Photopolymerization of butyl acrylate-in-water microemulsions: Polymer molecular weight and end-groups

Solubilization of butyl acrylate in water using sodium dodecyl sulfate (SDS) and 1-pentanol produced transparent oil-in-water microemulsions stable at room temperature. These microemulsions were polymerized using a two-component water-soluble initiator system comprising of Rose Bengal (RB) and methyldiethanolamine (MDEA). These compounds undergo photo-induced electron transfer upon absorption of visible light to produce amine radicals active in free radical polymerization. Analysis of the NMR spectra of polymers revealed only monomer peaks and amine fragments which were incorporated as the polymer ends. Effect of initiator composition on polymer length was also investigated using GPC. When RB concentration was increased with constant concentration of excess MDEA, the average chain length decreased up to a specific concentration where after the polymer length reached an asymptotic value. Experiments were performed to identify this asymptotic value and it was observed that as the MDEA concentration was increased, the asymptotic values of number average degree of polymerization decreased.