分散共聚法制备特殊形态高分子微球的研究

以聚乙二醇 (PEG)大分子单体为反应性稳定剂 ,在丙烯腈的分散共聚反应中添加少量苯乙烯以形成疏水性核 ,制备得到了亚微米级高分子微球 .透射电子显微镜研究表明 ,该高分子微球具有特异的形态结构 .同时研究了分散共聚体系中各种反应因素对微球形态和直径的影响 ,结果表明 ,苯乙烯单体的添加量、PEG大分子单体的浓度及分子量、混合溶剂的组成对微球直径和形态均有明显的影响 .X 射线光电子能谱 (XPS)研究结果表明 ,微球表面聚集有亲水性PEG链 ,核为疏水的聚 (丙烯腈 苯乙烯 ) ,即形成的特异形态的PEG接枝高分子微球亦为复合型结构     

Structural regulation of a peptide-conjugated graft copolymer: a simple model for amyloid formation

The self-assembly of peptides and proteins into beta-sheet-rich high-order structures has attracted much attention as a result of the characteristic nanostructure of these assemblies and because of their association with neurodegenerative diseases. Here we report the structural and conformational properties of a peptide-conjugated graft copolymer, poly(gamma-methyl-L-glutamate) grafted polyallylamine (1) in a water-2,2,2-trifluoroethanol solution as a simple model for amyloid formation. Atomic force microscopy revealed that the globular peptide 1 self-assembles into nonbranching fibrils that are about 4 nm in height under certain conditions. These fibrils are rich in beta-sheets and, similar to authentic amyloid fibrils, bind the amyloidophilic dye Congo red. The secondary and quaternary structures of the peptide 1 can be controlled by manipulating the pH, solution composition, and salt concentration; this indicates that the three-dimensional packing arrangement of peptide chains is the key factor for such fibril formation. Furthermore, the addition of carboxylic acid-terminated poly(ethylene glycol), which interacts with both of amino groups of 1 and hydrophobic PMLG chains, was found to obviously inhibit the alpha-to-beta structural transition for non-assembled peptide 1 and to partially cause a beta-to-alpha structural transition against the 1-assembly in the beta-sheet form. These findings demonstrate that the amyloid fibril formation is not restricted to specific protein sequences but rather is a generic property of peptides. The ability to control the assembled structure of the peptide should provide useful information not only for understanding the amyloid fibril formation, but also for developing novel peptide-based material with well-defined nanostructures.     

Macromonomer synthesis using α‐(2‐methyl‐2‐phenylpropyl)acrylates as addition–fragmentation chain‐transfer agents expelling the cumyl radical

α‐(2‐Methyl‐2‐phenylpropyl)acrylate (RS‐2) was examined as a C? C bond‐cleavage type addition–fragmentation chain transfer (AFCT) agent in the benzene solution polymerizations of styrene (St), ethyl methacrylate (EMA), and cyclohexyl acrylate (CHA) with the objective of achieving efficient macromonomer synthesis by radical polymerization. The AFCT efficiency was evaluated in terms of the decrease in the number‐average molecular weight (M_n) upon the addition of the AFCT agent and the number of unsaturated end groups introduced per chain (f). The AFCT efficiency was rationalized by the consideration of the relative importance of AFCT as an end‐forming event and the competition between ‐fragmentation and crosspropagation as adduct radical reaction pathways. In St and EMA polymerizations at 60 °C, RS‐2 resulted in higher f values and lower M_n values than methyl α‐(2‐methyl‐2‐carbomethoxypropyl)acrylate (MMA‐2), and this suggested the facilitation of ‐fragmentation due to the expulsion of the more stable cumyl radical from the RS‐2 adduct radical. Higher f values were observed for MMA‐2 than for RS‐2 in CHA polymerization because of unsaturated end group formation by ‐fragmentation of midchain radicals. However, RS‐2 resulted in lower M_n values for poly(CHA) than MMA‐2 because of a smaller contribution of crosspropagation. Retardation in the presence of the AFCT agents was affected by the balance between b‐fragmentation and crosspropagation and by the addition rate of the propagating radical to the AFCT agent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6021–6030, 2004     

β-Cyclodextrin epichlorohydrin copolymer as a solid-phase extraction adsorbent for aromatic compounds in water samples

A novel solid-phase extraction (SPE) procedure for trace aromatic compounds in water samples has been developed using 12 aromatic compounds as model compounds and GC-MS and UV spectrophotometry for detection. The method is based on the fact that β-cyclodextrin (β-CD) epichlorohydrin (ECH) copolymer (β-CDEP) can extract non-ionized aromatic compounds quantitatively from aqueous samples. The polymer used is a colorless, transparent and insoluble solid with a maximum capacity of 0.82 μmol aromatic compounds per gram. It was synthesized by co-polymerization of β-CD and ECH and characterized by FT-IR and UV. β-CDEP does not contain double bonds, and therefore it does not have appreciable absorbance in the UV region. The optimum pH range for the extraction of aromatic compounds is 2.5-5.0. The method has high extraction efficiency with the recoveries between 90 and 101% for aromatic compounds at 0.02-1.67 ppm levels, and the analytes can be easily eluted by methanol washing after preconcentration.     

Polymer blends based on the β-modification of polypropylene

iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer.     

嵌段共聚物/均聚物共混体系的结晶行为 I. 非球状共聚物胶束的作用

将Leibler, Whitmore和Mayes等近期关于非晶嵌段共聚物“稀固体溶液”的理论应用于嵌段聚共聚物结晶型“稀固体溶液”结晶行为的研究。发现球状共聚物胶束既可起成核剂作用, 也可起抑制成核作用。报导了当共聚物胶束由球形变为非球形时, 共聚物胶束的上述作用都会发生较大的变化, 并根据Leibler和Mayes分别提出的球形和非球形胶束理论解释了这一实验现象。     

聚膦腈-g-聚己内酯共聚物的合成与表征

通过三甲基碘硅烷与聚二(2-甲氧基乙氧基)膦腈侧链上的醚键反应后水解得到侧链含部分羟基的聚膦腈,然后利用聚膦腈的侧链羟基在异辛酸亚锡催化作用下,引发己内酯单体开环聚合制备了聚膦腈-g-聚己内酯共聚物.该共聚物中聚己内酯链段的接枝率和侧链长度可通过改变三甲基碘硅烷和己内酯单体的投料来控制.     

含疏水链节的聚N-异丙基丙烯酰胺共聚物的温敏性

采用溶液聚合法合成了一系列N-异丙基丙烯酰胺(NIPAM)与甲基丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯或甲基丙烯酸丁酯的无规共聚物,用浊度观测法和光散射法测定了不同共聚物水溶液的温敏相转变行为.结果表明:所得共聚物的低临界溶解温度(LCST)均低于均聚物PNIPAM的,酯类单体的结构和含量对共聚物的LCST有显著影响,其中酯基上的烷基对共聚物LCST的影响能力大于丙烯酸酯α位上的烷基,前者对增大共聚物的疏水性有更大贡献.通过NIPAM与特定丙烯酸酯单体进行无规共聚可以合成转变温度低于PNIPAM均聚物且具有预设LCST数值的水溶性温敏聚合物.     

聚合物受限结晶的研究进展

随着纳米材料研究的迅速发展,聚合物由于其分子固有的纳米尺度结构,无论作为纳米器件或在模板应用方面都受到广泛瞩目.在微纳领域的应用中,特定受限环境下,结晶聚合物的结晶行为也因此受到广泛关注.本文从均聚物(及无规共聚物)和半晶型嵌段聚合物两方面总结了近年来聚合物受限结晶领域的研究进展.对于均聚物和无规共聚物,人们主要关注其在薄膜、超薄膜条件下的受限结晶性能,关注点为随着膜厚减小而引入的空间效应和界面效应对聚合物结晶性能的影响.而对于半晶型嵌段共聚物受限结晶的研究则多从本体出发,来研究纳米相分离与结晶的竞争过程、纳米相分离区域对于可结晶嵌段结晶生长的几何限制(空间效应)以及嵌段连接点(结晶嵌段的末端)对于结晶嵌段结晶行为的影响.