US 10,005,868 B2  66  65  -continued  -continued  [Synthesis Example 2-1] Synthesis of Polymer 1  Monomer 6  P AG monomer 2  Synthesis Example 2  Synthesis of Polymer Compound (Polymer)  Polymers 1 to 6 were synthesized by using Monomers 1  to 6 obtained in Synthesis Examples 1-1 to 1-6. The struc- tures of PAG monomers 1 and 2 used in Synthesis Example  2 and Comparative Synthesis Example are as follows.  A 2 L flask was charged with 9.3 g of Monomer 1, 3.5 g  of methacrylic acid 3-hydroxy-1-adamantyl ester, 10.2 g of  methacrylic acid 2-oxooxolan-3-yl ester, and 40 g of tetra› hydrofuran as a solvent. This reaction vessel was cooled to  - 70° C. in a nitrogen atmosphere, then degassed under  reduced pressure and blown with nitrogen three times. After  heating to room temperature, 1.2 g of azobisisobutyronitrile  (AIBN) was added thereto as a polymerization initiator. The  temperature was then increased to 60°  C., and the solution  reacted for 15 hours. The reaction solution was precipitated  in 1 L of isopropyl alcohol, filtered, and dried at 60°  C. to  obtain a white polymer.  The obtained polymer was analyzed by  $^{13}$C-NMR,  $^{1}$H-NMR, and GPC, consequently finding the following  results.  Copolymerization Composition Ratio (Mole Ratio)  Monomer  1:  methacrylic acid 3-hydroxy-1-adamantyl ester:  methacrylic acid 2-oxooxolan-3-yl ester=0.25:0.15:0.60  Weight average molecular weight (Mw)=9,800  Molecular weight distribution (Mw/Mn)=l.62  This polymer compound was named Polymer 1.  P AG monomer 1  0  0  Polymer 1  0 