A polymer that has a main chain comprising repeating units represented by formula and repeating units represented by formula and satisfies requirements,,, and, wherein R 1 represents hydrogen, a methyl group, or an ethyl group, and R 2 represents an acetoxy group, a methoxycarbonyl group, an ethoxycarbonyl group, or a tert-butoxycarbonyl group;: the ratio of the number of the repeating units represented by formula to the total number of the carbon atoms that constitute the main chain of the polymer is from 4.0% to 7.5%;: the ratio X represented by formula is from 82% to 100%; X = 100 × A / B where A represents the total number of the carbon atoms of the carbonyl groups of the R 2 s of all the repeating units that satisfy the following requirement (a2-1) and are represented by formula, (a2-1): no functional group represented by the following formula,,,, or is bonded to any of the carbon atoms C 1, C 2, and C 3, where C 1 is a carbon atom that bonds to a repeating unit represented by formula, C 2 is a carbon atom that bonds to C 1, and C 3 that bonds to C 2, wherein R 3, R 4, R 5, R 6, R 7, and R 8 each independently represent an alkyl group or hydrogen; and B is the total number of the carbon atoms of the carbonyl groups of the R 2 s of all the repeating units represented by formula;: the polymer has a melting point of 42°C to 90°C as measured with a differential scanning calorimeter; and: the molecular weight distribution (Mw/Mn) as measured in accordance with the description of the polymer is from 1.5 to 4.: the ratio of the number of the repeating units represented by formula to the total number of the carbon atoms that constitute the main chain of the polymer is from 4.0% to 7.5%;: the ratio X represented by formula is from 82% to 100%; X = 100 × A / B where A represents the total number of the carbon atoms of the carbonyl groups of the R 2 s of all the repeating units that satisfy the following requirement (a2-1) and are represented by formula, (a2-1): no functional group represented by the following formula,,,, or is bonded to any of the carbon atoms C 1, C 2, and C 3, where C 1 is a carbon atom that bonds to a repeating unit represented by formula, C 2 is a carbon atom that bonds to C 1, and C 3 that bonds to C 2, wherein R 3, R 4, R 5, R 6, R 7, and R 8 each independently represent an alkyl group or hydrogen; and B is the total number of the carbon atoms of the carbonyl groups of the R 2 s of all the repeating units represented by formula; (a2-1): no functional group represented by the following formula,,,, or is bonded to any of the carbon atoms C 1, C 2, and C 3, where C 1 is a carbon atom that bonds to a repeating unit represented by formula, C 2 is a carbon atom that bonds to C 1, and C 3 that bonds to C 2, wherein R 3, R 4, R 5, R 6, R 7, and R 8 each independently represent an alkyl group or hydrogen; and B is the total number of the carbon atoms of the carbonyl groups of the R 2 s of all the repeating units represented by formula;: the polymer has a melting point of 42°C to 90°C as measured with a differential scanning calorimeter; and: the molecular weight distribution (Mw/Mn) as measured in accordance with the description of the polymer is from 1.5 to 4.