAM-b-PLA). Using ¹H NMR spectroscopy and dynamic light scattering, the micellization and the enzymatic degradation status were characterized. At 25 °C, the PNIPAM block is hydrophilic and the PLA core is prone to the enzymatic degradation, resulting in the disassembly of the micelles. While increasing the temperature to 45 °C, the PNIPAM collapsed onto the PLA core, protecting the PLA core from the attack by the enzyme, and the micelles exhibit a resistance to the enzymatic degradation. Furthermore, the enzymatic degradation rate of the micelles can also be tuned by changing the ratio of PEG to PNIPAM. With increasing content of PNIPAM, the conformation of the collapsed PNIPAM changes from patchy domains to a continuous and dense layer, and the enzyme accessibility to the PLA core is changed.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Synthesis and characterization of poly(ethylene glycol)-b-poly(l-histidine)-b-poly(l-lactide) with pH-sensitivity

In this paper, amphiphilic biodegradable methoxy-poly(ethylene glycol)-poly(l-histidine)-poly(l-lactide) (mPEG–PH–PLLA) triblock copolymers with pH sensitivity were synthesized. The properties of mPEG–PH–PLLA triblock copolymers were investigated by GPC, ¹H NMR, DSC, TGA, XRD and polarized optical microscopy. The results showed that the thermal properties of the triblock copolymers varied with the chain length of PH blocks. The glass transition temperatures (Tg) of the triblock copolymers increased with increasing poly(l-histidine) chain length. The morphologies of PLLA crystals changed from spherulite to dendritic crystal. Moreover, the crystallization rate of triblock copolymers was faster than that of PLLA homopolymer. The pH sensitivity of the self-assembled mPEG–PH–PLLA nanoparticles was investigated. The mean diameter and morphology of the nanoparticles were characterized by DLS, AFM and TEM. The results showed that the mean diameter of mPEG₄₅–PH₃₀–PLLA₈₂ nanoparticles in pH = 5.0 was smaller than that in pH = 7.4.     

Synthesis and the effect of hydrophobic dodecyl end groups on pH-responsive micellization of poly(acrylic acid) and poly(ethylene glycol) triblock copolymer in aqueous solution

A pH-responsive triblock copolymer of poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) containing hydrophobic dodecyl end groups (C₁₂H₂₅-PAA-b-PEG-b-PAA-C₁₂H₂₅) with narrow molecular weight distribution (M _w/M _n?=?1.30) was synthesized via reversible addition-fragmentation chain transfer polymerization of acrylic acid (AA). Poly(ethylene glycol) (PEG) capped with S-1-dodecyl-S??-(??,????-dimethyl-????-acetic acid) trithiocarbonate (DDATC) end groups was used as the macro chain transfer agent (PEG macro-CTA) and 2,2??-azobisisobutyronitrile (AIBN) as initiator for monomer acrylic acid. The effect of the hydrophobic dodecyl end groups on pH-sensitive self-association of C₁₂H₂₅-PAA-b-PEG-b-PAA-C₁₂H₂₅ in aqueous solution was investigated by fluorescence spectroscopy, dynamic light scattering and atomic force microscope. At pH ??5.5, the solution behavior of C₁₂H₂₅-PAA-b-PEG-b-PAA-C₁₂H₂₅ is like polyelectrolyte in aqueous solution, and the effect of dodecyl end groups is negligible. At pH <5.0, the hydrophobic dodecyl end groups contribute dominantly to the pH-sensitive micellization and result in the formation of micelles with stronger hydrophobicity and larger size at low concentration (critical micelle concentration is 0.062?g/L). In the range of pH 2.5?C3.5, the steady (R _h????35.0?nm) and narrow size distributed micelles (polydispersity index, PDI?<?0.2) can be obtained. The micelles formed by C₁₂H₂₅-PAA-b-PEG-b-PAA-C₁₂H₂₅ triblock copolymer in acidic solution are expected to have a core?Cshell?Ccorona structure, where the hydrophobic dodecyl groups form the core, and weak hydrophobic PAA/PEG hydrogen-bonded complexes form the shell and the uncomplexed PAA, and PEG chain segments form the corona.     

Stereocomplexed 8-armed poly(ethylene glycol)–poly(lactide) star block copolymer hydrogels: Gelation mechanism,mechanical properties and degradation behavior

Mixing aqueous poly(ethylene glycol)-poly(d-lactide) and poly(ethylene glycol)-poly(l-lactide) star block copolymer solutions resulted in the formation of stereocomplexed hydrogels within 1 min. A study towards the mechanism of the temperature dependent formation of stereocomplexes in the hydrogels using rheology and nuclear magnetic resonance experiments revealed that the formation of stereocomplexes is facilitated at higher temperatures, due to rearrangement in the micellar aggregates thereby exposing more PLA units available for stereocomplexation. The formed gels became temperature irreversible due to the presence of highly stable semi-crystalline stereocomplexed PLA domains. An enantiomeric mixture of 8-armed star block copolymers linked by an amide group between the poly(ethylene glycol) core and the poly(lactide) arms (PEG–(NHCO)–(PLA)₈) yielded hydrogels with improved mechanical properties and stability at 37 °C in PBS compared to 8-armed star block copolymers linked by an ester group. The possibility to be formed in situ in combination with their robustness make PEG–(NHCO)–(PLA)₈ hydrogels appealing materials for various biomedical applications.     

Micellization and sol-gel transition of novel thermo- and pH-responsive ABC triblock copolymer synthesized by RAFT

A well-defined thermo- and pH-responsive ABC-type triblock copolymer monomethoxy poly(ethylene glycol)-b-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b-poly(2-(diethylamino) ethyl methacrylate), mPEG-b-P(MEO₂MA-co-HMAM)-b-PDEAEMA, was synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer was endowed thermo- and pH-responsive, corresponding to the thermosensitive properties of P(MEO₂MA-co-HMAM) and pH-responsive properties PDEAEMA segments, respectively. The thermo- and pH-responsive properties of copolymer aqueous solutions were studied by UV transmittance measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM). The results showed that the N-hydroxymethyl acrylamide (HMAM) content in triblock copolymer affected the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The copolymer self-assembled into core-shell micelles, with the thermoresponsive P(MEO₂MA-co-HMAM) block and the hydrophilic PEG block as the shell, the hydrophobic PDEAEMA block as the core, in alkaline solution at room temperature. While in acidic media, when the temperature above the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution, the copolymer self-assembled into P(MEO₂MA-co-HMAM)-core micelles with mixed hydrophilic PEG and pH-responsive PDEAEMA coronas. Sol-gel transition temperature (T_sol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the concentration of the triblock copolymers and solution pH. Copolymer hydrogel loaded with bovine serum albumin (BSA) were used for the sustained release study. The results indicated that the hydrogel was a promising candidate for controlling protein drug delivery.     

Functionalization of amphiphilic coil-rod-coil triblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine) with florescence moiety and C60

We recently achieved quantitative synthesis of an amphiphilic coil-rod-coil triblock copolymer, poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine), by coupling in situ living diblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (P2VP-b-PHIC) using malonyl chloride in the presence of pyridine. This led to the introduction of an active methylene group that is a site for further functionalization in the rod block. The Michael addition reaction of the triblock copolymer with 7-(4-trifluoromethyl) coumarin acrylamide led to copolymer bearing a fluorescent pendent in the rod block. The fluorescent labeled copolymers were isolated in ∼94% yields. Similarly C₆₀ pendent was introduced to the rod block by the Bingel reaction. The yields of C₆₀ functionalized copolymers were ∼54%. The precursor and functionalized amphiphilic coil-rod-coil copolymer show diverse morphologies, such as micelles and vesicles by simply changing the solvent. For the C₆₀ functionalized block copolymer, structural constraints in micelles and vesicles prevented C₆₀ pendents to aggregate.     

Toughening of epoxy thermosets with nano-sized or micron-sized domains of poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) triblock copolymers synthesized using room temperature ester coupling reaction

Poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) (PEO-b-PBN-b–PEO) triblock copolymers with three different compositions were synthesized from poly(ethylene glycol) methyl ethers and carboxylic acid-terminated poly(butadiene-co-acrylonitrile) (CTBN) by ester coupling reaction at room temperature. The PEO-b-PBN-b-PEO was incorporated into anhydride cured epoxy thermosets to improve the fracture toughness by the formation of either nano-sized spherical micelles or micron-sized vesicles. The polymer chemical structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The morphology of PEO-b-PBN-b–PEO within the epoxy thermosets was investigated using a transmission electron microscope, an atomic force microscope, and a scanning electron microscope. Also, we conducted impact testing and plane-strain fracture toughness testing to evaluate the fracture toughness in terms of the impact strength and the critical stress intensity factors (K_IC) for the modified epoxy thermosets. The results revealed that all the PEO-b-PBN-b-PEO triblock copolymers are more effective in the toughening of epoxy thermoset compare to CTBN. We found that the 5 wt% PEO-b-PBN-b-PEO modified epoxy thermoset containing micron-sized vesicles exhibited the highest K_IC, which was 3.23 times as high as the K_IC of pristine epoxy thermoset. Besides, the glass transition temperature remained and the tensile modulus did not reduce remarkably when the amount of PEO-b-PBN-b-PEO added into epoxy was 5 wt%.     

Impacts of stereoregularity and stereocomplex formation on physicochemical, protein adsorption and cell adhesion behaviors of star-shaped 8-arms poly(ethylene glycol)-poly(lactide) block copolymer films

Biodegradable stereocomplex film exhibiting soft and stretchy character was prepared by simply blending between enantiomeric 8-arms poly(ethylene glycol)-block-poly(l-lactide) (8-arms PEG-b-PLLA) and 8-arms PEG-b-PDLA copolymers with star-shaped structure. The stereocomplex film exhibited higher T_g and PLA crystallinity than those of original copolymer films. Effects of stereoregularity and stereocomplexation on protein adsorption and L929 cells attachment/proliferation behaviors onto the films were analyzed from the viewpoint to design a new class of implantable soft biomaterial. The stereocomplex film was found to exhibit large amount of protein adsorption than original films. Furthermore, cell attachment efficiency and proliferation rate on the film were significantly enhanced by stereocomplexation. This stereocomplex material is expected to be applicable as degradable temporary scaffold for soft tissue regeneration. Consequently, it was indicated that the stereocomplex formation could be proposed to be a novel method to control the protein- and cell-adhesive properties of biodegradable matrix composed of PEG-PLA copolymer.     

Synthesis of double‐hydrophilic poly(methylacrylic acid)–poly(ethylene glycol)–poly(methylacrylic acid) triblock copolymers and their micelle formation

The aim of the work reported was to synthesize a series of double‐hydrophilic poly(methacrylic acid)‐block‐poly(ethylene glycol)‐block‐poly(methacrylic acid) (PMAA‐b‐PEG‐b‐PMAA) triblock copolymers and to study their self‐assembly behavior. These copolymeric self‐assembly systems are expected to be potential candidates for applications as carriers of hydrophilic drugs. Bromo‐terminated difunctional PEG macroinitiators were used to synthesize well‐defined triblock copolymers of poly(tert‐butyl methacrylate)‐block‐poly(ethylene glycol)‐block‐poly(tert‐butyl methacrylate) via reversible‐deactivation radical polymerization. After the removal of the tert‐butyl group by hydrolysis, double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers were obtained. pH‐sensitive spherical micelles with a core–corona structure were fabricated by self‐assembly of the double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers at lower solution pH. Transmission electron microscopy and laser light scattering studies showed the micelles were of nanometric scale with narrow size distribution. Solution pH and micelle concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible reason for the formation of the micelles is proposed. Copyright © 2010 Society of Chemical Industry     

Aqueous lubricating properties of charged (ABC) and neutral (ABA) triblock copolymer chains

Application of charged polymer chains as additives for lubricating neutral surfaces in aqueous environment, especially via polymer physisorption, is generally impeded by the electrostatic repulsion between adjacent polymers on the surface. In this study, we have investigated the adsorption and aqueous lubricating properties of an amphiphilic triblock copolymer, comprised of a neutral poly(ethylene glycol) (PEG) block, a hydrophobic poly(2-methoxyethyl acrylate) (PMEA) block, and a charged poly(methacrylic acid) (PMAA) block, namely PEG-b-PMEA-b-PMAA. After adsorption onto a nonpolar hydrophobic surface from aqueous solution, an equal and homogeneous mixture of neutral PEG and charged PMAA chains is formed on the surface, with an adsorbed polymer mass comparable to its fully neutral counterpart, PEG-b-PMEA-b-PEG. The lubricity of PEG-b-PMEA-b-PMAA showed significant improvement compared to fully charged polymer chains, e.g. poly(acrylic acid)-block-poly(2-methoxyethyl acrylate) (PAA-b-PMEA), which is attributed to dilution of charged moieties on the surface and subsequent improvement of the lubricating film stability.     

Self-assembly behavior of rod–coil–rod polypeptide block copolymers

Self-assembly behavior of rod–coil–rod poly(γ-benzyl-l-glutamate)-b-poly(ethylene glycol)-b-poly(γ-benzyl-l-glutamate) (PBLG-b-PEG-b-PBLG) triblock copolymers with various PBLG block lengths in aqueous solution was investigated. The PBLG-b-PEG-b-PBLG triblock copolymers are able to self-assemble into vesicles when PBLG block length is relatively short. Meanwhile, the initial polymer concentration was found to have influence on the self-assembly. Giant vesicles can be observed when the initial concentration is high. Dissipative particle dynamics (DPD) simulations about the vesicles revealed that the rigid rod blocks could be aligned parallelly with each other to form the monolayer vesicles wall. When the PBLG block length in the PBLG-b-PEG-b-PBLG triblock copolymers increases, the aggregate morphologies were observed to transform from vesicles to spherical micelles. Based on the experimental and simulation results, we proposed a possible mechanism of the morphological transitions of the rod–coil–rod triblock copolymer aggregates.     

Regular and irregular micelles formed by A LEL triblock copolymer in aqueous solution

Laser light scattering (LLS) techniques were used to characterize the micellization of poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (LEL) triblock copolymer (MW 1K-2K-1K) in aqueous solution. We observed the existence of both thermodynamically stable flower-like micelles (regular micelles) and large, less soluble nanoparticles (irregular micelles) in dilute aqueous solutions with the same preparation procedure. Both kinds of micelles were found to co-exist with single copolymer chains. The initial copolymer concentration determines the nature of the micelles. The regular core-shell micelle formation follows a closed association mechanism, resulting in flower-like micelles. The hydrophobicity of a L unit is estimated as ∼0.5-0.6 B (polyoxybutylene) units from the micellization parameters, which is quite consistent with earlier estimations obtained from EL diblock copolymers.     

PBT-b-PEO-b-PBT triblock copolymers: Synthesis,characterization and double-crystalline properties

We demonstrated here a facile method to synthesize novel double crystalline poly(butylene terephthalate)-block-poly(ethylene oxide)-block-poly(butylene terephthalate) (PBT-b-PEO-b-PBT) triblock copolymers by solution ring-opening polymerization (ROP) of cyclic oligo(butylene terephthalate)s (COBTs) using poly(ethylene glycol) (PEG) as macroinitiator and titanium isopropyloxide as catalyst. The structure of copolymers was well characterized by ¹H NMR and GPC. TGA results revealed that the decomposition temperature of PEO in triblock copolymers increased about 30 °C to the same as PBT copolymers, after being end-capped with PBT polymers. These triblock copolymers showed double crystalline properties from PBT and PEO blocks, observed from DSC and WAXD measurements. The melting and crystallization peak temperatures corresponding to PBT blocks increased with PBT content. The crystallization of PBT blocks showed the strong confinement effects on PEO blocks due to covalent linking of PBT blocks with PEO blocks, where the melting and crystallization temperatures and crystallinity corresponding to PEO blocks decreased significantly with increment of PBT content. The confinement effect was also observed by SAXS experiments, where the long distance order between lamella crystals decreases with increasing PBT length. For the triblock copolymer with highest PBT content (PBT₅₄-b-PEO₂₂₇-b-PBT₅₄), this effect shows a 30 °C depression on PEO crystals' melting temperature and 77% on enthalpy, respectively, compared to corresponding PEO homopolymer. The crystal morphology was observed by POM, and amorphous-like spherulites were observed during PBT crystallization.     

Synthesis of novel temperature responsive PEG-b-[PCL-g-P(MEO2MA-co-OEGMA)]-b-PEG (tBG) triblock-graft copolymers and preparation of tBG/graphene oxide composite hydrogels via click chemistry

Novel triblock-graft copolymers, poly ethylene glycol-b-[poly(ε-caprolactone)-g-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-oligo (ethylene glycol) methacrylate)]-b-poly ethylene glycol (PEG-b-[PCL-g-P(MEO₂MA-co-OEGMA)]-b-PEG) (tBG), were synthesized via ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). In the synthesis process, temperature responsive P(MEO₂MA-co-OEGMA) chains were grafted onto the PCL block of triblock copolymer PEG-b-PCL-b-PEG to improve its hydrophilicity. This method succeeded in increasing the solubility of PEG-b-PCL-b-PEG in water, and more importantly, endowing PEG-b-PCL-b-PEG with temperature sensitivity. By adjusting the feed ratio of 2-(2-methoxy ethoxy) ethyl methacrylate (MEO₂MA) and oligo (ethylene glycol) methacrylate (OEGMA) monomers, the lower critical solution temperature (LCST) of the tBG can be realized at about 37 °C. Taking advantage of the excellent mechanical property of graphene sheets, alkyne-functionalized graphene oxide (alkyne-GO) was introduced to cross-link tBGs and prepare tBG/GO composite hydrogel through click reaction between tBG-N₃ and alkyne-GO. Different from traditional cross-linkers, alkyne-GO acts as reinforcing filler in the composite hydrogel. Benefiting from superior properties of PCL, PEG, P(MEO₂MA-co-OEGMA) and GO, the as-prepared temperature responsive tBG/GO hydrogel exhibits excellent mechanical strength and toughness, demonstrating future potential applications in tissue engineering and biotechnology fields.     

pH-responsive PMAA-b-PEG-b-PMAA triblock copolymer micelles for prednisone drug release and release kinetics

pH-sensitive hydrophilic poly(methacrylic acid)-b-poly(ethylene glycol)-b-poly(methacrylic acid) (PMAA-b-PEG-b-PMAA) triblock copolymers were synthesized through atom transfer radical polymerization, and were characterized by FT-IR, ¹H NMR, and GPC. The as-synthesized polymers can self-assemble into stable and almost spherical nanomicelles in aqueous solution with an average size range from 18 to 89?nm, depending on the micellar concentrations, while they assumed well-defined spherical morphologies in PBS solutions. The micellization behavior in different media was investigated by a fluorescence spectroscopy technique, UV–Vis transmittance, and dynamic light scattering measurements. The critical micelle concentration and size of the micelles decrease with the increasing the length or molecular weights of PEG and PMAA chains. A pH-dependent phase transition behavior produces at a pH value of about 5.2, and the stable pH micellization behavior varied within a narrow pH range from ca. 4.8 to 7.4. These triblock copolymers are generally low cytotoxicity at a micellar concentration below 400?mg?L^?1, as revealed by the MTT assay. The prednisone release and release kinetics studies disclosed that these pH-sensitive polymeric micelles are good carriers for the drug delivery.