Investigation of photopolymerization using continuous flow reactors

This study has investigated the potential of using ultraviolet (UV) radiation for initiating polymerization of n-butyl acrylate (BA) in a narrow channel reactor made of borosilicate. A continuous flow system using a 90 cm long glass reactor with a circular cross section was used in conjunction with a UV flood lamp having peak intensity at 365 nm. Experiments were performed in order to study the influence of UV intensity, initiator concentration, exposure time, temperature, and reactor size on conversion and molecular weight distribution. The effect of temperature was studied by immersing the reactor in a water bath maintained at different temperatures. Narrow channel glass reactors, with diameters 1.5 mm, 1.0 mm, and 0.5 mm, were used to study the effect of light penetration depth on the polymerization kinetics. While the key outcome of this work has been in identifying the design space, several other scientific findings have evolved in the process. It was found that a photoinitiator concentration of 2.0 % w/w of monomer provided the highest monomer conversion in the range of UV intensities and exposure times investigated. The PDIs of the polymer obtained increased with initiator concentration upto 2.0 % w/w of BA. Monomer conversion increases with increase in the temperature and with decrease in the size of the reactor. The results of this investigation when compared with continuous thermal polymerization studies have shown that the polymerization kinetics are faster for photoinitiated systems and the PDIs of the polymer obtained were lower than those obtained by thermal polymerization. The effect of temperature is found to be more significant in the range of high monomer conversions. The branching in the polymers were also estimated and compared to the literature values. An error analysis for the experiments performed was carried out and it was found to be < 6%. A mathematical model incorporating the reactor geometry has also been developed for predicting the conversions and the results were compared with the experimental findings.