Syntheses and characterizations of bis(trialkoxysilyl)oligoimides. II. Syntheses and characterizations of fluorinated crosslinkable oligoimides with low refractive indices

Abstract

AbstractNovel crosslinkable fluorinated oligoimides were prepared in two steps. The first involved the synthesis of oligoimides terminated with nadic or allylic double bonds, and the second step was materialized either by a radical addition of mercaptotrialkoxysilane derivatives onto nadic double bonds or a hydrosilylation reaction of hydrogenotrialkoxysilane derivative onto allylic double bonds. Three kinds of crosslinking of the trialkoxysilane end groups were studied. The first kind entailed a thermal self‐crosslinking of trialkoxysilane groups. The second process of crosslinking incorporated a bicomponent system—the crosslinked agent was 1,1,1‐tris(4‐hydroxyphenyl)ethane (TRIOH). The trialkoxysilane groups reacted with the hydroxyl–phenol groups of TRIOH to give thermally stable phenoxysilane bonds as well as a crosslinking network. The last method was also a bicomponent system; the oxalic acid was added into an oligoimide solution where by thermal treatment water was created. The water molecules hydrolyzed the trialkoxysilane groups into silanol groups that polycondensed into a crosslinked network following a sol–gel process. The mechanism of the different crosslinking reactions was investigated by Fourier transform infrared spectroscopy and solid‐state 29Si NMR. The self‐crosslinked material prepared from precursor α,ω‐trimethoxysilyl fluorinated oligomer (Mn = 5500 g · mol−1) exhibited a 10 wt % loss temperature under air higher than 420 °C and a low birefringence (Δn = 0.008) at 1.300 μm. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2602–2619, 2001