- Award ID(s):
- 1808115
- NSF-PAR ID:
- 10112245
- Date Published:
- Journal Name:
- Journal of The American Society for Mass Spectrometry
- ISSN:
- 1044-0305
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Polyether based side-chain liquid crystalline (SCLC) copolymers with distinct microstructures were prepared using living anionic polymerization techniques. The composition, end groups, purity, and sequence of the resulting copolymers were elucidated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and tandem mass spectrometry (MS/MS). MALDI-MS analysis confirmed the presence of (CH3)3CO– and –H end groups at the initiating (α) and terminating (ω) chain end, respectively, and allowed determination of the molecular weight distribution and comonomer content of the copolymers. The comonomer positions along the polymer chain were identified by MS/MS, from the fragments formed via C–O and C–C bond cleavages in the polyether backbone. Random and block architectures could readily be distinguished by the contiguous fragment series formed in these reactions. Notably, backbone C–C bond scission was promoted by a radical formed via initial C–O bond cleavage in the mesogenic side chain. This result documents the ability of a properly substituted side chain to induce sequence indicative bond cleavages in the polyether backbone.more » « less
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For a single, intense 7 μm linearly polarized laser pulse, we found that the branching ratio for the fragmentation of ClCHO+→ Cl + HCO+, H + ClCO+, HCl++CO depended strongly on the orientation of the molecule (
J. Phys. Chem. Lett. 2012 ,3 2541). The present study explores the possibility of controlling the branching ratio for fragmentation by using two independent pulses with different frequencies, alignment and delay. Born‐Oppenheimer molecular dynamics simulations in the laser field were carried out with the B3LYP/6‐311G(d,p) level of theory using combinations of 3.5, 7 and 10.5 μm sine squared pulses with field strengths of 0.03 au (peak intensity of 3.15×1013W/cm2) and lengths of 560 fs. A 3.5 μm pulse aligned with the C‐H bond and a 10.5 μm pulse perpendicular to the C‐H bond produced a larger branching ratio for HCl++CO than a comparable single 7 μm pulse. When the 10.5 μm pulse was delayed by one quarter of the pulse envelope, the branching ratio for the high energy product, (HCl++CO 73%) was a factor of three larger than the low energy product (Cl + HCO+, 25%). By contrast, when the 3.5 μm pulse was delayed by one quarter of the pulse envelope, the branching ratio was reversed (HCl++CO 38%; Cl + HCO+, 60%). Continuous wavelet analysis was used to follow the interaction of the laser with the various vibrational modes as a function of time. © 2018 Wiley Periodicals, Inc. -
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