Determination of Sequence and Composition in Poly(Butyleneadipate-Co-Butyleneterephthalate) by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been used here for the analysis of an unfractionated copolymer sample of poly(butyleneadipate-co-butyleneterephthalate) (PBA/PBT). This is our first report on unfractionated samples, since previous studies by MALDI-TOF MS have concerned copolymer fractions. Mass-resolved peaks are seen up to 8000 Da. The peaks are due to oligomers which have a methylester and an hydroxy as end groups (CH₃O/OH), which desorb by uptake of a sodium cation. We compared the intensity of mass spectral peaks with the theoretical intensities generated using a Bernoullian distribution of sequences. The composition which gives the best match was searched by the MACO4 program and a value of 49/51 in favor of terephthalic units was found, in excellent agreement with the composition derived from the ¹H NMR data.