81  US 9,221,742 B2  82  include acetal structure groups, ketal structure groups, and  alkoxycarbonyl groups, examples of which are shown below.  Herein the broken line designates a valence bond.  Of the acid labile groups represented by R$^{6 }$in formula (1 b ), 65  alkoxymethyl groups having the general formula  (le)  are  most preferred.  Herein the broken line designates a valence bond. Re is a  straight, branched or cyclic C$_{1 }$-C$_{15 }$monovalent hydrocarbon  group.  Illustrative examples of the acid labile group having for› mula  (le)  are given below, but not limited thereto.  --- ,..,,a..._  ,..,,  --- ’C  .....__,,,.  ’C  H2  H2  ____ c,..,,o~  H2  (le) 