Characterization of Polyether and Polyester Polyurethane Soft Blocks Using MALDI Mass Spectrometry

Abstract

Selective degradation reactions combined with MALDI analysis have been applied for molecular weight (MW) determination of polyether and polyester polyurethane (PUR) soft blocks. Selective degradation allows recovery of the polyols, and direct observation of the soft block oligomer distribution is possible for the first time by using MALDI. Ethanolamine is applied for polyether PUR degradation. MALDI analysis indicates that the recovered polytetrahydrofuran (pTHF) MW distribution is nearly identical to the unreacted pTHF material. Reduction in the ethanolamine reaction time allows observation of oligomer ions containing the diisocyanate linkage, which provide identification of the diisocyanate. Ethanolamine is not used for polyester PUR's degradation because the ester bonds will be cleaved. Therefore, phenylisocyanate is applied for polyester PUR degradation. Polybutylene adipate (pBA) oligomers 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 linkage are also observed in the spectrum, providing a means for identifying the diisocyanate used for PUR syntheses. Size-exclusion chromatography (SEC) was combined with MALDI to provide accurate MW determination. Narrow MW fractions of the degraded and unreacted polyols were collected and analyzed by MALDI. This method allows precise calibration of the SEC chromatogram. The SEC-MALDI results provide significantly larger Mw and PD values than MALDI alone. Using SEC-MALDI, it was determined that the PD indexes of the pTHF and pBA samples are larger than the assumed values, which are based on the polyol synthesis reactions. The combination of selective degradation with SEC-MALDI, using either ethanolamine or phenylisocyanate, is a viable method for polyurethane polyol characterization.

Quantitative analysis of polypropyleneglycol mixtures by desorption/ionization on porous silicon mass spectrometry

“…Since Tanaka et al reported the successful ionization of PEGs by their unique soft laser desorption method [4], a variety of polyethers has been analyzed by MALDI-MS [12][13][14][15][16][17][18][19][20][21][22]; e.g., Li and coworkers reported characterization of complex polyethers [19] and Hercules and coworkers analyzed PTHF, a soft block in a polyurethane, after chemical degradation of the urethane bond by ethanolamine [20].…”

Mass spectra of copolymers

“…Mehl et al used ethanolamine to attack polyurethanes and phenyl‐isocyanate to attack polyester‐urethane block copolymers. The partial degradation process turned out to be totally selective (Mehl et al, 2000).…”

Polymer characterization by combining liquid chromatography with MALDI and ESI mass spectrometry

“…It has been reported that MALDI MS hyphenated to SEC and combined with selective degradation can provide information about the soft-block oligomer distribution in polyurethanes (PUR) [44]. Phenylisocyanolysis and ethanolaminolysis can liberate soft blocks from polyester-and polyether-based PUR.…”