Study On Design, Fabrication And Low Temperature Curing Of Functional Oligomides

This doctoral dissertation was built on the study of novel oxide bridge end-cap design and low temperature curing of phenylethynyl end-capped oligomides and sulfonated oligomides.This dissertation firstly gave an outline review for thermalsetting oligomides and fuel cell proton exchange membrane. Then an anhydride monomer containing ether oxide bridge,7-oxa-bicyclo [2,2,1] hept-5-ene-2,3-dicarboxylic anhydride (ONA) as a novel end-cap for the Polymerization of Monomer Reactant (PMR) type polyimides was investigated. Three molecular weight levels of the ONA end-capped PMR resins were evaluated. The effects of process conditions of these novel PMR resins on thermal and mechanical properties were investigated. It was demonstrated that the imidized prepolymers using the new end-cap have good processability, and the cured polyimide specimens exhibited as good thermal stability as the state-of-art RP46. It was suggested that the ONE end-cap can be considered as an economic replacement of NE for the synthesis of PMR type polyimide materials for high temperature applications.A low temperature(250℃) crosslinking method for phenylethynyl (PE) end-capped non-sulfonated and sulfonated oligomides was developped. The applications of low viscosity co-solvents N-methylpyrrolidinone/dimethyl ether of polyethylene glycol (NMP/DM-PEG-250) and N-methylpyrrolidinone/polyethylene glycol (NMP/PEG-400) as film forming co-solvents for PE-end-capped non-sulfonated and sulfonated oligomides, were investigated. The FT-IR, 13C-NMR, TGA and DSC provided the evidences that during curing process at 200-250℃the PEG molecules forming free radical species which initiate cure of the ethynyl groups resulting in a plasticized crosslinked polyimide membrane. For sulfonated polyimides, in addition to this reaction, the PEG solvent reacts with sulfonated groups to form a secondary crosslinked network via ethylene oxide sulfonate esters and ethylene oxide sulfonate side chains bonded to PI units. The dual crosslinked sulfonated polyimides have low water absorption, IEC and proton exchange capacity.The stability of sulfonated polyimides also was investigated by TGA, GC/MS and 13C-NMR. When the salt form of sulfonated polyimide was heated at 250℃, the evolution of triethylamine would accompany the formation of the sulfonic acid derivative. Additionally, the sulfonated polyimides were stable at 250℃without decomposition of sulfonic acid group. When the phenylethynyl end-capped polyimdes were cured at 250℃for 3 h in NMP/DM-PEG-250, the retention of sulfonic acid group was 97% which indicates no sulfonic acid decomposition was occured in this curing process.