roup, hydroxyl group and hydrogen atom, R5 is a group selected from the group consisting of alkyl groups containing 1 to 7 carbon atoms, alkoxy groups containing 1 to 4 carbon atoms, amino group and carboxyl group, x and y are integers in the range of 1???x???40 and 20???x+y???50,000, the viscosity of the composition, prior to crosslinking, being controlled with an organic solvent selected from th