Organic–inorganic composite materials as photoinitiator for controlling/living polymerization

Abstract

Titanium dioxide (TiO 2 )/graphitic carbon nitride (g-C 3 N 4 ) composites were first used as photoinitiator for photochemically mediated controlled/living polymerization of methyl methacrylate. The polymerization was successfully carried out in polyethylene glycol at room temperature with FeCl 3 Á6H 2 O/N,N,N 0 ,N 0 ,N 00 -pentamethyldiethylenetriamine as complex catalyst and ethyl 2-bromoisobutyrate as initiator in this case. A pseudo-first-order dependence of the monomer concentration on the polymerization time was observed. TiO 2 /g-C 3 N 4 was verified to be an efficient photoinitiator. The polymerization was controlled to produce poly (methyl methacrylate) with narrow molecular weight distribution and controlled number average molecular weight (M n,GPC ). The M n,GPC matched well with the theoretical values when using both UV and sunlight irradiation as light source. The effects of reaction conditions on the polymerization were investigated. The polymerization could be started and stopped through periodically switching on/off the light. The living nature was further supported by the chain extension experiments.

Heterogeneous photocatalytic organic synthesis: state-of-the-art and future perspectives

“…Fe 2 O 3 and TiO 2 /C 3 N 4 as photocatalysts can reduce Fe III to Fe II which then reacts with the alkyl halide to generate alkyl radicals, which initiate ATRP. 111,112 The heterogeneous photocatalyst can be easily recovered and reused in the polymer synthesis process and the photoactivation method enables the polymer synthesis to occur under mild reaction conditions. However, this approach suffers from low conversion yields and is easily hindered by the presence of dioxygen that scavenges free radicals.…”

“…6 a viable method to initiate the polymerisation process. [99][100][101][102][103][104][105][106][107][108][109][110][111][112] In such processes, a semiconductor is excited by light absorption and the photogenerated electrons and holes activate the initiators via reductive and oxidative steps, respectively, as illustrated in Fig. 7.…”