a is 0, 1, 2 or 3 and b is 0, 1 or 2, provided that the requirement a+??b???2 is satisfied and b???s in m???Si(R1 2-b)(Xb)???O??? groups may be either the same or different; and m is an integer of 0 to 19. [0011] In a still preferable embodiment, the invention relates to a curable composition as described above wherein the main chain skeleton of the polyoxyalkylene polymer serving as the componen