Functionalization of isotactic polypropylene with maleic anhydride by reactive extrusion: mechanism of melt grafting

In this work, chemical structures and molecular parameters of grafted materials of PP-g-MAH prepared by melt reactive extrusion were studied by using electrospray ionization-mass spectrometer and gel permeation chromatography. It was found that the initial radicals, due to homolitic scission of dicumyl peroxide could be combined with maleic anhydride (MAH) monomers as well as polypropylene (PP) molecular chains. The homopolymerization of MAH cannot occur and the MAH radicals undergo a dismutational reaction under the processing condition (180-190 degreesC). A modified mechanism of melt grafting MAH onto PP has been proposed tentatively on the basis of our experimental results and other experimental findings published in the literature. (C) 2001 Elsevier Science Ltd. All rights reserved.

Novel sodium sulfonate-functionalized poly(ether ether ketone)s derived from 4,4 '-thiodiphenol

Novel sodium sulfonate-functionalized poly(ether ether ketone)s derived from 4,4'-thiodiphenol with degree of sulfonation up to 2.0 were synthesized by nucleophilic polycondensation of various amount of 5,5 '-carbonylbis(2-fluorobenzenesulfonate) (1) and 4,4'-difluorobenzophenone (2) with 4,4'-thiodipheno (3). Component and structure of the polymers were confirmed by TR, NMR and elemental analysis. Wide angle X-ray diffraction patterns indicated an amorphous structure of the polymers. All the polymers showed excellent thermal stability and poor solubility in water. (C) 2001 Elsevier Science Ltd. All rights reserved.

Copolymerization of N-4-dibenzoylmethane maleimide with styrene

The copolymer of N-4-dibenzoylmethane maleimide (p-DBMI) with styrene (St) was prepared and characterized by gel permeation chromatography, thermal analysis and spectroscopy.

Novel macrocyclic aryl thioether ester oligomers: structure characterization and free-radical ring opening polymerization

Novel macrocyclic aryl thioether ester oligomers have been synthesized in high yield from phthaloyl dichloride and 4,4'-thiodiphenol under pseudo high dilution conditions. The cyclic nature was unambiguously confirmed by a combination of MALDI-TOF MS, gel permeation chromatography and NMR analyses. Single-crystal X-ray diffraction of cyclic ester dimer reveals no severe strain on the cyclic structure. The free-radical ring opening polymerization (ROP) of the macrocyclic oligomers was achieved to give high molecular weight polymers via a transthioetherification reaction. The molecular weight of the polymer resulting from ROP decreases as the conversion of cyclic oligomers increases after a polymerization period of 30 min.

Effect of crosslinking distribution on gas permeability and permselectivity of crosslinked polyimides

Crosslinking modification of polyimide, prepared from 3,3'4,4'-benzophenone tetracarboxyl dianhydride (BTDA) and 2,3,5,6-tetramethyl-1,4-diphenylenediamine (4MPDA), was performed by two methods, putting the polyimide in ambient environment for 4 months, and under UV irradiation for 2 or 8 h. The gas permeation properties of the crosslinked polyimides were investigated. The crosslinked polyimides induced by UV irradiation, in which crosslinking occurs in the surface layer, are of much higher gas permselectivity of hydrogen to nitrogen than that induced by the ambient environment, in which crosslinking takes place in the whole matrix, but their gas permeabilities for hydrogen are similar. (C) 1999 Elsevier Science Ltd. All rights reserved.

Poly(ethylene glycol)-block-poly(butyl acrylate). II. Characterization and properties

Poly(ethylene glycol)-block-poly(butyl acrylate) synthesized by radical polymerization in a one-step procedure were characterized by gel permeation chromatography, infrared, IH-NMR spectroscopy, and differential scanning calorimetry (DSC). The crystalline property, emulsifying property, and phase transfer catalytic effect in the Williamson reaction were studied. It was found that the crystallinity of the copolymer increased with an increase in both the content and molecular weight of poly( ethylene oxide) (PEO) sequences. DSC curves showed two distinct crystallization temperature due to the heterogeneous nucleation and homogeneous nucleation crystallization. The casting solvent significantly affected the morphology and crystallinity of the solvent cast films. Both the emulsifying volume and the phase transfer catalytic efficiency in the Williamson reaction increased with the amount and PEO content of the block copolymers used, but decreased with an increase in the molecular weight of PEO sequences. (C) 1998 John Wiley & Sons, Inc.

Oxygen permeating properties of the mixed conducting membranes without cobalt

A new series of mixed conducting oxides, Sr10-n/2BinFe20Om (n = 4, 6, 8, 10), were synthesized by a solid state reaction method, and they have high oxygen permeability. The oxygen permeation rate at 1150 K is 0.41 ml(STD)/ cm(2).min for n = 6 and 0.90 ml(STD)/cm(2).min for n = 10, which is two times higher than that for Sr1-xBixFeO3 (x = 0.5). For the Sr1-xBixFeO3 (x = 0.1, 0.3, 0.5) series, the oxygen flux increases with increasing Bi content. (C) 1998 Elsevier Science Ltd.

Interfacial characteristics of the self-assembly system of poly-L-lysine 3-mercaptopropionic acid gold electrode

The interfacial characteristics of poly-L-lysine (PL) attached on self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) were studied by an electrochemical method. The results indicated that PL\MPA layer inhibited partly the diffusion process of redox species in solution, and the electrode surface behaved like a microelectrode array. Its permeation effect was also strongly affected by Mg2+. The more Mg2+ ions were added into the electrolyte solution, the greater the difficulty with which the electron transfer of potassium ferricyanide took place. The three different conformations of PL on the electrode surface had different influences on the electron transfer processes of ferricyanide. PL in random coil state hindered most strongly the electron transfer behavior of ferricyanide,while the alpha-helical PL had nearly no effect and the effect of the beta-sheet state PL was intermediate of these. (C) 1997 Elsevier Science S.A.

Effects of molecular structure on the permeability and permselectivity of aromatic polyimides

Permeability coefficients of H-2, O-2, and N2 were measured under 10 atm at the temperature from ambient temperature up to 150 degrees C in a series of structurally different aromatic homo- and copolyimides, which were prepared from 4,4'-oxydianiline (ODA) or 4,4'-methylene dianiline (MDA) with various aromatic dianhydrides. The study shows that the molecular structure of the polyimides strongly influences gas permeability and permselectivity. As a result, the permeability coefficients of the polyimide membranes for each gas vary by over two orders of magnitude. In general, among the polyimide membranes studied, the increase in permeability of polymers is accompanied by the decrease in permselectivity, and the MDA-based polyimide membranes have higher permeability than ODA-based ones. Among the polyimides prepared from bridged dianhydrides, the permeability coefficients to H-2, O-2, and N-2 are progressively increased in the order BPDA < BTDA < ODPA similar to TDPA < DSDA ( SiDA < 6FDA, while H-2/N-2 and O-2/N-2 permselectivity coefficients are progressively decreased in the same order. The copolyimide membranes, which were prepared from 3,3',4,4' biphenyltetracarboxylic dianhydride (BPDA), bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA), and ODA, have favorable gas separation properties and are useful for H-2/N-2 separation applications. (C) 1996 John Wiley & Sons, Inc.

GAS PERMEABILITIES AND PERMSELECTIVITY OF PHOTOCHEMICALLY CROSS-LINKED POLYIMIDES

Photosensitive polyimide BTDA-3MPDA was modified by UV irradiation. The structure of UV-irradiated polyimides was investigated by FTIR and gel fraction measurements. The results showed that longer UV exposure time resulted in a higher extent of crosslinking. The gas permeabilities of hydrogen, oxygen and nitrogen through UV-irradiated polyimides were characterized in a temperature range from 30 degrees C to 90 degrees C. Photocrosslinking resulted in a sharp decline in gas permeability for hydrogen, oxygen, and nitrogen through polyimide in the initial stage of photocrosslinking. Then, as the crosslinked benzophenone percentage amounted to 28-38% for hydrogen, 17-31% for oxygen and 3-28% for nitrogen, the gas permeabilities showed another sharp decline. Gas permselectivity increased significantly with the progress of photocrosslinking, and it can be adjusted in a wide range by controlling the extent of crosslinking. Arrhenius plots of gas permeability for hydrogen and oxygen through UV-irradiated polyimides are straight lines; for nitrogen, however, change in the slope of the straight line is observed and activation energies for hydrogen and oxygen permeation show abrupt increases when crosslinked benzophenone percentage amounts to about 30%. UV-irradiated polyimides with simultaneous high gas permeability and permselectivity make them ideal candidate materials for gas separation. (C) 1995 John Wiley & Sons, Inc.

SOLUTION PROPERTIES OF POLYANILINE AND ITS DERIVATIVES

Solutions of polyaniline (PAn), poly(ortho-toluidine) (POT) and poly(ortho-anisidine) (PAs) in N-methyl pyrrolidinone (NMP) were examined by viscometric, gel permeation chromatographic (GPC) and theological methods. Strong intermolecular interaction and molecular aggregation are shown.

STRUCTURE AND PROPERTIES OF SEQUENTIALLY POLYMERIZED PROPYLENE-B-[ETHYLENE-CO-PROPYLENE]-B-PROPYLENE COPOLYMERS

The structure and properties of presumed block copolymers of polypropylene (PP) with ethylene-propylene random copolymers (EPR), i.e., PP-EPR and PP-EPR-PP, have been investigated by viscometry, transmission electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, gel permeation chromatography, wide-angle x-ray diffraction, and other techniques testing various mechanical properties. PP-EPR and PP-EPR-PP were synthesized using delta-TiCl3-Et2AlCl as a catalyst system. The results indicate that the intrinsic viscosity of these polymers increases with each block-building step, whereas the intrinsic viscosity of those prepared by chain transfer reaction (strong chain-transfer reagent hydrogen was introduced between block-building steps during polymerization) hardly changes with the reaction time. Compared with PP / EPR blends, PP-EPR-PP block copolymers have lower PP and polyethylene crystallinity, and lower melting and crystallization temperatures of crystalline EPR. Two relaxation peaks of PP and EPR appear in the dynamic spectra of blends. They merge into a very broad relaxation peak with block sequence products of the same composition, indicating good compatibility between PP and EPR in the presence of block copolymers. Varying the PP and EPR content affects the crystallinity, density, and morphological structure of the products, which in turn affects the tensile strength and elongation at break. Because of their superior mechanical properties, sequential polymerization products containing PP-EPR and PP-EPR-PP block copolymers may have potential as compatibilizing agents for isotactic polypropylene and polyethylene blends or as potential heat-resistant thermoplastic elastomers.

A SIMPLE METHOD FOR PREDICTION OF GAS-PERMEABILITY OF POLYMERS FROM THEIR MOLECULAR-STRUCTURE

A method for the prediction of gas permeabilities (P) through polymers from their chemical structure has been developed on the basis of the ratio of molar free volume to molar cohesive energy, V(f)/E(coh). The permeation of small gas molecules through polymer membranes is dependent on the chain packing density measured by V(f) and segmental motion of polymer chains measured by E(coh). But no simple relationship between P and V(f) or E(coh) alone was found. The permeability data of more than 60 polymers covering 7 orders of magnitude for six gases have been treated with linear regression analysis. All plots of log P vs. V(f)/E(coh) gave good straight lines. It is also found that a linear relationship holds when plotting both the intercepts and slopes of log P vs. V(f)/E(coh) lines against square of the diameters of gas molecules. Therefore, the permeabilities of all the non-swelling gases through a great variety of polymers can be estimated using two correlations above. Moreover, this method is more accurate than others in the literature and may found useful for the selection of gas separation or barrier membrane materials.

热浸镀钢材在海水中的氢渗透行为和脆性研究

氢渗透和拉应力的联合作用对海洋环境中的热浸镀钢材的安全构成潜在威 胁，本文以当前应用最广泛的三种商业化热浸镀钢材（热浸镀锌、锌-5%铝-稀土和锌-55％铝-1.6%硅）为研究对象，采用Devanathan-Stachurski双面电解池测试技术，测试了自渗氢电流密度曲线，研究了镀层与缺陷比例对氢渗透电流的影响，比较了镀层的氢渗透抑制性能及存在缺陷时的自渗氢能力，并结合镀层成分、结构及其腐蚀机理，探讨了其氢渗透机理；通过慢应变速率拉伸实验，获得了热浸镀钢材在不同充氢条件下的应力-应变曲线，比较了其力学性能参数，并配合断口的显微分析，评价了三种热浸镀钢材在海水中的氢脆敏感性，并对其氢脆机理进行了探讨。主要结果如下： (1) 热浸镀锌镀层的氢渗透抑制能力最弱，锌-5%铝-稀土镀层的氢渗透抑制能力较强，镀层存在缺陷时导致的阴极保护能促进氢渗透；锌-55％铝-1.6%硅镀层的氢渗透抑制能力最强，镀层存在缺陷时基本没有氢渗透电流。当镀层存在缺陷时，氢渗透电流密度的最大值随着镀层与暴露的钢材基体的面积比增大而增大。随着镀层中铝含量的增加，镀层结构越致密，镀层的耐腐蚀性能越好，完整镀层的氢渗透抑制能力越强，镀层存在缺陷时的自渗氢能力越弱。 (2) 热浸镀锌和锌-5%铝-稀土镀层钢材在海水中的氢渗透能明显降低材料的断后延伸率和能量密度，使其断裂方式由韧性转变为准解理；锌-55％铝-1.6%硅镀层在海水中对钢材基体进行阴极保护导致的氢渗透虽能显著降低其断后延伸率和能量密度，但其断裂方式以韧性为主，且断口存在局部的准解理撕裂形貌。随着预浸泡时间的增长，材料充氢量的增加，三种热浸镀钢材的氢脆敏感性提高。随着镀层铝含量的增加，热浸镀钢材在海水中的氢脆敏感性降低。

硫酸盐还原菌对热浸镀锌钢材在海水中的氢渗透行为和脆性的影响研究

硫酸盐还原菌(SRB)活动、拉应力和氢的联合作用将对海洋环境中热浸镀锌钢材构筑物的安全带来隐患。本文通过Devanathan－Stachurski双面电解池测试技术，检测了镀层完好及存在缺陷的热浸镀锌钢材在灭菌海水、灭菌培养基及接种SRB的培养基中的氢渗透电流曲线，探讨了镀层缺陷、培养基成分以及SRB对热浸镀锌钢材氢渗透行为的影响；采用电化学阻抗谱测试技术，研究了热浸镀锌钢材在上述介质中的腐蚀机制，并由此讨论了热浸镀锌钢材在不同条件下的氢渗透机制；通过慢应变速率拉伸试验(SSRT)，获得了热浸镀锌钢材在不同腐蚀介质中的应力-应变曲线，比较了其力学性能参数，进而通过断口分析，评价了热浸镀锌钢材在灭菌海水、灭菌培养基及接种SRB培养基中的氢脆敏感性。研究结果表明： (1) 镀层出现缺陷将对热浸镀锌钢材的氢渗透行为起促进作用，这类试样在灭菌海水和灭菌培养基中的平均氢渗透电流密度比镀层完好试样在相同介质中的平均氢渗透电流密度分别提高了250.76%和32.76%；培养基组分对热浸镀锌钢材的氢渗透行为起促进作用，镀层存在缺陷和镀层完好的热浸镀锌钢材试样在灭菌培养基中的平均氢渗透电流密度分别比其在灭菌海水中高181.22%和626.97%；SRB对热浸镀锌钢材的氢渗透行为起抑制作用，镀层存在缺陷及镀层完好的热浸镀锌钢材试样在接种SRB的培养基中的平均氢渗透电流密度分别比灭菌培养基中低90.84%、77.14%。 (2) 电化学测试结果表明，培养基组分能够加速热浸镀锌钢材的腐蚀，使试样表面更容易形成腐蚀缺陷，从而增加其自渗氢能力；活性SRB本身对热浸镀锌钢材的腐蚀和氢渗透起促进作用，但在本文实验条件下，SRB及其代谢产物形成的生物膜以及腐蚀产物组成的致密膜层能够通过阻挡层作用抑制腐蚀，并阻止氢的进入；扫描电镜(SEM)分析结果表明，暴露于接种SRB培养基中的热浸镀锌钢材试样表面有致密的产物膜层，而灭菌培养基中的试样表面没有明显腐蚀产物膜存在。 (3) 培养基组分对热浸镀锌钢材氢渗透行为的促进作用增加了其对氢脆的敏感性，热浸镀锌钢材在灭菌培养基中的断后延伸率和能量密度比在灭菌海水中分别降低了4.97%和5.59%；SRB对热浸镀锌钢材氢渗透行为的抑制作用降低了其对氢脆的敏感性，热浸镀锌钢材在接种SRB的培养基中的断后延伸率和能量密度比其在灭菌培养基中分别高7.78%和8.44%。