Blends of chlorinated isotactic polypropylene with poly(ethylene-co-vinyl acetate) II. Phase studies of the miscible blends

By measuring T_g, T_m and T_c (cloud point) phase diagrams for the four miscible blends of chlorinated isotactic polypropylenes (chlorine content 39.2 (CPP-40) and 49.8 wt.-% (CP-50)) with Poly(ethylene-co-vinyl acetate)s (vinyl acetate contents 40 (EVA-40) and 45 wt.-% (EVA-45)) were investigated. The blend of CPP-50 with EVA-40 was the most compatible of the four blend pairs.     

Aging Behavior of xPb(Fe2/3W1/3)O3· (1 –x)Pb(Fe1/2Nb1/2)O3 Ceramic

The aging behavior of a series of lead perovskite dielectrics with the compositions x Pb(Fe_2/3W_1/3)O₃·(1 – x )Pb(Fe_1/2-Nb_1/2)O₃, where 0 ≤ x ≤ 1, and the effect of dopants were studied. Below the Curie temperature ( T _c), the capacitance and the dissipation factor (tan δ) decrease approximately linearly with logarithmic time. The aging rate depends on the temperature difference, Δ T , between the aging temperature and T _c, and on the dopant concentration, but is independent of the measurement frequency between 1 and 1000 kHz. The maximum aging rate is about 3% per decade of time for capacitance and 5% per decade for tan δ at 1 mol% dopant concentration, and increases to 6.3% for capacitance and 8.5% for tan δ at 0.7 mol% dopant concentration. These results are consistent with an aging mechanism caused by changing ferroelectric domain structure with time, as proposed for BaTiO₃.     

Effect of solution properties on nanofibrous structure of electrospun poly(lactic‐co‐glycolic acid)

Electrospinning of poly(lactic‐co‐glycolic acid) (PLGA) in chloroform or 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was investigated, focusing on its solution parameters, to develop nonwoven biodegradable nanofibrous structures for tissue engineering. PLGA nanofibers were obtained by electrospinning of 15 wt % PLGA solution and the resulting average fiber diameters were varied with the range of 270–760 nm, depending on solution property. When small amounts of benzyl triethylammonium chloride (BTEAC) was added to the PLGA/chloroform solution, the average diameter was decreased from 760 to 450 nm and the fibers were densely amounted in a straight shape. In addition, the average fiber diameter (270 nm) of nanofibers electrospun from polar HFIP solvent was much smaller than that (760 nm) of nanofibers electrospun from nonpolar chloroform solvent. Therefore, it could be concluded that conductivity or dielectric constant of the PLGA solution was a major parameter affecting the morphology and diameter of the electrospun PLGA fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1214–1221, 2006     

A kinetic study on medium temperature desulfurization using a natural manganese ore

Natural manganese ores were selected as raw materials for the desulfurization sorbent because of economical efficiency and high reactivity on hydrogen sulfide. Initial reaction rates between H₂S and desulfurization sorbent of natural manganese ores were determined in a temperature range of 400-800°C using a thermobalance reactor. All reactions were first order with respect to H₂S and were expressed by the Arrhenius relation. When the sulfidation reaction was controlled by diffusion, the temperature dependence of the effective diffusivity was given by the Arrhenius equation. Activation energies and frequency factors were obtained from the product layer diffusion coefficient of various sorbents by plotting as an Arrhenius equation form. Several additives were mixed to improve the sulfidation capacity, and NiO was the best additive.     

Characterization and physical properties of polymethylphenylsilsesquioxane (PMPSQ) and hydroxyl‐functionalized polystyrene (PS–OH) hybrids

Polymethylphenylsilsesquioxane (PMPSQ–OH) and trimethylsilyl end‐blocked PMPSQ (PMPSQ–EC) were prepared. The thermal decomposition behavior of these polymers was studied by thermogravimetric analysis (TGA) and FT‐Raman spectroscopy. Hydroxyl‐functionalized polystyrene (PS–OH) was also prepared by anionic living polymerization. Thin hybrid films of PMPSQ/PS–OH with various blend ratios were obtained by spin‐coating on freshly cleaned glass. The surface morphology of the hybrid films was investigated by atomic force microscopy (AFM). In 80/20 PMPSQ/PS–OH hybrid film, the PS–OH component produced a very uniformly dispersed phase. This hybrid film contained small domains of PS–OH whose size ranged from 60 to 80 nm. As the content of PS–OH was increased, the domain morphology coarsened and phase inversion took place around 50 wt %. In the phase‐inversed system, the PMPSQ‐rich phase was uniformly distributed in the PS–OH‐rich continuous phase. In addition, temperature‐dependent dielectric properties of PMPSQ/PS–OH hybrids were investigated. Relaxation of the hybrids was observed with an increasing content of the PS–OH component due to the amorphous glass transition behavior of PS–OH. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2801–2812, 2003     

贮存稳定的EVA/SBS复合改性沥青的性能研究

利用乙烯-醋酸乙烯酯无规共聚物（EVA）与苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）对沥青进行复合改性并对其进行动态硫化处理，测试了动态硫化前后试样的针入度、软化点、5℃延度、贮存稳定性等常规性能．并利用应变控制流变仪与光学显微镜对试样做了动态力学性能分析和相形态观察。通过对动态硫化前后试样性能变化的分析比较，结果表明：动态硫化后，试样的低温性能良好，而且由于试样内部弹性交联网络的形成，使试样的高温物理机械性能及高温贮存稳定性均获得了提高，降低了试样的温度敏感性。     

A novel microneedle array for the treatment of hydrocephalus

We present a microfabricated 10 by 10 array of microneedles for the treatment of a neurological disease called communicating hydrocephalus. Together with the previously reported microvalve array, the current implantable microneedle array completes the microfabricated arachnoid granulations (MAGs) that mimic the function of normal arachnoid granulations. The microneedle array was designed to enable the fixation of the MAGs through dura mater membrane in the brain and thus provide a conduit for the flow of cerebrospinal fluid. Cone-shaped microneedles with hollow channels were fabricated using a series of microfabrication techniques: SU-8 photolithography for tapered geometry, reactive ion etching for sharpening the microneedles, 248 nm deep UV excimer laser machining for creating through-hole inside the microneedles, and metal sputtering for improved rigidity. Puncture tests were conducted using porcine dura mater and the results showed that the fabricated microneedle array is strong enough to pierce the dura mater. The in vitro biocompatibility test result showed that none of the 100 outlets of the microneedles exposed to the bloodstream were clogged significantly by blood cells. We believe that these test results demonstrate the potential use of the microneedle array as a new treatment of hydrocephalus.     

有机硅与丙烯酸接枝技术现状

本文综述了近期国内7种有机硅丙烯酸系接枝聚合物的研究工艺技术,其产品现已广泛应用于涂料、粘合剂、皮革、纺织、造纸等行业。阐述了各种工艺所使用的原材料及接枝过程中主要影响因素、并对技术成果进行了综合性分析,总结了该系列产品优异性能带来的美好发展前景。     

Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of high‐molecular‐weight poly(vinyl alcohol) with high yield by solution polymerization of vinyl acetate in methanol using 4,4′‐azobis(4‐cyanovaleric acid)

Vinyl acetate (VAc) was solution‐polymerized at 40°C and 50°C using 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) as an initiator and methanol as a solvent, and effects of polymerization temperature and initiator concentration were investigated in terms of conversion of VAc into poly (vinyl acetate) (PVAc), degree of branching (DB) for acetyl group of PVAc, and molecular weights of PVAc and resulting poly(vinyl alcohol) (PVA) obtained by saponifying with sodium hydroxide. Slower polymerization rate by adopting ACVA and lower viscosity by methanol proved to be efficient in obtaining linear high‐molecular‐weight (HMW) PVAc with high conversion and HMW PVA. PVA having maximum number–average degree of polymerization (P_n) of 4300 could be prepared by the saponification of PVAc having maximum P_n of 7900 polymerized using ACVA concentration of 2 × 10^?5 mol/mol of VAc at 40°C. Moreover, low DB of below 1 could be obtained in ACVA system, nevertheless of general polymerization temperatures of 40°C and 50°C. This suggests an easy way for producing HMW PVA with high yield by conventional solution polymerization without using special methods such as low‐temperature cooling or irradiation. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 4831–4834, 2006