双组分水性聚氨酯涂膜交联密度的研究

通过耐溶剂擦拭实验、溶胀率实验、盖尔分率实验、红外光谱、扫描电子显微镜(SEM)和差示扫描量热仪(DSC)测试等方法研究了不同玻璃化温度(Tg)的羟基组分、n(—NCO)∶n(—OH)及不同固化时间对双组分水性聚氨酯涂膜交联密度的影响。结果表明:羟基组分的Tg对涂膜的交联密度有较大影响,Tg为22℃的羟基丙烯酸分散体和水性HDI基固化剂交联的涂膜具有最大的交联密度;水性双组分聚氨酯涂膜在25℃条件下干燥7 d可达到最大的耐溶剂擦拭次数,异氰酸酯固化剂和羟基分散体的n(—NCO)∶n(—OH)值为1.5~2.0时制得的涂膜有较好的交联密度。     

制革生产过程中水的处理与回用

我国淡水资源短缺,水对于被称为高耗水、高污染的制革业的生存和发展有着重要的意义。制革过程中的中水回用可以有效节约水资源,降低污染,有利于实现制革业的清洁化生产。     

室温交联型水性聚氨酯皮革涂饰剂的制备及应用

以异佛尓酮二异氰酸酯(IPDI)、聚酯二元醇(PCL)及2,2-二羟甲基丙酸(DMPA)为主要原料合成了聚氨酯预聚体,引入含酮羰基的自制双羟基化合物(DDP)作为交联剂,并加入3-氨丙基三乙氧基硅烷(KH550)改性,制备了稳定的水性聚氨酯(WPU)皮革涂饰剂。采用傅立叶变换红外光谱(FTIR)和热性能分析(TGA)对水性聚氨酯的结构进行了表征,并探讨了KH550用量及酮肼交联对聚氨酯涂饰革物理性能的影响。结果表明:经改性WPU涂饰后的皮革抗张强度增大,涂层耐折牢度、耐干湿擦性能得到明显改善。     

The stability and functionality of chemically crosslinked microtubules

A variety of bifunctional crosslinking agents have been explored for stabilizing microtubule shuttles used for the active transport of nanomaterials in artificial environments. Crosslinking agents that target amine residues form intertubulin crosslinks that produce crosslinked microtubules (CLMTs) with structural and functional lifetimes that can be up to four times as long as those achieved with taxol stabilization. Such CLMTs are stable at temperatures down to -10 degrees C, are resistant to depolymerization induced by metal ions such as Ca2+, and yet continue to be adsorbed and transported by self-assembled monolayers containing the motor protein kinesin. However, crosslinkers that target cysteine residues depolymerize the MTs, probably by interfering with the guanosine triphosphate binding site. The impact of crosslink attributes, including terminal group chemistry, chain length, crosslink density, and specific location on the tubulin surface, on microtubule stability and functionality are discussed.     

Characteristic role of crosslinker on thermally induced volumetric contraction–expansion processes in poly(N‐isopropylacrylamide) networks and water systems

In this work, the degree of crosslinking on the volumetric contraction–expansion processes of hydrogels made of poly(N‐isopropylacrylamide) (NIPA) (initial amount: C_m) with varied amount (z) of crosslinking agent methylene‐bis‐acrylamide (BIS) in reference to most commonly used NIPA gel that was synthesized with C_m = 700 mM and z = 8.6 mM was investigated by applying our recently developed pycnometry. We focused on characteristic role of four polymeric NIPA residues directly bonded to a single BIS molecule by evaluating the total volume of gels per four NIPA residues directly bonded to a BIS molecule, plus associated water [ν_sp(gel)(NIPA)_bonded)(T)], and the corresponding number of water molecules per four NIPA residues [N_s(gel)(NIPA)_bonded)(T)]. We elucidated how these quantities characteristically contribute to changes in the volumetric contraction–expansion processes of hydrogels. A comparison of these quantities with the corresponding quantities for (NIPA)_unbonded residues clearly revealed a significant structural difference between (NIPA)_bonded and (NIPA)_unbonded. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reinforcement of polyurethane/epoxy interpenetrating network nanocomposites with an organically modified palygorskite

An organophilic palygorskite (o‐PGS) prepared by the treatment of natural palygorskite with hexadecyl trimethyl ammonium bromide was incorporated into interpenetrating polymer networks (IPNs) of polyurethane (PU) and epoxy resin (EP), and a series of PU/EP/clay nanocomposites were obtained by a sequential polymeric technique and compression‐molding method. X‐ray diffraction and scanning electron microscopy analysis showed that adding nanosize o‐PGS could promote the compatibility and phase structure of PU/EP IPN matrices. Tensile testing and thermal analysis proved that the mechanical and thermal properties of the PU/EP IPN nanocomposites were superior to those of the pure PU/EP IPN. This was attributed to the special fibrillar structure of palygorskite and the synergistic effect between o‐PGS and the IPN matrices. In addition, the swelling behavior studies indicated that the crosslink density of PU/EP IPN gradually increased with increasing o‐PGS content. The reason may be that o‐PGS made the chains more rigid and dense. As for the flame retardancy, the PU/EP nanocomposites had a higher limiting oxygen index than the pure PU. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of electron‐beam irradiation on ethylene–methyl acrylate copolymer

Ethylene–methyl acrylate copolymer (Elvaloy 1330) was irradiated by an electron beam at different levels of radiation both in the presence and absence of a trimethylolpropane trimethacrylate sensitizer at various dosages of incorporation. The mechanical, thermal, and electrical properties of these samples were compared. The mechanical properties were observed to reach an optimum maximum around 6 Mrad of irradiation and 1 phr of sensitizer incorporation. Furthermore, an increase in either the radiation dose or the sensitizer level helped very little to further modify the properties. The thermal properties as determined by the thermogravimetric analysis and differential scanning calorimetry studies were quite supportive of the observation made during the study of the mechanical properties. The thermal stability of the irradiated samples underwent an increase with increasing electron‐beam dosage. In a manner similar to those of the mechanical properties, the increase in thermal stability was found to reach a maximum at a particular level of treatment and sensitizer incorporation, beyond which there was marginal or no effect at all. The α transition temperature underwent a substantial increase with increasing crosslink density, as evidenced by the increase in gel content with increasing proportion of electron‐beam radiation dose. The other glass‐transition temperature, however, appeared to remain unaffected. The electrical properties, as described by the dielectric constant, volume resistivity, and breakdown voltage, appeared to be affected very little by the electron‐beam radiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Separation and preconcentration of some heavy‐metal ions using new chelating polymeric hydrogels

Two new chelating polymeric hydrogels, crosslinked polyacrylamide/triethylenetetraamine/CS₂Na (hydrogel I) and crosslinked polyacrylamide/diethylenetriamine/CS₂Na (hydrogel II), were prepared by the transamidation and dithiocarbamylation of crosslinked polyacrylamide. The products were characterized with elemental analysis and IR spectroscopy. In both polymeric hydrogels, the optimum pH for the removal of Cd(II), Pb(II), and Zn(II) ions ranged from 7 to 8, from 6 to 7, and from 7 to 8, respectively. The sorption isotherms of the investigated metal ions on the prepared hydrogels were developed, and the equilibrium data fitted the Langmuir and Freundlich isotherm models well. At the optimum pH for each metal ion, the maximum sorption capacities of hydrogel I toward Cd(II), Pb(II), and Zn(II) ions, estimated from the Langmuir model, were 5.3, 0.63, and 1.27 mmol/g, respectively, and those of hydrogel II were 4.1, 0.59, and 0.89 mmol/g, respectively. The experimental sorption capacities of hydrogel I toward Cd(II), Pb(II), and Zn(II) ions were 4.5, 0.6, and 1.2 mmol/g, respectively. In the case of hydrogel II, the capacities were 3.7, 0.52, and 0.88 mmol/g in the same prescribed order. The thermodynamic parameters (the free energy of sorption, enthalpy change, and entropy change) for cadmium, lead, and zinc sorption on the prepared polymers were also determined from the temperature dependence. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Covalent attachment of chromophores to chlorinated copolymers for optical waveguides: Synthesis and optical characterization

Polymeric optical devices are attracting increasing interest in the field of photonics because of the very appealing performances as structures for both propagating and modulating light signals according to the properties of the employed organic materials. This paper reports the preparation and characterization of low-loss polymer waveguides fabricated from chlorinated copolymers by photochemical crosslinking. A novel monomer derived from reaction between glycidyl methacrylate (GMA) and the chromophore Disperse Red 19 (DR19) was prepared and successfully copolymerized with GMA and chlorostyrene (CS) to obtain the dye-modified copolymer. The latter was crosslinked by photoinitiated polymerization of the pendant epoxy groups, to obtain stable polymeric waveguides. It was found that the major product of the reaction between GMA and DR19 was formed through transesterification of the methacrylate with elimination of glycidol, while traces of products deriving from the epoxy ring-opening reaction were detected. The presence of the nitro substituent on DR19 favoured chain-transfer reactions during the polymerization reaction, leading to a decrease in the polymerization degree. It was also observed that the presence of grafted DR19 negatively affected the crosslinking reaction, as a lower epoxy group conversion was observed for the modified copolymer. Thermal analysis showed increased thermal stability for the copolymer containing DR19. m-line spectroscopy was used to measure the refractive index at 632.8 nm. The experimental results confirm that the new class of chlorine-based polymeric materials represent a very attractive proposal in the panorama of materials employed in the fabrication of electro-optical devices for telecommunication applications.     

硅烷接枝交联HDPE／LLDPE共混物性能研究

采用引发剂过氧化二异丙苯（DCP）、硅烷偶联剂乙烯基三乙氧基硅烷（VTEOS）和催化剂二月桂酸二丁基锡（DBTL）,通过双螺杆挤出机对高密度聚乙烯（HDPE）和线性低密度聚乙烯（LLDPE）的共混物进行硅烷接枝交联反应。通过力学测试和DSC研究产物不同凝胶含量对其性能影响。研究表明硅烷交联聚乙烯的拉伸和冲击强度随交联度的增大而提高,但产物结晶度和熔点有所下降,同时结晶均匀性变差。