Wednesday, November 11, 2015: 10:10 AM
355B (Salt Palace Convention Center)
Conversion of cyclic esters by ring-opening transesterification polymeration (ROTEP) allows for transformation into aliphatic polyesters. A major class of catalysts utilized are the aluminum-salen catalysts. Two Al-salen catalysts (either with two- or three-carbon length backbones) are investigated to understand the operative mechanism. Additionally, the impact of steric (through inclusion of tert-butyl and methyl groups) and electronic (addition of OMe, Br or NO2 groups on the aromatic ring) features of the catalyst are used to gain insight into the thermodynamics of the reaction mechanism. Inclusion of the steric features in the two-carbon catalyst structure lead to an overall increase of 1.8 kcal/mol (mean unsigned difference) for the various stationary points along the pathways considered. Further modification to the electronic characteristics of the catalyst by switching from (OMe to Br to NO2), led to a decrease in the activation energy relative to OMe of -1.2 and -2.8 kcal/mol (Br and NO2 respectively). According to experimental results, the three-carbon catalyst shows a 100-fold rate enhancement over the original two-carbon catalyst. Investigation into the structural difference between the two catalyst structures has shown the two-carbon catalyst to have a more square pyramidal structure (t = 0.389) while the three-carbon catalyst is more trigonal bipyramidal (t = 0.799). Further work will aid in understanding the origin of the enhanced rate of the three-carbon catalyst.