POLYMERIZATION OF DIENE-CONTAINING LIPIDS AS LIPOSOMES BY RADICAL INITIATORS .4. EFFECT OF LIPID PACKING ON THE POLYMERIZATION PROFILE

1,2-Di(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine (DODPC) was polymerized as liposomes with a water-soluble radical initiator, azobis(2-amidinopropane) dihydrochloride (AAPD). DODPC liposomes were prepared with a tip-type sonicator and incubated at 4, 8, or 20 degree C. When DODPC liposomes were incubated at lower temperatures than the gel-to-liquid crystalline phase transition temperature (16 degree C for DODPC liposomes), these liposomes fused with each other to produce large unilamellar liposomes. An average radius was calculated from the **1H NMR signal intensity ratio for the choline methyl protons split by Eu**3** plus . Generally AAPD initiated radical polymerization of diene groups on the 2-acyl chains of DODPC because of nonequivalent acyl chain packing in bilayer membranes.