propyl; R1, R3, R4 and R5 are a hydrogen, an alkyl group from C1 to C20 including methyl, ethyl or propyl, or a halogen-substituted alkyl or silane group; R2 is defined as R1, or (X)g(R3)hC???{C(R3)(R4)}c; a is an integer from 1 to 3, and b is an integer from 0 to 2, wherein a+b=3; c is an integer from 0 to 1000; d is an integer from 1 to 50000; e and f are independently an integer from 0 to 4, w