Polymerization of liposomes composed of diene‐containing lipids by radical initiators. II. Polymerization of monodiene‐type lipids as liposomes

1‐Palmitoyl‐2(2,4‐octadecadienoyl)‐sn‐glycero‐3‐phosphocholine (POPC), a polymerizable lipid that contains one diene group in only a 2‐acyl chain, was polymerized as liposome in an aqueous medium. Polymerization was initiated by water‐insoluble azobisisobutyronitrile (AIBN), or water‐soluble azobis(2‐amidinopropane) dihydrochloride (AAPD). AIBN was mixed with monomeric lipids, and the mixture was dispersed in an aqueous medium by sonication to prepare AIBN‐containing monomeric lipid liposomes. On the other hand, AAPD was simply added to the liposome suspension. The POPC liposomes were easily polymerized by the addition of AAPD, a water‐soluble radical initiator, but few were polymerized by AIBN. The results suggested that the diene group in the 2‐acyl chain was in an aqueous phase and, therefore, easily polymerized by a water‐soluble radical initiator. The polymerized POPC liposomes were revealed to be more stable than those of monomeric ones because the scattered‐light intensity from the polymerized POPC liposome suspension changed a little by the addition of Triton X‐100. For only the polymerized ones, the liposome structure was confirmed by TEM after addition of an excess amount of Triton X‐100.