There's no single person who "discovered" thermoplastic materials. It's more accurate to say that the development of thermoplastics was a gradual process involving many inventors and scientists over several decades.

Here's a brief timeline of key developments:

* 1839: Charles Goodyear accidentally discovers vulcanized rubber, a process that involves heating natural rubber with sulfur, making it more durable and flexible. This is considered a crucial step towards synthetic materials.

* 1846: Christian Schönbein accidentally discovers guncotton (nitrocellulose), a flammable material that later finds use in plastics and explosives.

* 1862: Alexander Parkes invents Parkesine, considered the first synthetic plastic. It was a brittle material made from nitrocellulose and camphor.

* 1869: John Wesley Hyatt creates Celluloid, a more stable and versatile form of nitrocellulose plastic, paving the way for widespread use in toys, films, and other applications.

* 1907: Leo Baekeland invents Bakelite, the first synthetic thermosetting plastic. While not a thermoplastic, it inspired further research into plastics.

* 1930s: Polyvinyl chloride (PVC), polyethylene (PE), and polystyrene (PS) are developed. These are all thermoplastic materials with unique properties that have revolutionized many industries.

Therefore, attributing the discovery of thermoplastics to one person is impossible. The development of these materials was a collaborative effort built upon years of research and experimentation.