Visible light induced synthesis of PMMA microspheres

Poly(methyl methacrylate) microspheres with narrow particle size distribution were synthesized successfully under visible light (LED@420 nm) in this study, and no RAFT agent was involved. A novel acylphosphine oxide, (2,4-dimethylphenyl) phenylphosphine oxide (2,4-DMTPO), was used as the photoinitiator. Uniform microspheres with the weight-average diameter (D w ) of 1.03 μm and polydispersity index (PDI) of 1.06 were obtained upon irradiation for 30 min, when the ratio of methyl methacrylate (MMA) to solvent was 1:10, the amount of polyvinylpyrrolidone (PVP) and 2,4-DMTPO was 30 wt% and 2 wt% of MMA, respectively. However, no microspheres could be detected instead of large blocks when (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO) was the photoinitiator under the same condition. It could be due to the higher light absorption ability and quantum yield of 2,4-DMTPO at 420 nm than TPO. A possible formation mechanism of PMMA microspheres was proposed and the effects of photoinitiator, MMA, irradiation time, and PVP were discussed. Results shown that regular microspheres were formed when the irradiation time exceeded 30 min, and the amount of PVP was in the range of 25 to 40 wt% of MMA. Lowering the amount of photoinitiator to 0.5 wt% resulted in ca. 66% and 4% decrease of D w and PDI, respectively. This study may provide a rapid and energy saving way of synthesizing monodispersed PMMA microsphere, which would be benefit for the fields of coating, template, and so on.