Polyester Cyclic Oligomers via Ring-Chain Equilibration Depolymerization

POLYESTER CYCLIC OLIGOMERS VIA RING-CHAIN EQUILIBRATION (DEPOLYMERIZATION) 

Eignre 3.2 compares the level of cyclics on a molar, wt%, or yield basis as a fnnction of reaction concentration. Note that as the reaction concentration dropped, die yield increased to near 100 %, as predicted from theory. However, the amonnt of cyclic PBT on a molar or wt% in solution basis remained constant at the critical monomer concentration, which is about 0.050 M, regardless of the concentration of polymer in solntion. In fact, if one calculates the amount of cyclic present in an equilibrated melt (1-2 %), it is also about 0.05 M cyclic. The same amount of cyclic was generated via the ring—chain equilibration process, regardless of the reaction concentration only tire amount of polymer which remains as a by-product 

and only 11% at 2.7% solids from PET for reactions ran in diphenyl ether, and 29 % yield for a reaction at 2.4% solids in l-mediylnaphtlialene. Otherwise, the reactions appear similar to those reported by Branelle and co-workers [25, 26], except witli longer reaction times and higher temperatures. 

Reports of depolymerization studies carried out by Semiyen and co-workers at the University of York, UK, typically used much longer reaction times (24-72 h) for the depolymerization of PET [27], This group also reported that the titanates were ineffective catalysts for depolymerization, but it is not known whether measures to prevent titanate hydrolysis were taken. The York group also reported that the relative proportions of cyclic oligomers (trimer, tetramer, etc.) altered as the dilution ratio was changed. Similar results were seen with PBT. They have also reported fast-atom bombardment mass spectrometry (FAB-MS), LC-MS, GPC and X-ray crystallography data. The most recent work reports characterization of the cyclic oligomers from six ester and ether ester systems [29], 

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