聚甲醛与热塑性酚醛树脂相容性研究

考察了聚甲醛(POM)与热塑性酚醛树脂(Novolak)的相容性;浊点法研究结果表明,POM/Novolak共混物存在一个低位临界相转变温度.DSC测试表明,POM与Novolak共混后,共混物的熔点下降;通过DSC测试得到数据,采用Hoffman-Weeks平衡熔点外推法和Flory熔点下降方程推算出POM与Novolak的相互作用参数(χ)约为-0.032.FTIR研究表明,Novolak的羟基能够与POM的醚氧基形成氢键,导致共混物中Novolak的羟基峰向高频偏移.研究结果表明,POM与Novolak能够达到热力学相容.     

酚醛树脂的增容作用对聚甲醛/丁腈橡胶共混物的韧性、结晶形态和亚微相态的影响

考察了酚醛树脂(Novolak)的增容作用对聚甲醛(POM)/丁腈橡胶(NBR)共混物的韧性、结晶形态和亚微相态的影响.实验结果表明,POM与NBR不相容,直接共混不能提高POM的韧性;添加Novolak后,当NBR质量分数为40%时共混物发生“脆-韧”转变.POM/NBR共混物中POM球晶尺寸大,易形成应力集中点,导致增韧效果不佳;Novolak可通过与POM的分子链间相互作用,改变POM分子链固有的规程和排列方式,使球晶显著减小.亚微相态显示,POM/NBR呈现“海-岛”结构相态,NBR在基体中分散性很差;添加Novolak可提高NBR在基体中的分散性;当NBR质量分数达到40%时,NBR在基体中呈现带状网络结构.网带结构能够终止受外力作用而在基体中产生的银纹和剪切屈服,增加了共混物的破裂能,从而使共混物的韧性显著提高.     

聚甲醛/蒙脱土纳米复合材料非等温结晶动力学研究

聚甲醛/蒙脱土纳米复合材料非等温结晶动力学研究     

Preparation and characterization of polyoxymethylene‐copolymer/hydroxyapatite nanocomposites for long‐term bone implants

In this work, new polyoxymethylene (POM)/hydroxyapatite (HAp) nanocomposites for long‐term bone implants have been obtained via extrusion and injection molding processes and characterized by differential scanning calorimetry (DSC), temperature‐modulated DSC (TMDSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and tensile mechanical and in vitro stability tests. Based on the DSC results, it was found that the degree of crystallinity increases for POM/0.5% HAp sample and decreases for POM/1.0% HAp and POM/2.5% HAp. SEM and TEM observations for POM/HAp nanocomposites indicated that the dispersion of HAp in the polymer matrix was uniform and the diameter of the HAp particles was less than 100 nm for most of them. Young's modulus increases with increasing HAp concentration, whereby elongation at break decreases. On the contrary, HAp concentration does not have a significant influence on the tensile strength. TG results show that for POM/0.5% HAp, POM/1.0% HAp, and POM/2.5% HAp, thermal stability slightly increases in comparison to pure POM, whereas for POM/5.0 HAp and POM/10.0% HAp, lower thermal stability was observed. In vitro data reveal that with an increase of HAp content, bioactivity of nanocomposites increases; a good in vitro chemical stability of POM and POM nanocomposites was confirmed. Copyright © 2011 John Wiley & Sons, Ltd.     

Biophysical and cellular-uptake properties of mixed-sequence pyrrolidine-amide oligonucleotide mimics

Previously we introduced the positively charged pyrrolidine-amide oligonucleotide mimics (POM), which possess a pyrrolidine ring and amide linkage in place of the sugar-phosphodiester backbone of natural nucleic acids. Short POM homo-oligomers have shown promising DNA and RNA recognition properties. However, to better understand the properties of POM and to assess their potential for use as modulators of gene expression and bioanalytical or diagnostic tools, more biologically relevant, longer, mixed-sequence oligomers need to be studied. In light of this, several mixed-sequence POM oligomers were synthesised, along with fluorescently labelled POM oligomers and a POM-peptide conjugate. UV thermal denaturation showed that mixed-sequence POMs hybridise to DNA and RNA with high affinity but slow rates of association and dissociation. The sequence specificity, influence of terminal amino acids, and the effect of pH and ionic strength on the DNA and RNA hybridisation properties of POM were extensively investigated. In addition, isothermal titration calorimetry (ITC) was used to investigate the thermodynamic parameters of the binding of a POM-peptide conjugate to DNA. Cellular uptake experiments have also shown that a fluorescently labelled POM oligomer is taken up into HeLa cells. These findings demonstrate that POM has the potential for use in a variety of applications, alongside other modified nucleic acids developed to date, such as peptide nucleic acids (PNA) and phosphoramidate morpholino oligomers (PMO).     

Replicated Banded Spherulite: Microscopic Lamellar-assembly of Poly(L-lactic acid) Crystals in the Poly(oxymethylene) Crystal Framework

The morphologies of poly(L-lactic acid) (PLLA) spherulites,when crystallized within the pre-existed poly(oxymethylene)(POM) crystal frameworks,have been investigated.PLLA/POM blend is a melt-miscible crystalline/crystalline blend system.Owing to the lower melting point but much faster crystallization rate than PLLA,POM crystallized first upon cooling from the melt state and then melted first during the subsequent heating process in this blend system.Lamellar assembly of PLLA crystals within the pre-existed POM spherulitic frameworks was directly observed with the polarized light microscopy by selectively melting the POM frameworks.The investigation indicated that PLLA crystals fully replicated the spherulitic morphology and optical birefringence of the POM crystal frameworks,which was independent of Tc.On the other hand,POM could also duplicate the pre-existed PLLA morphologies.The result obtained provides us a possibility to design the lamellar assembly and crystal structures of polymer crystals in miscible crystalline/crystalline polymer blends.     

4,4'-二羟基二苯硫醚对聚甲醛结晶和熔融行为的影响

为了探究4,4'-二羟基二苯硫醚(TDP)的添加对聚甲醛(POM)熔融与结晶行为的影响,本文利用熔融共混的方法制备了POM/TDP共混材料。通过差示扫描量热仪(DSC)对共混材料的熔融与结晶行为进行了研究,利用广角X射线衍射仪(WAXD)对共混材料的晶体结构进行了研究。结果表明,在POM中添加TDP后,POM的晶面间距变大,晶体结构变的疏松,使POM的结晶温度(Tc)、结晶焓(ΔHc)、熔融温度(Tm)与熔融焓(ΔHm)均降低。当TDP质量分数增加到30%时,共混物的熔点与结晶温度较纯POM分别下降了15.2和12.8℃。在等温结晶过程中,随着TDP含量的增大,POM完成结晶所需的时间显著加长,共混物的结晶速率逐渐降低,结晶活化能逐渐升高,但TDP的加入对POM的晶型并没有影响。以上结果说明TDP的添加对POM的熔融与结晶行为影响很大,这将为POM结晶行为的调控提供依据。     

Integrating 31P DOSY NMR Spectroscopy and Molecular Mechanics as a Powerful Tool for Unraveling the Chemical Structures of Polyoxomolybdate‐Based Amphiphilic Nanohybrids in Aqueous Solution

Novel organic–inorganic hybrids of various sizes were generated by reaction of 1,8‐octanediphosphonic acid (ODP) and (NH₄)₆Mo₇O₂₄ in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH₄)₆Mo₇O₂₄ concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by ¹H, ³¹P, and ⁹⁵Mo NMR spectroscopy. Heteronuclear ³¹P DOSY (diffusion‐ ordered NMR spectroscopy) and molecular mechanics (MM) calculations were applied to determine the size and shape of the nanosized hybrids generated at various ODP/POM ratios. For this purpose, the structures of ODP/POM hybrids with variable numbers of ODP and POM units were optimized by MM and then approximated as cylinder‐shaped objects by using a recently described mathematical algorithm. The thus‐obtained cylinder length and diameter were further used to calculate the expected diffusion coefficients of the ODP/POM hybrids. Comparison of the calculated and experimentally determined diffusion coefficients led to the most probable ODP/POM hybrid length for each sample composition. The ³¹P DOSY results show that the length of the hybrids increases with increasing POM concentration and reaches a maximum corresponding to an average of 8 ODP/7 POM units per chain at a sample composition of 20 mM ODP and 14 mM POM. With excess POM, above the latter concentration, the formation of shorter‐chain hybrids terminated by Mo₇ clusters at one or both ends was evidenced on further increasing the POM concentration. The results demonstrate that the combination of ³¹P DOSY and MM, although virtually unexplored in POM chemistry, is a powerful innovative strategy for the detailed characterization of nanosized organic–inorganic POM‐based hybrids in solution.     

Effect of ionomers on mechanical properties, morphology, and rheology of polyoxymethylene and its blends with methyl methacrylate-styrene-butadiene copolymer

Two ionomers, ethylene-methacrylic acid copolymer ionized with sodium cation (EMA-Na) and zinc cation (EMA-Zn), were employed as impact modifiers to prepare blends with polyoxymethylene (POM) via a melt extrusion. A copolymer of methyl methacrylate-styrene-butadiene (MBS) used as a co-impact modifier was also incorporated into the blends. The mechanical properties, thermal properties, morphology, and rheology were studied. A moderate toughening was observed for POM/ionomer binary blends, which was attributable to the rubbery natural and good adhesion of the ionomers. EMA-Zn exhibited a much better toughening effect than EMA-Na because of its higher elasticity and stronger interaction with POM. The incorporation of the ionomers into POM/MBS blends resulted in an improvement of mechanical properties, which was attributable to the compatibilizing effect of ionomer on POM/MBS blending system. The observation of scanning electron microscopy demonstrated that the finer phase domains were caused by incorporation of ionomers, which, acting as a compatibilizer as well as an impact modifier, reduced the interfacial tension and improved the interfacial adhesion between the phases. Differential scanning calorimetry investigation indicated that the presence of ionomer in the blends disturbed the crystallization of POM and resulted in a decrease in the crystallinity of POM. The evaluation of melt flow index revealed an increase in viscosity of the blends by incorporation of the ionomers, which was caused the ionic interaction between POM and the ionomers.     

A new and highly efficient formaldehyde absorbent of polyoxymethylene

A new type of highly efficient formaldehyde (FA) absorbent of polyoxymethylene (POM), hexamethylenediamine–formaldehyde polycondensates (HF) was prepared by the condensation reaction of hexamethylenediamine (HA) and FA. The effects of the synthetic technique including FA/HA molar ratio, reaction temperature and dispersant dosage on the thermal stability of POM/HF were studied, and finely divided, slightly branched HF polycondensates with high molecular weight and relatively high processing thermal stability were obtained. The thermal stabilization effect of HF on POM was studied through the isothermal weight loss analysis, FA emission amount (FEA) measurement, and balance torque analysis, which showed that HF had better thermal stabilization effect on POM than the commonly used FA‐absorbent melamine (MA). In order to improve the crystallization performance and mechanical properties of POM, the nucleation effect of HF on POM was studied by means of polarized light microscopy (PLM), isothermal and nonisothermal differential scanning calorimetry (DSC), indicating that HF had remarkable nucleation effect on POM. The investigation of mechanical properties showed that the addition of HF could improve the impact toughness of POM to a certain degree. Copyright © 2008 John Wiley & Sons, Ltd.     

Visualization of Two-dimensional Single Chains of Hybrid Polyelectrolytes on Solid Surface

The polyacidic character of polyoxometalate(POM) clusters endows high ionic conductivity, making these clusters good candidates for solar and fuel cells. Covalent bonding of clusters to polymer chains creates poly(POM)s that are polyelectrolytes with both cluster functions and polymer performance. Thus, solution-processable poly(POM)s are expected to be used as key materials in advanced devices. Further understanding of poly(POM)s will optimize the preparation process and improve device performance. Herein, we report a study of the first linear poly(POM)s by directly visualizing the chains using scanning transmission electron microscopy. Compared with traditional polymers, individual clusters of poly(POM)s can be directly visualized because of the resistance to electron-beam damage and the high contrast of the tungsten POM pendants. Thus, cluster aggregates with diverse shapes were observed. Counting the number of clusters in the aggregates allowed the degree of polymerization and molecular weight distribution to be determined, and studying the aggregate shapes revealed the presence of a curved semirigid chain in solution. Further study of shape diversity revealed that strong interactions between clusters determine the diverse chain shapes formed during solution processing. Fundamental insight is critical to understanding the formation of poly(POM) films from solutions as key functional materials, especially for fuel and solar cells.     

多壁碳纳米管对聚甲醛性能的影响

将多壁碳纳米管(MWCNTs)和聚甲醛(POM)在转矩流变仪中熔融混合得到POM/MWCNT复合材料.研究了复合材料的形态,导热性能,导电性能,流变性能和结晶性能.结果表明,MWCNTs在没有经过处理的情况下能够均匀地分散在POM基体中;当向POM中添加1.0 wt%含量MWCNTs时,复合材料的导热系数上升到0.5289 W/(K m),比纯POM的导热系数0.198 W/(K m)提高1.5倍,通过有效介质方法(EMA)验证了体系导热系数提高幅度不大的原因是MWCNTs与POM之间形成了很高的界面热阻;当MWCNTs的含量为1.0 wt%时,体系产生了导电逾渗效应,逾渗值在0.5 wt%~1.0 wt%之间;MWCNTs对POM有显著的成核作用,当向POM中添加0.5 wt%含量的MWCNTs时,POM的结晶温度提高6℃左右,但当MWCNTs的添加量进一步增加时,结晶温度几乎不再变化,成核效果呈现"饱和"状态.另外,材料的复数黏度,储能模量和损耗模量随MWCNTs含量的增加而增加.     

多金属氧酸盐及其溶液自聚集行为研究进展

多金属氧酸盐(POM)是一类由过渡金属与氧原子桥连而成的阴离子簇合物,由于其特殊的分子结构及优异的物理化学性质,使其在催化、医药、材料科学、表面化学、超分子化学等领域有广泛的应用价值。 POM在稀的水溶液中能够发生自聚集,形成类似两亲分子溶液中的“有序聚集体结构”,赋予其新的结构和性质,以期开发出新型纳米器件及在催化、药物等领域得到应用。 本文介绍了POM的主要结构、性质和近年来的应用,阐述了其在溶液中自聚集行为的研究状况和新进展。     

A multiunit catalyst with synergistic stability and reactivity: a polyoxometalate-metal organic framework for aerobic decontamination

A combination of polyanion size and charge allows the Keggin-type polyoxometalate (POM), [CuPW(11)O(39)](5-), a catalyst for some air-based organic oxidations, to fit snuggly in the pores of MOF-199 (HKUST-1), a metal-organic framework (MOF) with the POM countercations residing in alternative pores. This close matching of POM diameter and MOF pore size in this POM-MOF material, [Cu(3)(C(9)H(3)O(6))(2)](4)[{(CH(3))(4)N}(4)CuPW(11)O(39)H] (1), results in a substantial synergistic stabilization of both the MOF and the POM. In addition, this heretofore undocumented POM-MOF interaction results in a dramatic increase in the catalytic turnover rate of the POM for air-based oxidations. While 1 catalyzes the rapid chemo- and shape-selective oxidation of thiols to disulfides and, more significantly, the rapid and sustained removal of toxic H(2)S via H(2)S + 1/2 O(2) → 1/8 S(8) + H(2)O (4000 turnovers in <20 h), the POM or the MOF alone is catalytically slow or inactive. Three arguments are consistent with the catalytic reactions taking place inside the pores. POM activation by encapsulation in the MOF likely involves electrostatic interactions between the two components resulting in a higher reduction potential of the POM.     

溶液自组装法构筑超分子杂化功能材料

以Anderson型多金属氧酸盐(POM)为构筑单元,通过共价键的方式将两个胆固醇分子连接到POM两端,制备了一种具有胆固醇-多金属氧酸盐-胆固醇结构的杂化分子,其在本体中通过自组装形成有序的六棱柱状结构。杂化分子的POM核在N,N-二甲基甲酰胺中具有良好的溶解性,而其胆固醇端基在甲苯中具有适当的溶解性。在甲苯体积分数为85.7%的条件下,杂化分子通过POM核与其胆固醇端基溶解性的差异、胆固醇端基之间较强的范德华力和POM核之间较强的相互静电作用力,可以自组装形成不同尺度的有序纤维结构,其相互缠绕最终形成典型的三维网状结构。在纤维结构中,杂化分子通过胆固醇层与POM层相互交替排列,在透射电镜表征中形成了明暗交替的层状精细结构。本研究工作在纳米材料的设计、组装和应用方面具有潜在的应用价值。     

丁腈橡胶对聚甲醛树脂的增韧机理研究

研究了丁腈橡胶（ＮＢＲ） 对聚甲醛（ＰＯＭ） 树脂的增韧机理,并比较了ＰＯＭ／ＮＢＲ 体系和ＰＯＭ／ 热塑性聚氨酯（ＴＰＵ） 体系的异同．结果表明,高丙烯腈（ＡＮ） 含量的ＮＢＲ 有着和ＴＰＵ 相近的溶度积参数,且其分子上的氰（ＣＮ） 基或双键对ＰＯＭ 分解时产生的甲醛及大分子自由基的捕捉作用,有利于改善ＮＢＲ 和ＰＯＭ 之间相容性,因而可和ＰＯＭ 树脂形成良好的合金体系;当ＮＢＲ 含量达４０ｗｔ％ 时,ＰＯＭ／ＮＢＲ 体系出现脆 韧转变,从逾渗机制、剪切带机制、类互穿网络（ＩＰＮ） 作用机制等角度进行考察的结果证明,ＮＢＲ 对ＰＯＭ 树脂的增韧行为以及ＰＯＭ／ＮＢＲ 共混合金体系的脆 韧转变规律与ＰＯＭ／ＴＰＵ 体系相一致．     

High melting thermoplastic/epoxy resin blends: Influence of the curing reaction on the crystallization and melting behavior

The influence of the cure process and the resulting reaction‐induced phase separation (RIPS) on the crystallization and melting behavior of polyoxymethylene (POM) in epoxy resin diglycidylether of bisphenol A (DGEBA) blends has been studied at different cure temperatures (180 and 145 °C). The crystallization and melting behavior of POM was studied with DSC and the simultaneous blend morphology changes were studied using OM. At first, the influence of the epoxy monomer on the dynamically crystallized POM was investigated. Secondly, a cure temperature above the melting point of POM (T_cure = 180 °C) was applied for blends with curing agent to study the influence of resulting phase morphology types on the crystallization behavior of POM in the epoxy blends. Large differences between particle/matrix and phase‐inverted structures have been observed. Thirdly, the cure temperature was lowered below the melting temperature of POM, inducing isothermal crystallization prior to RIPS. As a consequence, a distinction was made between dynamically and isothermally crystallized POM. Concerning the dynamically crystallized material, a clear difference could be made between the material crystallized in the homogeneous sample and that crystallized in the phase‐separated structures. The isothermally crystallized POM was to a large extent influenced by the conversion degree of the epoxy resin. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2456–2469, 2007     

Effect of Zinc Oxide on Morphology and Mechanical Properties of Polyoxymethylene/Zinc Oxide Composites

This paper studies the effects of zinc oxide (ZnO) on morphology and mechanical properties of pure polyoxymethylene (POM) and POM/ZnO composites. POM/ZnO composites with varying concentration of ZnO were prepared by melt mixing technique in a twin screw extruder. The dispersion of ZnO particles on POM composites was studied by scanning electron microscope (SEM). It is observed that the dispersion of ZnO particles is relatively good. The mechanical properties of the composites such as tensile strength, stress at break, Young's modulus and impact strength were measured. Increasing content of ZnO up to 4.0 wt% increases the impact strength of POM. Addition of ZnO beyond 4.0 wt% decreases the impact strength. The composites containing ZnO content greater than 2.0 wt% show increased Young's Modulus. The tensile strength and stress at break decrease with increasing ZnO content. This may be due to the compatibility between ZnO and POM.     

Synergistic effect of red phosphorus, novolac and melamine ternary combination on flame retardancy of poly(oxymethylene)

New flame retardant system for poly(oxymethylene) (POM) has been studied. The combination of red phosphorus with novolac and melamine was found to act as an effective flame retardant of POM. The base POM exhibited very low limiting oxygen index (LOI) value of 15.3, while the flame retarded POM gave remarkably high LOI value of 37.5 and UL94 V-1 ranking without dripping at 0.8 mm thickness. The results of cone calorimetry, thermogravimetry and FTIR analysis suggested that the flame retarding mechanism is the intumescent char formation in the condensed phase. Novolac having a phenolic hydroxyl group is miscible with POM, and in the flaming process, red phosphorus yields phosphine and its acidic product such as phosphoric acid due to hydrolysis and oxidation reactions. In addition, all of novolac, melamine and phosphine are able to readily react with formaldehyde generated from POM during burning to give the reinforced and cross-linked char network through the polyaddition and polycondensation reactions. Therefore, the red phosphorus/novolac/melamine ternary combination system could synergistically promote the high flame retardancy of POM without the flaming drips.