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

Sequence distributions and microstructures of block copolymers of poly(butylene terephthalate) and poly(tetramethylene glycol) (PBT/PTMG) were investigated by NMR spectroscopy. The two block copolymers that had same chemical compositions, but were expected to have different sequence distributions were 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 using NMR, the choice of solvents, the NMR experimental conditions, the H-1 and C-13 peak assignments and the methods of extracting sequence distributions were closely reexamined. Using phenol-d(6)/tetrachloroethane (TCE) as NMR solvent, various kinds of controlled 1D and 2D experiments were carried out for peak assignment and close quantification of the peaks. Next, the various parameters relating to the sequence distributions were calculated and those were compared for two samples. As the results, the sample that was made with one step feeding of PTMG was found to have nearly the same sequence distributions as expected by feed ratio. Though there were slight variations in microstructures of two samples, detailed statistical treatment (error analysis) of 10 independent data showed that there were not significant differences in sequence distributions. In the end of this report, the differences in the status of terminal groups of two samples were discussed by manifest H-1 signals.