"oup, a dicyclopentenyloxyethyl group, a cyclohexyl group, a norbonyl group, a norbornaneepoxy group, a norbornaneepoxymethyl group and an adamantyl group, 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 ran" . . . . .