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Cross-linked polymer microspheres are widely used in biomedicine, flat panel display, analytical testing, in vitro diagnostics, semiconductor chips, and light diffusion. However, the process of preparing micron-sized cross-linked polymer microspheres is complicated, and it is difficult to obtain a high crosslinking degree conveniently. In this work, we applied post-crosslinking strategy to prepare poly (methyl methacrylate) (PMMA) microspheres having a high crosslinking degree by dispersion polymerization, while the method separated the polymerization process and cross-linking process of microspheres. In the method, the silane coupling agents containing double bonds were used as the comonomer in polymerization and hydrolyzed to form Si–O–Si cross-linked structure at the later stage. The obtained microspheres are not only highly cross-linked but also have uniform particle size distribution and good thermal stability. The produced cross-linked PMMA microspheres exhibit great light diffusion properties and might be employed as a light diffusion agent in a polycarbonate matrix. We prepared the cross-linked PMMA microspheres by post-crosslinking method and mixed the cross-linked PMMA microspheres with the matrix PC to obtain the light diffusers. [ABSTRACT FROM AUTHOR]

Dielectric properties and microstructural evolution of A/B sites co-substituted BaBi4Ti4O15 Aurivillius-type ferroelectric are reported. The non-stoichiometric BaBi4−xTi4−xM′2xO15+δ (M′ = Cu2+, V5+) ceramics exhibits the normal dielectric permittivity (~ 102) and classical plate-like grains. As the potassium and bismuth cations are introduced, giant dielectric permittivity (~ 104) and abnormal growth of grain can be obtained in the non-stoichiometric Ba1−yMyBi3.91Ti3.91(Cu1/3V2/3)0.18O15+δ (M = K+, Bi3+) ceramics. Giant dielectric permittivity together with abnormal growth of grain are dependent significantly on the component of the ceramics. The bimodal grain size model is used to clarify the mechanism of the giant dielectric properties. These results are valuable for developing the applications of Aurivillius oxide in the high-temperature multilayer ceramic capacitor. [ABSTRACT FROM AUTHOR]

BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics with Cu2+ and W6+ co-substitution for the B-site Ti4+ were prepared by using the solid-state reaction process. It was desirable that piezoelectric properties of the BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics could be improved by inducing the larger lattice distortion with the oxygen vacancy defects neutralized and restrained. Results of the X-ray diffraction analysis confirmed that crystal cell parameter c decreased obviously with the increase in the crystal cell parameter a. Curie temperature, resistivity, and piezoelectric properties of the BBT ceramics are improved by the copper and tungsten modification. The maximum value of piezoelectric coefficient (~ 30 pC/N) can be obtained in the BaBi4Ti4−x(Cu0.5W0.5)xO15 ceramics. [ABSTRACT FROM AUTHOR]

Cross-linked poly(methyl methacrylate) (PMMA) microspheres have been successfully prepared by using the asymmetric cross-linker allyl methacrylate (AMA) via dispersion polymerization. The influence of the AMA amount and polymerization process on the PMMA particle size and morphology has been studied thoroughly. It was found that micron-sized, cross-linked PMMA particles with narrow size distributions could be obtained by a semi-continuous process with the asymmetric cross-linker AMA. The obtained micron-sized, cross-linked PMMA particles could be further used as a light diffusion agent in a polycarbonate matrix, and their light diffusion properties were significantly enhanced by increasing the gel content in the cross-linked particles. Moreover, the influence of the polymerization process, cross-linker content in PMMA and PMMA content in the polycarbonate matrix on light diffusion was carefully investigated. The results showed that the PMMA particles containing 5.0 wt% AMA, obtained by semi-continuous polymerization, had a higher haze and gel content and exhibited a better light diffusion effect than did the other particles. [ABSTRACT FROM AUTHOR]

Here we reported the synthesis of polyethylene glycol 2000 monomethyl ether (PEG)ylated hyperbranched poly (amido amine) ( h-PAMAM-g-PEG) and the study of an elaborate control over the structure transition by solvents. The double hydrophilic hyperbranched copolymers could form micelles with h-PAMAM core and solvophilic PEG shell in tetrahydrofuran (THF). It was found that the micellization stage was prolonged if more PEG chains were anchored onto h-PAMAM cores. After cross-linking the h-PAMAM cores, well-dispersed hollow spheres were obtained when the micelles were transferred into water from THF. More grafted PEG chains on h-PAMAM may prohibit the creation of a hollow cage upon the swelling of the hydrophilic h-PAMAM cores. Such engineered hollow spheres also retained the pH-sensitive fluorescence characteristic, identical with the luminescent behavior of the free h-PAMAM molecules. H-PAMAM-g-PEG hollow spheres with pH-sensitive fluorescence have a potential application as a drug delivery vehicle for chemotherapy. [ABSTRACT FROM AUTHOR]

We investigated the feasibility and efficacy of hyperbranched polyamidoamine (hPAMAM) mediated human vascular endothelial growth factor-165 (hVEGF) gene transfer into skeletal myoblasts for cardiac repair. The hPAMAM was synthesized using a modified one-pot method. Encapsulated DNA was protected by hPAMAM from degradation for over 120 min. The transfection efficiency of hPAMAM in myoblasts was 82.6 ± 7.0% with cell viability of 94.6 ± 1.4% under optimal conditions. The hPAMAM showed much higher transfection efficiency ( P < 0.05) than polyetherimide and Lipofectamine 2000 with low cytotoxicity. The transfected skeletal myoblasts gave stable hVEGF expression for 18 days. After transplantation of hPAMAM-hVEGF transfected cells, apoptotic myocardial cells decreased at day 1 and heart function improved at day 28, with increased neovascularization ( P < 0.05). These results indicate that hPAMAM-based gene delivery into myoblasts is feasible and effective and may serve as a novel and promising non-viral DNA vehicle for gene therapy in myocardial infarction. [ABSTRACT FROM AUTHOR]