The compound (A) can also be prepared by polymerization of the reaction product of the compound [5] with an α,β-unsaturated hydroxyl compound, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 2-hydroxybutyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, dipentaerythritol hexa(meth)acrylate, hexa(meth)acrylate of a compound formed by addition of dipentaerythritol with ε-caprolactone and the like, or with a corresponding α,β-unsaturated thiol compound. The compound (A) can also be prepared by copolymerization of the reaction product with an α,β-unsaturated compound having no functional groups. Examples of the α,β-unsaturated compound having no functional groups are: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, styrene, α-methylstyrene, p-vinyltoluene, acrylonitrile and the like.
