An NMR study of the effect of polymerization methods on segmented sequencedistributions of poly(butylene terephthalate) poly(tetramethylene glycol) block copolymers

Sequence distributions and microstructures of block copolymers of poly(buty lene terephthalate) and poly(tetramethylene glycol) (PBT/PTMG) were investi gated by NMR spectroscopy. The two block copolymers that had same chemical compositions, but were expected to have different sequence distributions we re synthesized by two different polymerization methods differing in feeding time of PTMG (sample I, one step feeding; sample 2, two step feeding). To figure out the small differences in microstructures of the two copolymers u sing NMR, the choice of solvents, the NMR experimental conditions, the H-1 and C-13 peak assignments and the methods of extracting sequence distributi ons were closely reexamined. Using phenol-d(6)/tetrachloroethane (TCE) as N MR solvent, various kinds of controlled 1D and 2D experiments were carried out for peak assignment and close quantification of the peaks. Next, the va rious parameters relating to the sequence distributions were calculated and those were compared for two samples. As the results, the sample that was m ade with one step feeding of PTMG was found to have nearly the same sequenc e distributions as expected by feed ratio. Though there were slight variati ons in microstructures of two samples, detailed statistical treatment (erro r analysis) of 10 independent data showed that there were not significant d ifferences in sequence distributions. In the end of this report, the differ ences in the status of terminal groups of two samples were discussed by man ifest H-1 signals.