Poly[4(5)-Vinylimidazole]/Polyvinylidene Fluoride Composites As Proton Exchange Membranes Jingjing Pan

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by RIT Scholar Works Rochester Institute of Technology RIT Scholar Works Theses Thesis/Dissertation Collections 4-1-2009 Poly[4(5)-vinylimidazole]/polyvinylidene fluoride composites as proton exchange membranes Jingjing Pan Follow this and additional works at: http://scholarworks.rit.edu/theses Recommended Citation Pan, Jingjing, "Poly[4(5)-vinylimidazole]/polyvinylidene fluoride composites as proton exchange membranes" (2009). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. Poly[4(5)-Vinylimidazole]/Polyvinylidene Fluoride Composites as Proton Exchange Membranes Jingjing Pan April 2009 Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemistry. Approved: _______________________________________ Thomas W. Smith (Advisor) ______________________________ Paul Rosenberg (Department Head) Department of Chemistry Rochester Institute of Technology Rochester, New York 14623-5603 Copyright Release Form: INVESTIGATION OF POLY[4(5)-VINYLIMIDAZOLE] COMPOSITES AND THEIR POTENTIAL AS PROTON CONDUCTIVE MEMBRANES I, Jingjing Pan, hereby grant permission to the Wallace Memorial Library of Rochester Institute of Technology to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. Jingjing Pan April, 2009 i Abstract In the present research, the morphology and thermal chemical characteristics of composite films comprised of poly(vinylidene fluoride) (PVF2) and poly[4(5)-vinylimidazole/vinylimidazolium trifluoromethylsulfonylimide] (PVIm/VIm+TFSI-]) were studied. In these composites, conditions such as choice of solvent and drying and annealing conditions can affect the crystal habit, crystallite size and degree of crystallinity of PVF2 as well as the distribution of the minor component, poly[4(5)- VIm/VIm+TFSI-]. Such composites may have potential in fuel cells as high-temperature proton- exchange membranes. When cast from either dimethylformamide (DMF) or dimethylacetamide (DMAC) at ambient temperature and dried at temperatures below 100˚C, PVF2 homopolymer films and + - PVF2//PVIm/VIm TFSI composite films were obtained in which the crystallites of PVF2 were β-phase. The films initially obtained were white, opaque films with limited strength and mechanical integrity. After + - heating to 200˚C, both the PVF2 films and the PVF2//PVIm/VIm TFSI films became stronger and more transparent. X-ray diffraction showed that prior to heating the PVF2 homopolymer film was β-phase and + - after heating to 200˚C PVF2 was α-phase. This was also the case with the PVF2//PVIm/VIm TFSI composites. In other words, the crystalline polymorph of PVF2 in the non-heated composite films was identical to that of non-heated homopolymer PVF2, and the PVF2 polymorph in the heated composite films was identical to that of heated homopolymer PVF2 films. DSC analysis showed that the melting point of crystals in heated PVF2 was lower than that in the non-heated PVF2. This difference in Tm (melting temperature) is attributed to the fact that PVF2 β-phase crystals have a higher melting temperature than that of the α-phase crystals. PVF2 composites cast from DMAC have a higher onset Tc (onset crystallization temperature) than do PVF2 composites cast from DMF. The crystallinity of PVF2 in the heated homopolymer films was lower than that in the non-heated films. The percent crystallinity in the composites was variable and depended, to some degree on the level of TFSI. In the composites cast from DMAC, the crystallinity is maximal at 15 mol% TFSI and decreases somewhat as the TFSI level is increased to 50 mol%. The crystallinity of PVF2 in the composites cast from DMF is minimal at 15 mol % TFSI and increases in concert with the TFSI level. The intimacy of the phases in the composites was assessed by evaluating the amount of PVIm/VIm+TFSI- that could be extracted with ethanol/water. It was found that, after heating, the amount of imidazole polymer that could be extracted dropped from about 81% to less that 16% of the imidazole polymer originally in the mixture. This observation coupled with the substantial transparency of the heated composites, is indicative of a nanoscopic composite in which the PVIm/VIm+TFSI- phase is intimately mixed with the amorphous phase of the majority PVF2 component. ii Table of Contents Acknowledgements v List of Tables vi List of Figures vii List of Abbreviations x I. Introduction and Background 1 A. The proton exchange membrane fuel cell 1 B. PVF2 and related to copolymers 6 C. Imidazole polymer systems 8 D. Poly[4(5)-vinylimidazole] 14 E. The work of Jinghang Wu 15 II. Experimental 17 A. Materials 17 B. Synthesis of 4(5)-vinylimidazole 17 C. Polymerization of 4(5)-vinylimidazole 17 1) Polymerization of 4(5)-vinylimidazole in benzene solution initiated by azobisisobutylnitrile 17 2) Polymerization of 4(5)-vinylimidazole in ethanol/water solution initiated by 4,4-azobis(4-cyano valeric acid) 18 D. PVF2 stock solutions 18 E. Poly[4(5)-vinylimidazole] solution with various mol% of protonated trifluoromethylsulfonylimide (TFSI) in DMF 19 F. Poly[4(5)-vinylimidazole] solution with various mol% of protonated trifluoromethylsulfonylimide (TFSI) in DMAC 19 + - G. PVF2(Kynar®301F) /poly[(4(5)-VIm/VIm TFSI ](4/1)V composite films in DMF 20 + - H. PVF2 /poly[(4(5)-VIm/VIm TFSI ](4/1)V composite films in DMAC 21 I. Characterization of the composite films 22 1) Differential Scanning Calorimetry (DSC) 22 2) X-ray Diffraction 23 3) Wide Angle X-ray Scattering (WAXS) at the Brookhaven Synchrotron 23 4) Extraction 24 5) Viscometry 24 iii III. Results and Discussions 27 A. Fabrication of PVF2/poly[4(5)-vinylimidazole/imidazolium TFSI] composite films 27 B. Characterization of the composite films 28 1) X-ray diffraction studies 28 + 2) Thermal analysis of PVF2//PVIm/Im composites 35 a. DSC analysis protocol 35 + b. Analysis of DSC spectra of PVF2 and PVF2//PVIm/Im composites cast from DMAC 37 + c. Analysis of DSC spectra of PVF2 and PVF2//PVIm/Im composites cast from DMF 41 d. Comparative analysis of Crystallinity and Tm of PVF2 + and PVF2//PVIm/Im films cast from DMAC and DMF 42 e. Discussion and analysis of latent heat of crystallization 45 3) Extractability 47 IV. Summary 50 V. References 52 iv Acknowledgements First of all, I would like to thank Dr. Thomas W. Smith, my advisor, for helping me to learn about polymers and for his patience. The support of Dr. Paul Rosenberg, Head of the Department of Chemistry, and Ms. Brenda Mastrangelo, Academic Advisor in the Department of Chemistry, for their support during my graduate career has been particularly appreciated. I would like to thank Dr. Andreas Langner, Dr. Christopher Collison and Dr. Massoud Miri for being my thesis committee members and for their advice. I also would like to thank my fellow graduate students whom I have worked beside during the past three years. I am grateful to Dr. Surendra K Gupta for his assistance with X-ray diffraction and I thank Mr. Tom Alston for his help with DSC measurements. As for National Technology Institute of Deaf (NTID), I greatly thank the National Technical Institute of Technology (NTID) Professionals and especially Dr. Dianna Brook for providing me with an academic fellowship during my graduate career. I want to give many thanks to Chairperson at the Department of Science & Mathematics, Dr. Vince Daniele, for his support and understanding. I’m so thankful to Ms. Gail Binder, my retired chemistry professor and advisor who made me love chemistry deeply and has been encouraging during my graduate school years. Also, I am grateful that Dr. Matthew Lynn, my current advisor, he has been supporting me and encouraging since Ms. Binder was retired. I want to take this opportunity to thank my sign language interpreter Cheryl Reminder for her work to help me in communication. Lastly, I must remember Ms. Sharon Rasmussen who was chairperson of NTID the Department of Science & Mathematics Support and tragically passed away last year. I want to express by gratitude to Professor Dr. Peggy Cebe from Tuft University, my first mentor who inspired me and led me into the world of polymers for the first time. My family is far away from me and I have not seen them for many years. I thank my parents, Yulin and Junying, and my brother Fanping for their love and encouragement. All in all, I have had many wonderful memories at RIT. I will remember wonderful people here and cherish the memories in my life. v List of Tables Table 1a. DSC results for first hearing scans for homopolymer PVF2 + - and composite films of PVF2 (Kynar®301F) and PVIm/Im TFSI cast from DMAC 39 Table 1b. DSC results for second hearing scans for homopolymer PVF2 + - and composite films of PVF2 (Kynar®301F) and PVIm/Im TFSI cast from DMAC 39 Table 2a. DSC results for first hearing scans for homopolymer PVF2 + - and composite films of PVF2 (Kynar®301F) and PVIm/Im TFSI cast from DMF 40 Table 2b. DSC results for second hearing scans for homopolymer PVF2 + - and composite films of PVF2 (Kynar®301F) and PVIm/Im TFSI cast from DMF 42 Table 3. DSC results for the cooling scan for composite films cast from DMAC and DMF 44 Table 4. Percent of PVIm/Im+TFSI- Extraction 48 vi List of Figures Figure 1. Illustration of a PEM fuel cell 1 Figure 2. Structure of Nafion® 3 Figure 3. Architectural Elements of Nafion® 4 Figure 4. Proton conductivity of different fully hydrated acidic polymers (for ion exchange capacities see Table 1), and a liquid, an adduct, and an oligomer containing heterocycles as proton solvent 5 Figure 5.

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