US 10,781,276 B2  35  36  (Synthesis Example 30) Synthesis of 2,4-dime› thoxy-4 ’-(2-methacry loxy )ethoxybenzophenone  <Synthesis of Compound C2 Constituting Sensitizer Unit  C>  (Synthesis Example 32) Synthesis of 1-(2,4-dime› thoxy)phenyl-1-[ 4’-(2-hydroxy)ethoxyphenyl]-1,1- dimethoxymethane  3.3  g  of 1-(2,4-dimethoxy)phenyl-1-[4’-(2-hydroxy)  ethoxyphenyl]-1,1-dimethoxymethane is obtained in the  same procedure as Synthesis Example 24 except that 2,4- dimethoxy-4’-(2-hydroxy)ethoxybenzophenone  is  used  instead of  1-(  4-hydroxyphenyl)-2-phenylethanedione.  5.4 g of 2,4-dimethoxy-4’-(2-methacryloxy)ethoxybenzo› phenone is obtained in the same procedure as Synthesis  Example  14  except that 2,4-dimethoxy-4’-(2-hydroxy)  ethoxybenzophenone is used instead of  1-(  4-hydroxyphe› ny 1)-2,2-dimethy 1-1-propanone.  (Synthesis Example 33) Synthesis of 1-(2,4-dime› thoxy)phenyl-1-[ 4’-(2-methacryloxy )ethoxyphenyl]- 1,  l-dimethoxymethane (Compound C2)  (Synthesis Example 31) Synthesis of 2,4-dime› thoxy-4’-(2-methacryloxy)ethoxybenzhydrol (Com› pound Cl)  3.7 g of 2,4-dimethoxy-4’-(2-methacryloxy)ethoxybenz› hydrol (compound Cl) is obtained in the same procedure as  Synthesis Example 27 except that 2,4-dimethoxy-4’-(2- methacryloxy)ethoxybenzophenone is used instead of 2,2’,  4,4’-tetramethoxybenzophenone and the residue obtained by  concentration is purified by column chromatography (ethyl  acetate/hexane=20/80 (volume ratio)).  3.7 g of 1-(2,4-dimethoxy)phenyl-1-[4’-(2-methacryloxy)  ethoxyphenyl]-1,1-dimethoxymethane (Compound C2) is  obtained in the same procedure as Synthesis Example  14  except that 2,4-dimethoxy-4’-(2-hydroxy )ethoxybenzophe› none is used instead of l-(4-hydroxyphenyl)-2,2-dimethyl› l-propanone.  [Chem.42]  ’-....0  0  0 ~0H  )yoyl~  0  0  o~o.  Jl  y  0  [Chem.44]  0  -- 0 [Chem.43]  .......... 0  0  , 0 ll’u 0 ~ 0 Y’  -- 0  (Compound Cl)  [Chem. 45]  .......... 0  0  0 Y’  -- 0  (Compound C2) 