Characterization of Physical and Chemical Properties of Synthetic Polymer using Ion Mobility-Mass Spectrometry
Shinsuke Kokubo
Doctoral thesis
Date of Examination:
2017-12-01
Date of issue:
2017-12-13
Advisor:
Vana, Philipp Prof. Dr.
Referee:
Vana, Philipp Prof. Dr.
Referee:
Koszinowski, Konrad Prof. Dr.
Referee:
Suhm, Martin Prof. Dr.
Referee:
Buback, Michael Prof. Dr.
Referee:
Mata, Ricardo Prof. Dr.
Referee:
Ehlers, Florian Dr.
Persistent Address: http://hdl.handle.net/11858/00-1735-0000-0023-3FAC-5
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Abstract
English
This thesis focuses on developing analytical methodologies based on ion mobility-mass spectrometry (IM-MS) for both physical and chemical properties of synthetic polymer. Beyond numerical experimental data, a comprehensive and visualized interpretation of polymer structure and topology was achieved by theoretical computational approach: molecular dynamics (MD) simulation and collision cross section (CCS) calculation. In the first study (Chapter 4), the CCS of polyethylene glycol (PEG) and polypropylene glycol (PPG) were measured in dependence of the number of monomer units (n) per chain. A model equation was applied to elucidate the main factor (characteristic ratio, Cn) determining the incremental tendency of CCS against n. For PEG and PPG, Cn of 3.96 and 5.76 were obtained respectively. Detailed evaluation of the data shows that the globule model has good agreement with the literature reference values. IM-MS experiments on charged poly(methyl methacrylate) (PMMA) and polystyrene (PS) also showed good accordance with reported values, verifying sufficient versatility of the proposed method. The presented procedure is extremely quick and easy to perform and provides stunningly rapid access to the conformation data of synthetic polymers. Rayleigh limit equation, describes physical process of electro-spray ionization, provides a useful relation between surface tension and radius of charged droplet. In the second study (Chapter 5), the lower threshold size of cation adducted polymer was analyzed by MS experiment. MD simulation gives convenient access to determine the radius of the critical stable charged polymer of diverse type in spherical dimension. This approach yielded very good result which in good agreement with the literature-known reference values of surface tension (PEG : 45.0 mN/m, PPG : 33.1 mN/m, PMMA : 40.0 mN/m and PS : 32.4 mN/m). The proposed method also provides an extremely swift and precise measurement for polymer without any external disturbances of solvents or impurities. In the third study (Chapter 6), doubly charged ion system was investigated as a model case study of multiply charged polymer. The dependency of the effective collision cross section on n was evaluated with MD simulations. Assuming a balance between elastic and Coulomb forces inside short and asymmetric doubly-charged chains, a method for determine relative dielectric constant (ετ) was developed. ετ was found to be 7.87 for PEG and 6.18 for PPG, respectively. The proposed method using IM-MS is clearly carried out in the absence of solvent inside the polymer yielding intrinsic material properties. The fourth study (Chapter 7) was designed to detect and classify isomer of star-polymer by utilizing precisely synthesized polyethylene glycol with multi-arm (star-PEG). Grafting pattern of star-PEG can be represented from experimental determined CCS of doubly charged species. Besides CCS dependency, energy resolved-ion mobility spectrometry (ER-IMS) was performed to identify the corresponding isomer. To compensate poor resolution in ion mobility spectrometry, the profile an ion mobility chromatogram (IMC) was deconvoluted with Gaussian functions was applied to extract peaks from IMC as an alternative procedure. Both IM-MS and ER-IMS measurement were demonstrated for each extracted IMC, and thus, IMC broadening could be concluded that coexisting isomers in commercial star-PEG. The cross-check in conjunction with CCS and ER-IMS analysis is powerful and reliable analytical methodology for a successful revealing isomer in star-polymer.
Keywords: Ion mobility mass spectrometry; Polymer; Molecular modeling; Characteristic ratio; Surface tension; Relative dielectric constant; Branching polymer
