Patent ID: 8168742

Claim:
A crosslinkable fluorinated aromatic prepolymer which is obtained by reacting starting materials in a condensation reaction in the presence of a HF-removing agent, wherein the starting materials are (1), (2) and (3): (1) either one or both of a compound (Y-1) having a crosslinkable functional group (A) and one or two phenolic hydroxyl groups; and a compound (Y-2) having a crosslinkable functional group (A) and a fluorinated aromatic ring, and (2) a fluorinated aromatic compound (B) represented by the following formula (1): wherein n is an integer ranging from 0 to 2, each of a and b which are independent of each other, is an integer ranging from 0 to 3, and each of Rf 1 and Rf 2 which may be the same or different from each other, represents a fluorinated alkyl group having at most 8 carbon atoms, and F in the aromatic ring indicates that the ring hydrogen atoms are all substituted by fluorine atoms), and (3) a compound (C) having at least 3 phenolic hydroxyl groups and which has crosslinkable functional groups (A) and ether bonds and has a number average molecular weight of from 1×10 3 to 5×10 5 wherein (C) is selected from the group consisting of 1,3, 5-trihydroxybenzene, trihydroxybiphenyl, trihydroxynaphthalene, 1,1,1-tris(4- hydroxyphenyl)ethane, tris(4-hydroxyphenyl)benzene, tetrahydroxybenzene, tetrahydroxybiphenyl, tetrahydroxybinaphthyl and tetrahydroxyspiroindan.