W/O、O/W型卵磷脂乳状液对CaCO3晶型的影响

Ｗ／Ｏ、Ｏ／Ｗ型卵磷脂乳状液对ＣａＣＯ３晶型的影响姚松年＊缪炜童华张操墨熊海涛（武汉大学分析测试科学系，武汉４３００７２）关键词：卵磷脂乳状液ＣａＣＯ３碳酸钙可以方解石、霰石、球霰石、胶状碳酸钙等形态存在且依次稳定性降低。珍珠是生物矿化产物，除氨基酸...     

Synthesis and characterization of thermosensitive copolymers for oral controlled drug delivery

Poly(N-isopropylacrylamide) (PNIPAAm) copolymers were synthesized in order to obtain co-polymers with a phase transition temperature slightly higher than the physiological temperature, as required by a new drug delivery concept described in a previous paper. Six hydrophilic comonomers bringing about a rise of the phase transition temperature were evaluated. The synthesized copolymers were characterized and the influence of the type and of the amount of the used comonomer on the phase transition temperature was discussed. Among the comonomers, Acrylamide (AAm), N-methyl-N-vinylacetamide (MVA), N-vinylacetamide (NVA), and N-vinyl-2-pyrrolidinone (VPL) were found to be capable to raise the phase transition temperature to a value slightly higher than 37 °C and to have adequate phase transition behavior. The selected four copolymers were subjected to an additional purification step that should make them fit to use as a controlling agent in drug delivery systems.     

Preparation and characterization of poly(ethyl acrylate)/bentonite nanocomposites by in situ emulsion polymerization

Transparent poly(ethyl acrylate) (PEA)/bentonite nanocomposites containing intercalated–exfoliated combinatory structures of clay were synthesized by in situ emulsion polymerizations in aqueous dispersions containing bentonite. The samples for characterization were prepared through direct‐forming films of the resulting emulsions without coagulation and separation. An examination with X‐ray diffraction and transmission electron microscopy showed that intercalated and exfoliated structures of clay coexisted in the PEA/bentonite nanocomposites. The measurements of mechanical properties showed that PEA properties were greatly improved, with the tensile strength and modulus increasing from 0.65 and 0.24 to 11.16 and 88.41 MPa, respectively. Dynamic mechanical analysis revealed a very marked improvement of the storage modulus above the glass‐transition temperature. In addition, because of the uniform dispersion of silicate layers in the PEA matrix, the barrier properties of the materials were dramatically improved. The permeability coefficient of water vapor decreased from 30.8 × 10^?6 to 8.3 × 10^?6 g cm/cm² s cmHg. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1706–1711, 2002     

Ethylene–vinyl acetate semi-batch emulsion copolymerization: Experimental design and preliminary screening experiments

Ethylene–vinyl acetate emulsion copolymers are useful materials for paint, adhesive, and coating applications. The kinetics of their production remain largely unstudied, probably due to the inherent difficulties associated with pressure polymerizations. Polymerizations at elevated pressures are in general more difficult to understand and control, and relatively more expensive since one has to consider the added cost of increased safety precautions. Reported here are the preliminary results of an extensive experimental investigation of the variables which govern the ethylene–vinyl acetate emulsion process. Two redox initiator systems have been identified as more suitable for the polymerization process. Two buffer systems, namely sodium acetate/acetic acid and potassium phosphate, have been used to effectively control pH. The addition of n-hexane has offered an effective method of enhancing the ethylene content in the copolymer produced. Several other important variables including agitation/mixing and emulsifier type and concentration have been identified and are discussed. These screening experimental observations have aided in the selection of suitable design levels for future, more focused experimentation to quantify the effects of reaction variables on the latex and copolymer properties of interest. A review of the existing literature on ethylene–vinyl acetate copolymer properties and processes is also included. © 1993 John Wiley & Sons, Inc.     

含聚氧化乙烯嵌段的三元多嵌段共聚物的合成和性能

用聚乙二醇、聚丙二醇、遥爪羟基聚苯乙烯和二氯甲烷在氢氧化钾存在下合成了氧亚甲基连接的聚氧化乙烯－聚氧化丙烯－聚苯乙烯多嵌段聚合物；并研究其乳化性能和相转移催化性能。     

乳化液膜法粗萘精制机理的研究

本文采用水和表面活性剂组成的乳化液膜对粗萘精制机理进行了研究，通过考察表面活性剂类型浓度以及内外相比例对液膜选择性和渗透速率的影响，建立了粗萘在液膜精制中的热力学模型。实验结果表明，粗萘中硫茚，甲基萘在液膜中具有较大的分离系数；表面活性剂类型是影响液膜选择性的主要因素；表面活性剂浓度和内外相比例则影响液膜的渗透能力。     

乳液法制备球形锰酸锂及其影响因素

文章介绍了目前锂离子电池正极材料球形化制备的情况，对乳液法二次造粒的方法及其机理进行了初步探讨。以微波合成法制备的LiMn2O4作为一次颗粒，采用一种特殊的乳液法二次造粒，初步制备了球形LiMn2O4正极材料。对二次造粒的产物进行了SEM、XRD分析，测试了其振实密度，发现在二次造粒过程中一次颗粒有一定生长，二次颗粒球状形貌还不够理想，分析了原因，为进一步研究打下基础。     

Ultra‐High Molecular Weight Alpha‐Amino Poly(Methyl Methacrylate) with High Tg through Emulsion Polymerization by Using Transition Metal Cation–Tertiary Amine Pairs as a Mono‐Centered Initiator

As some complexes of transition metal cations in high oxidation state can oxidize tertiary amines under proper conditions into aminoalkyl radicals to initiate polymerization of electron‐deficient vinylic monomers, they form mono‐centered redox‐initiation pairs for preparation of 100% alpha‐amino telechelic polymer. Radical emulsion polymerization of methyl methacrylate (MMA) is performed by using water‐soluble amines as a reducing agent and Fe^III or Cu^II as an oxidizing agent. Tertiary amines such as 2‐(N,N‐dialkylamino)ethanol and N,N,N′,N′‐tertramethylethylenediamine exhibit a higher initiation activity. Monomer conversion can reach 80% in 8 h and 95% in 16 h, leading to PMMA with an absolute weight‐average molecular weight above 1.5 × 10⁶ g mol^?1. The alpha‐amino terminal functionality is verified by ultraviolet‐induced diarylketone‐initiated radical bock polymerization by using these PMMA chains as the macro‐sensitizer. Such a facile heterogeneous technique results in syndiotactic‐rich high‐T_g PMMA (rr > 50%, T_g = 124–127 °C). PMMA chains may be oxidized by Fe^II–O₂ complexes to initiate further radical polymerization, leading to PMMA with a long‐chain branched architecture.

     

The Influence of Xanthate‐Based Transfer Agents on Styrene Emulsion Polymerization: Mathematical Modeling and Model Validation

A mathematical model was developed to account for the evolution of polymer product attributes in the emulsion polymerization of styrene. The effects of transfer agent, surfactant, initiator and temperature were investigated. Polymerization rate, and particle size decreased with increasing concentration of the transfer agent. The polymerization rate increased with increasing surfactant and initiator concentrations, while an increase in temperature led to a decrease of molecular weight but an increase of polymerization rate and particle size. Chain extension was successfully achieved in the presence of our RAFT agent. The model predictions compared well with our experimental results.

     

Energy Efficient Emulsion Polymerization Strategies

Polymerization strategies aiming at further reducing the environmental impact of the already “green” emulsion polymerization process were investigated. Life cycle assessment showed that non‐isothermal strategies starting at low temperature resulted in an environmental impact lower than the isothermal ones. Nevertheless, the major part of the environmental impact was due to raw materials. The effect of the polymerization strategy on polymer microstructure was investigated.