Global Polyoxytetramethylene Market By Type (PTMG 1000, PTMG 1800, and PTMG 2000), By Application (Spandex Fiber, Polyurethane Elastomer, and Copolyester-ether Elastomer), By Region and Key Companies - Industry Segment Outlook, Market Assessment, Competition Scenario, Trends and Forecast 2019–2028