Use of Di‐tert‐butyl‐dicarbonate Both as a Protecting and Activating Group in the Synthesis of Dipeptides

Amide formation from amino acids was achieved in an easy and convenient one‐pot procedure using di‐tert‐butyl dicarbonate both as a protecting and an activating agent. A number of dipeptides have been synthesized in good yields.     

Modelling and optimization of rebound resilience and hardness of defatted rice bran/calcium carbonate-filled NR vulcanisates

Hardness and rebound resilience of natural rubber (NR) vulcanisates filled with defatted rice bran (DRB)/calcium carbonate (CaCO₃) were modelled and optimized. Second-order polynomial functions were generated to model the properties and to generate contour plots. Predicted properties of NR vulcanisates showed good agreement with experimental results. Hardness of filled-NR vulcanisates increased with filler loading, whereas rebound resilience decreased. At a fixed hardness level, lower CaCO₃ loading can be used with partial DRB replacement. DRB incorporation into rubber compounds can improve their stiffness. Contour plots were used to identify DRB and CaCO₃ level ranges for achieving optimum hardness and rebound resilience.     

Synthesis,Characterization and Application of Amphiphilic Copolymer Poly(vinyl alcohol)-g-Poly(butyl acrylate)

An amphiphilic graft copolymer poly(vinyl alcohol)-g-poly(butyl acrylate) (PVA-g-PBA) was synthesized by grafting butyl acrylate (BA) onto poly(vinyl alcohol) (PVA) with potassium persulfate (KPS) as free radical initiator in N₂ atmosphere and aqueous medium. The formation of graft copolymer was confirmed by means of infrared spectroscopy (IR). The influences of initiator, monomer concentration and reaction time on the percentage of monomer conversion(C _M), graft degree(Gd) and graft efficiency(Ge) have been discussed in detail. PVA-g-PBA was used as compatibilizer in blends of chlorinated polyethylene (CPE)/ poly(acrylic acid-co-acrylamide)[P(AA-AM)], and the compatibility between CPE and P(AA-AM) was also investigated.     

An ESR Study of the UV Photolysis of Styrene and Maleic Anhydride at 90 K

Free radicals produced in styrene and maleic anhydride mixtures and in solutions in acetone and chloroform by UV photolysis at 90 K have been studied by electron spin resonance and changes observed on warming. A doublet spectrum observed in all systems containing maleic anhydride has been assigned to the radical formed by H addition to a carbonyl group in the monomer, and not to the corresponding radical on maleic anhydride units in the copolymer or to the maleic anhydride propagating radical. Interpretations of copolymerization mechanisms based on radicals produced in frozen comonomers in bulk or in solution by photolysis or radiolysis must therefore be viewed with caution.     

Effects of Sericite Modified by Macromolecular Dispersant on the Thermal,Mechanical and Electrical Properties of the NR/SBR Composites

A new hydrosoluble macromolecular dispersant and modifier, poly(ethylene glycol)-maleic anhydride-acrylic acid (PEG-MA-AA) terpolymer was synthesized via ring-opening reaction and free radical polymerization. The chemical structure of the PEG-MA-AA terpolymer was confirmed by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance spectroscopy (NMR), and its average molecular weight was determined by gel permeation chromatography (GPC). Modified sericite (MSE) was synthesized from sericite (SE) by the surface modification with PEG-MA-AA. The NR/SBR/MSE composites were prepared via the blending of the modified sericite and NR/SBR rubber. The thermal, mechanical and electrical properties of the composites were investigated by TGA, tensile test machine and high-insulation resistance meter. The results showed that the thermal stability and the mechanical and electrical insulation properties of NR/SBR/MSE composites were improved significantly. SEM also revealed that modified sericite possessed good dispersibility.     

利用高压水射流技术制备天然橡胶复合材料

首先利用超声空化作用将炭黑团聚体破碎、切割、分散在水中制得炭黑悬浮液,然后在高速射流场中,炭黑悬浮液被高速射流卷吸到天然胶乳中,在射流边界,由于二者存在极大的速度差,而形成一个湍流混合层,炭黑在湍流拉伸、剪切作用下微观分散到天然胶乳中.结果表明,与传统干法工艺相比,射流工艺可以使炭黑更均匀的分散到天然橡胶基体中.Payne效应结果表明射流工艺减弱了炭黑与炭黑之间的相互作用,增强了炭黑与橡胶之间的相互作用.同时射流工艺制备的复合材料硫化时间变短,硫化程度增加,硫化胶的撕裂强度提高了78%,回弹性提高了20%,DIN磨耗减小了33%.动态力学性能结果表明,射流工艺制备的复合材料在60℃左右具有更低的损耗因子.     

橡胶改性沥青储存稳定性试验研究

制作了普通橡胶沥青和脱硫橡胶沥青,并进行了不同储存温度或不同储存时间条件下2种橡胶改性沥青的稳定性试验.研究表明,脱硫橡胶沥青经高温静态储存后比普通橡胶沥青更易离析.经过高速剪切工艺,大颗粒的脱硫橡胶粒在沥青里大多分散成无明显颗粒的细小物质,其胶粉颗粒大小在2种橡胶沥青的性能比较中不产生影响;而普通橡胶粉剪切后基本保持...