Tocopherol-containing amphiphilic polymers: syntheses and vesicle-forming properties

Abstract

Four different novel tocopherol-containing single-chain nonionic amphiphilic monomers, N-[methyl-N-(tocopheryloxycarbonyl)methyl amino]ethyl methacrylate (TOM), N-[methyl-N-[tocopheryloxypoly (ethyleneoxy)carbonyl]methylamino]ethyl methacrylates (n=2, TOPM-2; n=5, TOPM-5; n=10, TOPM-10: n=mean moles of EO) were synthesized by the reaction of α-tocopherol derivatives and DMEMA, characterized by FT $1^H$ and ${13}^C$ NMR spectroscopy, FT IR spectroscopy, elemental analysis, and mass spectroscopy, and used for the formation of bilayer vesicles. The unpolymerized vesicles of these single-chain amphiphiles even though they have a single-chain tocopherol as a hydrophobic group showed evidences of closed bilayer vesicles, which were converted to well-defined closed polymeric vesicles having distinct morphology, enhanced stability and reduced permeability upon polymerization either by thermal polymerization with free radical initiator AIBN or KPS or by direct UV-irradiated (220-400nm) photopolymerization. The apparent weight-average molecular weights of polymers formed in the polymerized vesicles of TOM, TOPM-2, 5, 10, and TOM/TOPM-10(1:2) determined by GPC using toluene as an eluent were in the range of 47,100 and 401,800 g/mol and molecular weight polydispersity of these polymers were in the range of 1.5 and 4.1. Conversions of these polymers were in the range of 44 and 85 %. Phase transition temperatures ($T_c$) of polymerized vesicles of these amphiphiles were in the range of 55 and 77 ℃, which are rather higher values than those of their unpolymerized counterparts, 41 and 68 ℃. Uranyl acetate stained TEM photographs showed that polymerization of unpolymerized vesicles of TOM of led to the formation of mostly spherical polymeric vesicles having diameters below 600 Å and and those of TOPM-2, -5, -10, and TOM/TOPM-10(1:2) led to the formation of relatively small spherical polymeric vesicles having diameters below 500 Å and relatively large elliptic polymeric vesicles...