Organic monomeric glass formation by substituted ethylenediamine

Abstract

Dibenzoyl N-alkyl ethylene diamine compounds were prepared and characterized to explore the effects of rotational isomerism and hydrogen bonding on organic monomeric glass formation. The compounds were R 1CONHCH 2CH 2N(R)COR 1 with R = −CH 3 or −CH 2CH 3 and R 1 = phenyl, 4-nitrophenyl, or 3,5-dinitrophenyl. Rotation takes place about the amide bonds, and the R substituent provides a steric barrier to rotation. Intermolecular hydrogen bonding takes place between the CO sdsdsd HN and NO sdsdsd HN groups which suppresses nucleation when R 1 is nitro substituted. The undercooled melt viscosity and thermodynamic properties were used to compare the observed crystallization rate with that calculated from classical nucleation and growth theory. For R 1 = phenyl, the crystallization rate is close to that expected from the classical theory. For R 1 = 4-nitrophenyl or 3,5-dinitrophenyl, nucleation is suppressed through stabilization of rotational isomers by the network of hydrogen bonds in the quiescent state. The undercooled liquid of R 1 = 4-nitrophenyl exhibited rapid shear-induced crystallization during viscosity measurement. This is interpreted as the result of coupling between rotational isomers and the external flow field through the network of hydrogen bonding. An additional frequency factor that takes into account the interaction between rotational isomerism and the external network through hydrogen bonding is needed to modify the pre-exponential term in the nucleation rate equation.