POLYPHENYLENE SULFONIC ACIDS AS PROTON EXCHANGE MEMBRANES FOR FUEL CELLS by DAXUAN DONG Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Dissertation advisor: Dr. Morton H. Litt Department of Chemistry CASE WESTERN RESERVE UNIVERSITY May, 2012 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Daxuan Dong ______________________________________________________ Ph.D. candidate for the ________________________________degree *. Daniel A. Scherson (signed)_______________________________________________ (chair of the committee) Stuart J. Rowan ________________________________________________ Morton H. Litt ________________________________________________ Anthony J. Pearson ________________________________________________ Clemens Burda ________________________________________________ ________________________________________________ 01/20/2012 (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents Chapter 1. General Introduction………………………………………………………..1 1.1. Fuel cell fundamentals………………………………………………………………..1 1.2. Nafion® and other perfluorosulfonated polymers…………………………………….5 1.3. Sulfonated aromatic hydrocarbon polymers…………………………………….......12 1.3.1. Postsulfonation of existing aromatic hydrocarbon polymers.…………………...12 1.3.2. Direct polymerization from sulfonated aromatic hydrocarbon monomer unit….17 1.3.2.1. Polyarylene ether sulfone copolymers…………………………………………..17 1.3.2.2. Sulfonated polyimides…………………………………………………………..22 1.4. Motivation and justification in structural design of polyphenylene sulfonic acids…28 1.5. Overview of the dissertation………………………………………………………...29 1.6. References…………………………………………………………………………...30 i Chapter 2. Synthesis of high molecular weight poly(biphenylene-3,3’-disulfonic acid) (PBPDSA)……………………………………………………………………………….37 2.1. Introduction………………………………………………………………………….37 2.1.1. Existing synthetic methods for poly(p-phenylene) (PPP)…………………………37 2.1.2. Synthesis of high molecular weight PBPDSA…………………………………….48 2.2. Experimental section………………………………………………………………...51 2.2.1. Materials…………………………………………………………………………..51 2.2.2. Characterization techniques………………………………………………………51 2.2.3. Monomer and polymer synthesis…………………………………………………52 2.2.3.1. Monomer Synthesis……………………………………………………………..52 2.2.3.1.1. Synthesis of 4,4’-dibromobiphenyl-3,3’-disulfonic acid (DBBPDSA)……….52 2.2.3.1.2. Preparation of 4,4’-dibromobiphenyl-3,3’-disulfonic acid dilithium salt (DBBPDSA-Li) and di(benzyltrimethylammonium) salt (DBBPDSA-BTMA)………...52 2.2.3.2. Experiments towards the synthesis of high molecular weight homopolymer, PBPDSA…………………………………………………………………………………53 2.2.3.2.1. Polymerization of DBBPDSA-Li in NMP…………………………………….53 2.2.3.2.2. Polymerization of DBBPDSA-Li in DMF…………………………………….54 ii 2.2.3.2.3. Polymerization of high-vacuum dried DBBPDSA-Li and DBBPDSA-BTMA in DMF……………………………………………………………………………………...54 2.2.3.2.4. Polymerization of high-vacuum dried DBBPDSA-Li and DBBPDSA-BTMA in NMP……………………………………………………………………………………...55 2.2.3.2.5. Polymerization of high-vacuum dried DBBPDSA-Li in NMP at high concentration……………………………………………………………………………..56 2.2.3.2.6. Polymerization of thoroughly dried DBBPDSA-Li in NMP at low concentration……………………………………………………………………………..57 2.2.3.2.7. Polymerization of thoroughly dried DBBPDSA-Li (dried separately with activated copper powder) in NMP……………………………………………………….58 2.2.3.2.8. Scaled up polymerization of thoroughly dried DBBPDSA-Li (dried separately with activated copper powder) in NMP………………………………………………….59 2.2.3.3. Grafting high molecular weight PBPDSA polymer with neopentyl benzene…………………………………………………………………………………..59 2.3. Results and Discussion……………………………………………………………...60 2.3.1. Synthesis of high molecular weight PBPDSA…………………………………….60 2.3.1.1. Synthesis of PBPDSA in different solvents (DMF, NMP)……………………...60 2.3.1.2. Synthesis of PBPDSA from DBBPDSA with different counter ions…………...62 2.3.1.3. Polymerization of high concentration DBBPDSA-Li in NMP………………….65 iii 2.3.1.4. Polymerization of thoroughly dried DBBPDSA-Li (dried separately with activated copper powder) in NMP……………………………………………………….67 2.3.15. The key factors for the synthesis of high molecular weight PBPDSA…………..70 2.3.2. Grafting on high molecular weight PBPDSA polymer and conductivity measurements…………………………………………………………………………….74 2.4. Conclusions………………………………………………………………………….77 2.5. References…………………………………………………………………………...78 iv Chapter 3. Synthesis and grafting of polyphenylene copolymers…………………...81 3.1. Introduction………………………………………………………………………….81 3.2. Experimental section………………………………………………………………...87 3.2.1. Materials…………………………………………………………………………..87 3.2.2. Characterization techniques………………………………………………………87 3.2.3. Monomer and comonomer synthesis……………………………………………...88 3.2.3.1. Synthesis of 1,4-dibromobenzene-2,5-disulfonic acid dilithium salt (DBPDSA- Li)………………………………………………………………………………………...88 3.2.3.2. Synthesis of 2,7-dibromofluorene-3,5-disulfonic acid dilithium salt (DBFDSA- Li)………………………………………………………………………………………...88 3.2.3.2.1. Sulfonation of 2,7-dibromofluorene with fuming sulfuric acid…………….....88 3.2.3.2.2. Sulfonation of 2,7-dibromofluorene with chlorosulfonic acid………………..89 3.2.3.2.2.1. Synthesis of 2,7-dibromofluorene-3,5-disulfonyl chloride (DBFDSCl)……89 3.2.3.2.2.2. Synthesis of 2,7-dibromofluorene-3,5-disulfonic acid dilithium salt (DBFDSA-Li)……............................................................................................................91 3.2.3.2.3. Rearrangement of DBFDSCl………………………………………………….91 3.2.3.2.3.1. Rearrangement of DBFDSCl using 85% H2SO4……………………………92 3.2.3.2.3.2. Rearrangement of DBFDSCl using conc. H2SO4…………………………...92 v 3.2.3.3. Synthesis of 9,9’-dibenzyl-2,7-dibromofluorene-3,5-disulfonic acid dilithium salt (DBnDBFDSA-Li)……………………………………………………………………….92 3.2.4. Homopolymerization and copolymerization………………………………………93 3.2.4.1. Homopolymerization of DBFDSA-Li…………………………………………..93 3.2.4.2. Synthesis of copolymer: poly(phenylene disulfonic acid_co_fluorene disulfonic acid)(PxF1)……………………………………………………………………………....94 3.2.4.2.1. Syntheses of copolymer in NMP and DMSO (no coordination reagent)……...94 3.2.4.2.2. Synthesis of copolymer with coordination reagent 2,2’-bipyridyl (BPy)……..96 3.2.4.2.3. Synthesis of copolymer with coordination reagent, triethylene glycol dimethyl ether (TEGDME), added:………………………………………………………………...98 3.2.4.2.4. Synthesis of copolymer using argon/nitrogen drying…………………………99 3.2.4.3. Direct synthesis of grafted copolymer using alkylated comonomer…………...100 3.2.4.4. Direct synthesis of grafted copolymer using alkylated comonomer with argon/nitrogen drying…………………………………………………………………...101 3.2.5. Copolymer grafting reactions…………………………………………………....102 3.2.5.1. Titration of 2,7-dibromofluorene-3,5-disulfonic acid lithium salt (DBFDSA- Li)……………………………………………………………………………………….102 3.2.5.2. Model monomer alkylation reaction (Description of Run 7a, Table 3.5)……...102 3.2.5.3. Grafting on copolymers PxF1………………………………………………….103 3.2.5.3.1. Grafting copolymer (PxF1) with 1-bromodocosane…………………………103 3.2.5.3.2. Grafting copolymer (PxF1) with benzyl chloride using potassium tert-butoxide as a base………………………………………………………………………………...104 vi 3.2.5.3.3. Grafting copolymer (PxF1) using LiOH saturated solution as a base……….105 3.2.5.3.4. Other grafting reactions……………………………………………………...106 3.2.6. Crosslinking of grafted polymer films…………………………………………...106 3.3. Results and Discussion…………………………………………………………….107 3.3.1. Syntheses of comonomer and homopolymer…………………………………….107 3.3.1.1. Synthesis of comonomer 3,5-DBFDSA-Li…………………………………….107 3.3.1.2. Homopolymerization of DBFDSA-Li…………………………………………111 3.3.2. Copolymer synthesis……………………………………………………………..116 3.3.2.1. Copolymerization of DBPDSA-Li and DBFDSA-Li without coordination reagent…………………………………………………………………………………..116 3.3.2.2. Structure of copolymer PxF1 based on NMR and elemental analysis…………117 3.3.2.3. Copolymerization of DBPDSA-Li and DBFDSA-Li using 2,2’-bipyridyl (BPy) as a coordination reagent……………………………………………………………….120 3.3.2.4. Copolymerization of DBPDSA-Li and DBFDSA-Li with triethylene glycol dimethyl ether (TEGDME) as a coordination reagent………………………………….123 3.3.2.5. The effect of coordination reagents on the molecular weight of the resulting copolymer PxF1………………………………………………………………………...124 3.3.2.6. The effect of drying conditions on the molecular weight of the resulting copolymer PxF1………………………………………………………………………...126 3.3.3. Grafted copolymer……………………………………………………………….130 vii 3.3.3.1. Model grafting reactions……………………………………………………….130 3.3.3.2. Synthesis of grafted copolymer………………………………………………..132 3.3.3.3. Direct synthesis of grafted copolymer from alkylated comonomer……………139 3.3.4. Crosslinking the grafted copolymer……………………………………………...140 3.4. Conclusions………………………………………………………………………...141 3.5. References………………………………………………………………………….143 viii Chapter 4. Characterization and properties of copolymers and grafted copolymers……………………………………………………………………………..144 4.1. Introduction………………………………………………………………………...144 4.2. Experimental section……………………………………………………………….145 4.2.1. Materials…………………………………………………………………………145 4.2.2. Characterization techniques……………………………………………………...145 4.2.2.1. Viscosity measurements………………………………………………………..145 4.2.2.2. Polarizing Optical Microscopy (POM)………………………………………...148 4.2.2.3. One dimensional Wide Angle X-ray Diffraction (WAXD)……………………148 4.2.2.4. Water uptake…………………………………………………………………...150