content_image/910082.jpg content_image/910084.jpg content_image/910085.jpg content_image/910083.jpg
<img src='content_image/910082.jpg'>

-continued 

The acid labile group R 2 in recurring units (al) may be a group having the general formula (A-3)-23. 

<img src='content_image/910084.jpg'>

Herein R 23 - $^{1 }$is hydrogen, a C$_{1 }$-C$_{4 }$ alkyl, alkoxy, alkanoyl or alkoxycarbonyl, CcC$_{10 }$ aryl, halogen or cyano group, and m23 is an integer of 1 to 4. 

Examples of the monomer from which recurring units (al) having an acid labile group of formula (A-3)-23 substituted thereon are derived are shown below. 

<img src='content_image/910085.jpg'>

<img src='content_image/910083.jpg'>

-continued 

