Stabilized Nanoparticles Obtained from Synthetic Polykerizable Micelles and Vesicles.
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STABILIZED NANOPARTICLES OBTAINED FROM SYNTHETIC POLYKERIZABLE MICELLES AND VESICLES. OONSTANTINOS M. PALEOS NRC "Demokritos", Aghia Paraskevi,
15310 Attiki, Greece.
ABSTRACT The structural characteristics and the formation of monomeric and stabilized polymeric micelles and vesicles are reviewed. Characterization of these nanoparticles involved stability studies, molecular weight determination, permeability and fluorescence investigations, as well as electron microscopy and DSC studies. INTDFOUCTION Spherical micelles of 3-6 nm in diameter [1] are in a dynamic equilibrium with their monomers and can be stabilized either by the solubilization within them of appropriate monomers and subsequent polymerization, or by the polymerization of micelle-forming monomer surfactants [2]. Synthetic vesicles on the other hand with diameters from 30 to 300am possess greater kinetic stability than micelles [1]. In addition, the dependence of the structrure and size of vesicles on the mode of their formation [3,4] allows greater structural flexibility than micelles. However further stabilization [5,6] of these particles is required and this was achieved by addition polymerization or polycondensation. In the present study we will discuss the stuctural requirements for the formation of micelle and vesicle forming polymerizable surfactants and the diversified methods for the formation of the their polymerized counterparts. The stability of nanoparticles was the main property to be investigated. Furthermore their molecular weights were determined and the structure of micelles was investigated by fluorescence spectroscopy whereas vesicles were further characterized by permeability studies, electron microscopy, DSC and currently by video enhanced optical microscopy. Current and prospected applications of both monomeric and polymerized particles include their use as energy conversion systems [7,8], drug-carriers [5,9] in medicine, and as media for biomimetic reactions [10]. 1. POLYMERIZED MICELLES - FORMATION AND CHARACTERIZATION 1.1- Synthesis of micelle-forming rnolvmerizable surfactants. Surfactants bearing one long alkyl-chain coupled with a hydrophilic water above a critical concentration (CMC) head associate in forming micelles. Introduction of a polymerizable group does not in general HC=CH
[I-
H,C=CH
CH,
CH3, -N-CH, ( C H2),,
(CH(HI
H2C=C-CH, (CHO), CH,
C=o
~HH OaH
6- Na*
CH3
It
CH, I. Br CH,-N-CH (TCH,),,
IV
CH 3
III
Mat. Res. Soc. Symp. Proc. Vol. 171. '1990 Materials Research Society
V
88
drastically modify the basic molecular structure and the resulting monomers also aggregate forming micelles. The functionalization of surfactant structure by polymerizable groups can be performed either near the head or at the lipophilic group, as in monomers I-V. 1-2. General considerations of micellar polvmerization Studies on micellar polymerization have been limited to addition polymerization under conventional polymerization conditions. Certainly polymerized polycondensation cannot be ignored for the formation of aggr
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