Matrix-assisted laser desorption/ionization collision-induced dissociation of linear single oligomers of nylon-6.

Matrix-assisted laser desorption/ionization, collision induced-dissociation (MALDI-CID) has been used to obtain structural information for linear single oligomers of nylon-6. The effects of matrix and cationization agent in MALDI-CID analysis have been investigated. Fragmentation mechanisms are proposed for the series of ions that are observed in the MALDI-CID spectra of the hexamer, octamer and dodecamer. Fragmentation processes observed in the MALDI-CID spectra include cleavage of the end groups followed by dissociation of the m/z 113 unit. Cleavage of the oligamide chain occurs at the amide linkage, as well as at adjacent bonds. For the four matrices and three cationization agents investigated, 2,5-dihydroxybenzoic acid and sodium chloride showed the best performance for MALDI-CID analysis of the dodecamer. In addition, yields of the fragment ions in MALDI-CID spectra were found to be dependent on the chain length distribution.

Electrospray and matrix-assisted laser desorption/ionization mass spectral characterization of linear single nylon-6 oligomers.

Synthetic nylon-6 single molecular mass oligomers were studied by matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometry. These oligomers, considered as model compounds for the study of nylon-6 polymers, gave good mass spectrometric results using both MALDI and ESI. In spite of the gentle nature of both techniques, the MALDI and ESI spectra showed evidence of end-group cleavage from the oligomer chains. MALDI-MS was found to give similar fragmentation patterns for all of the oligomer samples. An increase in doubly charged ion signals with increasing oligomer mass was observed in the ESI mass spectra, as was end-group fragmentation. Signals from oligomer clusters were observed in ESI-MS for the dimer, tetramer and hexamer, most likely due to non-covalent bonding among the low-mass oligomer molecules.

Characterization of polyether and polyester polyurethane soft blocks using MALDI mass spectrometry

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.