The glass temperature transition is for glass, polymers, etc. (amorphous or semicrystalline materials), but not for leather.

Since, according to Wikipedia's definition, "Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin, with the linear formula (C3H3N)n," and since silk is produced by silk worms, the answer must be no.

Polyethylene is a pure substance.

Polyethylene is a semicrystalline homogeneous polymer with a molecular weigh profile based upon the production chemistry. Common forms include HDPE, MDPE, LLDPE, LDPE, UHMWPE, etc.

words beginning with semi: * semisolid * semipermanent * semi-formal * semicircle * semiconscious * semi-gloss * semipermeable * semiprecious * semisweet * semiofficial * semiprofessional * semiclassical * demidarkness * semimat * semimoist * semidomesticated * semiaquatic * semidivine * semidetatched * semicolon * semifitted * semiflexible * semidry * semilunar * semiautomatic * semiarid * semiconductor * semigovernmental * semiholiday * semiliquid * semimonastic * semiskilled * semitropical * semitrailer * semitranslucent * semisynthetic * semiterrestrial * semimonthly * semiweekly * semicrystalline * semipalmated * semiopaque * semipolitical * semipostal * semiyearly * semipro * semipublic * semirigid * semiprivate * semisacred * seminomad * semidesert

Polyethylene terephthalate (sometimes written poly(ethylene terephthalate), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber.

Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size < 500 nm) or opaque and white (particle size up to a few microns) depending on its crystal structure and particle size.