As such substituted silyl group having 1 to 20 carbon atoms, for example, mono-substituted silyl groups having 1 to 20 carbon atoms such as a methylsilyl group, ethylsilyl group, phenylsilyl group and the like, di-substituted silyl groups having 2 to 20 carbon atoms such as a dimethylsilyl group, diethylsilyl group, diphenylsilyl group and the like, tri-substituted silyl groups having 3 to 20 carb