Synthesis and Characterization of Phenylethynyl Terminated Poly(arylene ether sulfone)s as Thermosetting Structural Adhesives and Composite Matrices
Mecham, Sue Jewel
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High temperature, solvent resistant materials which also display good mechanical properties are desired for use as aerospace structural adhesives and polymer matrix/carbon fiber composites. High molecular weight amorphous poly(arylene ether sulfone) thermoplastic materials display many of these desirable characteristics but are deficient in solvent resistance. Previous attempts to prepare poly(arylene ether) based thermosets to improve solvent resistance have been largely unsuccessful due to processiblity issues from the low curing temperature and high glass transition temperature of the thermoset precursor. Incorporation of a high temperature curable (* 350Â°C) endgroup such as 3-phenylethynylphenol in the synthesis of controlled molecular weight poly(arylene ether sulfone) oligomers has allowed for a large processing window prior to the exothermic cure that forms the desired networks. Control of oligomer molecular weight and backbone structure has allowed for further control of the processing, thermal transitions and adhesive properties of the thermosets. A systematic series of phenylethynyl terminated oligomers derived from either bisphenol A, or wholly aromatic hydroquinone or biphenol has been synthesized and characterized to determine the influence of backbone structure, molecular weight, and endgroup structure on thermoset properties. The features most affected by backbone structure included thermal stability (weight loss behavior) as well as transition temperatures (Tg, Tm), and processing characteristics. Increasing molecular weight of the oligomer produced a decrease in the glass transition temperature of the network and an increase in the adhesive properties of the thermoset. Comparison of the curing behavior of the 3-phenylethynylphenol endcapped materials with other related phenylethynyl terminated compounds led to the synthesis and systematic investigation of the curing behavior of phenylethynyl endcappers in which the electronic environment in relation to the reactive ethynyl carbons was systematically varied. Electron withdrawing groups, eg. sulfone, ketone, imide on the aryl ring para to the acetylene bond enhanced the rate of cure and also appear to improve the lap shear adhesion to suface treated titanium adherands. Discussion of the background, synthesis and characterization are described in this dissertation.
- Doctoral Dissertations