The hydroxyl and carboxyl end-groups in poly(lactic acid) (PLA) were derivatized with trimethylsilylation or trifluoroacetylation to be detected by
1H DOSY or
19F DOSY with enhanced sensitivity. The diffusion coefficients (
D) for the derivatized end-groups of PLA in a chloroform-
d solution were determined by
1H and
19F DOSY analysis; the values agreed well with each other. The
D values for the end groups were found to be larger than those for the methyl and methine groups in repeating units of the PLA. The relative intensity of the
1H DOSY resonances due to the trimethylsilyl end-group and the main-chain methyl group allowed us to evaluate the dependence of the degree of polymerization on
D.
1H DOSY analysis of PLA treated with diphenylmethane diisocyanate (MDI) was also carried out to determine
D for the junction unit in the PLA. The result clearly indicated that the molecular weight of the PLA increased by the reaction of MDI and the hydroxyl end-groups.
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