Characterization of polyether and polyester polyurethane soft blocks usingMALDI mass spectrometry

Selective degradation reactions combined with MALDI analysis have been appl ied for molecular weight (MW) determination of polyether and polyester poly urethane (PUR) soft blocks. Selective degradation allows recovery of the po lyols, and direct observation of the soft block oligomer distribution is po ssible for the first time by using MALDI. Ethanolamine is applied for polye ther PUR degradation, MALDI analysis indicates that the recovered polytetra hydrofuran (pTHF) MW distribution is nearly identical to the unreacted pTHF material. Reduction in the ethanolamine reaction time allows observation o f oligomer ions containing the diisocyanate linkage, which provide identifi cation of the diisocyanate, Ethanolamine is not used for polyester PUR's de gradation because the ester bonds will be cleaved. Therefore, phenylisocyan ate is applied for polyester PUR degradation. Polybutylene adipate (pBA) ol igomers were directly observed in the MALDI spectra of the degraded pBA-PUR samples. Comparison of the degraded pBA-PUR oligomer distribution with the unreacted pBA material indicates that low-mass oligomers are less abundant in the degraded pBA-PURs, Oligomer ions containing the diisocyanate linkag e are also observed in the spectrum, providing a means for identifying the diisocyanate used for PUR syntheses. Size-exclusion chromatography (SEC) wa s combined with MALDI to provide accurate MW determination. Narrow MW fract ions of the degraded and unreacted polyols were collected and analyzed by M ALDI, This method allows precise calibration of the SEC chromatogram. The S EC-MALDI results provide significantly larger M-w and PD values than MALDI alone. Using SEC-MALDI, it was determined that the PD indexes of the pTHF a nd PEA samples are larger than the assumed values, which are based on the p olyol synthesis reactions. The combination of selective degradation with SE C-MALDI, using either ethanolamine or phenylisocyanate, is a viable method for polyurethane polyol characterization.