用液相色谱法分析聚对苯二甲酸丁二醇酯的解聚产物

采用超临界甲醇解聚的方法,将聚对苯二甲酸丁二醇酯（PBT）降解为对苯二甲酸二甲酯（DMT）和丁二醇两种单体。利用液相色谱法分析产物DMT,建立了较好的分析方法。其实验操作条件如下：色谱柱为DiamonsilC18,流动相为甲醇-水（3：1,y／y）,检测波长254nm。测定结果为DMT含量在0．005-0．25μg,线性关系良好。该方法具有高色谱分辨率、简单、准确、重复性好等特点。     

Unzipping and scrambling reaction-induced sequence control of copolymer chains via temperature changes during cationic ring-opening copolymerization of cyclic acetals and cyclic esters

A temperature change-dependent sequence transformation of copolymer chains was demonstrated by a method based on tandem depolymerization and transacetalization reactions during the cationic ring-opening copolymerization of cyclic acetals and cyclic esters. In this study, the position of polymerization-depolymerization equilibrium was controlled by the reaction temperature rather than by the decrease in monomer concentration under vacuum conditions, as in our previous study. First, the conditions for efficient copolymerization were optimized, with a particular focus on the structures of cyclic acetals and cyclic esters. Subsequently, sequence transformation induced by temperature change was examined during the copolymerization of 2-methyl-1,3-dioxepane (generated in situ from 4-hydroxybutyl vinyl ether) and δ-valerolactone using EtSO₃H. The homosequence length of cyclic acetals decreased during depolymerization (unzipping) at the oxonium chain ends upon increasing the temperature from 30 to 90 °C, while transacetalization (scrambling) of the main chain transferred midchain cyclic acetal homosequences to the oxonium chain ends. As a result of the cycle of unzipping and scrambling reactions, an alternating-like copolymer was obtained. Interestingly, the possibility of reversible sequence transformation upon heating and cooling was also demonstrated.     

Transforming polylactide into value‐added materials

The production of chemical building blocks and polymer precursors from biorenewable and sustainable resources is an attractive method to bypass traditional fossil fuel derived materials. Accordingly, we report the organocatalytic recycling of postconsumer polylactide (PLA) into value‐added small molecules. This strategy, using the highly active transesterification catalyst triazabicyclodecene, is shown to completely depolymerize PLA in the presence of various alcohols into valuable lactate esters. Using previously used PLA packaging material, the depolymerization is complete in minutes at room temperature and fully retains the stereochemistry of the lactate species. Further, the modularity and utility of this methodology with respect to polyester substrate is detailed by using a variety of functional alcohols to depolymerize both PLA and polyglycolide, with the corresponding ester small‐molecules being used to make new polymeric materials. The opportunities to transform waste streams into value‐added chemicals and new materials through simple and versatile chemistry hold significant potential to extend the lifecycle of renewable chemical feedstocks. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Qualitative analysis of enzymatic and chemical depolymerized low molecular weight heparins by UHPLC coupled with electrospray ionization quadrupole time‐of‐flight‐mass spectrometry

Complete heparin digestion with heparin lyase I and II results in a mixture of hexasaccharides and tetrasaccharides with 3‐O‐sulfo group‐containing glucosamine residues at their reducing ends. Because these tetrasaccharides are derived from antithrombin III‐binding sites of heparin, we examined whether this method could be applied to estimate the anticoagulant activity of heparin. Therefore, this paper presents a new low molecular weight heparin sample preparation method–chemical depolymerization. Qualitative analysis of the studied compounds and a comparison of their composition are an important contribution to the structural analysis of low molecular weight heparins, which has not been fully conducted so far. Qualitative on‐line liquid chromatography–mass spectrometric analysis of these resistant oligosaccharides is also described in this paper.     

Thermal depolymerization mechanisms of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Thermal degradation processes and decomposition mechanisms of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were investigated by using thermal gravity analysis(TGA), Gel permeation chromatography (GPC), elemental analyzer, pyrolysis-gas chromatography-mass spectrometry (PyGC-MS) and 1H nuclear magnetic resonance (1H NMR). The degradation activation energy was calculated via the dependence of residual mass on isothermal temperature. 1H NMR and PyGC-MS were used to investigate the chemical structure and component proportion of volatile gases and degradation residues which were produced by thermal decomposition, and to infer the process of macromolecular chain scission. Besides, the influence of the factors, such as outfield atmosphere, residual metal ions, on the degradation behaviors of PHBV was also studied. Finally, the PHBV thermal decomposition mechanisms were speculated on the basis of the degradation behaviors of molecular and chemical structure.     

Depolymerization of end-of-life poly(dimethylsilazane) with boron trifluoride diethyl etherate to produce difluorodimethylsilane as useful commodity

A straightforward protocol for the depolymerization of end-of-life poly(dimethylsilazane) using boron trifluoride diethyl etherate as depolymerization reagent to convert the Si-N to Si-F bonds was set-up. The application of the depolymerization reagent affords difluorodimethylsilane as major products, which can be a suitable synthon for the synthesis of new polymers (e.g., poly(dimethylsiloxanes) and allow an overall recycling of the [Me₂Si]-unit.     

Isolation of Functionalized Phenolic Monomers through Selective Oxidation and CO Bond Cleavage of the β‐O‐4 Linkages in Lignin

Functionalized phenolic monomers have been generated and isolated from an organosolv lignin through a two‐step depolymerization process. Chemoselective catalytic oxidation of β‐O‐4 linkages promoted by the DDQ/tBuONO/O₂ system was achieved in model compounds, including polymeric models and in real lignin. The oxidized β‐O‐4 linkages were then cleaved on reaction with zinc. Compared to many existing methods, this protocol, which can be achieved in one pot, is highly selective, giving rise to a simple mixture of products that can be readily purified to give pure compounds. The functionality present in these products makes them potentially valuable building blocks.     

Study on thermal degradation mechanisms of comb polyacrylates containing long fluorocarbon side chains by TG/FTIR

Thermal degradation of two series of polyacrylates containing long fluorocarbon chains [abbr.: PF_nA {HCF₂(CF₂)_n−1  CH₂ O C(O) , n = 4, 6, 8, 10} and abbr.: PFF_nEA {CF₃(CF₂)_n−1  CH₂CH₂ O C(O) , n = 6, 8, 10}] was investigated by TG /FTIR. Thermal degradation behavior of polymers changed depending on the type of tie groups, which link the fluorocarbon chains to the main chain, and also on the length of fluorocarbon chains. It was clarified that the apparent activation energies (ΔE_a ) of PF_nA series obtained by Ozawa's method varied in the order of PF₄A > PF₆A > PF₈A > PF₁₀A, while those of PFF_nEA series having tie group of  CH₂ CH₂ O C(O) were almost constant. The results for PF_nA series (tie group:  CH₂ O C(O) ) are attributable to the shield effect of long fluorocarbon chains on the back‐biting reaction in the thermal degradation of comb polymers rather than the change of C C bond dissociation energy in the main chain. It was found that TG curves of PFF_nEA series were shifted to the lower temperature region than those of PF_nA. This result can be attributable to the scission of side groups followed by the evaporation of fluorocarbon compounds and carbon dioxide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2794–2803, 2000