"p, R5 is a group selected from a group consisting of a tetrahydropyranyl group, a tetrahydrofuranyl group, a methyl group, an ethyl group, a propyl group, a tert-butyl group and 3-oxocyclohexyl group, and x+y+z=1 in which x is a variable in the range from 0.1 to 0.9 both inclusive, y is a variable in the range from 0.1 to 0.7 both inclusive, and z is a variable in the range from 0.01 to 0.7 both i" . . . . .