about 0 to about 0.75, b and c are each independently, from about 0.25 to about 1.0; Z is oxygen or N???R3; R2 is ???[CH2]n???; R3 is hydrogen or ???[CH2]m???CH3; R4 and R5 are each, independently, ???[CH2]m???CH3; X is selected from the group consisting of Cl, Br, I and acetate; W is a bridging group or atom; m is an integer from 0 to 20; n is an integer from 1 to 20; and Y is selected from the g