. . . "wherein R is an alkoxy group, R1 is a hydrogen atom or an alkyl group, n is an integer of 3 to 50, b is an integer of 5 to 150, a and c, the same or different, each is an integer from 0 to 5, such that a+c is an integer from 2 to 5, A is a CH???, CH3C???, CH3CH2C???, or a ???CH2???CH???CH2 ??? group, x, y and z, equal or different, are integers of 1 to 30 such that the sum of x+y+z???5, POA is eit" .