US 9,703,193 B2  97  98  -continued  -continued  Of the acid labile group R 6 ,  preferred are alkoxymethyl  groups having the formula (e2):  wherein Re is a straight, branched or cyclic C$_{1 }$-C$_{20 }$monova- lent hydrocarbon group such as alkyl.  Examples of the acid labile group of formula (e2) are  shown below, but not limited thereto.  H2  H2  ____ c_,.,.o~  H2  (e2)