A polymer brush includes a substrate material, a polymerization initiator layer containing a hydrolysis and condensation polymerization polymer comprising a first organosilane and a metal alkoxide on a surface of said substrate material, and polymer chains extending from a surface of the polymerization initiator layer. The first organosilane is a polymerization initiator group-containing organosilane having the following formula (I): X—R1-Ph-(R2)m—Si—R3nR43-n . . . (I) where X stands for a halogen atom, R1 stands for an alkylene group having 1 to 3 carbon atoms, Ph stands for a phenylene group, R2 stands for a C1 to C10 alkylene group optionally via an oxygen atom, R3 stands for an alkoxy group having 1 to 3 carbon atoms or chloro group, R4 stands for an alkyl group having 1 to 6 carbon atoms, m is 0 or 1, n is 1, 2 or 3.