Patent ID: 7119160

Claim:
A polyurethane having a structural unit represented by formula (I): wherein n represents an integer of 2 to 1000, R 1 represents substituted or unsubstituted lower alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl, R 2 , R 3 and R 4 independently represent a hydrogen atom, substituted or unsubstituted lower alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl, R 1 s, R 2 s, R 3 s, and R 4 s, when they are each present two or more in number, may be the same or different, and R 5 represents a hydrogen atom, substituted or unsubstituted lower alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl.