Reaction-Induced Liquid Crystalline Polybenzoxazine Bearing Aromatic Amide Side Branches.

In this study, a nematic phase structure is incorporated into polybenzoxazine to increase its thermal conductivity. A simple route for the synthesis of a thermally conductive polybenzoxazine containing liquid crystalline (LC) structure by grafting oligomeric p-sulfophenylene-terephthalamide (PSTA) is offered. Benzoxazine monomer of pHBA-da is synthesized via Mannich reaction of p-hydroxy benzoic acid, p-formaldehyde, and dodecyl amine. After ring-opening polymerization, the oligomer benzoxazine of OBZ─COOH is obtained. The OBZ─COOH/PSTA mixture is prepared by mixing PSTA with OBZ─COOH. Afterward, the grafted copolymer is named OBZ─PSTA copolymer. The liquid crystalline behavior of OBZ─COOH/PSTA is studied by polarized optical microscopy and small angle X-ray scattering analysis. The results show that the OBZ─PSTA forms the LC structure during isothermal and non-isothermal curing. The LC structure displays a floral textured nematic phase. The phase formation is induced by an amidation reaction. Due to the grafts of LC PSTA, the thermal conductivity of OBZ─PSTA is 0.296 W m-1 K-1 , which is 26% greater than OBZ─COOH. The glass transition temperature (Tg ) of OBZ─PSTA is 241 °C. The 5% (Td5 ) and 10% weight loss temperatures (Td10 ) of OBZ─PSTA are 346 and 362 °C, respectively.

Semi-Interpenetrating Polymer Network Anion Exchange Membranes Based on Quaternized Polybenzoxazine and Poly(Vinyl Alcohol-Co-Ethylene) for Acid Recovery by Diffusion Dialysis.

Acid recovery from acidic waste is a pressing issue in current times. Chemical methods for recovery are not economically feasible and require significant energy input to save the environment. This study reported a semi-interpenetrating polymer network (semi-IPN) anion exchange membranes (AEMs) for acid recovery by diffusion dialysis with excellent dimensional stability, high oxidation stability, good acid dialysis coefficient (UH +) and high separation factor (S). Semi-IPN AEMs are prepared by ring-open cross-linked quaternized polybenzoxazine (AQBZ) with poly(vinyl alcohol-co-ethylene), where AQBZ is obtained by Mannich reaction and Menshutkin reaction. All four proportions of semi-IPNs exhibit clear micro-phase separation, which is conducive to ion transport. The water uptake (WU) of the four semi-IPNs ranges from 14.2 % to 19.2 %, while the swelling ratio (SR) remains between 8.7 % and 11.3 %. These results indicate that the cross-linked structure in the designed semi-IPNs effectively control swelling and ensure dimensional stability. The thermal degradation temperature (Td5) of semi-IPN4:6 to semi-IPN7:3 varies from 309 °C to 289 °C, with an oxidation stability weight loss rate (WOX) ranging from 91.5 % to 93.5 %, demonstrating excellent thermal stability and oxidation stability. The semi-IPNs also show good UH + values ranging from 11.9-16.3*10-3 m/h and high S values between 38.6 and 45.9, indicating the promising potential of the semi-IPNs.

Synergistic Promotion of the Photocatalytic Preparation of Hydrogen Peroxide (H2 O2 ) from Oxygen by Benzoxazine and Si─O─Ti Bond.

Hydrogen peroxide (H2 O2 ) is considered one of the most important chemical products and has a promising future in photocatalytic preparation, which is green, pollution-free, and hardly consumes any non-renewable energy. This study involves the preparation of benzoxazine with Si─O bonds via the Mannich reaction, followed by co-hydrolysis to produce photocatalysts containing benzoxazine with Si─O─Ti bonds. In this study, a benzoxazine photocatalyst with Si─O─Ti bonds is synthesized and characterized using fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The size and elemental distribution of the nanoparticles are confirmed by transmission electron microscopy and scanning electron microscopy. The photocatalytic synthesis of H2 O2 is tested using the titanium salt detection method, and the rate is found to be 7.28 µmol h-1 . Additionally, the catalyst exhibits good hydrolysis resistance and could be reused multiple times. The use of benzoxazine with Si─O─Ti bonds presents a promising experimental and theoretical foundation for the industrial production of H2 O2 through photocatalytic synthesis.

Hypocrellin B-loaded, folate-conjugated polymeric micelle for intraperitoneal targeting of ovarian cancer in vitro and in vivo.

Photodynamic therapy (PDT) is considered an innovative and attractive modality to treat ovarian cancer. In the present study, a biodegradable polymer poly (ethylene glycol) (PEG)-poly (lactic acid)(PLA)-folate (FA-PEG-PLA) was prepared in order to synthesize an active-targeting, water-soluble and pharmacomodulated photosensitizer nanocarrier. Drug-loading content, encapsulation efficiency, in vitro and in vivo release were characterized, in which hypocrellin B (HB)/FA-PEG-PLA micelles had a high encapsulation efficiency and much slower control release for drugs compared to free drugs (P < .05). To evaluate the targeting ability of the HB/FA-PEG-PLA micelles, a cellular uptake study in vitro was carried out, which showed significantly enhanced uptake of HB/FA-PEG-PLA micelles in SKOV3 (FR+) compared to A2780 cancer cells (FR-). The enhanced uptake of HB/FA-PEG-PLA micelles to cancer cells resulted in a more effective post-PDT killing of SKOV3 cells compared to plain micelles and free drugs. Binding and uptake of HB/FA-PEG-PLA micelles by SKOV3 cells were also observed in vivo after ip injection of folate-targeted micelles in tumor-bearing ascitic ovarian cancer animals. Drug levels in ascitic tumor tissues were increased 20-fold (P < .001), which underscored the effect of a regional therapy approach with folate targeting. Furthermore, the HB-loaded micelles were mainly distributed in kidney and liver (the main clearance organs) in biodistribution. These results showed that our newly developed PDT photosensitizer HB/FA-PEG-PLA micelles have a high drug-loading capacity, good biocompatibility, controlled drug release, and enhanced targeting and antitumor effect, which is a potential approach to future targeting ovarian cancer therapy.

Weldable, Reprocessable, and Water-resistant Polybenzoxazine Vitrimer Crosslinked by Dynamic Imine Bonds.

Traditional polybenzoxazine thermosets cannot be reprocessed or recycled due to the permanent crosslinked networks. The dynamic exchangeable characteristics of imine bonds can impart the networks with reprocessabilities and recyclabilities. This study reported a weldable, reprocessable, and water-resistant polybenzoxazine vitrimer (C-ABZ) crosslinked by dynamic imine bonds. It was synthesized through a condensation reaction between an aldehyde-containing benzoxazine oligomer (O-ABZ) and 1,12-dodecanediamine. The resulting C-ABZ was able to be welded and reprocessed due to the dynamic exchange of imine bonds. The tensile strengths of the welded C-ABZ and the reprocessed C-ABZ after three cycles of hot-pressing were 76.7, 81.3, 70.8, and 58.1 Mpa, with corresponding tensile strength recovery ratios of 74.1 %, 78.6 %, 68.4 %, and 56.1 %, respectively. Furthermore, the polybenzoxazine backbone significantly improved the water resistance of the imine bonds. After immersing in water for 30 days at room temperature, the weight gain of C-ABZ was less than 1 % with corresponding tensile strength and tensile strength retention ratio of 59.5 Mpa and 57.5 %, respectively. Although the heat resistance of C-ABZ decreased slightly with increased hot-pressing cycles, a glass transition temperature (Tg, tanδ) of 150 °C was retained after the third hot-pressing. Overall, these findings demonstrate that the C-ABZ possesses excellent comprehensive performances.

Highly sensitive detection of polyborosiloxane (PBS) hydrolysis with mannitol using electrochemical methodology.

The complexation of polyhydric alcohols, such as mannitol, with boric acid ion promotes the ionization of boric acid. The hydrolysis performance of PBSs was determined using an electrochemical approach for the first time. Compared with the traditional methods, this approach includes the advantages of high sensitivity, continuity, and digitization.

Reprocessable Polybenzoxazine Thermosets with High Tgs and Mechanical Strength Retentions Using Boronic Ester Bonds as Crosslinkages.

In order to obtain reprocessable polybenzoxazine thermosets with high heat resistance and mechanical strength retentions, network structures without irreversible parts were constructed via crosslinking benzoxazine oligomers using boronic ester cross-linkers. Firstly, the benzoxazine monomer containing carbon-carbon double bonds was synthesized via the Mannich reaction. After thermal ring-opening polymerization, the benzoxazine oligomer containing carbon-carbon double bonds (OBZ) was yielded. Through the thiol-ene click reaction of the OBZ and dithiol cross-linker bearing boronic ester bonds, the polybenzoxazine thermosets using boronic ester bonds as crosslinkages (OBZ-BDB) were successfully synthesized. The structures of OBZ and OBZ-BDB were characterized by SEC, 1H NMR, and FT-IR measurements. Reprocessing experiments showed that OBZ-BDB has remarkable reprocessability. The retention rates of the tensile strengths through three generations of reprocessing were 98%, 95%, and 84%, respectively. Meanwhile, OBZ-BDB cross-linked by boronic ester bonds had brilliant thermal properties. The Tg of the original OBZ-BDB was 224 °C. With the increase of the reprocessing generations, the Tgs basically remained unchanged.

Polyphenylene sulfide fabric with enhanced oxidation resistance and hydrophobicity through polybenzoxazine surface coating for emission control in harsh environment.

Emissions from power generation and municipal waste incineration sources are primarily at high temperatures and contain corrosive gases, particulate pollutants and are enormously challenging on the performance of the filtration systems in use. Here, polyphenylene sulfide (PPS) nonwoven fabric, a primary material used commercially in such settings, is modified with a polybenzoxazine precursor as a coating to deliver improved thermal and oxidation resistance to the fibrous substrate. The polybenzoxazine precursor undergoes chain propagation and crosslinking upon the treatment process to provide a protective layer over the PPS fibers such that enhanced structural stability in a harsh environment was demonstrated. We have shown the improved overall tensile strength (+15%), Young's modulus (+26%), and more hydrophobic nature of the modified PPS fabric, while the superior environmental stability and better filtration performance could be achieved. Such methodology may lead to higher service temperature and extended service time of the PPS filtration bags in harsh fire exhaustion airstreams encountered in power plants or municipal garbage incineration facilities. The crosslinkable benzoxazine could also be the most cost-effective high temperature coating layer on fibers, enabling future high-performance air filtration materials.

Biodegradable tri-block copolymer poly(lactic acid)-poly(ethylene glycol)-poly(l-lysine)(PLA-PEG-PLL) as a non-viral vector to enhance gene transfection.

Low cytotoxicity and high gene transfection efficiency are critical issues in designing current non-viral gene delivery vectors. The purpose of the present work was to synthesize the novel biodegradable poly (lactic acid)-poly(ethylene glycol)-poly(l-lysine) (PLA-PEG-PLL) copolymer, and explore its applicability and feasibility as a non-viral vector for gene transport. PLA-PEG-PLL was obtained by the ring-opening polymerization of Lys(Z)-NCA onto amine-terminated NH(2)-PEG-PLA, then acidolysis to remove benzyloxycarbonyl. The tri-block copolymer PLA-PEG-PLL combined the characters of cationic polymer PLL, PLA and PEG: the self-assembled nanoparticles (NPs) possessed a PEG loop structure to increase the stability, hydrophobic PLA segments as the core, and the primary ɛ-amine groups of lysine in PLL to electrostatically interact with negatively charged phosphate groups of DNA to deposit with the PLA core. The physicochemical properties (morphology, particle size and surface charge) and the biological properties (protection from nuclease degradation, plasma stability, in vitro cytotoxicity, and in vitro transfection ability in HeLa and HepG2 cells) of the gene-loaded PLA-PEG-PLL nanoparticles (PLA-PEG-PLL NPs) were evaluated, respectively. Agarose gel electrophoresis assay confirmed that the PLA-PEG-PLL NPs could condense DNA thoroughly and protect DNA from nuclease degradation. Initial experiments showed that PLA-PEG-PLL NPs/DNA complexes exhibited almost no toxicity and higher gene expression (up to 21.64% in HepG2 cells and 31.63% in HeLa cells) than PEI/DNA complexes (14.01% and 24.22%). These results revealed that the biodegradable tri-block copolymer PLA-PEG-PLL might be a very attractive candidate as a non-viral vector and might alleviate the drawbacks of the conventional cationic vectors/DNA complexes for gene delivery in vivo.

Hydrogen-bonding-induced complexation of polydimethylsiloxane-graft-poly(ethylene oxide) and poly(acrylic acid)-block-polyacrylonitrile micelles in water.

Polydimethylsiloxane-graft-poly(ethylene oxide) (PDMS-g-PEO) copolymers form micelles in water with PDMS as the core and PEO as the corona. The introduction of poly(acrylic acid)-block-polyacrylonitrile (PAA-b-PAN) block copolymers in water leads to the formation of micellar complexes due to the hydrogen bonding between carboxyl groups and ether oxygens among the PAA and PEO chains in the corona of the micelles. The effects of pH, molar ratios (r) of PAA/PEO, and the standing time on the directly mixing these two micelles in water have been investigated using laser light scattering (LLS) and transmission electron microscopy (TEM). Our results showed that the complexation between PAA and PEO in the corona was greatly enhanced at a pH below 3.5. For a fixed pH value, the interactions between these two micelles in water were governed by the value of r. At r < ∼0.6, mixing the two micelles in water resulted in a large floccule because the smaller PAA-b-PAN micelles act as physical cross-links, which are absorbed onto one PDMS-g-PEO micelle and simultaneously bonded to PEO chains on the other micelles, forming bridges and causing flocculation. At ∼0.6 < r < ∼1.2, the mixing led to stable micellar complexes with a layer of PAA-b-PAN micelles absorbed onto the initial PDMS-g-PEO micelles. At r > ∼1.2, the resultant micellar complexes first remained stable, but they precipitated from solution after a long time standing.

Development of novel ST68/PLA-PEG stabilized ultrasound nanobubbles for potential tumor imaging and theranostic.

Nanobubbles (NBs) have received wide attention as theranostic agents and been extensively explored in various applications, especially in cancer. The aim of this study was to develop a novel kind of NBs which possess high echogenicity and good stability. This novel ultrasonic nanobubbles (ST68/PLA-PEG NBs) consist of perfluoropropane gas stabilized by Span 60 and Tween 80 (ST68) surfactant and synthesized PLA-PEG-NH2 block copolymers, and were prepared through the methods of mechanical shaking and low-speed centrifugation. A series of experiments were carried out to evaluate the physicochemical properties, echogenicity and cytotoxicity of this novel NBs. According to the amount ratio of copolymers to surfactant, the NBs were divided into 5 groups (0%, 5%, 10%, 15% and 20%). Group "10%" were the optimum NBs, with a size of 675.6 nm, polydispersity index of 0.39. Moreover, these NBs gave a maximum contrast intensity of 31.0 ±â€¯0.2 dB over baseline and little loss of contrast signal after 10 min. In conclusion, this novel kind of ST68/PLA-PEG NBs which exhibited a high echogenicity and good stability were successfully prepared, and they may offer a potential strategy for drug delivery and tumor-targeted theranostic.

Development and evaluation of novel tumor-targeting paclitaxel-loaded nano-carriers for ovarian cancer treatment: in vitro and in vivo.

BACKGROUND: Ovarian cancer is the most leading cause of death and the third most common gynecologic malignancy in women. Traditional chemotherapy has inevitable drawbacks of nonspecific tumor targeting, high toxicity, and poor therapeutic efficiency. In order to overcome such shortcomings, we prepared a novel nano-carrier drug-delivery system to enhance the anti-tumor efficiency. METHODS: In vitro characterizations of nano-carriers were determined by TEM, DLS. Cell viability was measured by MTT method. RT-PCR was performed to measure the expression of FARα in three ovarian cancer cell lines. The drug-release study and the uptaken study were measured in vitro. The pharmacokinetic and the drug distribution study were verified by HPLC methods in vivo. The enhanced anti-tumor efficiency of FA-NP was evaluated by the tumor inhibitory rate in vivo. RESULTS: Paclitaxel (PTX)-loaded nanoparticles (NPs) (PTX-PEG-PLA-NP and PTX-PEG-PLA-FA-NP) were prepared successfully, and the drug-release study showed that the cumulative release rates of NP groups were much less than free PTX group. The pharmacokinetic study showed that the elimination phase of two kinds of NP groups were much longer than that of PTX group. The drug distribution in different tissues showed that the peak-reach time was 2 h in the PTX group and 6 h in both NP groups. All of these results confirmed the excellent slow-release effects of both kinds of nano-carriers. More importantly, we confirmed that PTX-PEG-PLA-FA-NP had greater uptake by SK-OV-3 cells than PTX-PEG-PLA-NP and free PTX in vitro. A drug-distribution study of tumor-bearing mice demonstrated that the PTX concentration of tumor tissues in the PTX-PEG-PLA-FA-NP group was 3 times higher than the other two groups. PTX-PEG-PLA-FA-NP was uptaken much more by SK-OV-3 cells than PTX-PEG-PLA-NP and free PTX. Eventually, based on the slow-release effect and tumor-targeting characteristics of PTX-PEG-PLA-FA-NP, a cytotoxicity test indicated that PTX-PEG-PLA-FA-NP was much more toxic to SK-OV-3 cells than the controls. The tumor inhibitory rate in the PTX-PEG-PLA-FA-NP group of tumor-bearing mice was about 1.5 times higher than the controls. The tumor targeting and anti-tumor efficiency of PTX-PEG-PLA-FA-NP were confirmed both in vitro and in vivo. CONCLUSIONS: We developed an ovarian cancer targeting nano-carrier drug delivery system successfully, which showed perfect ovarian cancer targeting and anti-tumor effect, thus have the potential to be a new therapy strategy for ovarian cancer patients.

Enhanced effect of photodynamic therapy in ovarian cancer using a nanoparticle drug delivery system.

Nanoparticles are promising novel drug delivery carriers that allow tumor targeting and controlled drug release. In the present study, we prepared poly butyl-cyanoacrylate nanoparticles (PBCA-NP) entrapped with hypocrellin B (HB) to improve the effect of photodynamic therapy (PDT) in ovarian cancer. An ovarian cancer ascites model using Fischer 344 rats and PBCA-NP entrapped with HB (HB-PBCA-NP) were formed successfully. The pharmacodynamic characteristics and biodistribution of the HB-PBCA-NP system were evaluated by comparison with HB dimethyl sulfoxide (HB-DMSO) and testing at various time-points following intraperitoneal drug administration. HB-PBCA-NP-based PDT combined with cytoreductive surgery was then administrated to the tumor-bearing animals. Kaplan-Meier survival analysis was performed to assess the therapeutic effect of the nanoparticle system. The serum HB concentration peaked 4 h after drug administration in the nanoparticle system, and 1 h with HB-DMSO. The peak exposure time of tumor tissues was also extended (4 vs. 2 h), and PBCA-NP remained present for much longer than HB-DMSO. Although PDT combined with surgery prolonged the survival time significantly compared with surgery alone (84 days, P<0.05), there was no significant difference in the survival time of animals that received either HB-PBCA-NP- or HB-DMSO-based PDT after cytoreductive surgery (99 vs. 95 days, P=0.293). PBCA-NP exhibited potential advantages in controlled drug release and tumor targeting, which was beneficial for HB-based PDT. PDT combined with surgery prolonged the survival time, suggesting that this might be an alternative treatment option for ovarian cancer.

A peptide-mediated targeting gene delivery system for malignant glioma cells.

Glioblastoma multiforme (GBM) is the most common and malignant glioma. Although there has been considerable progress in treatment strategies, the prognosis of many patients with GBM remains poor. In this work, polyethylenimine (PEI) and the VTWTPQAWFQWV (VTW) peptide were modified and synthesized into GBM-targeting nanoparticles. The transfection efficiency of U-87 (human glioblastoma) cells was evaluated using fluorescence microscopy and flow cytometry. Cell internalization was investigated to verify the nanoparticle delivery into the cytoplasm. Results showed that the methods of polymer conjugation and the amount of VTW peptide were important factors to polymer synthesis and transfection. The PEI-VTW20 nanoparticles increased the transfection efficiency significantly. This report describes the use of VTW peptide-based PEI nanoparticles for intracellular gene delivery in a GBM cell-specific manner.

Gadolinium-loaded polymeric nanoparticles modified with Anti-VEGF as multifunctional MRI contrast agents for the diagnosis of liver cancer.

Molecular imaging is essential to increase the sensitivity and selectivity of cancer diagnosis especially in the early stage of tumor. Here, we designed a novel multifunctional polymeric nanoparticle contrast agent (Anti-VEGF PLA-PEG-PLL-Gd NP) simultaneously modified with Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) and anti-vascular endothelial growth factor (VEGF) antibody to deliver Gd-DTPA to the tumor area and achieve the early diagnosis of hepatocellular carcinoma (HCC). The Anti-VEGF PLA-PEG-PLL-Gd NPs exhibited high T(1) relaxivity and no obvious cytotoxicity under the experimental concentrations in human hepatocellular carcinoma (HepG2) cells. The results of in vitro cell uptake experiments demonstrated that the uptake process of NPs was both concentration and time depended. Compared with non-targeted NPs, the Anti-VEGF antibody modified NPs showed much higher cell uptake in the HepG2 cells. During in vivo studies, the targeted NPs showed significantly signal intensity enhancement at the tumor site (mouse hepatocarcinoma tumor, H22) compared with non-targeted NPs and Gd-DTPA injection in tumor-bearing mice and the imaging time was significantly prolonged from less than an hour (Gd-DTPA injection group) to 12 h. These results demonstrated that this novel MRI contrast agent Anti-VEGF PLA-PEG-PLL-Gd NPs showed great potential in the early diagnosis of liver tumors.

Gadolinium-conjugated PLA-PEG nanoparticles as liver targeted molecular MRI contrast agent.

A nanoparticle magnetic resonance imaging (MRI) contrast agent targeted to liver was developed by conjugation of gadolinium (Gd) chelate groups onto the biocompatible poly(l-lactide)-block-poly (ethylene glycol) (PLA-PEG) nanoparticles. PLA-PEG conjugated with diethylenetriaminopentaacetic acid (DTPA) was used to formulate PLA-PEG-DTPA nanoparticles by solvent diffusion method, and then Gd was loaded onto the nanoparticles by chelated with the unfolding DTPA on the surface of the PLA-PEG-DTPA nanoparticles. The mean size of the nanoparticles was 265.9 ± 6.7 nm. The relaxivity of the Gd-labeled nanoparticles was measured, and the distribution in vivo was evaluated in rats. Compared with conventional contrast agent (Magnevist), the Gd-labeled PLA-PEG nanoparticles showed significant enhancement both on liver targeting ability and imaging signal intensity. The T(1) and T(2) relaxivities per [Gd] of the Gd-labeled nanoparticles was 18.865 mM(-1) s(-1) and 24.863 mM(-1) s(-1) at 3 T, respectively. In addition, the signal intensity in vivo was stronger comparing with the Gd-DTPA and the T(1) weight time was lasting for 4.5 h. The liver targeting efficiency of the Gd-labeled PLA-PEG nanoparticles in rats was 14.57 comparing with Magnevist injection. Therefore, the Gd-labeled nanoparticles showed the potential as targeting molecular MRI contrast agent for further clinical utilization.

Biocompatible Nanocomplexes for Molecular Targeted MRI Contrast Agent.

Accurate diagnosis in early stage is vital for the treatment of Hepatocellular carcinoma. The aim of this study was to investigate the potential of poly lactic acid-polyethylene glycol/gadolinium-diethylenetriamine-pentaacetic acid (PLA-PEG/Gd-DTPA) nanocomplexes using as biocompatible molecular magnetic resonance imaging (MRI) contrast agent. The PLA-PEG/Gd-DTPA nanocomplexes were obtained using self-assembly nanotechnology by incubation of PLA-PEG nanoparticles and the commercial contrast agent, Gd-DTPA. The physicochemical properties of nanocomplexes were measured by atomic force microscopy and photon correlation spectroscopy. The T(1)-weighted MR images of the nanocomplexes were obtained in a 3.0 T clinical MR imager. The stability study was carried out in human plasma and the distribution in vivo was investigated in rats. The mean size of the PLA-PEG/Gd-DTPA nanocomplexes was 187.9 +/- 2.30 nm, and the polydispersity index was 0.108, and the zeta potential was -12.36 +/- 3.58 mV. The results of MRI test confirmed that the PLA-PEG/Gd-DTPA nanocomplexes possessed the ability of MRI, and the direct correlation between the MRI imaging intensities and the nano-complex concentrations was observed (r = 0.987). The signal intensity was still stable within 2 h after incubation of the nanocomplexes in human plasma. The nanocomplexes gave much better image contrast effects and longer stagnation time than that of commercial contrast agent in rat liver. A dose of 0.04 mmol of gadolinium per kilogram of body weight was sufficient to increase the MRI imaging intensities in rat livers by five-fold compared with the commercial Gd-DTPA. PLA-PEG/Gd-DTPA nanocomplexes could be prepared easily with small particle sizes. The nanocomplexes had high plasma stability, better image contrast effect, and liver targeting property. These results indicated that the PLA-PEG/Gd-DTPA nanocomplexes might be potential as molecular targeted imaging contrast agent.

Liquid-to-liquid relaxation of polystyrene melts investigated by low-frequency anelastic spectroscopy.

Polystyrene melts with a narrow distribution of molecular weights far above the glass transition have been investigated by use of low-frequency anelastic spectroscopy. A liquid-to-liquid relaxation occurs when the molecular weight (Mn) is either above or below the critical molecular weight (Mc) for chain entanglement. As the molecular weight increases, the relaxation temperature (Tp) increases and the movement of the polymer chain is easier for short chains than for long chains. In the range we investigated (Mn∼1.0 × 104-2.1 × 105), the relaxation time (τp) corresponding to the dissipation peak is related to the molecular weight by [Formula: see text]. This is consistent with theoretical prediction. We suggest that the dissociation of the chain clustering is responsible for the liquid-to-liquid relaxation.