丁苯胶乳的合成研究

以丁二烯和苯乙烯为单体、十二烷基硫醇为乳化剂,通过一步法合成了大粒径丁苯胶乳（SBR）.结果表明：乳化剂浓度、电解质浓度、固含量及单体加入方式是控制丁苯胶乳粒径大小的关键因素.通过适时补加乳化剂,选取适宜的电解质浓度、固含量及采用种子半连续加料方式有利于控制SBR粒径大小及分布.     

小角X射线散射研究乳胶分散液的微观结构

采用同步辐射小角X射线散射（SAXS）技术观察了2种不同乳胶体系的微观结构以及将其混合对结晶行为的影响。 结果表明,体积分数为50%的苯乙烯-丙烯酸丁酯共聚物乳胶液在室温下没有结晶。 通过对散射强度曲线的拟合,乳胶粒子的平均半径是76 nm,小于动态光散射的测量值（80 nm）。 然而,50%的苯乙烯-丁二烯共聚物乳胶液发生了结晶。 利用面心立方（fcc）结构和晶格常数为212 nm的晶格衍射进行拟合,发现散射曲线中的所有Bragg衍射峰均对应1个或多个晶面指数。 将2种乳胶液混合后各个衍射峰仍能分辨出来,这说明原始乳液中的部分微晶在混合过程中仍然稳定存在。     

Significant role of bacterial undecaprenyl diphosphate (C55-UPP) for rubber synthesis by Hevea latex enzymes

Washed bottom fraction (BF) membrane-bound particles of centrifuged fresh Hevea latex were found to be very active in rubber biosynthesis (RB). The washed BF membrane (WBM) showed higher RB activity and is strongly stimulated by anionic surfactants--more by DOC than SDS. WBM enzymes system can synthesize rubber either with allylic isoprenes (higher RB) or without (lower RB). Washed rubber particles (WRP), used generally in RB assays, had very low RB activity compared to the much higher activity observed for WBM. Bacterial undecaprenyl diphoshate (C(55)-UPP) was very active allylic initiator for rubber synthesis by WBM. Comparisons of allylic UPP with the shorter ones (C(15)-FPP, C(20)-GGPP) showed that UPP was the most effective. WBM activity orders were UPP > GGPP > FPP. The DOC activated WBM synthesized less polyprenyl intermediates (butanol extractable) but more final rubber product (toluene/hexane extract), different than FPP and GGPP. WBM enzymes were highly versatile in using diverse different allylics, but UPP was most preferable. WRP was found a little active for UPP with DOC, but still much lower than WBM. Rubber product analysis by RP-TLC with acetone/hexane solvent system showed that WBM was mostly rubber, but WRP was mainly the intermediates. Quantitative analysis showed that WBM labeled rubber was confined to the origin spot, different than WRP as mainly labeled intermediates. It was thus confirmed that the WBM plays the key role in RB functions, and not WRP as mostly reported. WBM served as the actual rubber synthesis site, and bacterial UPP was very good RB initiator.     

Nanoscale NMR velocimetry by means of slowly diffusing tracer particles

The resolution of NMR velocimetry is inherently limited by random displacements due to molecular self-diffusion, and has so far not extended below a few tens of microns. We report here an extension to the nanoscale domain, a result achieved by the use of slowly diffusing, NMR-visible core-shell latex particles. These particles comprise an oil core surrounded by a solid polymer shell, making spheres of diameter 370 nm. Using these particles in the annulus of a concentric cylinder Couette cell, we have measured flow-induced displacements down to a few hundreds of nanometers, allowing the observation of the solid-to-liquid transition of a glassy system. We envisage new possibilities for NMR velocimetry as an experimental tool for colloidal chemistry and physics.     

具有有界位势的Lagrange系统的周期解

本文考虑Lagrange系统 d/dt ?/?(q,q)-?/?q(q,q)=0 (?)这儿?(q,ξ)=1/2 wum form i,j=1 to n a_(ij)(q)eξξ-V(q),q∈R~n,ξ∈R~n 。假设位势函数V有界,并且lim V(q)/|q|~2 =δ>0,V(q)=V(-q),则系统(?)具有一个以适当大的正数T为周期的非平凡解。     

非线性退缩椭圆型方程dirichlet问题多重解的存在性

本文利用临界点理论,研究一类非线性退缩椭圆型方程dirichlet问题多解性.在嵌入非紧的条件下,证明泛函在给定集上满足 ( P S) 条件     

Effect of the structure of latex particles on adhesion. Part II: Analogy between peel adhesion and rheological properties of acrylic copolymers

This article, the second part of this series, concerns the development of an analogy between the peel behavior of pressure-sensitive adhesives and the dynamic mechanical properties of the corresponding copolymers. The adhesive copolymers used were synthesized by emulsion polymerization processes. Their physical and dynamic mechanical properties were characterized and presented in Part I of this series. In this study, an analogy was built up between the force in a peel test as a function of peel velocity, F_p(v_p), and the loss modulus of the adhesive as a function of the angular frequency in a dynamic mechanical experiment, G″(ω). This was done by superimposing the curves of F_p versus v_p and those of G″ versus ωβ₀/β, where β₀/β is a shift factor with β being a parameter in the Kaelble theory and β₀ being some reference value of the Kaelble parameter. When the curves of F_p ～ v_p and those of G″ ～ ωβ₀ were plotted together, they followed the same trend of variation. This analogy between G″(ωβ₀/β) and F_p(v_p) was further confirmed by the fact that the apparent activation energies of the primary glass transition for G″(ω) and F_p(v_p) are virtually the same, suggesting that the analogy between G″(ω) and F_p(v_p) is dictated by the glass transition. The existence of the above-mentioned analogy between G″(ω) and F_p(v_p) shows that the performance of an adhesive can be evaluated or predicted from the dynamical loss modulus of the corresponding (co)polymer. ©1995 John Wiley & Sons, Inc.     

Purification and Characterization of a Proteolytic Enzyme from Fig Latex

Ficin is an important component of plants in Ficus family such as fig latex. It is of special significance in medicine and industry because it exhibits activity throughout a wide range of temperature and pH values. In this work, we purified a component of ficin from the latex homogeneity of Shandong fig trees, and the properties of the purified ficin were studied. The current findings revealed that heavy metal ions were able to inhibit ficin, while DTT, L-cysteine, and β-ME were found to promote ficin activity. It was also observed that the half life of ficin at 65 °C was longer than 1 h and the Michaelis constant（Km） for casein hydrolyzation was determined to be 1.56 mg/mL. Our study shows that this purified ficin is a cysteine protease.     

Incorporation of Polyoxometalates Into Polystyrene Latex by Supramolecular Encapsulation and Miniemulsion Polymerization

Submicrometer polystyrene (PS) latex doped with functional polyoxometalates (POMs) has been elaborated via two steps. The first step is the electrostatic encapsulation of POMs by polymerizable surfactants through the replacement of counterions, forming the supramolecular complexes which are organic compatible. And the second step is the incorporation of the complexes into PS latex chemically by miniemulsion polymerization. TEM images indicate that POMs are evenly dispersed in the hybrid latex, and spectral characterizations demonstrate that the properties of POMs are well retained, leading to the functional features of polymer latex, such as luminescence and coloration. Furthermore, the supramolecular encapsulation and the hydrophobic latex matrix provide an effective protection to POMs, which greatly enhances their stability against the ambient acid or basic environment.

     

Enhancing mechanical properties of prevulcanized natural rubber latex via hybrid radiation and peroxidation vulcanizations at various irradiation doses

At present, there are three popular vulcanization processes being used in natural rubber latex industries, which are sulfur, radiation and peroxide vulcanization. Sulfur vulcanization produced products with superior mechanical properties compared to radiation and peroxide vulcanization. This paper discussed the effect of gamma irradiation dose on hybrid radiation and peroxidation vulcanizations in improving the mechanical properties of radiation vulcanized natural rubber latex (RVNRL). Latex compounding formulations are developed based on 2.5?parts per hundred rubber (phr) of hexanediol diacrylate (HDDA) as the sensitizer, 0.1?phr of tert-butyl hydroperoxide (t-BHPO) as the co-sensitizer and 2.5?phr of Aquanox LP antioxidant. The RVNRL was prepared and irradiated at various gamma radiation doses of 2, 4, 6, 8, 10 and 12?kiloGray (kGy). The rubber film obtained from irradiation at 6?kGy had tensile strength, modulus @ 500% and modulus @ 700% of 27.0, 3.0 and 11.0?MPa, respectively, which is more than 37% increment compared to the control film. Besides, the crosslink percentage of the rubber film showed 4% increment from 90% to 94%.