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 permitted determination of the alpha- and beta-form unit cells. While the alpha-form lattice parameters and cell agree well with those proposed in the literature, a different cell is proposed for the beta-form (monoclinic, P2(1)/n11 space group; 4 chains, with a = 1.304 nm, b = 0.926 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 from at least one additional two-chain unit cell (gamma) were found, indicating a large degree of PEN polymorphism. The gamma unit cell has not yet been determined. Nascent melt-polymerized samples were also examined, giving rise to both beta- and gamma-type patterns. The gamma-patterns arise from extended-chain single crystals of variable thickness.