Syntheses of Macrocyclic Amides from L-Amino Acid Esters by RCM

IntroductionThe discovery of stable and defined carbenecomplexes of molybdenum and ruthenium as efficientprecatalysts for olefin metathesis has made this transfor-mation one of the most important C—C bond formingreactions[1—11]. Specifically, ring-closi…     

Facile Fabrication of PBS/CNTs Nanocomposite Foam for Electromagnetic Interference Shielding

In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending poly (butylene succinate) (PBS) with carbon nanotubes (CNTs) followed by foaming with supercritical CO₂. The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Increasing the CNT content from 0 to 4 wt % leads to an increase of approximately 3 orders of magnitude in storage modulus and nearly 9 orders of magnitude in enhancement of electrical properties. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm³/g. This study provides a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties.     

Synthesis and mechanochemical properties of biobased ABCBA-type pentablock copolymers comprising poly-d-lactide (A), poly-l-lactide (B) and poly(1,2-propylene succinate) (C)

The ABCBA pentablock copolymers (p-d -l -PPS) comprising poly(d -lactide) (PDLA: A), poly(l -lactide) (PLLA: B) and poly(propylene succinate) (PPS: C) were successfully synthesized by two-step ring-opening polymerization (ROP) of d - and l -lactide using a dihydroxy-terminated PPS as a macro-initiator. The pentablock copolymers revealed the high stereocomplex (sc) crystallinity, thermal stability and elastomeric property in their solution-cast films. It was found that the T_g was found to be proportional to the PPS content, whereas the T_m was proportional to their average block length. The thermal resistivity of the copolymer films was found to be as high as 202°C owing to their sc formation. The copolymers also showed improved stereocomplexibility compared to the enantiomeric mixtures of triblock copolymers (PLLA-PPS-PLLA and PDLA-PPS-PDLA) having similar PLLA and PDLA chain lengths. These pentablock copolymers can afford thermoplastic elastomers or flexible plastic materials having a 100% bio-based content, showing high heat-resistive property.     

Novel aromatic carboxamides from dehydroabietylamine as potential fungicides: Design,synthesis and antifungal evaluation

The present study was carried out to design and synthesize a number of novel aromatic carboxamide derivatives of dehydroabietylamine. The preliminary antifungal assay indicated that most of title compounds displayed moderate to good antifungal activity toward the six fungal strains in vitro. Compounds 3i, 3q, 4b and 4d showed significant antifungal activity against Sclerotinia sclerotiorum, with EC₅₀ values ranging from 0.067 ～ 0.393 mg/L. Compounds 3i, 4b and 4d also showed pronounced mycelial growth inhibition activities against B. cinerea and A. solani. Furthermore, in the in vivo assay, compound 4b exhibited brilliant protective activity against S. sclerotiorum-infected rape leaves. Meanwhile, the in vivo bioassay on tomato plants infected by B. cinerea showed that compound 3i and 4d displayed excellent protective activity at 200 mg/L, which were near to boscalid. Primary mechanistic study revealed that 4b could inhibit sclerotia formation as well as reduce the exopolysaccharide level. SEM and TEM analysis indicated that 4b possessed a strong ability to destroy the surface morphology of mycelia, cell structure and seriously interfere with the growth of the fungal pathogen. In addition, 4b exhibited good inhibitory activity (IC₅₀ = 23.3 ± 1.6 μM) toward succinate dehydrogenase (SDH). Molecular modeling study confirmed the binding modes between compound 4b and SDH. The above antifungal results and fungicidal mechanism study revealed that this class of dehydroabietylamine derivatives could be potential SDH inhibitors and lead compounds for novel fungicides development.     

Thermal Degradation Behavior and Kinetic Analysis of Biodegradable Polymers Using Various Comparative Models, 1

Thermal degradation behavior of a biodegradable polymer (PBS) has been investigated by conventional and MTGA methods. The kinetic parameters of degradation were calculated by a general analytical solution and by the Coats‐Redfern, Ozawa, Horowitz‐Metzger, and MTGA methods. The results reveal that the reaction mechanism at lower temperature is probably the F1 model through the reaction of random chain cleavage via cis‐elimination. However, the reaction mechanism at higher temperature is likely to be D1 model because of the dominant diffusion control effect.

     

静电纺丝法制备PBS纳米纤维膜及缓释血小板内生长因子的PBS纳米纤维膜的生物活性评价

利用静电纺丝法制备了聚丁二酸丁二醇酯(PBS)纳米纤维膜及PBS和富血小板血浆(PRP)的混合纳米纤维膜. 通过扫描电子显微镜、 3-(4,5-二甲基噻唑-2)-2,5-二苯基四氮唑溴盐(MTT)比色法、 支架表面细胞荧光染色法、 材料溶血行为及Elisa法检测体外释放综合评价了支架材料的性能及生物活性. 结果表明, 纳米纤维膜对人骨肉瘤细胞系MG63细胞增殖具有促进作用; 生长因子在最初的突释后, 随材料降解而缓释; 支架材料溶血率为0.1475%(<5%), 符合医用材料的溶血实验要求.     

聚丁二酸丁二酯的无卤阻燃性能的研究

本文研究了聚苯基膦酸二苯砜酯(PSPPP)对聚丁二酸丁二酯(PBS)的阻燃作用。研究发现,在PBS中仅添加4wt%的PSPPP,其垂直燃烧就可以达到UL-94 V-0级,极限氧指数达到34,PSPPP对PBS表现出高效阻燃作用。然而,PSPPP对PBS有促进降解的作用,破坏了PBS的力学性能。通过在PBS/PSPPP体系中添加0.5wt%氧化锌后,有效抑制了PBS的降解,力学性能得到改善。     

Novel tocopheryl compounds. Part 16: Nitration of α-tocopheryl acetate—a mechanistic study

The reaction of α-tocopheryl acetate (vitamin E acetate, 3) with concentrated nitric acid proceeds according to a non-radical, two-step mechanism, producing 5-nitromethyl-γ-tocopheryl acetate (4) in good yields. In the first step, oxidation of 3 affords a benzylic cation intermediate (8), which in the second step adds nitrite to give 4. The acetyl group, which stabilizes intermediate 8 intramolecularly, remains bound to the tocopheryl moiety throughout the reaction.     

生物可降解聚丁二酸/苯基丁二酸丁二醇酯系列共聚物的合成及其结晶行为

合成了一系列聚丁二酸/苯基丁二酸丁二醇共聚酯(PBSBS),利用DSC、1H-NMR和X射线等测试手段对共聚物组成、热力学性能、结晶性能、等温结晶行为进行了表征和研究.结果表明,含苯基的共聚单元的引入显著改变了聚丁二酸丁二醇酯(PBS)的热力学性能4,利用Hoffman-Week曲线得到的共聚物平衡熔点随共聚组分含量的增加显著降低,玻璃化转变温度则明显升高,结晶熔点符合无规共聚物的Flory方程.此外,利用Avrami方程对均聚物PBS以及共聚物PBSBS-10分别进行了等温结晶行为研究,结果表明共聚使结晶速率降低,PBS和PBSBS-10的Avrami指数分别介于2.8~3.0和2.7~2.9之间,结晶方式为三维生长异相成核,X射线测试结果表明共聚不影响晶体结构.     

聚(丁二酸丁二酯-co-丁二酸丙二酯)的等温结晶行为研究

以1,4-丁二酸、1,4-丁二醇和1,3-丙二醇为原料通过直接熔融缩聚法合成了聚丁二酸丁二酯(PBS),聚丁二酸丙二酯(PPS)和聚(丁二酸丁二酯-co-丁二酸丙二酯)(PBSPS)等脂肪族聚酯.利用1H-NMR,WAXD,DSC和POM等研究了聚酯的结晶结构和结晶动力学过程等结晶行为.PBSPS的结晶晶型与PBS一致,说明只有丁二酸丁二酯(BS)单元结晶而丁二酸丙二酯(PS)单元处于无定形区.聚酯等温结晶后,在升温熔融过程中出现了多重熔融峰.分析表明多重熔融峰主要来自于聚酯升温过程中的熔融-重结晶行为.利用Avrami方程分析了聚酯的等温结晶动力学,Avrami指数n为2.2~2.8,说明聚酯等温结晶时主要以异相成核的三维生长方式进行;随着PS单元的增多,聚酯的表观结晶活化能升高,也就是说BS单元的结晶变得困难.POM观察到聚酯等温结晶时都出现了环带球晶现象,球晶形态会随着结晶温度和化学结构差异而改变.