Transcript Polyamides
Polymers What is a polymer? A molecule of large molar mass that consists of many repeating subunits called monomers. What is a monomer? A monomer is a molecule of relatively low molar mass that is linked with other similar molecules to form a polymer. Polyamides What are polyamides? A polyamide is a polymer family that contains recurring amide groups of: R-CO-NH-R’ as integral parts of the main polymer compound. They are formed either by the polymerization of an amino acid or the condensation of a polyamine with a carboxylic acid in which the structural units are linked by amide or thioamide groupings bonding them together. Polyamides The monomers in polyamide are joined together by peptide bonds, they occur both naturally such as in proteins but mostly synthetically such as various nylons. Peptide bond: A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water. This usually occurs between amino acids and can be seen here: Forming a Polyamide History of Polyamides Polyamides have existed in nature (proteins) longer then humans have existed on earth. However the first signs of polyamides synthetically were in 1664 when a Chinese emperor developed a project to manufacture synthetic yarn. Many types of polyamides were discovered at different times in history but they were not recognized as such until later on. Polyamide 6 for example was discovered in 1936 by Paul Slack and sold as Perlon but nylon was truly discovered in 1933 by Dr. Wallace Hume Carothers (as polyamide 6.6). Nylon Nylons are synthetic polyamides that are in their own family of synthetic polymers. It is made of monomers linked by peptide bonds and is frequently referred to as polyamide (PA). A molecule of water is given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers. In nylon 6,6, R' has 6 carbon alkanes and R has 4 carbon alkanes, but one also has to include the two carboxyl carbons in the diacid to get the number it donates to the chain. In Kevlar, both R and R' are benzene rings and this shows how broad and limitless the polyamide group is. Industrial Fabrication of Nylon 6.6 Nylon-6,6 is made by polymerizing hexanedioic acid and 1,6diaminohexane. Adipic Acid = Hexanedioc Acid Hexamethylene Diamine = 1,6-diaminohexane Nylon Polymerization Reaction Because the hexanedioc acid is acidic and the amine is basic, they first react together to form a salt. The salt is then converted into nylon-6,6 by heating it under pressure at 350°C. Lewis Structure of the Nylon 6,6 polymer – note the amide bond Formation of Nylon Monomers The monomers can both be made from cyclohexane. Oxidation of the cyclohexane opens the ring of carbon atoms and produces a -COOH group at each end. That gives you the hexanedioic acid. Some of that can then be converted into the 1,6diaminohexane. The acid is treated with ammonia to produce the ammonium salt. The ammonium salt is heated to 350°C in the presence of hydrogen and a nickel catalyst. This both dehydrates the salt and reduces it to the 1,6-diaminohexane. “ (ChemGuide.com) Disadvantages Advantages High heat resistance Resistant to abrasion Tough and resistant Strong chemical resistance Flame Retardant Heat Stabilized High moisture pick-up causes instability Requires UV stabilization High shrinkage in molded sections Low moisture resistance limits mechanical/electrical applications Low resistance to strong acids and bases Attacked by oxidizing agents Applications Automotive Applications Bearings Electrical/Electronic Applications Clothing and Consumer Products Housing and construction (gears) Industrial Applications Bibliography www.wikipedia.com www.britannica.com http://www.chemguide.co.uk/organicprops/amides/polyamid es.html http://www.bpf.co.uk/bpfindustry/plastics_materials_Nylons_ PA.cfm http://www.chemheritage.org/EducationalServices/nylon/stor y/story03.html