Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids

The ionic complex of mesitoyl bromide with aluminum bromide in a 1∶1 composition (Mst-1) does not initiate the isobutylene polymerization inn-hexane or methylene dichloride at −78 °C. The corresponding ionic complex of the 1∶2 composition (Mst-2) acts as a cationogenic initiator of the polymerization. The addition of excess Lewis acid or introduction of organic electron acceptors increases the initiating activity of the Mst-1 complex and activates acyl complexes of the 1∶2 composition including Mst-2. The results are discussed in terms of the effect of specific solvation on the nucleophilicity of counteranions, which makes the addition of the monomer to the carbocation possible. For Part 9, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 52–56, January, 1998.     

Application of dye-partition technique to the determination of the rates of initiation in radical polymerization

Summary Dye-partition technique as an useful method of measuring kinetic chain length (v), rate of initiation (R _i ), initiator efficiency (f), and the parameter [=(2k _t)^1/2 k _p] etc. in radical polymerization using styrene and methylmethacrylate as monomers in dimethyl formamide medium and 4,4 azobis-4-cyanopentanoic acid as the initiator to produce dye responsive carboxyl ended polymers has been discussed. The values ofR _p,f and obtained by this method compare fairly well with those obtained by a standard method, viz., molecular weight method. The magnitude off much less than unity and constancy in its value under different concentrations of monomers and initiator indicate that almost all radicals surviving geminate recombination is captured by the monomers. The precautions necessary for applying this method have also been discussed.

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Zusammenfassung Farbstoff-Verteilungstechnik als nützliche Methode zur Messung der kinetischen Kettenlänge (v), Initiationsgeschwindigkeit (R _i ), des Initiator-Wirkungsgrades (f), und des Kennwertes (2k,^1/2 k _p ) (=) etc. bei der radikalischen Polymerisation von Styrol und Methylmethacrylat in Dimethylformamid-Medium mit 4,4'-Azobis-4-cyanopentansäure als Initiator zur Bildung von mit Farbstoffen reagierenden Carboxylatendgruppen in den Polymeren, wurde diskutiert. Die durch obengenannte Methode festgestellten Werte vonR _p ),f und sind ungefähr mit den durch übliche Methoden festgestellten Werten vergleichbar (durch Molekulargewicht-Methode).Die konstante Größenordnung von 'f, die viel weniger als eins beträgt, weist darauf hin, daß alle die paarweise Rekombination überlebenden Radikale von den Monomeren abgefangen werden. Die zur Anwendung dieser Methode nötigen Vorsichtsmaßnahmen sind auch diskutiert worden.

     

Notched Ring Test for Measuring Slow Cracking Resistance in Plastics Pipes and Fittings

It is known, that the lifetime of polyethylene pipes is essentially limited by slow crack growth (SCG). For state of the art PE materials common SCG testing methods have reached their limits with respect to extension of testing times. A comparatively new method is the Notched Ring Test (NRT) as developed by Choi et al.^[1] Pipe rings notched at the inner wall are used. The test is carried out in 80 °C water under constant bending load. The arrangement of the notch at the inner wall reduces testing times using the residual stress of extruded pipes. A disadvantage of this method is that there is no clearly defined failure time because SCG takes place between two phases of creeping. The output of this test is an “on-set slow cracking time” (crack initiation), obtained by analysis of the displacement curve. In this work it has been shown that the NRT method yields to brittle fracture within acceptable time frames.^[2] Methods for data analysis are presented. This test could be very useful applied in research and development for resin evaluation and as a tool in quality control in pipe production for evaluating the process conditions.     

Extrusions and intrusions in fatigued metals. Part 1. State of the art and history†

Current state and historical progress in experimental and theoretical studies of surface relief appertaining to persistent slip bands (PSBs) and leading to fatigue crack initiation in cyclically deformed metals is presented as a thorough critical overview. A comprehensive inventory of microscopic techniques used for this study is tabulated chronologically with emphasis to their applicability to polycrystals. The most relevant experimental characteristics concerning surface relief evolution, namely the form of extrusions and intrusions in single- and polycrystalline materials, are surveyed. Theoretical models and computational simulations of extrusion and intrusion formation and fatigue crack initiation are critically reviewed.     

Domino free radical photopolymerization based on phototriggered base proliferation reaction and redox initiation

A detailed evaluation of the kinetics of domino free radical photopolymerization (DFRP) based on phototriggered base proliferation reaction and redox initiation was described in the condition of eliminating the heat of polymerization via reacting in the thin polymer films. First, domino photoinitiating system made a substantial breakthrough in the photoefficiency of amine generation in contrast to photocaged base system, exhibiting marked improvement in the photosensitivity. Second, both the structural feature of base amplifier (BA) and reaction temperature as two important factors impacting the proliferation rate have been detailed. Third, different domino photoinitiating components, such as BAs, peroxides, and acrylates, were investigated in the thin polymer films. It is shown that both primary and secondary BAs are efficient catalysts for DFRP. Furthermore, polymerization rate shows a consistent dependence on the pK_a value of the proliferated amine. Finally, remarkable post conversion after irradiation was achieved in DFRP. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1560–1569     

Cuso4‐amine redox‐initiated radical polymerization of methyl methacrylate mediated by a CuCl2 complex: Homogeneous reverse ATRP

Kinetic results of CuSO₄/2,2'‐bipyridine(bPy)‐amine redox initiated radical polymerization of methyl methacrylate (MMA) at 70 to 90 °C in dimethylsulfoxide suggest that such initiation is characteristic of a slow rate and a low initiator efficiency, but tertiary amines exhibit a relatively higher rate. UV‐Vis spectroscopy confirms the alpha‐amino functionality of PMMA chains. CuCl₂/bPy successfully mediates the redox‐initiated radical polymerization of MMA with aliphatic tertiary amines in a fashion of slow‐initiated reverse atom transfer radical polymerization (ATRP), i.e. both the initiator efficiency of aliphatic tertiary amines and the average molecular weight of PMMA increase gradually, while the molecular weight distribution remains narrow but become broader with the conversions. As the PMMA chains contain alpha amino and omega C‐Cl moieties, UV‐induced benzophenone‐initiated radical polymerization and Cu^ICl/bPy‐catalyzed ATRP initiated from PMMA lead to block copolymers from terminal functionalities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2562‐2578     

Electro-optic properties of nematic and ferroelectric liquid crystalline nanocolloids doped with partially reduced graphene oxide

Flakes of partially reduced graphene oxide (PRGO) were doped in nematic liquid crystals (NLCs) and ferroelectric liquid crystals (FLCs), respectively. The dielectric and electro-optical properties of NLCs doped with those flakes have been investigated. Threshold voltage and switching times are reduced by 30%–50%. This is primarily due to the decrease of the elastic properties of the nanocolloids compared to the non-doped nematics. The influence of the PRGO flakes on the spontaneous polarization, tilt angle and switching time of FLCs was investigated too. Such flakes reduce the response time by 40%–60%, increases spontaneous polarization by 20%–25% and increase the tilt angle by 15%–20%.     

纯三元及含Zr, Ga元素磁粉的各向异性

未经均匀化热处理的纯三元及含Zr, Ga元素的SC合金铸片经优化的HDDR工艺处理都可以制备各向异性NdFeB磁粉。这表明：元素的添加及SC铸片是否进行了均匀化热处理都不是HDDR磁粉各向异性形成的必要条件。磁粉各向异性形成的关键因素在于HDDR工艺的调节,即适当地加快歧化反应过程,减缓脱氢再结合过程以及控制脱氢再结合时的合适氢气压强均有利于磁粉各向异性的形成。本文将为制备低成本高各向异性磁粉提供重要的指导。     

新型聚中性红膜修饰碳糊电极的制备、表征及应用

运用一种新型的化学引发-电聚合方式将中性红膜固定到碳糊电极表面,制备出聚中性红薄膜修饰碳糊电极(PNR/CPE)。利用循环伏安法(CV)和交流阻抗谱(EIS)对修饰电极的电化学性能进行研究,借助于扫描电子显微镜(SEM)对修饰电极表面进行表征,并采用红外吸收光谱法(IR)和紫外可见吸收光谱法(UV-Vis)对PNR薄膜结构进行测试。结果表明,中性红成功地固定在碳糊电极表面,修饰电极的表面呈现特定的立体化结构,表面的电活性位点增多,电催化性能增大。在优化条件下,将该电极应用于鲱鱼精DNA(hs DNA)的检测,PNR电极上出现了1对较强的氧化还原峰,峰电流与其浓度在1.0×10~(-6)~8.0×10~(-5)mol/L范围内呈良好的线性关系,检出限为1.0×10~(-7)mol/L。     

Calibration of Stress-triaxiality Dependent Crack Formation Criteria: A New Hybrid Experimental–Numerical Method

A new experimental technique has been developed to investigate the onset of fracture in metals at low and intermediate stress triaxialities. The gage section of a flat specimen has been designed such that cracks are most likely to initiate within the specimen center, remote from the specimen boundaries. Along with the specimen, a biaxial testing device has been built to apply a well-defined displacement field to the specimen shoulders. The stress state within the specimen is adjusted by changing the biaxial loading angle. Using this new experimental technique, the crack initiation in metals can be studied experimentally for stress triaxialities ranging from 0.0 to 0.6. The stress and strain fields within the specimen gage section are determined from finite element analysis. The reliability of the computational model of the test set-up has been verified by comparing the simulation results with laser speckle-interferometric displacement measurements during testing. Sample experiments have been performed on the Al-7Si-Mg gravity die casting alloy. A three-step hybrid experimental–numerical calibration procedure has been proposed and applied to determine a phenomenological crack formation criterion for the Al-7Si-Mg alloy.