Stephanie Kwolek originally intended to pursue a career as a doctor, after her seamstress mother told her she was too much of a perfectionist to work a career in fashion. In 1946, Kwolek graduated with a Bachelor of Science degree with a major in chemistry from the Margaret Morrison Carnegie College of Carnegie Mellon University. She had hoped she could earn enough money from a temporary job in a chemistry-related field to pay for medical school.
William Hale Church offered Kwolek a position at DuPont in Buffalo, New York. During her interview, Church told her that DuPont would reach out in about two weeks to tell her whether she had been hired. Kwolek asked if DuPont could let her know sooner as she had another offer already, and Church called his assistant into his office to dictate Kwolek’s offer letter in front of her.
At the time, DuPont was looking for a petroleum-based polymer fiber that would be lighter and harder-wearing than steel in radial tires. World War II had also emphasized the need for lightweight, wearable armor to protect both bodies and equipment; soldiers had gone without body armor because there was no material strong enough to stop a rifle but light enough to wear in battle.
Though Kwolek intended to work for DuPont only temporarily, the polymer research was so interesting and challenging that she dropped her plans for medical school and made chemistry a lifetime career. Her research group moved to Delaware in 1950. Kwolek was engaged in the search for new polymers and a new condensation process that takes place at lower temperatures of 0 to 40ºC. The low-temperature polycondensation processes that she developed employed very fast-reacting intermediates, and made it possible to prepare polymers that cannot be melted and only begin to decompose at temperatures above 400ºC.
Kwolek is best known for her work during the 1950s and 1960s with aromatic polyamides (“aramids”), a type of polymer that can be made into strong, stiff, and flame-resistant fibers. She determined solvents and polymerization conditions for producing poly-m-phenylene isophthalamide, a compound that DuPont released in 1961, as a flame-resistant fiber with the trade name Nomex.
Nomex has excellent thermal, chemical and radiation resistance, and can withstand temperatures up to 370ºC (700ºF). Nomex hoods are used in racing and firefighting equipment, as well as by military tank drivers. A Nomex hood is placed on the head on top of a firefighter’s face mask, protecting the portion of the head not covered by the helmet and face mask from the intense heat of the fire. Nomex shirts and trousers are used as part of firefighter PPE in wildfire suppression work. Racing car drivers and military pilots wear suits constructed of Nomex. In the U.S. space program, Nomex has also been used for the Thermal Micrometeoroid Garment on the Extravehicular Mobility Unit and ACES pressure suit, and as thermal blankets on the payload bay doors, fuselage, and upper wing surfaces of the Space Shuttle Orbiter; and as airbags for Mars Pathfinder, Mars Exploration Rover, Galileo atmospheric probe, Cassini-Huygens Titan, AERCam Sprint, and the upcoming Crew Exploration Vehicle.
After developing Nomex, Kwolek continued her work into poly-p-benzamide and poly-p-phenylene terephthalamide, which adopted highly regular rodlike molecular arrangements in solution. From these two first-ever liquid crystal polymers, fibers were spun that displayed unprecedented stiffness and tensile strength. The polymer poly-p-phenylene terephthalamide was released commercially under the name Kevlar.
At the time, the liquid crystal polymer in solution had to be melt-spun at over 200ºC, which produced weaker and less stiff fibers. Kwolek sought t reduce the melt-condensation process for forming Kevlar polymer to 0 to 40ºC to avoid the high melt-spinning temperature. Kwolek’s solution of Kevlar was low viscosity, turbid, and buttermilk in appearance, unlike conventional polymer solutions that were usually clear or translucent, with a molasses-like viscosity. Her type of cloudy solution was typically thrown away, and Kwolek was denied the use of the spinneret, used to extrude a polymer solution to form fibers, because of fear the solution would clog the machine. She persuaded the spinneret technician to test her solution, and was amazed to discover that the new fiber would not break like nylon.
Kevlar was not only stronger than nylon, but it was also five times stronger than steel by weight. Kwolek learned that the fibers could be made even stronger by heat-treating. The polymer molecules are shaped like rods or matchsticks, which gives Kevlar its extraordinary strength.
Kevlar is used in more than 200 applications, including tennis rackets, skis, parachute lines, boats, airplanes, ropes, cables, bullet-proof vests, tires, firefighter boots, hockey sticks, cut-resistant gloves, and armored cars. Further, Kevlar has been used in bomb-proof materials, hurricane safe rooms, and bridge reinforcements. The polymer has saved lives as a lightweight body armor for police and the military; conveyed messages across the ocean as a protector of undersea optical-fiber cable; and suspended bridges with super-strong ropes.
For Kwolek’s discovery of Kevlar, she was awarded DuPont’s Lavoisier Medal for outstanding technical achievement in 1995, as a “Persistent experimentalist and role model whose discovery of liquid crystalline polyamides led to Kevlar aramid fibers.” As of 2014, she was still the only female employee to receive the honor. Kevlar also generated billions of dollars in revenue for DuPont.
In 1959, Kwolek won a publication award from the American Chemical Society for her publication of “The Nylon Rope Trick,” which demonstrates a way of producing nylon in a beaker at room temperature. The demonstration is still a common classroom experiment, and the process was extended to high molecular weight polyamides.
Over Kwolek’s 40-year career, she earned 28 patents, and even after retirement in 1986, continued as a consultant. She received the Chemical Pioneer Award from the American Institute of Chemists and an Award for Creative Innovation and the Perkin Medal from the American Chemical Society. In 1995, Kwolek was added to the National Inventors Hall of Fame. In 2003, she was inducted into the National Women’s Hall of Fame. The Royal Society of Chemistry grants a biennial Stephanie L. Kwolek Award to recognize exceptional contributions to the area of chemistry from a scientist working outside the UK.