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To realize intelligent and low-cost protective materials, the development of compounds with smart stress-responsive properties and self-healing abilities over a wide temperature range is a major research goal. In this study, a series of impact hardening polymers (IHPs) with stress-responsive properties and self-healing ability in low temperature were synthesized via the condensation copolymerization of silicone polymers with various chain lengths and boron contents. The results of rheological analysis indicate that the IHPs have self-healing ability at low temperatures (healing times of less than 30 h and healing efficiencies better than 80% at −25 °C). Moreover, the relative shear stiffening effect (RSTe), which describes the stress-responsive ability of the IHP, exceeded 2000. In addition, the self-healing mechanism of IHP was investigated by Fourier transform infrared spectroscopy microscopy and pulsed 1H-NMR measurements. The results suggested that reversible dynamic cross-linking arising from the boron compound and the reduction in the threshold entanglement density owing to the longer length of the flexible polymeric backbone is crucial to impart low-temperature self-healing ability and stress-responsive properties to IHP.

Stable water-in-oil (W/O) emulsions can produce at many industrial production occasions. However, most materials for its separation have serious fouling problems. To overcome this shortcoming, we fabricated an easy cleaning multifunctional starch-based material with unique wetting behavior which could realize efficient separation and purification of W/O emulsions. This material has a hierarchical structure and superoleophilic and under oil superhydrophobic surfaces which could separate various W/O emulsions in a high separation efficiency and flux without external pressure. In addition, the decrease of separation flux was not observed for this material, which can be reused more than 10 times after washing with ethanol and drying after each separation cycle. Furthermore, this material also could realize efficient removal of dyes and heavy-metal and rare-earth ions simultaneously during a separation process. The material shows great potential for separating and purifying stable W/O emulsions produced during the industrial production.

A series of chemically cross-linked microgel composite hydrogels (MCH gels) with excellent toughness and stretchability were prepared using core–shell polymer microspheres as cross-linking junctions. In our strategy, MCH gels are obtained by connecting microspheres with polyacrylamide (PAAm) chains chemically grafted onto their surfaces, where an organic cross-linking agent is completely unnecessary. The mechanical behavior of the MCH gels was analyzed, and superresolution fluorescence microscopy and scanning electron microscopy were used to investigate their toughening mechanism. The results indicated that the homogeneous network structure resulting from the good compatibility between the core–shell microspheres and matrix was an important reason for the excellent toughness of the MCH gels. In addition to interactions among H bonds in the grafted PAAm chains, reversible deformation of the core–shell microspheres acting as cross-linking junctions, which arises from the flexibility of the microspheres, and the effect of cavitation between the microspheres and matrix could also effectively dissipate energy during deformation of the MCH gels.

The convenient synthesis of core-shell nanoparticles containing degradable components is very desirable given the potential applications of such nanoparticles in biomaterials. A facile approach for producing monodisperse starch-polystyrene nanocomposites with well-defined core-shell structures in the absence of a surfactant was developed. The initially-formed Pickering emulsions underwent conversion into seeded emulsions during the polymerization, wherein the amphiphilic starch-based nanospheres (SNPs) serve as stabilizer and seed. A possible mechanism for this transition was explored based on the morphology and size variations of the emulsion droplets and the resultant nanospheres. The effects of the monomer concentration, SNP content and size, and pH on the core-shell nanospheres were investigated. With increasing monomer concentration, the core size of the particles remained almost unchanged, while the shell layer thickness increased almost linearly. The size of the core-shell nanospheres can be regulated by adjusting the pH and the SNP content and size.

An in situ hydrogel based on oxidation cholesterol starch (OCS) and O-carboxymethyl chitosan (CMCT) that is completely devoid of potentially cytotoxic small molecule cross-linkers and does not require complex manoeuvres or catalysis has been formulated and characterized. The network structure was created by Schiff base formation. The mechanical properties, internal morphology and swelling ability of the injectable hydrogel were examined. Rheological measurements demonstrated that increasing the concentration of the monomer improved the storage modulus. SEM showed that the hydrogel possessed a well-defined porous structure. In addition, the Schiff base reaction was acid sensitive. Under acid conditions, the hydrogel could hydrolyse quickly compared with high pH conditions. Doxorubicin (DOX) was used as a model drug to investigate the control and release properties of the hydrogel. The cytotoxic potential of the hydrogel was determined using an in vitro viability assay with L929 cells as a model and the results revealed that the hydrogel was non-cytotoxic.

Understanding the interfacial activity of polysaccharide nanoparticles adsorbed at oil–water interfaces is essential and important for the application of these nanoparticles as Pickering stabilizers. The interfacial properties of starch-based nanospheres (SNPs) at the interface of an n-hexane–water system were investigated by monitoring the interfacial tension at different bulk concentrations. The three-phase contact angle (θ) and the adsorption energy (ΔE) increased with increasing size and degree of substitution with octenyl succinic groups (OSA) in the particles. Compared with the OSA-modified starch (OSA-S) macromolecule, the SNPs effectively reduced the interfacial tension of the n-hexane–water system at a relatively higher concentration. These results and the method reported herein are useful for selecting and preparing polysaccharide nanoparticles as Pickering stabilizers for oil–water emulsions.

Conventional hydrogels freeze and harden at sub-zero temperatures and their mechanical properties are considerably inadequate for practical load-bearing applications. These drawbacks hinder their application possibilities. In this work, we propose a new strategy based on Pickering emulsion polymerization to fabricate novel organohydrogels with antifreeze properties. Ethylene glycol (EG) is introduced into the aqueous phase of the Pickering high internal phase emulsion (HIPE) to effectively inhibit water from freezing. The resulting bicontinuous organohydrogels are prepared through simultaneous polymerization in the external and internal phases to provide enhanced mechanical properties and good hydrophilic-oleophilic properties. Furthermore, the organohydrogels are more stable than conventional hydrogels under ambient conditions and remain unfrozen and mechanically flexible down to −40 °C.

A series of amphoteric hydrophobic-associative flocculants with outstanding flocculation efficiency and salt tolerance, poly(acrylamide/acrylic acid/dimethyl benzyl aminoethyl acrylate chloride), are successfully prepared (named AAB series) and used to flocculate the montmorillonite suspensions. The solution properties of AAB copolymer are systematically evaluated by viscometer, rheology and steady-state fluorescence analysis. The results suggest that the space network structure forming via hydrophobic-associating interaction can increase solution viscosity and improve the bridging capacity of copolymers. Meanwhile, the apparent viscosity in salt solution increases with increase in the concentration of salt stemming from the anti-polyelectrolyte effect of polyampholyte. Further, the flocculation performances of flocculants in 1 wt% montmorillonite suspensions are evaluated by turbidity, optimal dosage and settlement rate measurement. The results elaborate that the flocculation performances of amphoteric hydrophobic-associating AAB flocculants are better than that of commercial flocculants (cationic and anionic polyacrylamide) and homemade cationic flocculant (AAB-0-5) independent of the type and concentration of salt. The novel ampholyteric hydrophobic-associative flocculants will exhibit intriguing prospective in industry water treatment, in that the anti-polyelectrolyte effect of polyampholyte and hydrophobic-associating interaction can endow excellent flocculation efficiency and salt tolerance.

Polysaccharide-based hydrogels are remarkable materials for the biomedical fields because of its excellent biodegradation and biocompatibility. In this work, a novel polysaccharide-based hydrogel was fabricated by in situ crosslinking of starch-based nanoparticles and polyvinylamine. Starch was decorated with cholesterol group and aldehyde groups. TEM and DLS showed that the cholesterol modified oxidation starch (OCS) exhibited a core-shell nanoparticles with mean size of ∼143 nm in aqueous. The hydrogel was then synthesized via Schiff base reaction. Rheological measurements demonstrated the incorporation of cholesterol groups not only reduced the gel time but also improved the storage modulus of the hydrogel compared with the oxide starch crosslinked hydrogel. SEM showed the OCS based hydrogels possess a well-defined porous structure. Furthermore, doxorubicin (DOX) was used as model drug to investigate the control and release properties of OCS hydrogels. This OCS hydrogel would be a promising drug carrier for biomedical applications.

Biodegradable thermosensitive hydrogels have attracted great interest because of their potential in biomedical applications. Herein, we present a novel, thermoresponsive poly(2-(2-methoxyethoxy)ethyl methacrylate) hydrogels with starch-based nanospheres as cross-linkers (NMH). NMHs exhibit a narrow lower critical phase transition temperature (LCST) range and high mechanical strength compared with conventional, small molecular cross-linked hydrogels (CMH). Fourier transform infrared (FT-IR) spectroscopy confirms that the NMHs are degradable in aqueous medium. The phase transition temperature of the NMHs is ∼4 °C compared with ∼25 °C for CMH. The NMHs can sustain strength of 12.2 MPa, 10 times more than that of CMH. Moreover, the deswelling rate of NMHs is faster than CMH. The different concentrations of nanospheres can efficiently regulate the various properties of NMHs. The NMHs have excellent properties because of its even network structure formed by nanosphere cross-linkers.

Fundamental understanding of the fracture process and toughening mechanisms of double network (DN) hydrogels is critical for rational design of the next generation of tough DN gels with desirable mechanical properties. However, current knowledge of DN gels from synthesis methods to toughening mechanisms mainly comes from chemically cross-linked DN gels. Little is known about hybrid physically chemically cross-linked DN gels. Herein, we synthesize tough DN hydrogels by combining two types of cross-linked polymer networks: a physically cross-linked first network of agar and a covalently cross-linked second network of polyacrylamide (PAM). The resulting Agar/PAM DN gels achieved high toughness of 500–1000 J/m2. More importantly, we reveal several differences and similarities between hybrid Agar/PAM DN gels and chemically linked PAMPS/PAM DN gels. First, different from the nearly velocity-independent mechanical properties in chemically linked DN gels, hybrid Agar/PAM DN gels show velocity-dependent fracture b...

High strength, stimuli-responsive poly(acrylamide) composite hydrogels (PAAm CH gels) were prepared by grafting polymerization of acrylamide (AAm) onto temperature-sensitive core–shell microgels. These microgels, composing of poly(N-isopropylacrylamide) as core and polyvinylamine (PVAm) as shell, were used as both initiator and crosslinker to form a robust three-dimensional network via bonding the poly(acrylamide) (PAAm) backbone. The CH gels exhibited a remarkably rapid shrinking rate and transmittance switch in response to the environmental temperature change, which the conventional chemically cross-linking PAAm hydrogels (PAAm OR) were short of. Even compared to the bulk PNIPAAm hydrogels (PNIPAAm OR) crosslinked with N,N′-methylenebisacrylamide (MBA), the CH gels were featured with faster responsive rate, which could be attributed to the formation of interconnected water transportation channels between the microspheres and PAAm gel matrix due to the fast shrinking of microgels. Moreover, the effects of microgel species and content on swelling and mechanical properties of CH gels were also systematically investigated. The results elaborated that the CH gels could be compressed almost 99% without breaking and completely recovered their original shape when the stress was removed. And the optimized compressive strength of CH gels could be up to 21.94 MPa. Based on the analysis of CH gel mechanical properties, the influence of microsphere content on effective network chains density of CH gels was discussed through rheology measurements. Finally, the essential reinforcement on mechanical properties was mainly contributed to the homogeneous microstructure of hydrogel network and the energy dissipation mechanism of microgels in gel matrix.

A cationic surfactant monomer, dimethyldodecy1(2-acrylamidoethypammonium bromide (AMQC(12)) was synthesized. A family of hydrophobic-associating cross-linking hydrogels (HAC-gels) fabricated via the self-assembly of amphiphilic multiblock copolymers of acrylamide and AMQC-12 can be synthesized by free-radical aqueous solution micelle copolymerization in the absence of surfactants using the one-pot method. The HAC-gels possessed outstanding mechanical performance, with optimal tensile strength, compressive strength, and elongation at break of 250 kPa, 14 MPa, and 1850%, respectively. Meanwhile, the HAC-gels exhibited self-healing property, and tetrahydrofuran (THF) significantly accelerated their self-healing process. The recovery hysteresis of hydrophobic-associating hydrogels prepared in the presence of surfactants can be eliminated because of homogeneity of the hydrogel network and the dynamic and mobile properties of physical cross-linking junctions. Investigations on the mechanical property and structure evolution of hydrogels revealed that the hydrophobic-associating interaction was the driving force of self-assembly of amphiphilic multiblock copolymers. Furthermore, spherical micelles and macroscopic cross-linking network can be easily switched reversibly by regulating copolymers concentration. (C) 2013 Elsevier Ltd. All rights reserved.

Starch is successively modified by acetic anhydride and phthalic anhydride, and then starch-based nanospheres are fabricated by a simple nanoprecipitation procedure. These pH-responsive amphiphilic starch-based nanospheres of uniform size are used as particulate emulsifiers to stabilize Pickering emulsions. CLSM and SEM characterization find that starch-based nanospheres adsorbed at the interface between oil phase and water phase. Moreover, the catastrophic inversion and transitional inversion of such emulsions can be easily achieved by varied the water/oil volume ratio and pH of aqueous dispersion, respectively.

Fluorescein isothiocyanate (FITC) is covalently attached onto the starch acetate, and the fluorescein-labeled starch acetate can self-assemble to form uniform nanospheres in water. The size of the fluorescent nanospheres can be easily controlled by adjusting the polymer concentration in acetone and the proportions of the water and organic phases. The fluorescent intensity of the nanospheres increases with increasing pH, and its fluorescent intensity has no major effect in the physiologically relevant range from pH 5.7 to pH 8 compared with free FITC. Fluorescence quenching studies prove that the fluorescent nanospheres showed a super fluorescent stability without self-association. The fluorescent nanospheres are degradable and can be potential applied for pH-sensing in biological samples.

2-Furyloxirane (FO), a monomer usually obtained from a nonpetroleum route, was prepared from the epoxidation reaction of furfural and trimethylsulfonium chloride. About 200-300 g FO can be obtained in each preparation process. Although anionic polymerization of FO generally gives low-molecular-weight polymers even after long periods of polymerization, the reaction was greatly improved when macrocyclic ether was used as a cocatalyst to potassium tert-butoxide. When 18-crown-6 was used as a cocatalyst, poly(2-furyloxirane) (PFO) with a number-average molecular weight (M(n)) of 41.5 kg/mol and a polydispersity index of 1.3 was obtained at 94% yield after polymerization at 40 degrees C for 72 h. The PFO obtained contained a 61.7% head-to-tail (H-T) structure in the absence of the macrocyclic ether, and it reached 70.6% when cryptand[2,2,2] was used as a cocatalyst. PFO with higher regioregular structures showed improved thermal properties. For PFO with M(n) of around 20.0 kg/mol, its glass transition temperature (T(g)) increased from -3 to 6 degrees C when the H-T content was increased from 61.7 to 70.6%. Raising the M(n) of PFO also raised T(g). For PFO with 68.9% H-T structure, its T(g) could reach 7 degrees C when M(n) was increased to 40 kg/rnol. This study shows two effective ways to improve the thermal and mechanical performances of the polymer. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1434-1442, 2011

A robust method to prepare hydrogels with high mechanical strength is presented. Core/shell nanospheres with derivatizable allyl groups in the shell were first prepared. Starch-based nanospheres were used as crosslinker to prepare polyacrylamide hydrogels. The starch-based nanospheres were bridged by acrylamide to form crosslink points in the hydrogel network. They possess an extremely high mechanical strength. The results show that starch-based nanosphere hydrogels can sustain strengths of 10.34 MPa, which is 60 times greater than for a normal hydrogel. The mechanical properties of SNH can be tailored by varying the content of SN. This approach offered a new way of making functional hydrogel with biodegradable component as a substitute for tissue.

Novel microstructured and pH sensitive poly(acryliac acid-co-2-hydroxyethyl methacrylate)/poly(vinyl alcohol) (P(AA-co-HEMA)/PVA) interpenetrating network (IPN) hydrogel films were prepared by radical precipitation copolymerization and sequential IPN technology. The first P(AA-co-HEMA) network was synthesized in the present of PVA aqueous solution by radical initiating, then followed by condensation reaction (Glutaraldehyde as crosslinking agent) within the resultant latex, it formed multiple IPN microstructured hydrogel film. The film samples were characterized by IR, SEM and DSC. Swelling and deswelling behaviors and mechanical property showed the novel multiple IPN nanostuctured film had rapid response and good mechanical property. The IPN films were studied as controlled drug delivery material in different pH buffer solution using cationic compound, crystal violet as a model drug. The drug release followed different release mechanism at pH 4.0 and pH 7.4, respectively.

Acetylated corn starches with different degrees of substitution (DS 0.85, DS 1.78, DS 2.89) were synthesized by the reaction of corn starch with acetic anhydride in the presence of acetic acid under varying reaction temperatures. The product was characterized by FTIR spectroscopy, 1 H NMR, X-ray diffraction and contact angle measurement. Acid-base titration and 1 H NMR methods were employed to determine the degree of substitution of product. FTIR spectroscopic analysis showed that the characteristic absorption intensities of esterified starch increased with increase in the degree of substitution, and the characterized peak of hydroxyl group almost disappeared in the spectrum of DS 2.89 acetylated starch. The detailed chemical microstructure of native starch and acetylated starch was confirmed by 1 H NMR, 13 C NMR and 13 C– 1 H COSY spectra. Analysis of 1 H NMR spectra of acetylated starches was assigned accurately. Strong peaks in X-ray diffraction of acetylated starch revealed that new crystalline regions were formed. Compared with native starch, the hydrophobic performance of acetylated starch esters was increased. The contact angle of acetylated starch with DS 2.89 was 68.2°.

Dodecenly succinic anhydride (DDSA) starches were prepared commercially by the base catalyzed reaction of DDSA in pre-emulsion with starch granular in aqueous slurry. The results indicated that the degree of substitution and reaction efficiency were 0.0256% and 42.7%, respectively, at the parameters for the preparation of DDSA starches in starch slurry 30%, DDSA/starch radio 10% (wt/wt), pH 8.5–9.0, reaction temperature 313 K. After modification, product surface chemical composite had been changed which was prone to migrate into less polar solution. The chemical structural characteristics were investigated by methods of FTIR and 1 H NMR. The results of X-ray diffraction showed the native A-type crystalline pattern, indicating that reaction of corn starch with DDSA caused no change in the crystalline structure. Compared to native starch, the hydrophobic performance of esters was greatly increased. With the DS increasing, contact angles were gradually increased, however, the adhesion works were decreased. The maximum contact angle of DDSA starch could attend to 123°, and the corresponding adhesion work was 33.2 mJ m −2 .

Dispersion copolymerization of acrylamide (AM) with 2-methylacryloylxyethyl trimethyl ammonium chloride (DMC) has been carried out in aqueous salts solution containing ammonium sulfate and sodium chloride with poly(acryloylxyethyl trimethyl ammonium chloride) (PDAC) as the stabilizer and 2,2'-azobis[2-(2-inidazolin-2-yl)propane]-dihydro chloride (VA-044) as the initiator. A new particle formation mechanism of the dispersion polymerization for the present system has been proposed. The effects of inorganic salts and stabilizer concentration on dispersion polymerization have been investigated. The results show that varying the salt concentration could affect the morphology and molecular weight of the resultant copolymer particles significantly. With increasing the stabilizer concentration, the particle size decreased at first and then increased, meanwhile the effect on the copolymer molecular weight was the contrary. These results had been rationalized based on the proposed mechanism.

The structure of hydrated poly(aspartic acid) sodium (PAANa) and in blended PAANa, which was blended with poly(vinyl alcohol) (PVA), is characterized by means of high-resolution solid-state 23Na NMR. There are two peaks in dried pure PAANa, which are assigned to associated ions (about −16 ppm) and isolated ions or end group ions of PAANa (7.2 ppm), respectively. With an increase in hydration, the 23Na chemical shifts of these two peaks are changed to tend toward 0 ppm, and the line width at half the height of the 23Na resonance decreases. In contrast, in the blended samples, the 23Na resonance shapes and chemical shift values are significantly changed depending on the ratio of the PAANa/PVA blends and the temperature. On the basis of these experimental results, the structure of the blends was elucidated.

Solid state 13 C CP/MAS NMR measurements have been carried out on poly(aspartic acid) sodium (PAANa)/poly(vinyl alcohol) (PVA) blends over a wide range of temperatures. From these experimental results, it is found that the main-chain conformations of PAANa in PAANa/PVA blends take the α -helix form over a wide range of blend ratios, and, in contrast, the conformation and dynamics of the side chains of PAANa are strongly influenced by the formation of an intermolecular hydrogen bond between the carboxyl group of the side chains and the hydroxyl group of PVA. The behavior of the proton spin–lattice relaxation times in the rotating frame ( T 1 ρ (H)) and the laboratory frame ( T 1 (H)) indicates that when the blend ratio of PAANa and PVA is 1:1, they are miscible.

High-resolution 13 C CP/MAS NMR and pulse 1 H NMR experiments were carried out for hydrated poly(aspartic acid) sodium salt, in order to investigate the conformation and molecular motion of the polymer. From these experimental results, it is found that the main-chain conformation of poly(aspartic acid) sodium salt which takes an α-helix form in the dry state is not drastically affected by an addition of water. In the 13 C CP/MAS NMR spectrum, a new peak at ca. 184 ppm appears, which comes from the formation of hydrogen bond between the carbonyl carbon of the side chains and water, and the intensity of the peak is associated with the water content. The 13 C spin-lattice relaxation time ( T 1 ) experiments show that the T 1 values for the individual carbons of the polymer are decreased with an increase in the water content. This shows that the mobility of the polymer is increased with an increase in the water content. Further, the 1 H spin-spin relaxation time ( T 2 ) experiments show that the polymer has the two or three components with different molecular motion. With an increase in the water content or temperature, the T 2 values of hydrated PAANa are increased. This shows that the molecular motion is increased. In the high water content, the polymer has a signal component in the molecular motion. This shows that the polymer is uniformly hydrated.

High-resolution 13C CP/MAS NMR spectra of poly(aspartic acid) (PAA) and its sodium salt (PAANa) obtained with various neutralization numbers, n (=[COONa]/[COOH+COONa], where [x] is the molar concentration of x), have been measured over a wide range of temperatures, in order to elucidate the conformation and its stability in the solid state. From these experimental results it was found that, at room temperature (25°C), the main chain of PAA takes a mixture of right-handed α (αR)-helix, ω-helix and β-sheet forms and, with an increase in temperature from 25°C to 180°C, changes from αR-helix form and ω-helix form to β-sheet forms. On the other hand, the main chain of PAANa takes the right-handed αR-helix form in the temperature range from 25°C to 210°C. With a decrease in the neutralization number, PAANa changes to PAA and the NMR spectra are correspondingly changed.

2-Furyloxirane(FO) with purity of over 99% was prepared in 80% yield by epoxidation of furfural with trimethylsulfonium chloride and potassium hydroxide in acetonitrile/water solution. Polymerization of FO was realized using tri-isobutyl aluminum (Al(i-Bu)3) as catalyst, when Al(i-Bu)3 concentration was 0.009 mol/L, poly(2-furyloxirane)(PFO) with M n of 3.4 kg/mol and a polydispersity index of 1.5 was obtained in yield of 88% after polymerization at 25 °C for 48 h. The corresponding PFO showed glass transition temperature (T g ) of Ca. 1 °C and 5 wt% thermal decomposition temperature(T d ) of 260 °C. The obtained PFO was almost 100% head-to-tail structure, and it was a good plasticizer and thermal stabilizer for poly(propylene carbonate)(PPC), an alternate copolymer of propylene oxide and carbon dioxide. For PFO/PPC polyblend with PFO loading of 2 wt%, its T d increased by 50 °C from 214 °C of pure PPC to 264 °C, while its elongation at break increased from 13% of pure PPC to 29%.

Starch-based vesicles with controlled size have been successfully achieved by a simple nanoprecipitation procedure from starch mixed ester.

Nanometric and monodisperse starch acetate nanospheres can be prepared through a simple procedure of nanoprecipitation, by the dropwise addition of water to an acetone solution of starch acetate, without any stabilizing agent. This is the first report of the preparation of starch-based nanospheres by this method. The size of the nanospheres obtained can be easily controlled by a number of simple and efficient modifications, i.e., through regulation of the polymer concentration in acetone, the proportions of the water and organic phases, and the molecular weight and degree of substitution of the starch esters. A number of reasons are suggested to explain the observed transitions in the particle size. Fluorescence spectroscopic studies proved that these types of nanospheres could be potentially used for the encapsulation of hydrophobic drugs.

Two di-nuclear non-ionic MRI contrast agents, (Gd-DO3A)2-BMQX and (Gd-DO3A)2-BMP, have been designed and synthesized by fusing the DO3A units together with a quinoxalinyl or pyrazinyl moiety. They have improved longitudinal relaxivities of 5.23 and 5.16 mM Gd−1 s−1, respectively, at 20 MHz magnet, 37 °C and pH 7.0. In addition, they possess high thermodynamic stability and kinetic inertness. The cytotoxicity studies indicated that the toxicity of these two agents were low. All these properties satisfy the requirements for clinical applications.