Short answers, pulled from the story.
Polypropylene polymerization was first demonstrated in 1951 by Phillips Petroleum chemists J. Paul Hogan and Robert Banks. The stereoselective polymerization that produced isotactic polypropylene was discovered by Giulio Natta and Karl Rehn in March 1954, and the Italian firm Montecatini began large-scale commercial production of isotactic polypropylene in 1957.
Tacticity describes how methyl groups are oriented along the polypropylene chain. Isotactic polypropylene has methyl groups all on the same side, producing a semi-crystalline, rigid, heat-resistant material. Atactic polypropylene has randomly arranged methyl groups, creating an amorphous, rubber-like material. Syndiotactic polypropylene has alternating methyl groups and can only be made with metallocene catalysts.
Polypropylene is used in injection-molded products such as caps, containers, automotive parts, and batteries; in biaxially oriented film for snack food and confectionery packaging; in nonwoven fabrics for diapers, sanitary products, and face masks; in piping systems; in ropes; and as a concrete additive to reduce cracking. It is the second-most widely produced commodity plastic in the world.
Polypropylene mesh erodes surrounding tissue over a period ranging from days to years. Its use as a transvaginal mesh for treating pelvic organ prolapse raised particular concern, and on the 3rd of January 2012 the FDA ordered 35 manufacturers to study the side effects of these devices. A separate study found polypropylene was the most common microplastic fiber in the olfactory bulbs of 8 of 15 deceased individuals examined.
Less than 1 percent of polypropylene generated was recycled as of 2015. Mechanical recycling is the primary method, but polypropylene degrades more severely under heat than polyethylene because its methyl side group is susceptible to thermo-oxidative and photo-oxidative breakdown. Polypropylene carries resin identification code number 5.
Polypropylene's resistance to fatigue makes it the standard material for plastic living hinges, such as those on flip-top bottles. The material can flex repeatedly without fracturing, provided the polymer chain molecules are oriented across the hinge to maximize strength.