NOVEL POLYMER ARCHITECTURES VIA THE SELECTIVE POLYMERIZATION OF LYOTROPIC LIQUID-CRYSTALS OF HETEROBIFUNCTIONAL AMPHIPHILES

The reactivity of polymerizable amphiphiles in supramolecular assembli es, such as lipid bilayers, is dependent on the mode of initiation, th e polymerizable group, and the position of the reactive group in the a mphiphile. This report describes the synthesis, characterization, and polymerization of a novel heterobifunctional lipid, 2,4,12,14-tetraene hexadecanoyl)phosphatidylcholine (1), that contains a diene and a dien oyl group in the sn-2 acyl chain. The difference in polarity of local sites of each group within the bilayer makes it possible to perform si multaneous or selective polymerizations of these groups. Simultaneous polymerization of both reactive groups was achieved by either redox po lymerization or direct photoirradiation. Selective polymerization of t he dienoyl was accomplished by photoirradiation with filtered light fr om a high pressure Hg/Xe lamp. The diene was selectively initiated by thermal decomposition of AIBN. The degree of polymerization depended s trongly on the initiation chemistry. Photoirradiation gave oligomers, whereas radical polymerization with redox or AIBN afforded polymers wi th relative number average degrees of polymerization of 200 and 350, r espectively. Both diene and dienoyl groups formed 1,4-poly(diene) rega rdless of the mode and order of the polymerization applied. The polyme rs obtained from hydrated bilayers of 1 by either simultaneous polymer ization of both reactive groups or sequential selective polymerization of each group were not cross-linked. The absence of cross-linking at high conversions to polymer and the size of the solubilized surfactant -polymer micelles are consistent with the formation of ladder-like pol ymers with parallel chains tethered together by a hexa-methylene space r.