Changfeng Yi

Self-assembled magnetic fluorescent polymeric micelles for magnetic resonance and optical imaging.

Stable and cytocompatible hybrid PEGylated micelles with multimodal imaging capabilities are described. The F3O4-encapsulated polymeric micelles composed of cores containing magnetic nanoparticles and polyethylene glycol (PEG) shells are synthesized by self-assembly of amphiphilic poly(HFMA-co-VBK)-g-PEG copolymers and oleic acid stabilized Fe3O4 nanoparticles. The Fe3O4 magnetic nanoparticles in the core produce T2-weighted MR imaging functionalities, whereas the small fluorescent monomer carbazole in the polymer shell introduces good fluorescent properties. The multifunctional micelles exhibit excellent paramagnetic properties with the maximum saturation magnetization of 9.61 emu/g and transverse relaxivity rate of 157.44 mM(-1) S(-1). In vivo magnetic resonance imaging (MRI) studies reveal enhanced contrast between the liver and spleen. Fluorescence spectra show characteristic emission peaks from carbazole at 350 nm and 365 nm and vivid blue fluorescence can be observed by 2-photon confocal scanning laser microscopy (CLSM). In vivo optical imaging demonstrates the unique fluorescent characteristics of the Fe3O4-encapsulated polymeric micelles in the liver and spleen and the excellent multifunctional properties suggest potential clinical use as nanocarriers in magnetic resonance imaging and optical imaging.

Design and preparation of novel fluorescent polyimides containing ortho-linked units and pyridine moieties

Abstract A novel pyridine-containing aromatic diamine monomer, 4-[4-hydroxyphenyl]-2,6-bis[4-(2-aminophenoxy)phenyl]pyridine (p,o-HAPP), was synthesized by a modified Chichibabin reaction of p-Hydroxybenzaldehyde and a substituted acetophenone, 4-(2-nitrophenoxy)acetophenone (p,o-NPAP), followed by a reduction of the resulting dinitro compound 4-[4-hydroxyphenyl]-2,6-bis[4-(2-nitrophenoxy)phenyl]pyridine with Pd/C and hydrazine monohydrate. The aromatic diamine was employed to prepare a series of pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides in N,N-dimethylformamide (DMF) via the conventional two-step method. The inherent viscosities of the resulting poly(amic acids) and PIs were in range of 0.62–0.76 and 0.52–0.64 dL/g, respectively. The obtained novel PIs exhibited high solubility in common organic solvents, such as m-Cresol, DMF, N,N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone (NMP), tetrahydrofuran, and chloroform. Meanwhile, flexible PI films were obtained, which had excellent thermal stability, with the glass transition temperature (T g) of 259.8–323.4 °C and the temperature at 10% weight loss of 485.5–576.4 °C in nitrogen atmosphere. The protonated polymer showed UV–vis absorption in the region 200–400 nm and displayed strong fluorescence intensity (470 nm) in NMP solution.

Emulsifier‐free emulsion copolymerization of styrene and butyl acrylate with cationic comonomer

Emulsifier-free emulsion copolymerization of styrene (St) and butyl acrylate (BA) in the presence of a cationic functional comonomer, N-dimethyl, N-butyl, N-ethyl methacrylate ammonium bromine (DBMA) was carried out using azobis (isobutyl-amidine hydrochloride) (AIBA) as an initiator. The surface properties of particles were studied by testing the actual value of N + and C + (NH 2 )(NH 2 ) on the surface of the particles and the surface charge density. The copolymer particles were characterized using TEM. The effects of reaction temperature, DBMA content, AIBA content, ionic strength, etc., on the conversion of the monomer and the average diameter (Dw) and number (Np) of copolymer particles were investigated. Under constant ionic strength, the average diameter of copolymer particles (Dw) decreased with increasing AIBA and DBMA concentrations and decreased with increasing reaction temperature also. Moreover, it increased with increasing St content in the monomer feeding. Under a constant concentration of the comonomer and initiator as well as the constant monomer composition, Dw shows a change process of increase-decrease-increase in the ionic strength plot. The polymerization reaction rate increased with increasing the DBMA content, AIBA content, and increasing temperature. The surface charge properties of the particles were mainly decided by the DBMA content, AIBA content, ionic strength, etc. The methods of feeding the monomer affects the morphology, structure, size, and surface charge density of the particles.

Styrene-butyl acrylate-N,N-dimethyl N-butyl N-methacrylamidino propyl ammonium bromide emulsifier-free emulsion copolymerization

Emulsifier-free emulsion copolymerization of styrene (St) and butyl acrylate (BA) in the presence of cationic functional comonomer N,N-dimethyl N-butyl N-methacrylamidino propyl ammonium bromide (DBMPAB) was carried out using azobis(isobutylamidine hydrochloride) (AIBA) as initiator. The surface properties of particles were studied by testing the actual value of -N + ≡ and -C(NH 2 ) 2 + on the surface of particles and the surface charge density. The copolymer particles were characterized by transmission electron microscopy (TEM). The effects of reaction temperature, DBMPAB content, AIBA content, and ionic strength on conversion of monomer, average diameter D w ) and number (N p ) of copolymer particles were investigated. Under constant ionic strength the average diameter of copolymer particles (D W ) decreased with increasing AIBA and DBMPAB concentration, and decreased with rising reaction temperature. At constant concentration of comonomer and initiator and constant monomer composition, D w showed an increasc-decrease-increase with ionic strength plot. The polymerization rate increased with increasing DBMPAB content, AIBA content and rising temperature. The surface charge properties of particles were mainly decided by DBMPAB content, AIBA content, and ionic strength.

Self-assembled magnetic luminescent hybrid micelles containing rare earth Eu for dual-modality MR and optical imaging

In this study, we report new water-soluble multifunctional nanomaterials based on amphiphilic poly(HFMA-co-Eu(AA)3Phen)-g-PEG copolymers and oleic acid modified Fe3O4 nanoparticles. The nanoparticles can self-assemble to form magnetic and luminescent hybrid micelles and show a spherical morphology, paramagnetic properties with a maximum saturation magnetization of 7.05 emu g-1, and a high transverse relaxivity of 340 mM-1 s-1. According to in vivo magnetic resonance imaging (MRI) experiments, excellent contrast of the liver and spleen was achieved after injection of the hybrid micelles. Fluorescence spectra show characteristic emission peaks from the rare earth Eu at 616 nm and vivid red fluorescence can be observed by 2-photon confocal laser scanning microscopy (CLSM). In vivo optical imaging demonstrates the unique fluorescent characteristics of the magnetic and luminescent hybrid micelles in the liver and spleen and the excellent multifunctional properties suggest the possibility of clinical use as nanocarriers in magnetic resonance imaging and optical imaging.

Synthesis and characterization of highly soluble and optically transparent polyimides derived from novel fluorinated pyridine-containing aromatic diamine

A novel fluorinated pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[2-(4-amino-2-trifluoromethyphenoxy)phenyl]pyridine (o, p-6FPAPP), was prepared in a three-step synthetic route. This aromatic diamine was then employed to synthesize a series of fluorinated pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides via the conventional two-step method. The inherent viscosities of the resulting poly(amic acid)s (PAAs) and PIs were in the range of 0.71–0.89 and 0.62–0.84 dL/g; all the PIs obtained by chemical imidization were readily soluble in common organic solvents such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and so on. Meanwhile, transparent, strong and flexible PI films were obtained, which had good thermal stability, with the glass transition temperature (Tg) of 195.2°C–232.7°C, the temperature at 10% weight loss of 530.2°C–546.0°C in nitrogen atmosphere, and good optical transparency with the cutoff wavelengths of 354–382 nm, as well as outstanding mechanical properties with tensile strengths of 96.4–105.8 MPa, tensile modulus of 1.57–1.88 GPa and elongations at break of 9.5%–13.4%. The PI films were also found to possess low water uptake of 0.52%–0.67%.

Emulsifier-free emulsion polymerized poly(MMA-HEMA-Eu(AA)3Phen)/Fe3O4 magnetic fluorescent bifunctional nanospheres for magnetic resonance and optical imaging

Integration of biocompatibility with superparamagnetic Fe3O4 nanoparticles and luminescence rare earth complexes Eu(AA)3Phen was carried out to form bifunctional nanospheres for using in bioimaging applications. The nanospheres Poly(MMA-HEMA-Eu(AA)3Phen)/Fe3O4 exhibit magnetic and fluorescent properties that are favorable for the use in drug delivery, magnetic separation and MR imaging for biomedical research. The TEM and SEM studies reveal that the bifunctional nanospheres have core-shell structure, in a spherical shape with a size ranging from 140 nm to 180 nm. In MRI experiments, a clear negative contrast enhancement in T2 images and the r2 reaches 568.82 (mmol·L-1)-1·s-1. In vivo magnetic and fluorescence resonance imaging results suggest the nanospheres are able to preferentially accumulate in liver and spleen tissues to allow dual-modal detection of cancer cells in a living body.

In situ solution polymerization for preparation of MDI-modified graphene/hyperbranched poly(ether imide) nanocomposites and their properties

Firstly, fully exfoliated graphene oxide (GO) colloidal dispersion in N-methyl-2-pyrrolidone (NMP) with high concentration is obtained by a solvent-exchange method and further used to prepare superior GO-MDI with free isocyanato groups by chemical modification. Then, the yielded GO-MDI is employed to prepare two kinds of MDI-modified graphene/hyperbranched poly(ether imide) (GE-MDI/HBPEI) nanocomposites via in situ random solution co-polycondensation or crosslinking reaction, followed by synchronous thermal imidization and reduction. The chemical modification of GO endows GO-MDI with good solubility in organic solvents to prepare GE-MDI/HBPEI nanocomposites with high filler content. GO-MDI is further used as a multi-functional co-monomer or crosslinker to be introduced into the HBPEI backbone with full compatibility of the guest and host at the molecular level. Finally, the performance tests show that the heat resistance, thermal stability, mechanical strength and modulus, and gas barrier properties of the obtained two kinds of nanocomposites are significantly improved or enhanced compared with pure HBPEI, and the impacts become more and more significant with the increase of GO-MDI content, but their mechanical toughness show trends of increase at first then decrease with the increase of GO-MDI content. Comparisons also show that at the same GO-MDI content, the heat resistance, thermal stability, mechanical strength and modulus of the nanocomposites obtained by in situ random solution co-polycondensation are all superior to those obtained by in situ random solution crosslinking reaction, except the mechanical toughness and gas barrier properties of the former are less than the latter. This effective approach provides a possibility for enriching and developing high performance PEI-based composites with various forms of GE for advanced engineering or functional materials.

Magnetic, fluorescent, and thermo-responsive poly(MMA-NIPAM-Tb(AA)3Phen)/Fe3O4 multifunctional nanospheres prepared by emulsifier-free emulsion polymerization

Magnetic, luminescent, and thermoresponsive multifunctional nanospheres composed of modified Fe3O4 nanoparticles as the core and rare earth complex Tb(AA)3Phen as the shell are synthesized by emulsifier-free emulsion polymerization. The core–shell spherical structure has a size between 140 and 220 nm and exhibits strong green fluorescence of the rare earth complex Tb(AA)3Phen. In the R2 relaxivity and in vivo MRI studies, the R2 relaxivity of the nanospheres is 562.56 mM–1 s–1 and enhanced T2-weighted images are observed from the nanospheres in the liver and spleen after injection as a contrast agent. The excellent superparamagnetic, thermosensitive, and fluorescent properties render the nanospheres useful in biomedical engineering and optical imaging.

Synthesis and characterization of thermally stable, hydrophobic hyperbranched polyimides derived from a novel triamine

A novel aromatic triamide 1,3,5-tri[4-(4-aminophenoxy)phenyl] benzene (TAPOPB) with prolonged chain segments and ether bonds was successfully prepared through a three-step reaction. Then a series of hyperbranched polyimides (HBPIs) were synthesized using A2 + B3 polycondensation from various commercial aromatic dianhydrides and TAPOPB. The HBPIs showed good solubility, thermal stability with glass transition temperatures (T g) between 218°C and 320°C, and temperature at 10% weight loss of 502.1–561.7°C in nitrogen atmosphere. Meanwhile, they had decent mechanical properties whose tensile strength and modulus were higher than 72.37 MPa and 1.039 GPa, respectively. Water uptake of less than 0.96% was obtained. The truncation wavelengths of the films were all greater than 400 nm with a good application prospect in UV protective coating. Most contact angles were more than 90°, promising to be used as hydrophobic material.