Thermogravimetric kinetics of polymer degradation: Science or fiction?

Weight changes in thermogravimetry are dependent on the volatility of the degradation products. Thus, molecular weight determinations (or related studies) must fist be undertaken to prove whether or not nonvolatile chain fragments will be removed only at high temperatures. In this case both thermal stability and kinetic studies by thermogravimetry are senseless. But even if volatile products are formed, the kinetic parameters will depend on the conversion degrees because of the kinetic chain character of the polymer degradation. Changes in reaction mechanism aggravate the situation; it is thus problematic to define in such conditions reliable kinetic parameters. Values calculated from a single TG curve are valid for specific conditions only, but of no sense from the general kinetic view.     

A puckered 2D copper coordination polymer with dimensions 14.91×12.63 Å

The polymeric complex [Cu(spcp)₂(H₂O)]_n·(H₂O)_2n (spcp⁻=4-sulfanylmethyl-3-phenylcarboxylate pyridine) with puckered grids of dimensions 14.91×12.63 Å was obtained in the reaction of the Cu(OAc)₂·5H₂O with Na(spcp) by solvothermal method.     

A rare 2D coordination polymer of graphite-like structure extended by infinite silver–oxygen–silver bonds

The reaction of AgNO₃ and H₃btb (H₃btb = 1,2,3-benzenetricarboxylic acid) leads to the isolation of {[Ag(μ₂-H₂O)(μ₂-H₂btb)]}_n · 1.5nH₂O (1), which crystallizes in the orthorhombic space group Fddd with a = 11.436(2) Å, b = 6.876(1) Å, c = 58.837(1) Å, V = 4626.5(2) Å³, Z = 32. Silver ions are connected by both strong Ag?Ag interaction and μ₂-H₂O bridges to form hexagonal Ag₆ subunits, and are further assembled into a high ordered 2D grid, presenting an interesting graphite-like 6³ net. Both the fluorescence and the crystal transformation after dehydration are studied.     

Sequential transformation and utilization of natural network polymer “LIGNIN”

Lignin is the most abundant and complicated natural polymer, forming long-term carbon flow in the ecosystem. Lignin is composed of phenyl propane units which are the combination of glycerol- and polyhydric phenol units. A key for sequential functionality control is how to control C1- (7%) and C2- (50%) aryl ethers selectively. The cleavage of C1 aryl ethers results in the transformation of polymer structures from network to linear-type, and that at C2 leads to depolymerization to dimer–oligomer level. The originally designed sequential transformation system includes two steps: 1st step; the selective control of C1 structures to give 1,1-bis(aryl)propane type units, leading to the standardization of C1 functionality, 2nd step; the selective control of C2 structures using intramolecular switching devices [1,1-bis(aryl)propane-2-O-aryl ether units], leading to the change of molecular weight and phenolic activity. The polymers, lignophenols, derived from native lignin through C1 control are multi-functional lignin-based materials, linear types of lignin subunits with phenol derivatives at C1. Sequential applications have been designed originally.     

A molecular layer “fabric” with orthogonally woven coordination polymer chains

Crystals of [Cu(ox)(dpa)(H₂O)]_n (1, ox = oxalate, dpa = 4,4′-dipyridylamine) were prepared by hydrothermal reaction of potassium copper oxalate and dpa. Single-crystal X-ray diffraction showed the formation of orthogonally oriented sets of 1D [Cu(ox)(dpa)(H₂O)]_n chains that interlock in a 1D + 1D ➔ 2D manner to form woven “warp-and-woof” supramolecular layers. Thermogravimetric analysis indicated that the structure of 1 remained stable to about 175 °C.     

Hydrogen-bond directed 2D → 3D polythreading of a new luminescent Cd(II) coordination polymer

Solvothermal reactions of Cd(II) salts with biphenyl-3,4′,5-tricarboxylic acid (H₃L) and melamine (MA) afford a new coordination polymer, namely [Cd₃(L)₂(MA)₂(H₂O)₂]_n (1). Single crystal X-ray analysis reveals that compound 1 displays a new 2D → 3D polythreaded motif directed by intermolecular hydrogen bonds, in which large opened windows of each (3,6)-connected layer are threaded by two dangling MA molecules from adjacent layers in the opposite direction. In addition, the luminescent property of 1 was also investigated in the solid state at room temperature.     

A 3D oxalate-bridged [CuIIFeII] coordination polymer as molecular precursor for CuFe2O4 spinel—photocatalytic features

A 3D heterometallic oxalate-bridged coordination polymer [Cu^IIFe^II₂(H₂O)(terpy)(C₂O₄)₃]_n (terpy = 2,2′:6′,2″-terpyridine) ( 1 ) was investigated both as photocatalyst for the organic dye removal and as a single-source precursor for the preparation of the copper ferrite (CuFe₂O₄) nanocrystals by thermal processing. The dual functionality of 1 was supported by the degradation of aqueous solutions of rhodamine B (RhB) and methylene blue (MB) solutions under visible (Vis) and ultraviolet (UV) light irradiation, powder X-ray diffraction data collection at room temperature, and the optical and scanning electron microscopy analyses. A close inspection of the X-ray diffraction patterns unveiled qualitative and quantitative information on the phase composition obtained after the single-source molecular precursor route to spinel oxide. By optimizing the temperature levels and setting the controlled heating rate at 6 h of holding time, the phase composition of thermal processing of 1 was evaluated—thermal treatment of 1 at 950°C for 6 h and a heating/cooling rate of 10°C min⁻¹ resulted in the formation of solely tetragonal spinel phase of CuFe₂O₄, whereas the formation of both tetragonal and cubic CuFe₂O₄ phases was observed at 950°C by the heating rate of 30°C min⁻¹. To obtain the high-temperature cubic CuFe₂O₄ oxide, compound 1 was heated and then quenched at 925°C, which led to the formation of the cubic spinel ferrite as the main crystalline oxide phase. Moreover, the photocatalytic properties of the t-CuFe₂O₄ spinel were investigated under the same conditions as for 1 . The optical bandgap energies were estimated from UV–Vis absorption spectra for both metal oxide and precursor powder.     

光化学合成维生素D2和D3

综述了光化学法合成维生素Ｄ２和Ｄ３的研究进展。     

Sustainable polymer reaction engineering: Are we there yet?

Polymers are a class of materials that provide unparalleled benefits to humanity, fulfilling countless needs in an exceedingly broad range of applications. Because of their ubiquity and current ways of producing them, polymers also pose significant challenges to the environment. Inspired by a previous publication on sustainable polymer reaction engineering, an update is provided on the latest trends in the use of renewable starting materials for polymers, efforts in process intensification and water‐based polymerization, as well as approaches to dealing with the end of the polymers' application life. We seek to answer the question about how far along we are regarding the achievement of completely sustainable polymer processes.     

3D“电臀”策略

现代OL每天大多数时间都是坐着,工作时对着电脑,回家后看书上网,从来都不爱做运动,而在炎炎夏日穿比基尼时,扁平的臀部,或是臀部皮肤粗糙都是大忌。想要塑造圆润迷人的美臀,记得每天做臀部功课,三个星期就可改变你的臀部问题!     

Ibuprofen–polymer precipitation using supercritical CO2 at low temperature

A process for the SAS coprecipitation of ibuprofen with the polymers poly(l-lactic acid) and Eudragit L100 was successfully carried out. The particle size was reduced to micrometer and near nanometer ranges. The morphology of the raw material changed to spherical upon processing for both poly(l-lactic acid)/ibuprofen particles and eudragit/ibuprofen particles. The eudragit-based particles were significantly smaller than those obtained with poly(l-lactic acid). Ibuprofen release profiles were determined for simulated gastric and intestinal fluids in order to study the effect of the polymer and to identify the appropriate systems for different administration routes. The in vitro release profiles for both polymer/drug systems showed a slower and more controlled release in comparison to the unprocessed ibuprofen. Moreover, the effects of pressure, temperature, initial concentration of the solution and drug-to-polymer ratio on the particle size and morphology of these drug/polymer systems have been evaluated. According to the XRD, DSC and FTIR data, physicochemical interactions do not occur between ibuprofen and the polymers and a proportion of the ibuprofen molecules probably remained on the microparticle surface.     

An intriguing 4d–4f heterometallic coordination polymer with 1D pseudo-nanotube architectures

A new one-dimensional (1D) 4d–4f heterometallic coordination polymer [ErAg(Himdc)₂(H₂O)₃] (1) (H₃imdc = 4,5-imidazoledicarboxylic acid) is synthesized under hydrothermal condition and characterized by elemental analysis, IR, PXRD and single crystal X-ray diffraction. Complex 1 crystallizes in the triclinic space group P-1, showing a 1D metal–organic pseudo-nanotube with a 4.014 × 12.027 Å² cross-section. Furthermore, it assembles into a 3D supramolecular architecture via hydrogen bonds between pseudo-nanotubes. The complex 1 exhibits solid-state photoluminescence and high thermal stability.     

Two stacked 2Dchiral/2Dchiral → 2Dachiral sheets based on V-shaped imidazolyl ligand and flexible aliphatic acids

Two new stacked 2D_chiral/2D_chiral → 2D_achiral coordination polymers {[Cd(BIDPE)(pim)]·(H₂O)}_n (1) and {[Cd(BIDPE)(glu)]·(H₂O)}_n (2) were prepared under hydrothermal conditions based on V-shaped ligand 4,4′-bis(imidazol-1-yl)diphenyl ether (BIDPE) and flexible polycarboxylic acids. In addition, the solid-state photoluminescent spectra were measured at room temperature.     

维生素D2生产新工艺

经预处理、萃取、浓缩、结晶等过程从富含麦角固醇的菌丝体中提取麦角固醇,并用自制紫外光源和反应器将其转化为维生素D_2。此新工艺成本低,麦角固醇转化率高,具有良好的经济效益,得到的麦角固醇和维生素D_2分别符合SIGMA公司试剂标准和国家药典标准。     

Optically active thermosensitive amphiphilic polymer brushes based on helical polyacetylene: preparation through “click” onto grafting method and self-assembly

Optically active, thermosensitive, and amphiphilic polymer brushes, which consist of helical poly(N-propargylamide) main chains and thermosensitive poly(N-isopropylacrylamide) (PNIPAm) side chains, were prepared via a novel methodology combining catalytic polymerization, atom transfer radical polymerization (ATRP), and click chemistry. Helical poly(N-propargylamide) bearing α-bromoisobutyryl pendent groups was synthesized via catalytic polymerization, followed by substituting the –Br moieties with azido groups. Then, alkynyl terminated PNIPAm formed via ATRP was successfully grafted onto the azido functionalized helical polymer backbones via click chemistry, providing the expected polymer brushes. GPC, FT-IR, and ¹H-NMR measurements indicated the successful synthesis of the novel amphiphilic polymer brushes. UV–vis and CD spectra evidently demonstrated the helical structures of the polymer backbones and the considerable optical activity of the final brushes. The polymer brushes self-assembled in aqueous solution forming core/shell structured nanoparticles, which were comprised of optically active cores (helical polyacetylenes) and thermosensitive shells (PNIPAm).     

Ionic polymer–metal composite mechanoelectric transduction: effect of impedance

Ionic polymer–metal composites (IPMCs) are commonly used as soft actuators due to their electromechanical response. However, the reverse phenomenon, i.e. IPMC's ability to generate charge on application of mechanical strain (mechanoelectric response), is not very well understood. The concept of mechanoelectric transduction and its dependence on complex IPMC architecture comprising of electrode, polymer and composite layer is illustrated with a phenomenological model. The impedance model takes into account the charge transport inside the polymer and layer properties in terms of their impedances. The model lucidly indicates the significance of capacitance in IPMC transduction. The impedance model is used for studying IPMC step and frequency response and the effect of IPMC capacitance on its application as energy harvester.     

Alternative feedstocks: a continuing trend in the polymer industry?

Polymers as we know them today have been developed from the feedstock available at the time of their formulation, i.e. crude oil in particular. Fossil feedstocks are used primarily for heating, cooling and fuelling engines in automobiles and power plants. Due to environmental awareness, increasing oil prices and strong progress in biotechnology in recent decades, new feedstocks will become available for fuels. Bio‐refineries will emerge in parallel with the existing oil refineries, and the feedstocks produced by these bio‐refineries will in part also be used to make polymers. This paper elucidates the historical developments and the possibilities for protecting our planet from pollution and global warming. Copyright © 2011 Society of Chemical Industry