Transverse lipid migration (flip-flop) of 2-F, a head-group-labelled dipalmitoylphosphatidylcholine (DPPC), in surface-differentiated 1:7 coliposomes with unlabeled DPPC (2-NF), is facilitated by added N-isopropylacrylamide (NIPAM) polymers at temperatures above the extended --> contracted transition temperatures of the polymers (30-33 degrees C). The effectiveness of the polymers is sensitive to the identity of the substituents on their amide nitrogens; an octadecyl residue is particularly potent, whereas a butylpyrenyl substituent is ineffective. Evidence is also presented for interliposomal polymer transfer above the liposomes’ gel --> liquid crystal transition temperature.