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Herein RL 41 is as defined above. 

Illustrative examples of the acid labile group of formula (L4) are given below. 

<img src='content_image/921097.jpg'>

Examples of the tertiary C$_{4}$ -C$_{20 }$alkyl groups, trialkylsilyl groups in which each alkyl moiety has 1 to 6 carbon atoms, and C$_{4}$ -C$_{2}$ , oxoalkyl groups, represented by XA, are as exemplified for RL 04 . 

Illustrative examples of the recurring units of formula (2) are given below, but not limited thereto. Herein RA is as defined above. 

<img src='content_image/921098.jpg'>

-continued 

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-continued 

