LIQUID-CRYSTALLINE MAIN-CHAIN POLYMERS WITH A POLY(P-PHENYLENETEREPHTHALATE) BACKBONE .2. FIBER SPINNING AND MECHANICAL-PROPERTIES OF POLYESTERS WITH ALKOXY SIDE-CHAINS

Fiber spinning and mechanical properties of four rigid polyesters with alkoxy substituents of different length and placement were evaluated. Properties of oriented fibers from the polymer with dodecyloxy substi tuents on the terephthalate moiety, PTA12HQ, were significantly affect ed by the crystal modification. At room temperature the following prop erties (tensile modulus E, tensile strength sigma(b), and strain at br eak epsilon(b)) could be obtained: E = 9.5 GPa, sigma(b) = 85 MPa and epsilon(b) = 1.1% for phase L(f) (the ''frozen in layered mesophase'') ; E = 10.4 GPa, sigma(b) = 59 MPa and epsilon(b) = 0.6% for modificati on A; E = 17.3 GPa, sigma(b) = 158 MPa and epsilon(b) = 1.2% for modif ication B. Because of the higher amount of main chains per cross-secti onal area the polymer with hexyloxy side chains, PTA6HQ, showed better properties at a comparable degree of molecular orientation: E = 24 GP a, sigma(b) = 270 MPa, epsilon(b) = 1.4%. Fibers obtained from the pol yester with dodecyloxy substituents on the hydroquinone moiety, PTAHQ1 2, were too brittle to handle. The polyester with dodecyloxy substitue nts on both moieties, PTA12HQ12, was spun from the isotropic melt. Bec ause of the obtained low degree of orientation, properties (E = 1 GPa, sigma(b) = 40 MPa, and epsilon(b) = 6.3%) were governed by interactio ns between the chains (the main chains are not load-bearing). (C) 1993 John Wiley & Sons, Inc.