Polymers of carbonic acid 32: Influence of catalysts on propagation and cyclization in the interfacial polycondensation of bisphenol A with diphosgene

Bisphenol A was polycondensed with diphosgene in a dichloromethane/aqueous NaOH system. Temperature, time, and molar ratios of the reactants were optimized according to a previously elaborated optimization of the hydrolytic polycondensation of bisphenol A bischloroformate. Five of the following catalysts were examined: triethylamine, 4‐(N,N‐dimethylamino)pyridine (DMAP), ethyldiisopropylamine (EDPA), tetrabutylammonium hydrogen sulfate, and triethylbenzylammonium chloride (TEBA‐Cl). Triethylamine and DMAP accelerated the hydrolysis of diphosgene by formation of a hydrophilic acylammonium salt. Therefore, the molecular weights decreased with higher concentration of these tert‐amines. However, the molecular weights increased (weight‐average molecular weight up to 10⁶) with higher concentrations of tetraalkylammonium salts because these catalysts favor chain growth in the organic phase via “naked” phenoxide ions without catalyzing the hydrolysis of diphosgene. EDPA gave poor results under all circumstances. Cyclic polycarbonates were discovered in all samples. Their fraction increased with the average molecular weight of the samples. When samples prepared with triethylamine or TEBA‐Cl were fractionated, cycles having molar masses up to 15,000 Da were detected by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 890–904, 2003     

Die Beeinflussung des Kristallhabitus beim chemischen Transport

On the Influence of Chemical Transport on the Habit of Crystals The chemical transport of silicon with silicon tetrachloride as transporting agent leads to crystals with octahedral shape. On the other hand in the presence of adsorbable impurities the transported silicon crystallizes in the shape of long needles. Chemical transport reactions of tellurium are successful with iodine or sulphur. The presence of adsorbable transporting agents has considerable influence on the habit of crystals.