Investigation Of Parameters Enabling Admicellar Reversible Addition-Fragmentation Chain Transfer (Raft) Polymerization

To date, enormous studies on admicellar polymerization have been recorded since the initial reports in the 1980’s. This technique which offered the advantage of using inexpensive materials and facile procedures, proven to be a successful surface modification technique. Nevertheless, one has to tailor every particular case due to the contribution of various factors in the process. Therefore, understanding the fundamentals parameters affecting the characteristics of polymer formed by admicellar polymerization have become a great interest. The effect of oxygen on the requisite amount of initiator and the polymer formed through the admicellar polymerization of styrene on silica particles was studied using cetyltrimethylammonium bromide (CTAB) as the adsorbed surfactant bilayer template, 2,2\u27-azobisisobutyronitrile (AIBN) as a water-insoluble initiator or 4, 4\u27-azobis (4-cyanovaleric acid) (V-501) as a water-soluble initiator. We demonstrated that deoxygenated admicellar polymerization via purging the headspace with nitrogen prior to the initiation of the admicellar polymerization of styrene on the surface of porous silica substrates produced satisfactory yield (high apparent conversion) and higher molecular weight polymer even at low initiator loading (ie. M/I 1000). Meanwhile insufficient polymer can be collected from control samples performed without deoxygenation at the same ratio. At moderate initiator loading (ie. M/I 150), we observed lower molecular weight polymer with slightly lower conversion when performed in the presence of oxygen. This can be explained by the mechanism of initiator consumption by oxygen causing the early termination and increases the rate of dead chain formation. Admicellar polymerizations using the water-soluble initiator exhibited higher Mw polymer compared to the systems using the water-insoluble initiator due to less degree of partitioning of water-soluble initiator in the admicelle compared to water-insoluble initiator, resulting in fewer polymerization sites and higher molecular weight polymer. Results from deoxygenated admicellar polymerization offers a potential to implement oxygen sensitive technique such as reversible addition-fragmentation chain transfer (RAFT) polymerization in admicellar polymerization in order to obtain more advanced thin films. Our initial investigation focuses on admicellar RAFT polymerization of styrene, 4-methylstyrene, and 4-methoxystyrene inside cetyltrimethylammonium bromide (CTAB) admicelles on the surface of silica particles using AIBN and 2,2\u27-Azobis(2-methylpropionamidine) dihydrochloride (V-50) as the free radical initiator and 4-cyano-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid (CDP) and 2-phenyl-2-propyl benzothioate (CDB) as the chain transfer agent. The preliminary results demonstrate the ability to reduce the molecular weight of the formed polymer films and suggest the living characteristics of RAFT polymerization inside admicelles compared to the traditional admicellar polymerization technique though there were poor control on the molecular weight distribution