Small molecules accumulated during polycondensation of poly(ethylene terephthalate)

Analysis of Gel Permeation Chromatograms (GPC) of poly(ethylene terephthala te) show an abnormally high concentration of dimer. Electrospray mass spect rometry also showed that the dimer was the major short chain oligomer in PE T spinneret sublimate, rather than the ring trimer, which is usually consid ered to be the major low molecular weight impurity. Using the Florey postul ate it is possible to transform the GPC to p = f(x) where x is the number o f repeat units (x) and p the probability of formation of an ester bond in t he oligomer. This analysis clearly showed that the dimer had an anomalous p robability (p much greater than 1) indicating it is unusually unreactive co mpared to other oligomers of PET. Molecular modeling analysis of the dimer indicated the presence of a low energy conformation involving hydrogen bond ing between the terminal hydroxy and the carbonyl. This folded conformation is 9 kJ mol(-1) lower in energy than non-hydrogen bonded conformations thu s accounting for its low reactivity compared to other oligomers of PET.