Structure of odd–even nylons derived from 2-methylpentamethylenediamine. Effect of the side methyl group

Abstract

Structure and morphology of lamellar crystals of two polyamides derived from 2-methylpentamethylenediamine (MPMD) and dibasic acids with 4 or 8 methylenes have been studied by transmission electron microscopy, electron diffraction and X-ray diffraction. The crystallographic unit cell of MPMD-6 is triclinic with a=4.85, b=5.90, c (chain axis)=30.4 Å, α=115.40, β=99.9 and γ=61.1°, the chain axis direction is not coincident with the c ∗ reciprocal axis. These dimensions suggest a hydrogen-bonded sheet structure with a single hydrogen bond direction and a twist of 180° in the odd diamine unit. MPMD-10 shows two crystalline structures. The most abundant being a monoclinic unit cell with a=4.79, b=5.67, c (chain axis)=36.3 Å and γ=61.8°. The less abundant structure was only observed in oriented fibers and was similar to the MPMD-6 crystalline structure. Single crystals of both MPMD-6 and MPMD-10 polyamides grow preferentially along their single hydrogen bond direction.