CHARACTERIZATION OF FLUOROELASTOMER NETWORKS .1. INFRARED-ANALYSIS

Fluorocarbon compounds based on vinylidene fluoride copolymers and dihydroxy nucleophiles were prepared to determine the network forming structures of the cured materials. Previous attempts to achieve this goal consisted of model compound reactions, of prevulcanization events, and of materials cured under conditions only approaching industrial vulcanization conditions. The proposed structures derived from these studies could be different from the entities that will come in contact with alternate fuels such as methanol/gasoline blends when used in automotive applications. The evolution of the solid-state chemistry during cure and the final network structure needed to be defined. Thus, infrared vibrational spectra for 25-mum thick sections from key stages of processing were recorded. These spectra established directly, for the first time, that bisphenol-AF (BPAF) serves as the crosslinker during cure. Additionally, persistent unsaturation is formed on the elastomer backbone after crosslinking. Curing for extended periods of time produces no observable effect on the network. Furthermore, postcuring reduces residual hydrofluoric acid in the compound and results in two new absorptions at 2851 and 2920 cm-1, indicative of amorphous regions of polyvinylidene fluoride (PVF2). Although these findings help define the final network structure, there remain uncertainties about the pathway leading to the final structure. The data serve as input to understanding the fracture behavior and long term performance of this class of materials. It also could serve as a starting point for studies dealing with the enhancement of certain fluorocarbon properties such as low temperature behavior. (C) 1993 John Wiley & Sons, Inc.