Crosslinking chemistry for high-performance polymer networks

A new thermally reactive monomer has been designed and synthesized that brings novel crosslinking chemistry to high-performance polymers. This monomer (XTA) is a derivative of terephthalic acid and was based on the thermal chemistry of benzocyclobutene. Various model compounds have been synthesized to investigate substituent effects on benzocyclobutene reactivity. Irreversible reaction exotherms around 350[deg]C were observed in these model compounds using differential scanning calorimetry. Based on these studies, polyaramid and poly(aryl ether ketone) XTA copolymers were synthesized. The formation of an insoluble network resulted after heat treatment of these polymers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31246/1/0000152.pd

The use of difunctional benzocyclobutene monomers in polymer synthesis.

The use of substituted benzocyclobutenes in polymer synthesis has recently attracted interest due to their thermal reactivity, via generation of a ring-opened intermediate at elevated temperatures. This reactive intermediate has been found to form new covalent bonds with itself as well as with suitable dienophiles. The reaction which takes place does not produce small molecules as volatiles, does not require the use of catalyst, and is thermally irreversible in polymer systems studied thus far. A review of the previous art and background of benzocyclobutene monomers was discussed. The mechanism for reactivity in the solid state and the thermal crosslinking versus degradation pathways were considered, with emphasis on solid-state spectroscopic techniques. In this work, a new benzocyclobutene-based monomer, crosslinkable terephthalic acid (XTA) was described and the feasibility of incorporation into several step-growth polymers was investigated. The physical properties of synthesized copolymers containing XTA were reported and discussed. The design of subsequent BCB-based monomers with greater cyclobutene functionality is described. Benzocyclobutene and dicyclobutabenzene hydrocarbons were selectively difunctionalized in a para orientation for subsequent conversion to either biphenyl diacid monomers or to asymmetric intermediates. Model aramid compounds for each of the new monomers were prepared and their thermal reactivity was studied. The ring-opening temperature of the model compounds was found to decrease with increasing cyclobutene content in the monomers. The new XXTA monomers along with terephthalic acid (TA) were copolymerized into normal aramid (MPDI) copolymers, thermoplastic (PET) and thermotropic (HBA/HNA) polyesters resulting in crosslinkable materials with a narrow processing temperature window below the XTA reaction threshold. Processing conditions were not affected by incorporation of XTA, except to lower the ceiling temperature and onset of degradation. Flame resistant properties were measured by limiting oxygen index (LOI). The unsymmetrical intermediates were also used to build nonlinear optically-active (NLO) compounds, which demonstrated application of the XTA thermal reactivity in an oriented state. The ability to form optically anisotropic films in an electric field was demonstrated and the resulting films were irreversibly cross-linked. The use of biphenyl BCB monomers in NLO materials was discussed based on a postulated cross-link structure and the crystal structure of the synthetic intermediate.Ph.D.Polymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130131/2/9712095.pd