u and v are independently 0, 1, 2 or 3, provided both are not zero; provided that when R16 is CH═CH or C═CH , v is 1; provided that when {HEAD ~ R17} is {TAIL ~ CH}═CH or C═CH , u is 1; provided that when v is 2 or 3, the R16 s can be the same or different; and provided that when u is 2 or 3, the R17 s can be the same or different; and 