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Liquid crystal block oligomers of linear and star topology
Abstract
A series of thermotropic block oligomers of linear and star topologies were synthesized and characterized. The synthesis involved attaching mesogenic 4-(4-butoxybenzoyloxy)benzoyl and 4-(4-butoxybenzoyloxy)benzoyloxy-4-benzoyl groups to linear and star hydroxy terminated poly(butadienes) of low molecular weights and low polydispersities. The effects of topology and weight percent hard segment on melting temperatures, enthalpies of fusion, rheological behavior, and morphological properties were studied. Most of these studies focused mainly on 4-(4-butoxybenzoyloxy) benzoyloxy-4-benzoyl-terminated poly(butadienes). Techniques employed to study these properties included differential scanning calorimetry, thermal gravimetric analysis, solid-state rheology, and X-ray diffraction. Star-block oligomers, in general, displayed greater melting temperatures and enthalpies of fusion than their linear analogs. The highest Tm and $\Delta$Hm were observed for the materials of highest weight percent hard segment. In a crystallization study, melting temperatures increased with increasing crystallization temperature. Stars crystallized more efficiently than their linear analogs. Thermal stability of all compounds synthesized proved greatest for 2-ring end-capped block oligomers and the pentad copolymer. Superior rheological properties were observed, in general, for the stars by solid-state rheometry. From WAXD, linear and star block oligomers showed similar crystalline structures in the microdomains. Microdomain size was obtained by SAXD for linear and star block oligomers of highest hard-block content. Evidence of more defined phase separation was observed for the linear topology.
Subject Area
Polymers
Recommended Citation
Milliken, Kenneth Troy, "Liquid crystal block oligomers of linear and star topology" (1994). Doctoral Dissertations Available from Proquest. AAI9420663.
https://scholarworks.umass.edu/dissertations/AAI9420663