Phase behaviour and solution properties of sulphobetaine polymers |
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| Affiliation: | 1. Chemical Engineering Research Center, School of Chemical Engineering and Technology, Tianjin 300072, PR China;2. Tianjin Key Laboratory of Membrane Science and Desalination Technology, State Key Laboratory of Chemical Engineering, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin 300072, PR China;1. Department of Biomedical Sciences and Engineering, National Central University, Taoyuan 32023, Taiwan;2. Department of Chemical and Materials Engineering, National Central University, Taoyuan 32023, Taiwan;3. Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931, USA;4. Division of Rhinology, Department of Otolaryngology Head and Neck Surgery, Taipei Veterans General Hospital, Taipei 11217, Taiwan;5. School of Medicine, National Yang-Ming Chiao Tung University, Taipei 11221, Taiwan;6. R&D Center for Membrane Technology, Chung Yuan Christian University, Taoyuan 32023, Taiwan;7. NCU-Covestro Research Center, National Central University, Jhong-Li, Taoyuan 32023, Taiwan;1. Center for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA;2. Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, 60637, USA;3. Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX, 77005, USA;1. School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300350, China;2. The State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China;3. School of Materials Science and Engineering, State Key Laboratory of Hollow Fiber Membrane Materials and Processes, Tianjin Polytechnic University, Tianjin 300387, China |
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| Abstract: | Aqueous polyelectrolytes have been extensively studied and comprehensively described in numerous books and reviews. In contrast, systematic investigations of aqueous polyzwitterions are few. This paper describes the detailed phase behaviour and solution properties of a homopolymer based upon a recently available sulphobetaine monomer, N-(3-sulphopropyl)-N-methacrylooxyethyl-N,N-dimethyl ammonium betaine (SPE). In addition, such properties are probed at the molecular level by static and dynamic light scattering, as well as laser Raman spectroscopy. Poly[N-(3-sulphopropyl)-N-methacrylooxyethyl-N,N-dimethyl ammonium betaine], P(SPE), of 4.35 × 105Mw shows remarkable phase behaviour. It exhibits both an upper critical solution temperature (UCST) and an ‘apparent inverted’ lower critical solution temperature (LCST), i.e. a 1-phase region flanked by two 2-phase regions. Moreover, the UCST occurs at an order of magnitude lower polymer concentration than predicted by theory or demonstrated by experiment with conventional polymers. The aqueous solubility of (SPE) depends upon polymer molecular weight, as well as the concentration and structure of added salts. ‘Soft’ salt anions and cations are more effective solubilizers than ‘hard’ anions and cations. Furthermore, solutions of P(SPE) display ‘antipolyelectrolyte behaviour’, i.e. viscosities which increase with increasing salt concentrations. Static light scattering experiments indicate that the solvent quality for P(SPE) increases with increasing salt concentration. Dynamic light scattering measurements show that the polymer diffusion coefficients decrease and the chain dimensions increase with increasing salt concentrations. Moreover, laser Raman spectroscopy indicates that the local environment around the zwitterion functionalities is also modified by changes in salt concentration. Based upon such molecular level probes, models have been proposed to account for the P(SPE) phase behaviour and solubility. Thus, P(SPE) is depicted as a collapsed coil in water because of intra-group and intra-chain associations. The unusual phase behaviour of P(SPE) in water is rationalized in terms of a shift from intra- to interinteractions. In turn, NaCl breaks up the intra-associations and promotes polymer solubility. |
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