A possible route to the controlled synthesis of polymethyloxirane oligomers using bimetallic μ-oxoalkoxides

Soluble μ-oxo-bimetallic trinuclear alkoxides are known to be very effective catalysts for the ring-opening polymerization of oxiranes. In the particular case of methyloxirane, oligomers are formed in addition to high molecular weight polyethers. An alkoxide-alcohol exchange reaction has proved to be an efficient way to form oligomers preferentially, when the monomer-alcohol molar ratio is small. Upon increasing this ratio, formation of high MW chains occurs increasingly. The use of Ti instead of Al in Al, Zn μ-oxo-n-butoxide in the presence for phenoxyethanol as a co-initiator inhibits formation of exceedingly long polyether chains and the chain length is basically controlled by the monomer to all potential initiating species molar ratio until MW of ca. 6000. Substitution of phenoxyethanol by polypropylene glycol has led to oligomers of a monomodal MW distribution and a MW of 13,000. This study has highlighted that conditions unfavorable to coordination of the polyether chains onto the catalyst improve the control of the oligomer formation. © 1995 John Wiley & Sons, Inc.     

The ring opening and oligomerisation reactions of an epoxide and an episulfide on aluminosilicates in the liquid phase

The ring opening reactions of propylene oxide (methyloxirane) or ethylene sulfide )thiirane) were studied in the liquid phase over HZSM-5, HY-FAU or AlMCM-41 at 363 K or 423 K and under 1 or 20 bar pressure in a batch reactor. The proportion of these routes were identified: (i) single C−O scission providing non-cyclic products, (ii) double C−O cleavage leading to the loss of the heteroatom, (iii) oligomerisation resulting in cyclic dimers and the trimer of thiirane and a non-cyclic dimer of methyloxirane. The reaction pathway depended on the conditions and the solid acids used. Findings are compared to those in the gas phase over the same solid acids. Transformation mechanisms are also suggested.     

The structures of low molecular weight glycerin propoxylates: An experimental,semi-empirical,and Monte Carlo study

A simple Monte Carlo model has been developed for calculating the structural features and properties of low molecular weight triols produced by the base-catalyzed propoxylation of glycerin. The model computes the probability of a reaction to a specific oligomer from the local site reactivities of model compounds with an adjustment for the molecular weight of the reacting oligomer. The resulting product array is then used to calculate typical polymer properties such as average molecular weight, polydispersity, and average chain length. Trial rate constants were estimated from the activation energies of MNDO-PM3 semi-empirical molecular orbital theory. For the compounds used to model the oligomer chain end groups, the activation enthalpies were found to be within the ranges reported for experimental values. Although the predicted enthalpies of activation were significantly higher for the alkoxylation directly at glycerin, this was found to be attributable to intramolecular hydrogen bonding in the reactants that was disrupted in the transition states. Although the hydrogen bonding energies were higher than what are normally considered typical, comparison tests showed that the calculated energies agreed well with experimental values of alkoxide anion–alcohol systems. The PM3 rate constants, when used to calculate Monte Carlo probabilities, predicted the isomer distribution of the four isomeric monopropoxylates with a error of 4%. Optimization of the model reduced this to 0.5%. However, to accurately predict the oligomer distribution of higher molecular weight adducts and other properties, the correction term (M₀/M_i)^b had to be included, where M₀/M_i is the ratio of the molecular weight of glycerin to the molecular weight of the oligomer undergoing alkoxylation, and b is assigned the value 0.7. Although b is empirical, it is consistent with a simple molecular mechanics (MM2) conformational study of the relative availability of the reactive end groups. When the final model was used to simulate the propoxylation of glycerin for a variety of PO/glycerin ratios, it was found to accurately reproduce properties such as primary hydroxyl content, polydispersity, oligomer distribution, and change in the monopropoxylate isomer ratio as a function of bulk PO/glycerin ratio. © 1995 John Wiley & Sons, Inc.     

氟磺酰基二氟乙酰氟,六氟环氧丙烷和六氟丙烯加成反应的研究

本文研究了FO_2SCF_2COF、HFPO和HFP在F~(?)催化下的三元加成反应。我们发现在反应开始时存在着一个反应速度增长的过程,这个过程的长短受溶剂的用量和反应温度的影响。 (CF_3)_2CFCOCF(CF_3)OCF_2CF_2SO_2F只有在5℃以上和乳化催化剂的存在下才生成。通过~(19)F NMR的研究,我们认为FO_2SCF_2COF、HFPO和HFP对于F~(?)的反应活性存在如下的顺序: FO_2SCF_2COF>HFPO>HFP     

环氧丙烷在盐酸中开环反应的机理

环氧丙烷;环氧丙烷在盐酸中开环反应的机理