Aromatic Polyamides“Aramids”.pptVIP

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 Homopolymer repeat units: AB homopolymers – Type 3 AABB homopolymers – Types 1 and 2 Copolymers Aromatic units Diamine and diacid chloride – DuPont Low temperature Monomer purity and concentration Amide solvent (NMP, HMPA, DMA) Poly(p-phenylene terephthalamide) (PPTA) Kevlar? DuPont – Bair, Blades, Morgan, Kwolek AKZO – Leo Vollbracht, Twaron? Higashi synthesis - phosphorus-containing activating agent Silylated diamine with diacid chloride Copolymers Copolymerization of three or more aromatic diamines and diacid halides. Improved solubility, thermal properties, fiber properties Technora? 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) High thermal stability (Td ≥ 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 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 In solution of proper concentration, liquid crystalline domains form, in which there is a high degree of order of the s