CHARACTERIZATION OF FLUOROELASTOMER NETWORKS .1. INFRARED-ANALYSIS

Fluorocarbon compounds based on vinylidene fluoride copolymers and dih ydroxy nucleophiles were prepared to determine the network forming str uctures of the cured materials. Previous attempts to achieve this goal consisted of model compound reactions, of prevulcanization events, an d of materials cured under conditions only approaching industrial vulc anization conditions. The proposed structures derived from these studi es could be different from the entities that will come in contact with alternate fuels such as methanol/gasoline blends when used in automot ive applications. The evolution of the solid-state chemistry during cu re and the final network structure needed to be defined. Thus, infrare d vibrational spectra for 25-mum thick sections from key stages of pro cessing were recorded. These spectra established directly, for the fir st time, that bisphenol-AF (BPAF) serves as the crosslinker during cur e. Additionally, persistent unsaturation is formed on the elastomer ba ckbone after crosslinking. Curing for extended periods of time produce s no observable effect on the network. Furthermore, postcuring reduces residual hydrofluoric acid in the compound and results in two new abs orptions at 2851 and 2920 cm-1, indicative of amorphous regions of pol yvinylidene fluoride (PVF2). Although these findings help define the f inal network structure, there remain uncertainties about the pathway l eading to the final structure. The data serve as input to understandin g the fracture behavior and long term performance of this class of mat erials. It also could serve as a starting point for studies dealing wi th the enhancement of certain fluorocarbon properties such as low temp erature behavior. (C) 1993 John Wiley & Sons, Inc.