Scattering studies from polymer blends

An ultraquenching technique was used to prepare thin (ca. 1000 Å) amorphous films of polypivalolactone and poly(4-methyl-pentene-1). These films were characterized by electron microscopy, electron diffraction, and dynamic mechanical analysis. Other ultraquenched films of these polymers were crystallized by annealing for various times in the vicinity of their glass transition temperatures. Electron microscopy and electron diffraction were used to follow the reorganization of their structures.

Evidence for a double T_g in polypivalolactone (PPVL) was found, with crystallization of annealed, ultraquenched films occurring just above T_g (L) = 270°K. A T_g (U) = 340°K was noted. When the disordered glass was annealed above T_g (L), polypivalolactone crystallized into the a crystal form, which is composed of antiparallel chain segments, suggesting a chain-folded crystallization mechanism.

Poly(4-methyl-pentene-1) (P4MP1) gave evidence for T_g (L) = 220°K and T_g (U) = 325°K by dynamic mechanical analysis. However, morphology and electron diffraction showed that significant crystallization of ultraquenched polymer did not occur until T_g (U) was reached. X-ray data also supported this conclusion, which is explained by the lower density of the crystal phase of P4MP1 (compared to amorphous material) below 320°K. Long-term annealing of films at T_g (U) resulted in the formation of single-crystal structures, again indicative of a mechanism of chain-folded crystallization from the glass.