Sequence distribution in polyethylene/tetramethylene terephthalate copolyesters by 13C-NMR

¹³C-NMR gives sequence information in copolyesters synthesized from ethylene glycol (EG), 1,4-butane diol (BD), and methyl terephthalate (TP). The EG-TP-EG and BD-TP-BD blocks are distinguishable from the unsymmetrical diester sequence EG-TP-BD. The carbonyl and aromatic quaternary carbons of terephthalate have different chemical shifts but identical relaxation times and nuclear Overhauser enhancements in the three different triad sequences. Peak areas indicate random copolymerization of the three copolyesters studied.