Synthesis and characterization of well-defined methacrylic-based block ionomers

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.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Chemistry

Department dc:contributor.department

Chemistry

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1991

Author dc:creator

• DePorter, Craig Donald

Chair dc:contributor.committeechair

• McGrath, James E.

Committee members dc:contributor.committeemember

• Tanko, James M.
• Ward, Thomas C.
• Taylor, Larry T.
• Gibson, Harry W.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-07282008-134318

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/38862