86  US 9,046,772 B2  85  such groups. Examples of the acid labile group XE are groups  of formulae (Ll) to (L4), tertiary alkyl groups of 4 to 20  carbon atoms, trialkylsilyl groups in which each alkyl moiety  has 1 to 6 carbon atoms, andoxoalkyl groups of 4 to 20carbon  atoms, like the acid labile group XA mentioned above.  Illustrative examples of the recurring units having formula  (4E) are given below, but not limited thereto.  A polymer comprising recurring units of formula ( 4E) is  decomposed under the action of acid to generate a hydroxyl  group so that its solubility in various solvents may change.  The acid labile group XE may be selected from a variety of  -continued 