纤维素酶降解结合超滤后处理制备低聚壳聚糖

纤维素酶降解与超滤结合制备壳聚糖,工艺简单可行,产品平均分子量小而分布窄,收率高。试验确定纤维素酶对壳聚糖降解的最佳反应条件为:温度(T)=50℃,时间(t)=3.5~4.0 h,纤维素酶用量与壳聚糖比值(n)=0.1,pH=4.6。降解产品经过超滤处理后可以获得平均分子量在5 000左右的优质壳聚糖产品。     

碱木质素超/亚临界乙醇体系解聚机理研究

采用微型高温高压反应釜,在超/亚临界乙醇体系,进行麦草碱木质素的解聚实验,通过扫描电子显微镜(SEM)、气相色谱/质谱联用仪(GC/MS)及红外光谱仪(FT-IR)对解聚产物进行分析,探讨大分子结构的解聚机理。结果表明,碱木质素在乙醇临界点条件(240℃,7.2 MPa)解聚获得最低残焦得率,数值为16.5%。碱木质素在亚临界乙醇体系解聚过程,碱木质素熔融形成直径1.0-2.0μm的微球分散于乙醇中,结构单体间少量醚键和苯环侧链Cα均裂断裂,形成酚类、酯类、酮类和酸类产物;碱木质素在超临界乙醇体系解聚过程,熔融微球直径明显缩小,解聚时发生大量结构单体间醚键、苯环侧链Cα断裂及酯类产物的二次分解反应,解聚产物中酯类产物含量(11.94%)降低,酚类产物得率(52.14%)提高。     

Application of a depolymerization model for predicting thermochemical hydrolysis of hemicellulose

Literature data were collected and analyzed to guide selection of conditions for pretreatment by dilute acid and water-only hemicellulose hydrolysis, and the severity parameter was used to relate performance of different studies on a consistent basis and define attractive operating conditions. Experiments were then run to confirm performance with corn stover. Although substantially better hemicellulose sugar yields are observed when acid is added, costs would be reduced and processing operations simplified if less acid could be used while maintaining good yields, and understanding the relationship between operating conditions and yields would be invaluable to realizing this goal. However, existing models seldom include the oligomeric intermediates prevalent at lower acid levels, and the few studies that include such species do not account for the distribution of chain lengths during reaction. Therefore, the polymeric nature of hemicellulose was integrated into a kinetic model often used to describe the decomposition of synthetic polymers with the assumption that hemicellulose linkages are randomly broken during hydrolysis. Predictions of monomer yields were generally consistent with our pretreatment data, data reported in the literature, and predictions of other models, but the model tended to overpredict oligomer yields. These differences need to be resolved by gathering additional data and improving the model.     

用PET解聚产物合成聚氨酯密封胶

以聚对苯二甲酸乙二醇酯(PET)醇解得到的聚酯多元醇(PDA Mn=200~500)为软段、二苯基甲烷-4,4'-二异氰酸酯(MDI)为硬段,制备了一系列端-NCO基的湿-固化型聚氨酯密封胶。不仅为废聚酯瓶回收利用提出了新方法,而且合成了一种新的材料聚酯型聚氨酯密封胶。     

Acyclic diene metathesis (ADMET) depolymerization: Ethenolysis of 1,4-polybutadiene using a ruthenium complex

α,ω-Vinyl-terminated butadiene oligomers can be generated through the cross-metathesis of ethylene and high molecular weight 1,4-polybutadiene catalyzed by the complex RuCl₂(CHPh)(PCy₃)₂. The effect of varied ethylene pressure is studied in order to obtain the highest conversion to the monomer 1,5-hexadiene. A dramatic increase in yield of this monomeric diene is realized relative to previous published attempts utilizing a well-defined group VI metal alkylidene in the same chemistry. Traces of side products are observed, and alternate mechanisms for their formation were proposed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1857–1861, 1999     

Role of back-biting for generation of hybrid dimers and trimers on flash pyrolysis of poly(styrene-co-methacrylonitrile)

The role of the back-biting reaction for generation of dimers and trimers on flash pyrolysis of poly(styrene-co-methacrylonitrile) by pyrolysis gas chromatography with the use of a Curie-point pyrolyzer has been investigated. Yields of each monomer, dimer, and trimer changed depending on the sequence distribution as well as on copolymer composition and pyrolysis temperature. The degradation behavior was explained by the competition between the back-biting reaction and depolymerization. It was found that the hybrid dimers and trimers were produced mainly by the back-biting reaction, which was followed by β-scission, and hence yields of hybrid dimers and trimers correctly reflect the sequence distribution of the copolymer of styrene and methacrylonitrile without interference from the second reaction of monomers regenerated in the flash pyrolysis. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2747–2753, 1999     

Selective complete decomposition of poly(n‐hexylisocyanate) and its use in a new molecular design method

Poly(n‐hexylisocyanate) (PHIC‐NH) as a rod‐like polymer having a ? NH group at one end of the polymer chain was found to instantly (less than a few seconds) be completely decomposed by CH₃O^?Na⁺ in tetrahydrofuran/CH₃OH under a mild experimental condition ([CH₃O^?Na⁺] < 1 mol L^?1 at room temperature).The mechanism of the decomposition for the PHIC‐NH consists of two steps: the first is abstraction of the proton for PHIC‐NH by Na⁺ with a slow reaction rate, and the second is the consequent depolymerization of PHIC‐N^? based on the equilibrium polymerization with a rapid depolymerization rate. The decomposition rate constants (k_d) depend on M_w of PHIC‐NH, namely k_d ～ M_w^?1.0. The decomposition of the PHIC‐NR having an end‐capped ? NR group was completely depressed. Using an “all or nothing” mechanism for the decomposition, the (PHIC)_3.43 comb‐shaped polymer and polystyrene (PSt)‐graft‐(PHIC‐NH)_4.28 graft copolymer were, respectively, decomposed to produce (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 in a series with different numbers of PHIC‐NH combs and PHIC‐NH grafts by regulating the amount of CH₃O^?Na⁺ and the decomposition time. Molecular structure of (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 was discussed from a viewpoint of PSt‐reduced chain dimension per molar mass. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Fast screening of Depolymerized Lignin Samples Through 2D-Liquid Chromatography Mapping

Lignin valorization and particularly its depolymerization into bio-aromatics, has emerged as an important research topic within green chemistry. However, screening of catalysts and reaction conditions within this field is strongly constrained by the lack of analytical techniques that allow for fast and detailed mapping of the product pools. This analytical gap results from the inherent product pool complexity and the focus of the state-of-the-art on monomers and dimers, overlooking the larger oligomers. In this work, this gap is bridged through the development of a quasi-orthogonal GPC-HPLC-UV/VIS method that is able to separate the bio-aromatics according to molecular weight (hydrodynamic volume) and polarity. The method is evaluated using model compounds and real lignin depolymerization samples. The resulting color plots provide a powerful graphical tool to rapidly assess differences in reaction selectivity towards monomers and dimers as well as to identify differences in the oligomers.