Penetration and exchange kinetics of primary alkyl amines applied to reactive poly(pentafluorophenyl acrylate) thin films

Abstract

We investigated the mechanism of primary amine-induced post-polymerization modification of active ester polymer thin films composed of pentafluorophenyl acrylate (PFPA) polymers. The most important physical parameters in the post-polymerization modification are the molecular weight of the PFPA polymers and the aliphatic chain length of the primary amines. The effects of these two parameters on the penetration depth, as well as the exchange kinetics were systematically studied by neutron reflectivity and quartz crystal microbalance with dissipation, accompanied by the measurement of surface morphological changes by an atomic-force microscopy and optical microscopy. The spin-cast PFPA polymer thin films showed distinctive differences in the exchange kinetics, as well as the penetration depth of amines as a function of the PFPA polymer molecular weight. The aliphatic chain length of primary alkyl amines markedly influenced the penetration kinetics into low-molecular weight poly(PFPA) films, whereas there was no significant penetration effect on the high-molecular weight films. The high-molecular weight of the poly(PFPA) films led to the deceleration of the dissolution of amine-functionalized polymer chains in a good solvent. The results of this study may provide a good physical background for developing reactive poly(PFPA) thin film platforms based on simple and quantitative post-modification with amine-containing molecules. The poly(pentafluorophenyl acrylate) thin film provides a reactive surface platform through facile post-modification with primary alkyl amines. We report the effect of the most important parameters in this reaction, molecular weight of the reactive polymers and the aliphatic chain length of primary amines, on the degree of exchange of the thin films. The studies with neutron reflectivity and quartz crystal microbalance offer physical backgrounds for developing versatile functional thin films based on this chemistry, in terms of penetration and exchange kinetics as a function of molecular weight of reactive ester polymers and primary amines.