Crystal Structures and Morphology of Thin Film, Melt Crystallized Poly ethylene naphthalate

Mukerrem Cakmak

Abstract

Application of electron diffraction (ED) to poly(ethylene naphthalate) (PEN) crystallized isothermally from the melt at 260°C has permitted determination of the α-and β-form unit cells. While the α-form lattice parameters and cell agree well with those proposed in the literature, a different cell is proposed for the β-form (monoclinic, P21/n11 space group; 4 chains, with a = 1.304 nm, b = 0.926 nm, c = 1.300 nm, α = 131.47°, β = γ = 90°, ρ = 1.368 g/cm). The β-form crystals were large, resembling hedrites (axialites). A number of different, single-zone ED patterns from at least one additional two-chain unit cell (γ) were found, indicating a large degree of PEN polymorphism. The γ unit cell has not yet been determined. Nascent melt-polymerized samples were also examined, giving rise to both β-and γ-type patterns. The γ-patterns arise from extended-chain single crystals of variable thickness.