Temperature‐dependent self‐assembly and rheological behavior of a thermoreversible pmma–PnBA–PMMA triblock copolymer gel

Self‐assembly and mechanical properties of triblock copolymers in a mid‐block selective solvent are of interest in many applications. Herein, we report physical assembly of an ABA triblock copolymer, [PMMA–Pn BA–PMMA] in two different mid‐block selective solvents, n‐butanol and 2‐ethyl‐1‐hexanol. Gel formation resulting from end‐block associations and the corresponding changes in mechanical properties have been investigated over a temperature range of ?80 °C to 60 °C, from near the solvent melting points to above the gelation temperature. Shear‐rheometry, thermal analysis, and small‐angle neutron scattering data reveal formation and transition of structure in these systems from a liquid state to a gel state to a percolated cluster network with decrease in temperature. The aggregated PMMA end‐blocks display a glass transition temperature. Our results provide new understanding into the structural changes of a self‐assembled triblock copolymer gel over a large length scale and wide temperature range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 877–887     

Computerized system with a hard-wired data-acquisition unit for potentiometric stripping analysis

The system comprises an electrochemical module interfaced to an controlled by an Apple-IIe microcomputer. A high data-acquisition rate (660 kHz) is achieved by equipping the electrochemical module with a separate memory which is updated in hardware during recording of the stripping step. When a preset cut-off potential is exceeded, data acquisition is automatically terminated, and potentiostatic conditions are resumed. The electrochemical module also contains facilities for instrumental control. The controlling program for the microcomputer is written in assembler code, which can be linked to BASIC routines if necessary. Examples are given to illustrate the advantages of fast data acquisition in improving detection limits and reducing deposition times.     

Gegenüberstellung verschiedener lösungsverfahren zur ermittlung kinetischer parameter anhand von experimentalwerten

The kinetic parameters have been calculated by the differential method according to Freeman and Caroll, the modified differential method, and the integral method according to Coats and Redfern. The calculations have been performed on the base of thermogravimetric data obtained on the recording vacuum thermoanalyzer TA 1 (Mettler). The automatic processing of measured values for off-line operation was carried out by means of data transfer (Mettler) using the small computer KRS 4200. Information on the system and the accuracy of data transfer is given.The methods have been compared for the dehydration of calcium oxalate, the formation of metakaolinite, the oxidation of petroleum coke, and the dehydration of montmorillonite. Using the differential method, in part, kinetic parameters have been obtained which cannot be interpreted in a physical sense. In order to determine the causes of different results, the effects of various mathematical procedures have been studied. This study and the comparison with literature data indicate that the programme for the determination of kinetic parameters by the integral method as described gives the most reliable results.     

K

Tetrahedral framework structures with topologies that show close relationships to the feldspar group or to gismondine are formed by the zincoborophosphates A[ZnBP(2)O(8)] (see picture). The compounds are readily accessible under mild hydrothermal conditions (T(max)=170 degrees C) and are thermally remarkably stable (for example, 940 degrees C for A=Cs). Metalloborophosphates are a new class of compounds, which are expected to provide access to zeolite-like microporous systems.     

Organometallic Homogeneous Catalysis—Quo vadis?

Homogeneous catalysis is the success story of organometallic chemistry. Otto Roelen's initial discovery of hydroformylation in 1938 not only entailed large-capacity production plants but was later followed by systematic research into the catalytic chemistry of the ever-growing class of organometallic compounds. Further developments in industrial chemistry towards clean, low-temperature, low-pressure, and economic processes—in feedstock or in the fine chemicals and polymer area—clearly depend on improved catalysts. Molecularly defined, tailor-made structures are the safest prerequisites for chemical selectivity; hence, organometallic compounds with their overwhelming variety of compositions and structures offer the most promising approach. Wilkinson's catalysts [HRh(CO){P(C₆H₅)₃] and [ClRh{P(C₆H₅)}₃}₃] are outstanding examples. On the other hand, process technology has to be considered also (for example catalyst-product separation and hear-exchange problems). The following review attempts to critically assess the future trends and present demands in the applied area of orgnometallic catalysis–a “gentle art” that is far from being a mature field.