Aromatic Polyamides “Aramids” Beth Neilson CH 392N February 19, 2009

Outline Definition / Invention Preparation Physical properties Fiber spinning Applications

Federal Trade Commission definition for aramid fiber: A manufactured fiber in which the fiber- forming substance is a long-chain synthetic polyamide in which at least 85% of the amide (-CO-NH-) linkages are attached directly between two aromatic rings Invention –DuPont – Morgan, Kwolek et. al. –Japan, Netherlands Aramids AmideAromatic Aromatic polyamide

Homopolymer repeat units: AB homopolymers – Type 3 AABB homopolymers – Types 1 and 2 Copolymers Chemical Structure Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

Aromatic units Chemical Structure Backbone:Pendent Groups: Bridging Units: Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

AB Homopolymers AABB Homopolymers –Polycondensation of diacid halides with diamines Solution polycondensation Interfacial polycondensation Melt or vapor phase polymerization Preparation Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

Diamine and diacid chloride – DuPont –Low temperature –Monomer purity and concentration –Amide solvent (NMP, HMPA, DMA) Solution Polycondensation Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

Poly(m-phenylene isophthalamide) Nomex® Kwolek, S. L.; Morgan, P. W.; Sorenson, R. W. U.S. Patent , November 13, DuPont, 1967 Solution Polycondensation

Poly(p-phenylene terephthalamide) (PPTA) Kevlar® DuPont – Bair, Blades, Morgan, Kwolek AKZO – Leo Vollbracht, Twaron® Solution Polycondensation Kwolek, S. L. U.S. Patent , Blades, H. U.S. Patent , Bair, T. I.; Morgan, P. W. U.S. Patent , 1972.

Higashi synthesis - phosphorus-containing activating agent Advantages: Eliminates acid chloride starting material Can tune reactivity by changing Ar’ Solution Polycondensation Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177. Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

Silylated diamine with diacid chloride Increases reactivity of aromatic diamine Faster reaction Elimination of Me 3 SiCl rather than HCl Higher molecular weight Solution Polycondensation Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

Copolymers –Copolymerization of three or more aromatic diamines and diacid halides. –Improved solubility, thermal properties, fiber properties –Technora® Solution Polycondensation

Preparation of AABB homopolymers, copolymers Aromatic diamine with diacid halide High molecular weight –Low temperature –Monomer stoichiometry, purity, concentration –Solvent –Salt concentration –Monomer structure (silylated amines) –Reagents (triarylphosphites, pyridine) Solution Polycondensation Summary

High thermal stability (T d ≥ 400°C) High tenacity (tensile strength) Chemical resistance Unique solution properties –Low solubility –Liquid crystallinity in p-aramids due to chain rigidity Structure dependent –Meta vs. para linkages –Structure of aromatic backbone Physical Properties Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

Liquid crystal – substance that has properties of both a solid and a liquid –Thermotropic – phase transition occurs with temperature change –Lyotropic Liquid crystallinity occurs only in solution Varies as a function of polymer concentration and temperature Liquid Crystallinity Odian, G. Principles of Polymerization, 4 th Ed. Wiley: New York, 2004.

In solution of proper concentration, liquid crystalline domains form, in which there is a high degree of order of the solute molecules. –Para linkages result in rod-like extended chain structure. –Hydrogen bonding Crystallization from liquid crystal solutions results in polymers with highly ordered extended-chain morphology Gives rise to polymers with higher strength and modulus Liquid Crystallinity of p-Aramids Odian, G. Principles of Polymerization, 4 th Ed. Wiley: New York, 2004.

Dry-jet Wet Spinning Spinning Solution –10-20 wt% polymer –100% H 2 SO 4 (H 2 O free) Elongation aligns crystalline domains Precipitates out of coagulation bath Crystallinity of solution is translated to fiber Aramid Fiber Spinning Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

Tenacity and Modulus –Spinning and drawing conditions Wet vs. dry Heat treatment –Polymer composition –Molecular weight Properties of Aramid Fibers Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

Kevlar ® Applications of Aramids

Nomex ® Technora ® Applications of Aramids

Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.