Feb.4,2021  30  US 2021/0033971 Al  case,  RL 11  and  RL 12  are each independently a C$_{1 }$-Cg  alkanediyl group.  RL 13  is each independently a C$_{1 }$-C$_{10 }$ saturated hydrocarbylene group which may be straight,  branched or cyclic. Bl and Dl are each independently an  integer of Oto 10, preferably Oto 5, and Cl is an integer of  1  to 7, preferably  1  to 3.  [0085]  In formulae (AL-2a) and (AL-2b ), LA is a (Cl+l)› valent C$_{1 }$-C$_{50 }$ aliphatic or alicyclic saturated hydrocarbon  group, aromatic hydrocarbon group or heterocyclic group. In  these groups, some carbon may be replaced by a heteroatom› containing moiety, or some carbon-bonded hydrogen may be  substituted by a hydroxyl, carboxyl, acyl moiety or fluorine.  LA is preferably a C$_{1 }$-C$_{20 }$ saturated hydrocarbylene group,  saturated hydrocarbon group ( e.g., trivalent or tetravalent  saturated hydrocarbon group), or  CcC$_{30 }$ arylene group. The  saturated hydrocarbon group may be straight, branched or  cyclic.  LB  1s  -CO---0-,  -NHCO---0- or  -NHCONH-.  [0086]  Examples of the crosslinking acetal groups having  formulae (AL-2a) and (AL-2b) include groups having the  formulae (AL-2)-70 to (AL-2)-77.  [0082]  Of the acid labile groups having formula (AL-2),  suitable cyclic groups include tetrahydrofuran-2-yl, 2-meth› yltetrahydrofuran-2-yl, tetrahydropyran-2-yl, and 2-methyl› tetrahydropyran-2-yl.  [0083]  Also included are acid labile groups having the  following formulae (AL-2a) and (AL-2b ). The base polymer  may be crosslinked within the molecule or between mol› ecules with these acid labile groups.  [0084]  In formulae (AL-2a) and (AL-2b),  RL 11  and  RL 12  are each independently hydrogen or a C$_{1 }$-Cg saturated  hydrocarbyl group which may be straight, branched or  cyclic. Also,  RL $^{11 }$and  RL $^{12 }$may bond together to form a ring  with the carbon atom to which they are attached, and in this  (AL-2)-76  CAL-2)-75  (AL-2)-67  CH3  I  -CH-0  (AL-2)-68  (AL-2)-69  (AL-2a)  RLII  RLII  I  I  -C---tO-Rm-t;;;-o-LA-----to---t RL13-0-t;;;--C-]  I  Bl  DI  I  Cl  RLl2  RLl2  (AL-2b)  (AL-2)-70  (AL-2)-71  (AL-2)-72  -continued  (AL-2)-73  CH3  CH3  I  I  -CH -O-CH2CH20CH2CH20CH2CH2-0-CH- (AL-2)-74  c~  c~  I  I  -cH-o-cH,cH,ouom,cH,-o-cH-