Polypeptide‐Shelled Poly(propylene imine) Dendrimers and Their Complexing Properties towards Copper(II) Ions

Summary: Polypeptide‐shelled poly(propylene imine) dendrimers were realized by ring‐opening polymerization of α‐amino acid N‐carboxyanhydrides, initiated by dendrimers as core molecules. Polypeptides with 2nd generation core were used as model compounds to investigate interior complexes between metal ion and surface‐modified dendrimers. Micro‐calorimetric measurements outlined the formation of approximate 1:1 complexes between Cu^II and polypeptide‐shelled dendrimers and the influence of polypeptide chain compositions on differential molar heats of complexation.

Composition of one of the polypeptides synthesized.     

In situ Synthesis of Magnetic Iron Oxide Nanoparticles in Thermally Responsive Alginate‐Poly(N‐isopropylacrylamide) Semi‐Interpenetrating Polymer Networks

A novel semi‐interpenetrating polymer network based on alginate and poly(N‐isopropylacrylamide) (PNiPAAm) has been synthesized that shows response to temperature and magnetic fields. Highly homogeneous porous hydrogels are obtained by copolymerizing N‐isopropylacrylamide and bis‐acrylamide in the presence of an aqueous alginate solution. The synthesis of magnetic iron oxides by in‐situ oxidation of iron cations coordinated to the alginate network results in a hydrogel with an enhanced deswelling rate with respect to pure PNiPAAm.

     

Synthesis of Strong Electrolyte Temperature‐Sensitive Hydrogels by Radiation Polymerization and Application in Protein Separation

Strong electrolyte temperature‐sensitive hydrogels were synthesized by radiation polymerization using N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methylpropanesulfonate. The influence of irradiation dose and mole ratio of the monomers was examined by swelling measurements in aqueous solution and organic solvents. The hydrogels without any pollution were applied in concentrating protein.

Effect of irradiation dose on swelling ratios of P(NIPA‐co‐NaAMPS) hydrogels.     

Bioresorbable Hydrogels Prepared Through Stereocomplexation between Poly(L‐lactide) and Poly(D‐lactide) Blocks Attached to Poly(ethylene glycol)

Block copolymers were synthesized by ring‐opening polymerization of L ‐lactide or D ‐lactide in the presence of mono‐ or dihydroxyl poly(ethylene glycol), using zinc metal as catalyst. The resulting copolymers were characterized by various techniques, namely ¹H NMR spectroscopy, differential scanning calorimetry (DSC), X‐ray diffractometry, and Raman spectrometry. The composition of the copolymers was designed such that they were water soluble. Bioresorbable hydrogels were prepared from aqueous solutions containing both poly(L ‐lactide)/poly(ethylene glycol) and poly(D ‐lactide)/poly(ethylene glycol) block copolymers. Rheological studies confirmed the formation of hydrogels resulting from stereocomplexation between poly(L ‐lactide) and poly(D ‐lactide) blocks.

Ring‐opening polymerization of L (D )‐lactide in the presence of dihydroxyl PEG using zinc powder as catalyst.     

A Cationic Water‐Soluble Poly(p‐phenylenevinylene) Derivative: Highly Sensitive Biosensor for Iron‐Sulfur Protein Detection

Summary: A new water‐soluble cationic ammonium‐functionalized poly(p‐phenylenevinylene) (PPV‐NEtMe) was successfully synthesized and exhibited high sensitivity (K_sv = 6.9 × 10⁷ M ⁻¹) on rubredoxin, a type of anionic iron‐sulfur (Fe‐S) proteins. Further investigation showed that the biosensitivity of the cationic conjugated polymer is strongly dependent on the nature of the buffer solution and the concentration of the conjugated polymer used in the analyses.

The schematic diagram of anionic rubredoxin detected by PPV‐NEtMe.     

A Facile Route to Prepare Organic/Inorganic Hybrid Nanomaterials by ‘Click Chemistry’

An organosilane with an alkyne group at the non‐condensable end, [(2‐propynylcarbamate)propyl]triethoxysilane, has been synthesized. Condensation of this organosilane with tetraethoxysilane can be achieved by a co‐condensation strategy to produce silica nanoparticles with surface alkyne functionality. The size and uniformity of size distribution of the silica nanoparticles are influenced by varying the concentration of the added organosilane. The alkyne‐functionalized silica nanoparticles are coupled directly with azide‐modified polymers by ‘click chemistry’ to yield organic–inorganic hybrid nanomaterials.

     

Macromol. Biosci. 3/2009

The effect of Ph‐OH group content on gelation time, mechanical properties, hydrophobicity, and cellular adhesiveness of hydrogels produced from carboxymethylcellulose derivatives is investigated. A higher Ph‐OH group content induces faster gelation and yields more brittle and hydrophobic gels. After 4 h of seeding, a larger number of L929 fibroblasts adhere to the hydrogel of the CMC‐Ph that contains 15.4 Ph‐OH groups per 100 repeat units of uronic acid (97% adhesion rate) than to the gel of CMC‐Ph with only 8.4 Ph‐OH groups (62% adhesion rate). The results demonstrate that controlling the Ph‐OH group content is an effective and useful way to control cellular adhesion and proliferation on the hydrogels, as well as gelation time and mechanical properties of the gels.

     

Tailoring Polymeric Hydrogels through Cyclodextrin Host–Guest Complexation

A close correllation between molecular‐level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β‐cyclodextrin (β‐CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host–guest complexation between β‐CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra‐ and intermolecular host–guest complexation are found to control poly(acrylate) isomeric inter‐strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.

     

Thermosensitive and Dissolution Properties in Nanocomposite Polymer Hydrogels

We investigate the phase transition behavior and dissolution resistant properties of thermo‐sensitive nanocomposite hydrogels made from PEO‐PPO‐PEO triblock copolymer (Pluronic F127) and Laponite silicate nanoparticles. The rapid dissolution properties of F127 copolymer hydrogels usually limit their use as sustained release drug carriers. We overcome this limitation by synergistic combination of nanoparticle gelation characteristics with polymer thermo‐sensitivity. We present a proof of concept that the temperature‐dependent phase transitions can be shifted as a function of hydrogel composition and that the dissolution of the polymer hydrogels as well as the release of a model drug, albumin, can be significantly slowed down by addition of nanoparticles. The dissolution resistant properties generated will prove useful in the future formulation, processing and application of our polymer hydrogels for sustained release drug delivery carriers.

     

Thermoresponsiveness of Integrated Ultra‐Thin Silicon with Poly(N‐isopropylacrylamide) Hydrogels

Stimuli‐sensitive polymer materials have limited device functionality, design and manufacturing flexibility although they are pushed to enable smart device applications. Here we demonstrate the capability of integrating thermoresponsive poly(N‐isopropylacrylamide) (PNIPAAm) hydrogels with silicon nanoribbons, and enable the stiff silicon ribbons to become adaptive and drivable by the soft environmentally sensitive substrate, such as becoming mechanically stretched and compressed on temperature change. These and related soft/hard smart devices and systems may open new opportunities in biomedical applications.

     

Synthesis of Well‐Defined Telechelic Aromatic Polyamides by Chain‐Growth Polycondensation: Application to the Synthesis of Block Copolymers of Polyamide and Poly(tetrahydrofuran)

Well‐defined telechelic‐type aromatic polyamides having a secondary amino group and a phenyl ester moiety at each chain end were prepared by the chain‐growth polycondensation of phenyl 4‐(octylamino)benzoate ( 1 ) with initiator 2 (N‐tert‐butoxycarbonylated 1 ), followed by deprotection of the N‐protecting group of the initiator unit. This polycondensation was applied to the synthesis of well‐defined di‐ and triblock copolymers of aromatic polyamides and poly(tetrahydrofuran) (poly(THF)) by the reaction of the terminal secondary amino group of the polyamide with the living cationic propagating group of poly(THF).

Block copolymers of polyamide and poly(tetrahydrofuran).     

The Use of an Emulsion Templated Microcellular Poly(dicyclopentadiene‐co‐norbornene) Membrane as a Separator in Lithium‐Ion Batteries

The preparation of open‐cell macroporous membranes made by the ring opening metathesis polymerization (ROMP) of a mixture of norbornene and dicyclopentadiene, and their basic applicability as separators in lithium‐ion batteries, is discussed. Cyclic voltammetry (CV) measurements of negative electrodes (graphite) and positive electrodes (LiCoO₂) are performed and the results prove the absence of parasitic decomposition reactions within the membrane at high oxidative or reductive potentials. Furthermore, LiCoO₂/Li half cell cycling studies of 100 charging/discharging cycles reveal that the newly disclosed separator and conventional commercial polyolefin based separators have similar performance. These results demonstrate that a potential weakness in the newly disclosed separator, namely residual double bonds present in the polymer network, does not limit the use of this material as a separator in lithium‐ion batteries.

     

Highly Extensible Bio‐Nanocomposite Fibers

Here, we show that a poly(ethylene oxide) polymer can be physically cross‐linked with silicate nanoparticles (Laponite) to yield highly extensible, bio‐nanocomposite fibers that, upon pulling, stretch to extreme lengths and crystallize polymer chains. We find that both, nanometer structures and mechanical properties of the fibers respond to mechanical deformation by exhibiting strain‐induced crystallization and high elongation. We explore the structural characteristics using X‐ray scattering and the mechanical properties of the dried fibers made from hydrogels in order to determine feasibility for eventual biomedical use and to map out directions for further materials development.

     

Temperature‐Sensitive Poly(N‐isopropylacrylamide) Hydrogels with Macroporous Structure and Fast Response Rate

Macroporous temperature‐sensitive poly(N‐isopropylacrylamide) (PNIPA) hydrogels were prepared by a novel phase‐separation technique to improve the response properties. In comparison with a conventional PNIPA hydrogel prepared in water, these macroporous hydrogels, prepared by polymerization in aqueous sucrose solutions, have higher swelling ratios at temperatures below the lower critical solution temperature and exhibit much faster response rates to temperature changes.

Scanning electron microscopy image of the surface of a PNIPA hydrogel, prepared in 1.50 M aqueous sucrose solution.     

Gold Nanoparticles Functionalized by a Dextran‐Based pH‐ and Temperature‐Sensitive Polymer

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.

     

Ethylene and Ethylene/Propylene Polymerization Behavior of Bis(phenoxy‐imine) Zr and Hf Complexes with Perfluorophenyl Substituents

The catalytic properties of bis(phenoxy‐imine) Zr and Hf complexes incorporating perfluorophenyl groups with methylaluminoxane were investigated. The fluorinated complexes produced far higher‐molecular‐weight polyethylenes and ethylene/propylene copolymers with increased activities compared with the non‐fluorinated congeners. Moreover, the fluorinated complexes displayed a higher incorporation ability for propylene.

Structures of complexes 1 – 4 .     

Synthesis of Folic Acid Functionalized PLLA‐b‐PPEGMA Nanoparticles for Cancer Cell Targeting

Poly(L ‐lactic acid)‐block‐poly(poly(ethylene glycol) monomethacrylate) (PLLA‐b‐PPEGMA) has been prepared by the ring‐opening polymerization of lactide with a double‐headed initiator, 2‐hydroxyethyl 2′‐methyl‐2′‐bromopropionate (HMBP), followed by atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethacrylate (PEGMA). PLLA‐b‐PPEGMA nanoparticles with encapsulated Fe₃O₄ are prepared by a solvent evaporation/extraction technique, and then further functionalized with folic acid, a cancer targeting ligand. Our results show that such functionalized PLLA‐b‐PPEGMA nanoparticles have good potential as carriers for targeted drug delivery in cancer treatment.

     

A Novel Highly Resilient Nanocomposite Hydrogel with Low Hysteresis and Ultrahigh Elongation

Summary: A series of high clay content Laponite XLS/polyacrylamide (PAAm) nanocomposite hydrogels (S‐M gels) with excellent resilience, low elastic hysteresis, and ultrahigh elongation, have been successfully synthesized. Based on our results, it is concluded that the mechanical properties of nanocomposite hydrogels probably depend to a great extent on the hydrophilicity and flexibility of the macromolecules. Moreover, it is found that the transparency during the in‐situ polymerization of S‐M gels does not change, which is quite different from clay/poly(N‐isopropylacrylamide) nanocomposite hydrogels.

Formation of nanocomposite hydrogels using Clay‐S by in‐situ polymerization.     

Liquid Adsorption Chromatography Separation of Star Poly(methyl methacrylate)s

Liquid adsorption chromatography, in combination with full adsorption–desorption and precipitation–redissolution techniques, is a powerful procedure for the fractionation of mixtures in the synthesis of star polymers. An easy separation of 4‐ and 6‐arm star poly(methyl methacrylate)s from their single arm precursors could be carried out by both procedures, with differences of separation efficiency also depending on the molecular weight of the precursor and the number of arms.

Size exclusion chromatograms of retained and eluted fractions obtained by liquid adsorption chromatography/full adsorption–desorption separation with a tetrahydrofuran/cyclohexane eluent system (53:47 wt.‐%) for a crude reaction mixture (dotted line) containing a 4‐arm star PMMA polymer and a single‐arm precursor (solid lines a and b, respectively).     

Investigation into Molecular Diffusion in Hydrogels Using the Refractive Index Method

An in‐situ refractive index method is applied to study the diffusion process of sucrose in hydrogels. Diffusion was monitored by recording the refraction of a laser beam when passing through a triangular hydrogel cell. The distribution of refractive index changes was obtained from the deviated distance of the linear beam and converted to the distribution of concentration. By employing Fick's second law, the diffusion behavior was investigated and the diffusion coefficient was obtained.

Schematic picture of the refractive index equipment to study the diffusion process.