Formation and structure of high mechanical performance fibers. II. Flexible polymers

Conditions for the formation of high performance fibers from flexible and semi-flexible polymers are reviewed in terms of the chemical structure, chain conformation, super structure, and modeling. Small cross-sectional area and extended conformation are important factors for designing the high-performance polymers. Tensile modulus decreases significantly by only a small contraction of main chain from the planar zigzag conformation. Model calculation for the estimation of the ultimate tensile strength includes the evaluations of bond strength and the kinetic theory for rupture of primary and secondary bonds. Presence of defects such as chain ends are also considered. Macroscopic defects can be evaluated based on Griffith's theory. Drawability, which is important for the production of high performance fibers, can be improved through the control of entanglement. Experimental and industrial procedures for the production of high performance fibers such as gel spinning of polyethylene, pressurized drawing of polyoxymethylene, controlled shrinkage and drawing of polytetrafluoroethylene, and solid state co-extrusion of high molecular weight poly(ethylene terephthalate) are also reviewed. (C) 2002 John Wiley & Sons, Inc.