A composition including at least one first divalent unit represented by formula: Each Rf is independently selected from the group consisting of Rfa—(O)t—CHF—(CF2)n—; [Rfa—(O)t—C(L)H—CF2—O]m—W—; Rfb-O—(CF2)p-; F(CkF2k)—(O—CkF2k)P—O—CF2—; and CF3—O—(CF2)3—(OCF(CF3)—CF2)Z—O-L1-. Each Q is independently selected from the group consisting of a bond, —C(O)—N(R1)—, and —C(O)—O—. Each X is independently selected from the group consisting of alkylene and arylalkylene, wherein alkylene and arylalkylene are each optionally interrupted by at least one ether linkage and optionally terminated by —N(R1)—C(O)— or —O—C(O)—. R and R1 are each independently selected from the group consisting of hydrogen and alkyl having from 1 to 4 carbon atoms. Rfa represents a partially or fully fluorinated alkyl group having from 1 to 10 carbon atoms and optionally interrupted with at least one oxygen atom. Rfb is selected from the group consisting of CF3CFH— and F(CjF2j)-. Methods of reducing surface tension of a liquid, making foams, and treating a surface using the compositions are also disclosed.