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The synthesis, characterization and mechanical testing of novel liquid crystalline poly(ester-amide)s and their blends with nylon-6,6
Abstract
The principal objective of this research was to prepare an LCP/nylon-6,6 blend having enhanced tensile properties relative to nylon-6,6. It was hoped that amide-containing LCPs having a flexible spacer groups would have either good interfacial adhesion or partial miscibility with nylon-6,6. Rigid-rod polyamides containing a biphenol mesogenic unit did not exhibit a LC phase. Polymers having a mesogenic group consisting of three p-substituted aromatic units and a flexible spacer were, however, shown to form the nematic phase. The thermotropic LCPs were prepared in high molecular weight by the solution polycondensation of various N,N$\sp\prime$-trimethysilyl-N,N$\sp\prime$-dimethylpolyalkylenediames and terephthaloylbis(4-oxybenzoyl chloride). The polymers contained N-methylimino groups in order to reduce interchain hydrogen bonding, such that a LC phase could form below the onset of polymer degradation. The loss in interchain hydrogen bonds may, however, yield polymers having a compromise in mechanical properties. The LC poly(ester-amide)s showed maxima in the loss tangent by dynamic mechanical thermal analysis from 67$\sp\circ$C to 116$\sp\circ$C, depending on the flexible spacer length, which were probably glass transition temperatures. Nylon-6,6/LCP solution cast films were shown to be partially miscible, as indicated by the perturbation of the mechanical relaxations associated with the pure LCP. The poly(ester-amide)s were melt-extruded with nylon-6,6 using various melt-processing temperatures. Each of the "as spun" nylon-6,6/LCP melt-extruded blends were shown to be compatible by DMTA. However, in some cases, phase separation occurred during post drawing. The tensile properties of the pure LC poly(ester-amide)s were shown to be significantly less than all-aromatic LCPs such as Vectra$\sp\circler$. Blends containing LCPs having long flexible spacer units showed no improvement in tensile properties relative to nylon-6,6, while modest improvement was observed for blends containing an LCP having shorter six methylene flexible spacer units when melt-extruded at 275$\sp\circ$C. Blends containing an LC poly(ester-amide) having a short six methylene flexible spacer unit showed a considerable improvement in tensile modulus when melt-extruded at 300$\sp\circ$C, but a reduction in tensile strength. The significant enhancement in tensile modulus is attributed to molecular interchange reactions.
Subject Area
Polymers|Plastics
Recommended Citation
McCarthy, Thomas Fitzgerald, "The synthesis, characterization and mechanical testing of novel liquid crystalline poly(ester-amide)s and their blends with nylon-6,6" (1993). Doctoral Dissertations Available from Proquest. AAI9316694.
https://scholarworks.umass.edu/dissertations/AAI9316694