Structural formation and gelation behavior of cold-crystallized poly(trimethylene terephthalate)

Experimentally observed a +-type Hv and a circular-type Vv scattering patterns from small-angle light scattering (SALS) measurement indicated a random assembly of sheaf-like or rod-like superstructure for poly(trimethylene terephthalate) (PTT) under cold-crystallization. The long period and crystallite thickness of cold-crystallized PTT have been determined by small-angle X-ray scattering (SAXS). The crystallite thickness is very small, ca 2 nm, which is close to the c-axis (chain axis) of unit cell in PTT crystal, 18.64 Å. The intermolecular crystallization may be viewed as a behavior of physical gelation. The liquid–solid transition in PTT crystallization from glassy state through the gel point has been investigated by dynamic mechanical experiments. The power law relaxation modulus, E(t)=St−Δ identifies the gel point, and small frequency window is sufficient to determine the relaxation exponent, Δ. The gel point occurs at the very early stage of crystallization, in which the relative degree of crystallinity is found to be about 2–3%. The Δ value is ca 0.52, which is independent of crystallization temperature.