The effect of vesicle size on the photopolymerization products of the polymerizable diacetylene lipid 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) has been examined using size exclusion chromatography (SEC) and mass spectrometry. Lipid polymers from 50-, 100-, 300-, and 600-nm vesicles have the same molecular weight range with a prominent polystyrene equivalent molecular weight peak between 1.6 x 10(6) and 2.2 x 10(4). The observed intensity of this peak increased as vesicle size was increased from 50- through 300-nm diameter, but was decreased in 600-nm diameter vesicles. After acid catalyzed transesterification of the lipid polymers, the derived acyl chain polymers were examined by SEC. These polymers have a common prominent peak corresponding to a polystyrene equivalent molecular weight between 2.5 X 10(4) and 2.2 x 10(3). Size exclusion chromatography (SEC) and chemical ionization mass spectrometry revealed the presence of the polymerized acyl-chain dimer and trimer after methanolysis of the lipid polymer.