表面修饰乙烯－乙烯醇共聚物膜的“原地”聚离子复合化及其若干性能

表面修饰乙烯－乙烯醇共聚物膜的“原地”聚离子复合化及其若干性能张军，王大力，刘新三（天津市合成材料研究所，天津，３００２２０）李福绵（北京大学化学系，北京，１００８７１）关键词聚离子复合物，“原地”聚离子复合，磷酸酯化，乙烯－乙烯醇共聚物膜聚离子复合...     

表面“原位”聚离子复合修饰的乙烯-乙烯醇共聚物膜的结构

聚离子复合物(Polyionic complexes,PICs)是由聚正离子和聚负离子所构成的高度亲水的合成材料,可以通过不同聚离子的组合使其带有"净"电荷.因此,它具有优良的血液相容性.PIC透析膜对小分子电解质和低分子物质有很高的透过性[1],然而,在高含水状态下PIC离子键的水合使其强度明显降低,并且由于其只溶于一定组成的三组份屏蔽溶剂(Shielding solvent),因此,给加工制膜带来诸多不便.乙烯-乙烯醇共聚物(Ethylene-vinyl alcohol copolymer,EVAL)表现出一定的亲水性,并且高分子链中含疏水性链段,有一定的机械强度,是一种性能很好的成膜材料,由EVAL制成的膜已应用于血液过滤等领域[2].     

壳聚糖／褐藻酸钠聚离子复合膜的渗透汽化分离性能研究

以红外光谱和扫描电镜表征壳聚糖／褐藻酸钠聚离子复合膜的结构与表面形态。研究了该膜组成、料液浓度、温度等对乙醇－水溶液的渗透汽化分离性能的影响。实验结果表明，壳聚糖／褐藻酸钠聚离子复合膜不仅对乙醇－水溶液，而且对许多水溶性有机溶剂与水的溶液都具有很高的渗透汽化脱水的选择分离性能。     

A modification of the surface of the thin membranes of EVAL (ethylene vinylalcohol copolymer) by Langmuir-Blodgett films

The surface modification of the membrane as an artificial kidney made of two kinds of ethylene-vinylalcohol copolymers with 32 and 44 mol % contents of ethylene group (EVAL) have been studied by depositing the polymer monolayer on the membrane surface using the Langmuir-Blodgett technique.The permeability to PSS (physiological salt solution) and albumin rejection of the membranes were measured against the number of multilayers. The UFR (ultrafiltration rate) of PSS containing albumin decreased with the increase of the built up layers up to 2 layers and showed constant values from 3 to 10 layers of LB films.On the other hand, albumin rejection increased with the increase of built up layers. Albumin rejection for these deposited membranes of multilayer of EVAL-32 showed 21 times effectiveness more than that of ordinary membrane and 16 times for EVAL-44.Modification of the membrane has been performed by such a network structure formed by the built-up films.     

Effect of evaporation temperature on the formation of particulate membranes from crystalline polymers by dry-cast process

The membrane formation of crystalline poly(ethylene-co-vinyl alcohol) (EVAL), poly(vinylidene fluoride) (PVDF), and polyamide (Nylon-66) membranes prepared by dry-cast process was studied. Membrane morphologies from crystalline polymers were found to be strongly dependent on the evaporation temperature. At low temperatures, all the casting solution evaporated into a particulate morphology that was governed by the polymer crystallization mechanism. The rise in the evaporation temperature changed EVAL membrane structure from a particulate to a dense morphology. However, as the temperature increased PVDF and Nylon-66 membranes still exhibited particulate morphologies. The membrane structures obtained were discussed in terms of the characteristics of polymer crystallization in the casting solution theoretically. At elevated temperatures the crystallization was restricted for the EVAL membrane because the increase rate in the polymer concentration was fast relative to the time necessary for growth of nuclei. Nonetheless, the time available for PVDF and Nylon-66 with stronger crystalline properties was large enough to form the crystallization-controlled particulate structure that differed in particle size only. In addition, particles in the PVDF membrane were driven together to disappear the boundary, but those in the Nylon-66 membrane exhibited features of linear grain boundary. The difference in particle morphology was attributed to the Nylon-66 with the most strongly crystalline property. Therefore, the kinetic difference in the crystallization rate of the polymer solution play an important role in dominating the membrane structure by dry-cast process.     

Reversible electrochemical detection of nonelectroactive polyions

Selective extraction principles for the recognition of nonelectroactive polyions such as heparin and protamine exist, but the high ionic valency renders the extraction process irreversible. A response principle for the reversible detection of such polyions is proposed here. The extraction of the polyionic analyte to the membrane and its subsequent back-extraction is now controlled electrochemically. The principle is established with a protamine electrode, and excellent stability and reproducibility are demonstrated. This method has important implications for the design of chemical recognition principles for polyionic analytes.     

Eval membranes for blood dialysis

Both dry- and wet-process were employed for preparing membrane of ethylene-vinylalcohol copolymer (EVAL) for blood dialysis. Asymmetric and symmetric, dense or porous membranes were prepared by the dry-process. The relationship between the structure of membranes and the experimental variables is explained by using a solubility curve model. This model predicts the membrane structure successfully under various conditions, including the change of temperature of the environment, the solvent system and the temperature of polymer solution. For wet-processes, the casting solutions were coagulated in a precipitation bath (water). Three different structures were obtained: finger type, sponge type and particle-bonded type. The cloud point experiment and the polymer segment motion help to understand and control the membrane structure. Some properties of the EVAL membrane for blood dialysis are shown. It is comparable with or better than the commercialized one. This study may prove useful in determing the controlling parameters for the preparation of membranes from other polymers.     

树脂填充EVAL纤维吸附剂的制备及其吸附性能表征

采用具有亲水性的乙烯-乙烯醇共聚物(EVAL)作为纤维吸附剂基质材料,粉末型Lewatit阳离子交换树脂CNP80ws为功能材料,采用可控相分离方法,制备了不同表面形态结构的树脂填充EVAL吸附剂.当使用外部液体调控相分离过程时,在纤维的表面形成了粗糙的开孔结构,并且随树脂的填充量提高纤维表面的粗糙度与开孔度有所提高.研究结果表明:树脂填充EVAL纤维吸附剂具有较大的吸附容量与较高的脱附率,其吸附容量不低于53.9mg BSA/g吸附剂(树脂填充量50%).     

Chitosan nanoparticle as protein delivery carrier--systematic examination of fabrication conditions for efficient loading and release

Chitosan nanoparticles fabricated via different preparation protocols have been in recent years widely studied as carriers for therapeutic proteins and genes with varying degree of effectiveness and drawbacks. This work seeks to further explore the polyionic coacervation fabrication process, and associated processing conditions under which protein encapsulation and subsequent release can be systematically and predictably manipulated so as to obtain desired effectiveness. BSA was used as a model protein which was encapsulated by either incorporation or incubation method, using the polyanion tripolyphosphate (TPP) as the coacervation crosslink agent to form chitosan-BSA-TPP nanoparticles. The BSA-loaded chitosan-TPP nanoparticles were characterized for particle size, morphology, zeta potential, BSA encapsulation efficiency, and subsequent release kinetics, which were found predominantly dependent on the factors of chitosan molecular weight, chitosan concentration, BSA loading concentration, and chitosan/TPP mass ratio. The BSA loaded nanoparticles prepared under varying conditions were in the size range of 200-580nm, and exhibit a high positive zeta potential. Detailed sequential time frame TEM imaging of morphological change of the BSA loaded particles showed a swelling and particle degradation process. Initial burst released due to surface protein desorption and diffusion from sublayers did not relate directly to change of particle size and shape, which was eminently apparent only after 6h. It is also notable that later stage particle degradation and disintegration did not yield a substantial follow-on release, as the remaining protein molecules, with adaptable 3-D conformation, could be tightly bound and entangled with the cationic chitosan chains. In general, this study demonstrated that the polyionic coacervation process for fabricating protein loaded chitosan nanoparticles offers simple preparation conditions and a clear processing window for manipulation of physiochemical properties of the nanoparticles (e.g., size and surface charge), which can be conditioned to exert control over protein encapsulation efficiency and subsequent release profile. The weakness of the chitosan nanoparticle system lies typically with difficulties in controlling initial burst effect in releasing large quantities of protein molecules.     

Synthesis and Biomedical Properties of Poly-[(Ethylene-Vinylalcohol)-g-Acrylamide]

This paper deals with the graft copolymerization of acrylamide (AM) onto ethylene-vinyl alcohol copolymer (EVAL) film initiated by cerium(IV) ion. It was found that both the chemical and diffusion factors had influences on the graft reaction. The reaction was initiated on the surface and then penetrated inward as the grafting percentage was increased. The permeability of urea through the grafted EVAL film was improved compared to that of the original film as was the blood compatibility.