henyl group or a cycloalkyl group having 3 to 12 carbon atoms, m is 1 or 2 ##STR3## wherein R6 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R7 is a hydrogen atom or a methyl group, each of R8, R9 is an alkyl group having 1 to 4 carbon atoms, and each of R5, R10 is an alkyl group having 1 to 12 carbon atoms, a phenyl group, an alkyl-substituted phenyl group or a cycloalkyl group