Two‐step cavitation in semi‐crystalline polymer during stretching at temperature below glass transition

Cavitation behavior in poly(4‐methyl‐1‐pentene) upon stretching below glass transition temperature was investigated by in situ ultra‐small angle X‐ray scattering technique. Strong stress‐whitening was observed indicating an extensive occurrence of cavitation in the material during tensile deformation below Tg. The X‐ray scattering patterns suggest oriented disc‐shaped cavities with normal mostly parallel to the stretching direction occurred. Structural parameters of such cavities such as thickness, radius, and tilting angle of the normal of the disc with respect to the stretching direction have been successfully calculated using a model fitting procedure. The results exhibited a two‐step process of cavitation that small amount of large cavities appeared first and then small cavities were triggered extensively in the samples at larger strains. This two‐step cavitation phenomenon can be weakened after the quenched sample was annealed or the sample was prepared by slow cooling. This peculiar two‐step cavitation process can be understood as a result of high frozen in internal stress in quenched sample that led to local failure of the materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2007–2014     

聚醋酸乙烯酯/聚丙烯酸甲酯互穿网络聚合物的研究——4.橡胶态模量和网络间的互穿缠结

用动态粘弹谱仪测定了分步法互穿网络聚合物,聚醋酸乙烯酯/聚丙烯酸甲酯(PVAc/PMA-IPN)的橡胶态模量。实验值与从方程E_R=φ_Ⅰ~1/3·E_(R,Ⅰ)~0+φ_(Ⅱ)E_(R,Ⅱ)~0所得理论值的比较,表明网络问有明显的互穿缠结,网络Ⅰ交联程度对其的影响大于网络Ⅱ。并结合实验结果对Binder-Frisch理论中,ΔS_(ent)∝N_(c,Ⅰ)~(-1)·N_(c,Ⅱ)~(-1/2)关系的合理性进行了讨论。     

四乙基二氟化氢铵催化的基团转移聚合

用三种引发剂进行了二氟化氢负离子催化的基团转移聚合,得到了窄分布的,实测分子量和理论分子量相近的一系列聚甲基丙烯酸酯产物,合成了分子量达20万以上的聚甲基丙烯酸甲酯,探讨了引发剂和催化剂用量对产物的分子量和分散性的影响,认为过量的催化剂使产物的分散性加大和实测(?)_n大于理论M_n。得到了控制聚合的最佳催化剂和引发剂浓度比。     

端羟基聚丁二烯型聚氨酯/聚苯乙烯(或聚甲基丙烯酸甲酯)互穿网络的形态和玻璃化转变

互穿聚合物网络(IPN'S)已经成为高聚物共混改性,高聚物间相容性的一个重要研究领域,IPN材料的宏观性能与其微观形态有着密切的关系,如能通过改变结构、组成、交联密度及合成条件等因素来控制IPN的形态,则就可以入为地制备各种性能优良的材料。本文用透射电镜和差示扫描量热仪对同步法合成的端羟基聚丁二烯型聚氨     

微接触印刷法制造聚合物多层次准三维立体微结构

Microstructures of various polymers, such as polystyrene and polymethyl methacrylate, were fabricated with microcontact printing, directly using the corresponding dilute polymeric solutions as “inks”, whose concentrations were about 10 g/L. By repeatedly cross-stamping with the inks, multilayer quasi-three-dimensional polymeric microstructures could be obtained. Both optical photographs and SEM photos showed clear microstructures, which were nearly accurate replication of the original patterns in the PDMS stamps. Microlines of poly-bis-(p-toluene sulfonate)-2,4-hexadiyne-1,6-diol) (PTS) were also fabricated by first processed microcontact printing with solution of the corresponding monomer TS/acetone as ink, then followed with UV polymerization of the monomer micropatterns at solid state. Unlike small molecule processes, the molecules of polymeric inks did not self assembly on the surface of substrates. The formation of polymeric microstructures could be ascribed to the fact that, after volatilization of solvents, polymers tend to stick to the surface of glass substrate which has higher surface free energy (about 72 mN/m), but not to the surface of PDMS stamp which has lower surface free energy (about 20 mN/m). Also the microcontact printing process was studied with optical microscopy, and the main factor--volatilization time of solvent was discussed. The results showed that the volatilization time of solvent is very crucial to the process of polymeric microcontact printing, and with too longer or too shorter volatilization time, the obtained microstructures would become discontinuous or distorted, respectively. For example, with a polystyrene/chloroform solution as ink, the optimal volatilization time was about 15~20 s.     

Shock‐tube spectroscopic water measurements and detailed kinetics modeling of 1‐pentene and 3‐methyl‐1‐butene

To understand the effects of the chemical structure of two C₅ alkene isomers on their combustion properties, and to highlight the major chemical reactions occurring during their high‐temperature oxidation, water time histories were measured behind reflected shock waves for the oxidation of 1‐pentene (C₅H₁₀‐1) and 3‐methyl‐1‐butene (3M1B) in 99.5% Ar. The experiments were carried out at three different equivalence ratios (φ = 0.5, 1.0, and 2.0) at pressures and temperatures ranging from 1.29 to 1.47 atm and 1 331 to 1 877 K, respectively. The H₂O quantification extends the database for 1‐pentene and provides new insights for 3M1B. These unique results were used to validate and to develop a new detailed kinetics model. Numerical predictions are presented, and the new model was able to capture the results with suitable accuracy, with 3M1B being notably more reactive than C₅H₁₀‐1. Sensitivity and rate‐of‐production analyses were performed to help explain the results. Under the present conditions, the reactivity is rapidly initiated by molecular dissociation of a fraction of the pentene isomers. The initiation phase then induces H‐atom abstraction by active radicals (H, OH, O, HO₂, and CH₃) to first produce alkenyl C₅H₉ radicals (or an alkyl radical and an alkenyl radical by breaking a C─C bond) and subsequent, smaller fragments. The difference in terms of reactivity between the isomers is essentially due to the fact that 3M1B has one particularly weak tertiary allylic C─H bond, which allows for fast H‐atom abstraction compared with 1‐pentene.     

A technique to study doped ablation in polymethyl methacrylate using molecular dynamics simulation

A doped polymer substrate is studied using molecular dynamics simulations. Photons are preferentially absorbed as thermal energy by a spherical portion of a polymethyl methacrylate sample. Once sufficient energy is absorbed to fragment the polymer-labeled cluster and cleave the residual polymer bonds, ejection of material occurs indicating ablation. The mechanism of ejection is analogous to our previous work where a dopant cluster was represented using a cluster of carbon atoms [P.F. Conforti, M. Prasad, B.J. Garrison, Physical Chemistry Chemical Physics, 10 (2008) 6002]. This labeling procedure can serve as an approximate method to qualitatively explore the effects of different parameters without becoming consumed in the details of the simulation setup procedure.     

The study of preparation and luminescence of polymethyl methacrylate/rare earth composite luminescent materials

The alkaline-earth–rare-earth–aluminate systems phosphors are the new types of phosphors, which process very bright, safer, and excellent photoluminescence. Because of hydrolysis, however, the capacity of luminescent materials will fall down and the use value of luminescent materials will also be lost. Water-resistant polymers, which can form a kind of water-resistant clad on the surface of luminescent material powder, will solve this problem and the significance of its application is important. In this study, the polymethyl methacrylate (PMMA)/rare earth composite luminescent materials were prepared through grafting emulsion polymerization of methyl methacrylate onto the surface of luminescent materials. To study the structure and properties of the PMMA/rare earth composite luminescent materials, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and photoluminescent properties were measured. From the curves of FTIR and TGA, we can find that the organic parts are attached with the inorganic parts in the PMMA/rare earth composite luminescent materials. The results of luminescent decay curves show that the resistance to water of the PMMA/rare earth composite luminescent materials is much better than that of the unmodified luminescent materials because the organic parts had been grafted on the luminescent materials.     

纳秒脉冲电压同轴电场下有机玻璃和尼龙的闪络特性

 利用基于SOS的SPG200高压脉冲功率装置研究了有机玻璃(PMMA)和尼龙1010在变压器油中的闪络特性。研究结果表明：闪络电压随内电极直径增加近似指数增加，随闪络距离延长近似线性增加，相应的击穿时延也近似线性增加。受实验条件的影响，有机玻璃和尼龙1010的闪络性能略有差异。同轴径向电场降落集中在内电极表面附近一定径向距离内，同轴电场下的闪络电压主要由内电极表面电场与径向电场分布的均匀程度决定。增加内电极直径和延长闪络距离都可以提高闪络电压，而增加内电极直径的效果更显著。     

Isomerization of 4‐Methyl‐1‐pentene and 1‐Hexene Catalysed by Macroporous Ion Exchange Resin: A Kinetic Study

The isomerization of 4‐methyl‐1‐pentene and 1‐hexene, thermodynamically the most unstable propene dimers, was studied. The isomerization was catalyzed by strongly acidic ion exchange resins in the temperature range of 362‐384 K and under atmospheric pressure. The reaction scheme and kinetic equations, which best fit the experimental data are given.