CRYSTAL-STRUCTURES AND MORPHOLOGY OF THIN-FILM, MELT-CRYSTALLIZED, AND POLYMERIZED POLY(ETHYLENE-NAPHTHALATE)

Application of electron diffraction (ED) to poly(ethylene naphthalate) (PEN) crystallized isothermally from the melt at 260 degrees C has pe rmitted determination of the alpha- and beta-form unit cells. While th e alpha-form lattice parameters and cell agree well with those propose d in the literature, a different cell is proposed for the beta-form (m onoclinic, P2(1)/n11 space group; 4 chains, with a = 1.304 nm, b = 0.9 26 nm, c = 1.300 nm, alpha = 131.47 degrees, beta = gamma = 90 degrees , rho = 1.368 g/cm(3)). The beta-form crystals were large, resembling hedrites (axialites). A number of different, single-zone ED patterns f rom at least one additional two-chain unit cell (gamma) were found, in dicating a large degree of PEN polymorphism. The gamma unit cell has n ot yet been determined. Nascent melt-polymerized samples were also exa mined, giving rise to both beta- and gamma-type patterns. The gamma-pa tterns arise from extended-chain single crystals of variable thickness .