Thermopolymerizable composition and use thereof

A thermopolymerizable composition comprising at least one thermopolymerizable compound having a polymerizable functional group which compound becomes a polymer having a cross-linked and/or side-chained structure upon polymerization, at least one electrolyte and at least one polymerization initiator, wherein said thermopolymerizable compound contains a compound having a polymerizable functional group, represented by the following formula (1) and/or formula (2):

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• [wherein R1 and R3 independently represent hydrogen or an alkyl group, R2 and R5 independently represent a divalent group containing oxyalkylene, fluorocarbon, oxyfluorocarbon, and/or carbonate, R4 represents a divalent group having 10 or less carbon atoms, R2, R4 and R5 each may contain a hetero atom and may have any of linear, branched and cyclic structures, and x is 0 or an integer of from 1 to 10, provided that when a plurality of polymerizable functional groups represented by formula (1) or (2) are present in the same molecule, R1, R2, R3, R4, R5 and x among the respective polymerizable functional groups may be the same or different],
• and said polymerization initiator is an organic peroxide represented by the following formula (3):
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• [wherein X represents an alkyl or alkoxy group which may have a substituent, Y represents an alkyl group which may have a substituent, X and Y each may have any of linear, branched and cyclic structures, and m and n each represents 0 or 1, provided that a combination of (m,n)=(0,1) is excluded].