A series of novel temperature and pH responsive block copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(L ‐lysine) (PLL) were synthesized. The effect of pH and the length of PLL on the lower critical solution temperature (LCST) of PNIPAM, and the self‐assembly of these PLL‐based copolymers induced by temperature and pH changes were investigated by the cloud point method, dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM). These PNIPAM‐b‐PLL copolymers can self‐assemble into micelle‐like aggregates with PNIPAM as the hydrophobic block at acidic pH and high temperatures; and at alkaline pH and low temperatures, they can self‐assemble into particles with PLL as the hydrophobic block. The copolymers may have potential applications in biotechnological and biomedical areas as drug release carriers.
Poly(N‐isopropylacrylamide)‐block‐poly{6‐[4‐(4‐pyridyazo)phenoxy] hexylmethacrylate} (PNIPAM‐b‐PAzPy) was synthesized by successive reversible addition‐fragmentation chain transfer (RAFT) polymerization. In a water/tetrahydrofuran (H2O/THF) mixture, amphiphilic PNIPAM‐b‐PAzPy self‐assembles into giant micro‐vesicles. Upon alternate ultraviolet (UV) and visible light irradiation, obvious reversible swelling‐shrinking of the vesicles was observed directly under an optical microscope. The maximum percentage increase in volume, caused by the UV light, reached 17%. Moreover, the swelling could be adjusted using the UV light power density. The derivation of this effect is due to photoinduced reversible isomerization of azopyridine units in the vesicles.
A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.
Summary: A series of new polyisoprene‐block‐polylactide and polystyrene‐block‐polylactide diblock copolymers was prepared by combining the living anionic polymerization of isoprene or styrene, and the stereoselective ring‐opening polymerization of rac‐lactide. Aluminum and yttrium‐based polystyrene or polyisoprene macroinitiators yielded isotactic‐stereoblock and heterotactic‐enriched polylactide segments, respectively. A strong influence of the microstructure of the polylactide block on the aggregation properties in solution and morphological behavior of the solid materials in thin films has been observed.
General strategy used for the preparation of the diblock copolymers, illustrated here for poly(isoprene‐block‐lactide). Poly(styrene‐block‐lactide) copolymers were prepared similarly. 相似文献
Stable aqueous dispersions of nanoparticles were prepared by polyelectrolyte complex formation between well‐defined poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propane sodium sulfonate) and poly(ethylene glycol)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] diblock copolymers. Controlled synthesis of the copolymers was achieved by water‐based atom transfer radical polymerization (ATRP). The nanoparticles were characterized by a quite narrow and monomodal size distribution as evidenced by dynamic light scattering (DLS) and confirmed by atomic force microscopy (AFM) after solution casting and freeze‐drying.
Well‐defined diblock copolymers composed of poly(N‐octylbenzamide) and polystyrene were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene with a polyamide chain transfer agent (CTA) prepared via chain‐growth condensation polymerization. Synthesis of a dithioester‐type macro‐CTA possessing the polyamide segment as an activating group was unsatisfactory due to side reactions and incomplete introduction of the benzyl dithiocarbonyl unit. On the other hand, a dithiobenzoate‐CTA containing poly(N‐octylbenzamide) as a radical leaving group was easily synthesized, and the RAFT polymerization of styrene with this CTA afforded poly(N‐octylbenzamide)‐block‐polystyrene with controlled molecular weight and narrow polydispersity.
Summary: The synthesis of magnetic magnetite nanoparticles coated with amphiphilic block copolymers of poly(ethyl methacrylate)‐block‐poly(2‐hydroxyethyl methacrylate) for use as new potential carriers for hydrophobic drug delivery is reported. The results show that a new core‐shell‐corona structural material is obtained with a very narrow molecular weight distribution of the hydrophobic segment (PDI = 1.10). UV‐Vis results show that 37% of progesterone is released from the nanoparticles after 22 h, much slower than free release (99% after 14 h), which demonstrates that the presence of the hydrophobic segment can effectively control the release of hydrophobic drugs.
Synthesis of an amphiphilic block polymer poly(ethyl methacrylate)‐block‐poly(2‐hydroxyethyl methacrylate) on magnetite nanoparticles and their use as potential drug carriers 相似文献
Summary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation.
Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO113‐b‐PDMA82) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.
Blue‐light‐emitting 2,7‐carbazole‐based conjugated copolymers have been prepared by Yamamoto or Suzuki cross‐coupling reactions. By introducing highly substituted aromatic comonomers, fully soluble high‐molecular‐weight copolymers have been obtained. Moreover, these amorphous polymeric materials exhibit good thermal stability and interesting redox properties. All these features make these new conjugated polymers highly promising for the development of single‐polymer‐layer blue‐light‐emitting diodes.
Summary: Laser‐induced fluorescence spectroscopy of the optical probe Nile Blue A in polymer clay nanocomposites is described. Concentration quenching of the fluorescence dominates the probe behavior until the clay platelets are physically separated by polymer intercalation. Further separation into an exfoliated structure results in an intense increase in probe fluorescence. Preliminary results indicate the ability to discriminate between intercalated and exfoliated structures in nanocomposites formed by melt processing.
Poly(2‐hydroxyethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) (PHEMA‐b‐PNIPAM) was prepared by controlled surface‐initiated ATRP from silicon substrates, and the resulting block copolymers were successfully converted into the corresponding PSEMA‐b‐PNIPAM by esterification of the hydroxy groups on the PHEMA block using excess of succinic anhydride. The PSEMA‐b‐PNIPAM block copolymer brushes respond to both temperature and pH stimuli. The double‐responsive behavior of the block copolymer brushes in solution was investigated by height imaging and force–distance measurements of AFM. The results clearly show the responsive behavior of the smart block copolymer brushes.
Well‐defined polymethylene‐block‐polystyrene (PM‐b‐PS) diblock copolymers were synthesized via a combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) of styrene. A series of hydroxyl‐terminated polymethylenes (PM‐OHs) with different molecular weight and narrow molecular weight distribution were prepared using living polymerization of ylides following efficient oxidation in a quantitive functionality. Then, the macroinitiators (PM‐MIs ( = 1 900–15 000; PDI = 1.12–1.23)) transformed from PM‐OHs in ≈ 100% conversion initiated ATRPs of styrene to construct PM‐b‐PS copolymers. The GPC traces indicated the successful extension of PS segment ( of PM‐b‐PS = 5 000–41 800; PDI = 1.08–1.23). Such copolymers were characterized by 1H NMR and DSC.
A thermoresponsive substrate based on a triblock copolymer, poly(N‐isopropylacrylamide)‐block‐poly[(R)‐3‐hydroxybutyrate]‐block‐poly(N‐isopropylacrylamide) (PNIPAAm‐PHB‐PNIPAAm), co‐coated with gelatin, was developed for the culture and non‐enzymatic recovery of mouse embryonic stem cells. After culture, the cells could be detached by cooling at 4 °C for 20 min without trypsin digestion. The embryonic stem cells remained undifferentiated after culture on the gelatin/copolymer‐coated surfaces, similar to standard culture techniques. Overall, the triblock copolymer coating was superior to the PNIPAAm homopolymer coating in terms of supporting better cell growth, being more stable, presenting a more homogeneous surface coating, and maintaining pluripotency of the embryonic stem cells.
A poly(methyl methacrylate)‐block‐poly(acrylic acid)‐block‐poly(2‐vinyl pyridine)‐block‐poly(acrylic acid)‐block‐poly(methyl methacrylate) (PMMA‐PAA‐P2VP‐PAA‐PMMA), pentablock terpolymer has been synthesized by anionic polymerization with sequential addition of monomers and studied in aqueous media at low pH. The system exhibits combined properties and adopts the behavior of ‘telechelic’ polyelectrolytes and that of double hydrophilic polyampholytes. This complex behavior leads to the pentablock terpolymer forming a pH and temperature sensitive reversible hydrogel at very low polymer concentration.
Summary: Block copolymers of poly(ethylene oxide‐block‐2‐hydroxypropyl methacrylate) (PEO‐b‐PHPMA) with a range of molecular masses of the PHPMA block were obtained by controlled radical polymerization on a chip (CRP chip) using a PEO macroinitiator. A series of well‐controlled polymerizations were carried out at different pumping rates or reaction times with a constant ratio of monomer to initiator. The stoichiometry of the reactants was also adjusted by varying relative flow rates to change the reactant concentrations.
A schematic of a CRP chip and SEC traces of the PEO‐b‐PHPMA produced from different pump rates with a 1:100 ratio of initiator to monomer. The dashed peaks are the macroinitiator, PEO‐Br (left), and monomer, HPMA (right). 相似文献
Self‐assembly of poly(2‐vinylpyridine)‐block‐poly(ϵ‐caprolactone) (P2VP‐b‐PCL) diblock copolymer in the presence of a selective solvent is investigated by transmission electron microscopy and atomic force microscopy. Addition of water into a P2VP‐b‐PCL solution in N,N‐dimethylformamide at 20 °C produces elongated truncated lozenge shaped single crystals of uniform size and shape in large quantities. The single crystals are composed of PCL single‐crystal layer sandwiched between two P2VP layers tethered on the top and bottom basal surfaces. The formation of the single crystals is found to depend on the temperature. These findings provide a facile approach to the preparation of uniform single crystals in large quantities.
A novel approach is employed to produce core–corona nanospheres, which introduces a stereoregular hydrophilic part to an amphiphilic block copolymer. The resultant morphology is reported using isotactic‐poly(methacrylic acid)‐block‐poly(butyl acrylate). Infrared spectroscopy revealed a supramolecular interaction, and X ray diffraction revealed the crystallization of the outer isotactic‐poly(methacrylic acid) part. The nanostructure, which looks like a nanosized ‘grape’, was formed when nanospheres and nanofibers coexisted simultaneously and partially fused.
Pseudopolyrotaxanes 4a and 5a are synthesized by two paths: a) directly from the pseudorotaxane, and b) by complexing with cucurbituril (CB[6]) in water at room temperature after the polymerization. Free radical copolymerization with CB[6] (un)complexed monomer and N‐isopropylacrylamide (NIPAAM) is carried out using a redox initiator in aqueous media at room temperature. The properties of pesudorotaxanes ( 4a and 5a ) and polymers ( 4 and 5 ) are investigated by TGA, DSC, and turbidity measurements. The lower critical solution temperatures of the NIPAAM‐containing copolymers and CB[6] are significantly higher than those of pure NIPAAM copolymers. The pseudopolyrotaxanes 4a and 5a have a higher thermal stability, as a result of threading of the CB[6] rings onto the polymer side groups.
We report the synthesis of a novel pH‐responsive amphiphilic block copolymer poly(dimethylaminoethyl methacrylate)‐block‐poly(pentafluorostyrene) (PDMAEMA‐b‐PPFS) using RAFT‐mediated living radical polymerization. Copolymer micelle formation, in aqueous solution, was investigated using fluorescence spectroscopy, static and dynamic light scattering (SLS and DLS), and transmission electron microscopy (TEM). DLS and SLS measurements revealed that the diblock copolymers form spherical micelles with large aggregation numbers, Nagg ≈ 30 where the dense PPFS core is surrounded by dangling PDMAEMA chains as the micelle corona. The hydrodynamic radii, Rh of these micelles is large, at pH 2–5 as the protonated PDMAEMA segments swell the micelle corona. Above pH 5, the PDMAEMA segments are gradually deprotonated, resulting in a lower osmotic pressure and enhanced hydrophobicity within the micelle, thus decreasing the Rh. However, the radius of gyration, Rg remains independent of pH as the dense PPFS cores predominate.
