Type of Document Dissertation Author DePorter, Craig Donald URN etd-07282008-134318 Title Synthesis and characterization of well-defined methacrylic-based block ionomers Degree PhD Department Chemistry Advisory Committee
Advisor Name Title McGrath, James E. Committee Chair Gibson, Harry W. Committee Member Tanko, James M. Committee Member Taylor, Larry T. Committee Member Ward, Thomas C. Committee Member Keywords
- Methacrylic acid
Date of Defense 1991-11-05 Availability unrestricted Abstract
The work presented in this dissertation revolves around the incorporation of t-butyl methacrylate into block copolymers utilizing anionic living polymerization techniques. The synthesis of t-butyl methacrylate/n-hexyl methacrylate and t-butyl methacrylate/2-ethylhexyl methacrylate di- and triblock copolymers was done by initiation with 2-methyl-1,1-diphenylpentyllithium in THF at -78°C by established techniques, and predictable molecular weights and narrow molecular weight distributions were obtained. Subsequent selective acid catalyzed hydrolysis of the t-butyl ester followed by neutralization with an appropriate base allowed the formation of block ioncontaining polymers. The synthesis of triblock polymers of t-butyl methacrylate with butadiene and styrene/butadiene systems and their analogous block ionomers was also carried out utilizing difunctional organolithium initiation of the hydrocarbon monomers in cyclohexane. For the polymerization of the tbma, it was found that the addition of large quantities of a polar solvent, such as THF, endcapping with diphenylethylene, and low temperatures (ca. -70 °C) were necessary to avoid side reactions which were theorized to be carbonyl attack by the dienyl- or styryllithium species.
It was found that in the all methacrylic systems mentioned, when the t-butyl methacrylate blocks were in the ester form, i.e. not hydrolyzed to the acid or neutralized to the ionomer, the copolymers were phase mixed as evidenced by thermal analysis. Upon derivatization, however, the block polymers became phase separated. Morphological characterization of the block ionomers indicated that the morphology was dependent on both the ionic content and the ionic block length. Well defined, partially anisotropic, morphologies were observed by SAXS and TEM only in polymers that had both high ionic content and relatively large ionic block lengths. Elastomeric behavior was observed in copolymers with triblock architecture, but the materials degraded prior to plastic flow.
On the other hand, all of the diene- and styrene/diene-methacrylates exhibited a multiphase morphology in the precursor state. Analogously to the all methacrylic system, the block ionomers were elastomeric, with the rubbery plateau extended ca. 60 °C relative to the non-ionic precursors. Crosslinking of the poly(butadiene) phase occurred at the onset of plastic flow, rendering the ionomers unable to be thermally processed.
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