s an integer of 0-20; [0124] each of R1, R2, R3 and R4 is a hydrocarbon group with 1-12 carbon atoms or trimethylsilyl group; Y consists of linkage of the structural units [I] and [II] shown by the following formulas, ratio of the structural unit [I] and the structural unit [II] being [I]/[II]=0.1-200 and total number of the structural units [I] and [II] being 10-1000: [0125] wherein, each of R9 a